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Access to high-yielding germplasm increases agricultural productivity. Plant Variety Protection (PVP) is the most globally used form of Intellectual Property Protection. Commercially available varieties protected solely by PVP can be accessed for further breeding within the country or region of protection. Unlike the practice in most other countries, the USDA has a policy of providing parental inbred lines of hybrids into the public domain following expiration of their protection by PVP. Parental lines and varieties protected by utility patents are also available in the public domain following expiration of protection. These distributions represent fresh opportunities for researchers, hybrid seed producers and plant breeders, nationally and internationally. As a contribution to the continuing debate over ownership and access to plant germplasm we report distributions of maize (Zea mays L.) by the US National Plant Germplasm System (NPGS). During 1988–2015 the NPGS distributed 251,926 packets to 7,582 requestors, fulfilling 10,432 orders. Distributions were primarily to US entities (87%), with 32,520 (13%) to a total of 79 foreign countries. Of the total NPGS maize distributions reported here, 45,968 (18%) were expired or offPVP germplasm. We hope that access provided to this germplasm will act as a reminder that the primary benefit of the Multilateral System under the International Treaty on Plant Genetic Resources for Food and Agriculture (ITPGRFA) is indeed that of having facilitated global access to germplasm and that this concept will remain an important guiding principle during further implementation of the Treaty.

Cytoplasmic-genic male sterility systems (CMS) help control pollination in carrot and table beet breeding programs and hybrid seed production. A challenge common to these breeding programs is identification of F 1 hybrid progeny in crosses where both parents carry normal (N) cytoplasm. Such fertile × fertile crosses often produce both F 1 and selfed progeny, making identification of F 1 hybrids difficult. Such identification has tradition - ally been accomplished in carrot and table beet by visually scoring roots using heterosis for size. However, if heterosis is lacking, misidentification can result in systematic errors in the breeding process. We sought to determine how effective visual selection of hybrid progeny is in the context of table beet and carrot breeding programs. We used amplified fragment length polymorphisms (AFLp) markers to genotype parents and progeny in a variety of fertile × fertile crosses. progeny were also grown in the field and evaluated for hybridity based on visual selection using the phenotype of heterosis for size. Two of five fertile × fertile table beet crosses and three of five fertile × fertile car - rot crosses showed highly significant differences between visual selection for hybridity and AFL p marker analysis ( p < 0.01). Misidentification of roots as F 1 hybrids when they were actually self- pollinated occurred in some crosses as much as 75% of the time. Both type I, a hybrid root scored as an inbred, and type II, an inbred root scored as a hybrid, errors were committed. Across all mat - ings, type I errors occurred on average 40.9% of the time and type II errors occurred on average 8.5% of the time. Type II errors have important consequences because both parents are not rep - resented and recombined in the progeny resulting in further inbreeding. The results of this study indi - cate that using heterosis for size as a hybrid selec - tion method can be inaccurate for identification of hybrids in certain crosses and may introduce error into breeding programs.

Current red clover (Trifolium pratense L.) breeding methods for quantitative traits consist almost entirely of recurrent phenotypic selection. In many species, improved cultivars have been achieved through hybrid breeding methods, especially for highly nonadditive traits. Hybrid methods have previously been studied and developed in red clover; inbreeding depression was a hindrance to the utility of these breeding systems. In other forage legumes, population hybrids have been proposed as a way to achieve 50% hybrid seed while eliminating problems associated with inbreeding. This study proposes using gametophytic self-incompatibility S-locus in red clover to achieve population hybrids with 75% interpopulation hybrid seed; this would be accomplished by restricting S-alleles to three per population. To test this concept, fi ve S-allele restricted populations were developed. These fi ve restricted populations were randomly mated with a unrestricted population using bumble bees (Bombus impatiens Cresson) in fi ve separate screened enclosures. Halfsib seed was harvested off plants for paternity testing. On average, 75% of the progeny of the fi ve S-allele restricted population plants were hybrids, while 48% of the progeny of the unrestricted population plants were hybrids. Observed hybridity corresponded almost perfectly with expected hybridity. This study demonstrates the feasibility of increasing hybridity by restricting S-alleles within red clover populations.

Poor seed-set limits potential for soybean hybrid seed production. The objective of this study was to evaluate effects of different pollinators on the rate of seed set in three soybean cytoplasmic male sterile (CMS) lines, JLCMS9A, JLCMS82A, and JLCMS89A. The following five treatments were applied under net room isolation-conditions: (i) insecticide application and release of alfalfa leafcutter bees (Megachile rotundata) during flowering; (ii) insecticide application in the absence of leafcutter bees; (iii) release of alfalfa leafcutter bees during flowering without insecticide application; (iv) the absence of insecticide or alfalfa leafcutter bees during flowering; (v) plants without a net cover and pesticide application. Results indicated that the rate of pod production and seed set differ significantly between CMS lines and between treatments. Alfalfa leafcutter bees were an effective pollinator as evidenced by increases in pod-bearing rate and seed-set rate respectively from 21.35 to 53.22% and from 19.91 to 58.77% in the three CMS lines. The three CMS lines also showed significant differences in seed set, with JLCMS82A exhibiting the highest rate in all five treatments, followed by JLCMS9A and then JLCMS89A. These results suggested that thrips (Sericothrips variabilis) might have some effect on soybean pollination, but did not elicit a major influence based on the low increases in seed production. The natural insect population served an important role in outcrossing and seed set in soybean.

Yield testing fi nished inbreds to replace preliminary single-cross corn (Zea mays L.) yield tests will increase rate of commercial hybrid yield gains. Studies have shown that heterosis decreased 25%/50 yr, 10%/60 yr, and 35%/100 yr. Natural selection and artifi cial selection by plant breeders for adaptedness have increased parental inbred and hybrid seed yields, whereas percentage heterosis decreased. Four studies have shown inbred yields increased 1.9 to 3.5 times faster than heterosis yields. Pioneer HiBred generates 700 new inbreds tested in 6000 single-cross hybrids at 15 to 20 locations annually. Predicted, untested, newer hybrids are then made and tested extensively with commercial hybrids. Parental inbred yield testing is the next to last of several steps in hybrid development. Commercial hybrid development costs have increased logarithmically, whereas performance has increased linearly. Replacing preliminary testcross trials with fi nished-inbred yield trials is more effi cient. About 12,000 new fi nished inbreds can be evaluated annually with no testers and at least 50% fewer locations per inbred with the same testing effort as 700 new inbreds with testers. A calendar year per breeding cycle and annual production costs for 6000 hybrids will be saved. Corn yield trials detect stress susceptibility, which is more apparent in inbreds than in hybrids. Evaluation of more new inbreds will be conducive to increased genetic diversity that produces higher-yielding hybrids.

CERES-Maize simulates kernel set as a source-limited process based on average plant growth rate during the lag phase after flowering. Yet the number of kernels formed by maize (Zea mays L.) also depends on timely interaction between male and female flowers, which can limit formation of reproductive sinks under some conditions. Failure to account for sink-limited kernel set may contribute to simulation error observed under conditions that affect dynamics of pollen shed or silking, but do not alter crop growth rate. We developed algorithms for a Flowering Model to simulate sink-limited kernel set from flowering dynamics. This model was calibrated against kernel production in hybrid seed production fields and then linked to CERES-Maize. The Modified CERES-Maize was calibrated against two years of field data involving three hybrids, eight population densities, and seven N levels. Integrating the capacity to simulate sink-limited kernel set with source-limited kernel set increased simulation accuracy dramatically, relative to original CERES-Maize. For 13 commercial fields tested, Modified CERES-Maize decreased simulation error for kernels per plant from 17.1 to 2.3%, improved r 2 between measured and simulated values from 0.77 to 0.87, and decreased simulation error indicators mean error, root mean square error, and mean square deviation by 85, 40, and 64%, respectively. Modified CERES-Maize accounts for a much greater range of variability in the biological processes controlling kernel set.

Currently, information is lacking on gene flow in common wheat (Triticum aestivum L.) at distances greater than 300 m based on commercial-scale fields. The objective of this research was to measure pollen-mediated gene flow rates from a blue-aleuroned pollinator (T. aestivum cv. 'Purendo-38') to neighboring commercial fields of common wheat grown within a 10-km radius of a central pollinator field. In the 2-yr study, 33-ha (2002) and 20-ha (2003) fields of Purendo-38 were sown 200 km east-northeast of Saskatoon, Saskatchewan. Sixty-nine fields in 2002 and 76 fields in 2003 were identified as having overlapping flowering relative to Purendo-38. At maturity, up to 2 m2 samples were harvested from each corner of each recipient field. Gene flow was identified by the expression of a light-blue pigment in the aleurone layer of F 1 hybrid seed. In 2002 one case of gene flow was confirmed at 190 m northeast of the pollinator at a rate of 0.01%. In 2003 nine putative hybrid seeds were confirmed to be the result of gene flow between Purendo-38 and the recipient field using gliadin fingerprinting. Consequently, gene flow was confirmed at 0.01% at 500 m northeast, 630 m southeast, and 2.75 km northwest from the pollinator. In commercial production, gene flow in wheat occurs at trace levels (≤ 0.01%) at distances up to 2.75 km.

Corn (Zea mays L.) history and American westward expansion were intertwined when several hundred newer, better adapted, open-pollinated corn varieties were developed by human and natural selection. Chester E. Troyer was a pioneer corn breeder who bred ‘Troyer Reid’, an improved ‘Reid Yellow Dent’ variety. We relate how Chester got to the particular Indiana farm whose pervious, river-bottom soil affected natural selection. Better, deeper rooting probably helped Troyer Reid obtain more nutrients and water. Chester's formative years were spent as a teacher, and his later achievements included being honored four times as Corn King of the World and also as a successful corn breeder of productive corn varieties and proprietary hybrids. He was first to produce and sell hybrid seed corn in Indiana in 1925, received the Purdue University Certificate of Distinction and was a successful seed corn businessman and employer, successful gladiolus (Gladiolus × gandavensis Van Houtte) breeder of award winning varieties, successful banker, and beloved civic philanthropist. Troyer Reid accounts for about 15% of the background of documented U.S. Corn Belt hybrid corn through inbreds developed by Purdue University, Pioneer Hi-Bred International, University of Minnesota, and Iowa State University corn breeders.

Production of hybrid corn (Zea mays L) depends on cross-pollination between male and female inbred parents. As such, reproductive isolation of seed fields is required to ensure genetic purity of the hybrid progeny. Customer demand for improved genetic purity prompted the seed industry to examine the level of genetic purity resulting from current isolation practices. A 3-yr study was conducted to monitor purity of hybrid seed produced in 315 fields from 24 seed companies in North America. Each field was near a commercial corn field shedding pollen synchronously with the seed parent: a worse case scenario. Seed samples were collected at five locations along a 200-m transect established perpendicular to the nearest potential adventitious pollen source, and 100 seed from each location were subjected to isozyme analysis to determine percent out-crossing. Isolation distance, seed field size, field block size, number of border rows, adventitious field size, male:female row ratio, male population, and male pollen class were analyzed as continuous predictors and as variable class predictors of out-crossing at the field margins and field midpoints. Year had a significant (p ≤ 0.05) impact on observed out-crossing. Isolation distance, border rows, and male pollen class were significant predictors of out-crossing at the field margin but not at the field midpoint. A significant interaction between isolation distance and border rows was observed at both the field margin and midpoint. There also was an interaction between male:female ratio and male pollen class on out-crossing at the field margin. These results indicate that current practices used to isolate hybrid seed fields often achieve the goal of producing ≥99% genetically pure seed, but much higher levels of out-crossing can and do occur. Because out-crossing generally was greater and more variable at the field margins than at the field midpoint, adjustments to field management that focus on minimizing out-crossing at the field margins should lead to consistently high levels of genetic purity from hybrid seed fields.

The origin of U.S. Corn Belt corn (Zea mays L.), heterotic groups, and heterotic patterns becomes less obvious with more cycles of breeding. Heterosis is poorly understood; simple curiosity cries out for more information. I endeavor to shed light on the effect of adaptedness and heterosis on U.S. Corn Belt corn. I relate pertinent happenings in the phenomenal increase in U.S. corn production. I briefly review the origins of Northern Flint and Southern Dent races of corn and two major, persistent open-pollinated cultivars; and how corn hybridization was preceded and eased by hybrid species of the horse (Equus spp.). I discuss heterotic groups and patterns. The objective of U.S. corn breeding has been to adapt a tropical crop to a temperate climate. Adaptedness is important. Open-pollinated cultivars emphasized local adaptation, but some cultivars were more popular, widely grown, and better adapted over a broad geographic region. Hybrid seed corn companies grew larger by selling more widely adapted hybrids that favored germplasm from the more popular, widely grown, better adapted open-pollinated cultivars containing more genes for adaptedness. I examine morphological differences between inbred parents of a widely adapted hybrid. Relatively constant percentage of heterosis of well-adapted hybrids over years is due to seasonal climate affecting hybrids and their parent inbreds in a like manner because of their selection for adaptedness. Adaptedness has been more important than heterosis in the U.S. corn yield and production increases. Adaptedness in analogous heterotic species hybrids of the genus Equus, where body size is female dominant, apparently discriminates for body size between mules and hinnies that have virtually identical genotypes—adaptedness determines superiority over and above heterosis.

A cytogenetic method for producing hybrid seed using a nuclear gene for male sterility and an alien chromosome to obtain a pollination control system has been proposed in bread wheat (Triticum aestivum L.). Our objective was to transfer the alien chromosome 4E to the monogenic recessive male-sterile mutant Lanzhou (LZ), and then to establish an efficient cytogenetic system of maintaining the male sterility of the LZ mutant. After crossing the 4E disomic addition line 81529 (2n = 44) as male to LZ [2n = 42(msms) = 42], we obtained the 4E monosomic addition line [2n = 43(msms)] in the F 3 generation that had light-blue seed color. The line was homozygous for the male-sterile gene (msms) of the host wheat and also had good self-fertility. The self-fertilized seeds segregated into 64.3% white (nonblue) with genotype 2n = 42(msms), 32.1% light blue with genotype 2n = 43(msms) and 3.6% deep blue with genotype 2n = 44(msms) grains. All plants grown from the white grains were completely male sterile. All plants grown from the light-blue grains had good self-fertility whose progeny seeds segregated into white, light-blue, and deep-blue grains again in succeeding generations. All plants grown from the deep-blue grains were self-fertile and retained their deep-blue color in the succeeding generations. When white grain male-sterile lines were crossed using any cultivar as the male parent, the hybrid plants had male fertility restored. And, this is the basis for the 4E-ms system of producing hybrid wheat.

In hybrid maize (Zea mays L.) seed production, yield of the female parent is a major factor affecting production costs. As an alternative to using an inbred line as the female parent, sister-lines (SLs), the F1 between two highly related inbred lines (A3A*), have been used in seed corn production. Hybrids produced using SLs are referred to as modified single-cross (MSC) hybrids. This study examined (i) yield changes associated with MSC hybrids compared with their respective single-cross (SC) hybrid counterparts and (ii) differences in grain yield of inbred lines and SLs. Three families of six inbred lines each were used to produce three diallel groups of 15 SLs. Simple sequence repeat (SSR) primer pairs were used to establish the degree of relatedness between inbred lines. The SLs and the inbred lines were mated to four unrelated inbred lines to form MSC and SC hybrids. The SC and MSC hybrids were evaluated for grain yield, grain moisture, test weight, and broken stalks in six environments. The six inbred lines and 15 SLs from each family were grown in five environments and evaluated for grain yield, grain moisture, test weight, and broken stalks. Most of the MSC hybrids (72–83%, depending on inbred line family) werenot significantly different than the ‘‘best’’ SC counterpart. However, a low frequency of the MSC hybrids, 11 out of 180 (6.1%), had grain yields that were significantly lower than both SC hybrid counterparts. And surprisingly, three out of 180 (1.7%) of the MSC hybrids had grain yields that were significantly greater than both SC hybrid counterparts. The SLs used in this study exhibited an average grain yield that was two-fold greater and more stable or predictable than the inbred lines. These results suggest that there are definite advantages in utilizing SLs in hybrid seed production and that, in general, the performance of the resulting MSC hybrids is expected to be similar to the ‘‘best’’ SC hybrid counterpart.

In maize (Zea mays L.) hybrid seed production, achieving the optimum seed yield per unit land area often is based on limited information about the quantity of pollen shed by the male and practical experience synchronizing pollen shed by the male inbred with silk emergence by the female inbred. We recently reported that kernel production per hectare could be simulated fairly accurately under pollen-limited conditions from simple measures of pollen shed and silking dynamics. The objective of this study was to determine whether a simple mechanistic description of the flowering dynamics of male and female inbreds could be used to simulate and optimize kernel production in seed production fields. We estimated kernel production on the basis of flowering dynamics in six commercial seed fields located near Washington, IA, in 2002, which differed in the quantity of pollen production and silk emergence. In all cases, the fields were managed and harvested by standard seed industry methods. Harvested kernel number varied from 8.4 to 23.1 million kernels per female hectare. Simulated kernel number was closely correlated with these measured values (r 2 = 0.98). This result indicates that relative differences in kernel production can be assessed directly from inbred flowering dynamics. Examples are provided to show how inbred management can be modeled to optimize harvested kernel number for a given inbred pair. Model simulations, however, overestimated harvested kernel number by 11%, on average, which implies that other plant factors, such as pollen viability, prolificacy, pollen capture by the canopy, or kernel abortion in response to leaf removal during detasseling might have limited kernel production across the six seed fields. Information about these variables can be incorporated readily into the kernel set model to improve its accuracy. This study indicates that kernel production in a hybrid seed field can be simulated from simple measures of inbred flowering dynamics. The model is a useful tool for optimizing harvested kernels for an established inbred pair or for defining initial management protocols for new combinations of inbreds.

Hybrid sorghum [Sorghum bicolor (L.) Moench] seed production relies exclusively on cytoplasmic male sterility (CMS) systems and almost all hybrid sorghum seed is produced using the A1 CMS system. However, the reliance on a single CMS system increases the vulnerability of the crop to diseases and stresses that may attack that particular CMS system. Alternative CMS systems have been described and even used on a limited basis for hybrid seed production, but a direct comparison of the agronomic effects of different cytoplasms has not been possible because male-sterile lines with a common genetic background (and different cytoplasm) were not available. The recent development of isocytoplasmic A-lines allows more direct comparison of cytoplasmic effect on agronomic performance. The purpose of this study was to determine by means of a set of isocytoplasmic hybrids if cytoplasm per se influences agronomic performance. Twelve hybrid genotypes were created in three different cytoplasms (Al, A2, and A3 for a total of 36 hybrids), and they were evaluated for plant height, days to anthesis, and grain yield at Weslaco and College Station, TX, in 1998 and 1999. As expected, significant differences existed among hybrids for plant height, days to anthesis, and grain yield. Cytoplasm type had no effect on plant height and was of minimal practical effect on days to anthesis, but a significant reduction in yield was observed in A3 cytoplasm hybrids as compared with A1 and A2 cytoplasm hybrids. The specific reason for the reduced yield of A3 hybrids is not known, but seed set data indicated that it was not associated with fertility restoration. The results indicate that hybrids created in A2 cytoplasm yield comparably to the commonly used A1 cytoplasm and therefore, the A2 system will provide a suitable alternative for hybrid seed production should problems be encountered in the A1 CMS system.

The ability of the weedy species jointed goatgrass (Aegilops cylindrica Host) to form seed-bearing hybrids with wheat (Triticum aestivum L.) raises questions concerning the potential movement of herbicide-resistance genes from commercial wheat cultivars into the weed population. As a preliminary step for future gene-flow risk assessments, a study of jointed goatgrass × wheat hybrids collected from infested wheat fields in 1998 and 1999 was undertaken in Oregon. Jointed goatgrass accessions representing the range of variation in its worldwide distribution also were included in this study. The high molecular weight (HMW) glutenins, a group of wheat endosperm storage proteins, were used as genetic markers for characterizing this material. In the Oregon jointed goatgrass accessions, the seed protein analysis identified F 1 hybrid seed that was formed at a rate of 0 to 8% on a per field basis. The HMW glutenin patterns in the backcross seed threshed from Oregon hybrids showed a higher proportion of seeds formed from pollination by wheat than by jointed goatgrass. Analysis of the roots for remains of the maternal seed or spikelet indicated that most hybrid plants were of the F 1 generation and that either jointed goatgrass or wheat could be the female parent. These analyses suggested a hybridization dynamics in which jointed goatgrass serves as the predominant F 1 female parent and wheat as the predominant backcross male parent. Development of introgressed jointed goatgrass forms carrying wheat genes would be dependent on the presence of a continuous hybrid zone located near or within a persistent jointed goatgrass population.

Ergot caused by Claviceps africana Frederickson, Mantle & de Milliano has become an important constraint to Fl hybrid seed production in North and South America. Identification and utilization of sources of host-plant resistance would contribute to the effective control of this disease. A Design II mating scheme was used to test the combining ability of four reported sources of ergot resistance in sorghum [Sorghum bicolor (L) Moench]-IS8525, IS14131, IS14257, and IS14357. Male-sterile hybrids of these accessions and a susceptible check, TxARG1, were produced using five cytoplasmic-genetic male-sterile seed parents-A3Tx430, A3Tx436, A3Tx7000, A3KS70, and A3Tx2737. Parent lines and hybrids were planted in three replications at three locations and were evaluated for ergot resistance following artificial inoculation at flowering. Differences in ergot severity and ergot breakdown point (EBP) were used to quantify differences in resistance. The combined analysis of variance showed that the expression of ergot resistance was not stable with significant entry × location interaction. The analyses from two locations showed significant differences among hybrids, while the third location showed no differences. Regression analyses were performed to determine the relationship between weather variables at flowering and observed ergot severity. These analyses indicated a strong relationship between maximum daily temperature and ergot severity. Ergot infection was higher in cooler environments regardless of genetic background. IS8525 appeared to have the highest expression of ergot resistance in male-sterile genetic backgrounds on the basis of EBP and ergot severity ratings; however, the expression of resistance was only effective within a limited temperature range.

Ergot (caused by Claviceps africana Frederickson, Mantle & de Milliano) of sorghum [Sorghum bicolor (L.) Moench] recently has become a global disease problem and is a major threat to hybrid seed production. Host-plant resistance is one option for control; however, the genetic and physiological bases for ergot resistance are poorly understood. The objective of this study was to evaluate resistance to C. africana in 18 genetically diverse sorghum lines, including cultivated landraces and wild accessions, as well as in potential alternate hosts, including grassy weeds and range grasses commonly found in sorghum-producing areas in the central Great Plains of the USA. These entries were evaluated for ergot resistance in the greenhouse following spray inoculation with conidial suspensions during flowering. The results of this analysis indicated that only Sorghum ssp. were susceptible to ergot; however, within the sorghum germplasm pool, several wild accessions were identified with resistance to ergot. Two of these resistant entries, IS14131 and IS14257, were characterized further in male-sterile (A3 cytoplasm) genetic backgrounds to evaluate the physiological basis for their resistance. Parent lines, male-sterile hybrids, and susceptible checks were evaluated for ergot resistance following spray inoculation with ergot in experiments in a winter nursery at Guayanilla, Puerto Rico, and in a greenhouse at Manhattan, KS, during the winter and spring of 2000. The expression of ergot resistance in IS 14131 and IS14257 and in corresponding male-sterile hybrids suggests that these sorghums may harbor genes for resistance to ergot.

The estimation of hybrid rice seed purity is done conventionally by the grow out test (GOT), which is based on the assessment of morphological and floral characteristics in plants grown to maturity. For seed companies, large amounts of capital are locked up in the form of hybrid seed stock while awaiting the results of the GOT. With the objective of replacing the GOT with DNA based assays, cytoplasmic male sterile (CMS), restorer, and hybrid lines have been screened by means of microsatellite and sequence tagged site (STS) polymorphisms. A simple procedure for detecting heterozygosity and purity has been standardized and uses 6-d-old rice (Oryza saliva L.) seedlings, which could be used for detection of off-types in hybrid seed lots. The extent of heterozygosity within parental lines of rice hybrids was assessed and the results suggest that a single, appropriately chosen microsatellite marker should be sufficient for assessing hybrid seed purity.

The difficulty making crosses and lack of an efficient crossing technique have resulted in a very limited number of genetic studies and, consequently, limited improvement of foxtail millet [Setaria italica (L.) Beauv.]. Objectives of this study were to acquire knowledge of the anthesis habits of foxtail millet and to develop a technique for artificial hybridization of foxtail millet. To understand the process of anthesis, several variables were observed on five plants of each of five cultivars under greenhouse and growth chamber conditions during the summer of 1994. The efficiency of the crossing technique described was evaluated based on seed set from emasculated but non-pollinated checks, seed set from more than 6400, and percent hybrid plants among 30 F 1 plants from each of 21 cross-combinations. During the summer, anthesis of foxtail occurred between 1800 h and 0700 h, starting the third day, after the emergence of the spike. Few flowers opened and there was practically no anthesis between 0800 h and 1800 h. Anthesis initiated at or about one third down the spike and progressed up to the apex and down to the base. Each spike required from 10 to 13 d to complete anthesis. The number of florets opening on the second day averaged 36, which was an optimum for successful emasculation. Opening and closing of a single flower occurred in about 7 min. The crossing technique described was effective with an average 75% seed set, and more than 90% true hybrid seed or 67.5% hybrid seed set per flower crossed.

The performance of single-cross hybrids can only be enhanced by adding favorable alleles from donor inbred lines that are not present in either parent. The public inbred lines of cultivated sunflower (Helianthus annuus L.) have not been systematically screened as a source of new favorable alleles for enhancing hybrid performance. The objective of this study was to assess the merits of a sample of public inbred lines as donors of alleles for increasing the seed yield of three hybrids (HA383 × RHA373, HA372 × RHA377, and HA89 × RHA373). The net gain of favorable alleles and several other statistics were estimated from the seed yield means of 14 sterility maintainer (B) lines, four fertility restorer (R) lines, 81 B × B hybrids, and 42 B × R hybrids in field tests at Corvallis, OR and Casselton, ND in 1996 and 1997. HA383 × RHA373, HA372 × RHA377, and HA89 × RHA373 were the highest-yielding hybrids from three heterotic patterns. HA383 × RHA373 had the highest seed yield across years and locations (3285 kg ha -1 ) among all hybrids. The most promising donors for increasing the seed yield of HA383 × RHA373 were HA822, HA851, and HA372. Similarly, the most promising donors for increasing the seed yield of HA372 × RHA377 were HA821 and HA384, and the most promising donors for increasing the seed yield of HA89 × RHA373 were HA383, HA384, and HA821. The elite gene pool of sunflower seems to be a rich source of favorable alleles for increasing hybrid seed yields.

The availability of recessive genes for early flowering-daylength insensitivity offers an opportunity to synchronize the flowering of late-flowering or daylength-sensitive parents with that of early-flowering parents without necessarily affecting the flowering of their hybrids, provided that the earlier parent does not carry the same recessive allele. This study evaluated the hypothesis that incorporating the recessive e1 allele for early flowering-daylength insensitivity into a late-flowering, photoperiod-sensitive pollinator in pearl millet (Pennisetum glaucum) would synchronize its flowering and improve seed production with earlier-flowering female parents, without affecting the time to flowering or the performance of the resulting hybrids. An e1/e1 isoline of the late-flowering pollinator ICMP85410, produced by six backcrosses, flowered 16 days earlier under natural daylengths at Patancheru, India (17 deg N) and 19 days earlier under extended daylengths (equivalent to 29 deg N) than its near-isogenic E1/E1 counterpart. As a consequence, it successfully produced hybrid seed when sown simultaneously with early, male-sterile line 843A, whereas the late isoline failed under the same conditions. The E1/e1 versions of eight near-isogenic hybrids (on a range of eight E1/E1 male-steriles) flowered an average of 3 days earlier than their E1/E1 counterparts in 2 yr of tests under both natural and extended daylength conditions at the same location. This earlier flowering had small effects on hybrid yield components, consistent with known effects of earliness in the crop, but did not affect grain yield. The results indicated that the e1 allele is a powerful tool for exploiting heterosis between early-and late-flowering parents in pearl millet, which is otherwise difficult to realize without complicated seed production practices.

The F 1 generation of a testcross previously was not used to evaluate soybean [Glycine max (L.) Merr.] germplasm, primarily because production of large amounts of hybrid seed has been impractical and because evaluation of quantitative traits with one or a few plants does not give reproducible results. Recently, a method for efficiently producing testcross seed was developed by using the male sterility locus, Ms 6 , and a genetically linked seedling marker locus, W 1 . The objectives of this research were (i) estimation and comparison of heterosis and inbreeding depression values for agronomic traits of testcross lines; and (ii) determination of the utility of per se and testcross evaluation for selecting germplasm to be included in an existing cultivar development program. Two testers were used to evaluate six lines in three-row plots. Significant F 1 and F 2 midparent heterosis and inbreeding depression were observed for nearly all traits, including grain yield. The choice of tester was ascertained to be important in determining parental value of germplasm. Parental lines were evaluated by using a combination of per se performance, heterosis values, and a recently developed testcross statistic, T i . The T i value was better than F 1 midparent heterosis for identifying lines suitable for use in direct crosses. F 1 midparent heterosis was better than the T i value for identifying valuable Ines requiring pre-breeding effort. A combination of F 1 and F 2 midparent heterosis values identified lines likely to have genes with dominance effects; although, because of inbreeding depression, use of F 2 heterosis alone failed to identify valuable lines.

Spring canola acreage has increased in the Pacific Northwest over the past 5 yr. Traditional cultivars are inbred lines, although a high proportion of newer cultivars are hybrids. This study examined the magnitude of heterosis in spring canola to determine the potential advantage of hybrid cultivars. Four inbred cultivars, with diverse geographic origins of development, were hand-pollinated in a diallel design. Performance of F 1 hybrids and their respective inbred parents was evaluated under greenhouse conditions. Field trials were conducted at two locations to compare F 1 hybrids and F 2 progeny with inbred parents. Positive heterosis was found for yield, oil content, and oil quality, with the highest degree of heterosis observed for yield. Hybrids and F 2 progeny produced higher yield than inbred parents because of increased pod number (primarily on the main raceme), larger seeds, and later maturity. However, the magnitude of heterosis observed varied between hybrids. Inbred and hybrid cultivars also were compared in the Padfic Northwest Regional Canola Variety Trials. In these trials, the most adapted hybrids had a yield advantage compared with the most productive inbred cultivars. However, average yield and oil content of hybrids were not significantly different from inbred cultivars. Inbred cultivars tended to have higher oil content and matured earlier. Introduction of hybrid canola cultivars in the Pacific Northwest region has potential to increase canola acreage and grower profit. However, choice of hybrid parents and economics of high quality hybrid seed production will be important factors in hybrid canola cultivar development and acceptance.

Improved methods to produce hybrid soybean [Glycine max (L.) Merr.] seed could augment several types of research. Two previously described methods, the traditional method and the dilution method, require insect-facilitated cross-pollination of ms ms nuclear male-sterile plants. The traditional method requires a substantial time investment during flowering to remove fertile siblings, and the dilution method requires a substantial amount of land and pollen-parent seed. Because time, land, and seed are limited, a more efficient method would be valuable. The cosegregation method was developed, utilizing close genetic linkage between the W1 locus and the Ms6 locus. The W1 ___, seedling has a purple hypocotyl; the w1 w1 seedling has a green hypocotyl. The ms6 ms6 plant is male sterile and female fertile. Approximately 97% of the purple-hypocotyl seedlings, W1 ___, in a line segregating for the w1 and ms6 alleles in coupling phase will he fertile, Ms6 ___, and can be removed as a pollen source at the first-trifoliolate stage. Our objective was to evaluate and compare the three methods of hybrid soybean seed production for seed yield, efficiency, and hybrid seed purity and quality. We used a randomized complete-block design (three replications per location, three locations, two years). The cosegregation method gave higher seed yield, better efficiency, and equal or better seed quality (percentage germination, 100-seed weight) than the other methods. Male-sterile plants yielded an average of 28.6 seeds plant−1 with the cosegregation method, 18.2 seeds plant−1 with the traditional method, and 9.5 seeds plant−1 with the dilution method. The cosegregation method will be useful in several research areas, including genetic control of complex traits, prediction of parental value, recurrent selection, and commercialization of hybrid soybean.

Wet milling is an important use of maize (Zea mays L.) grain produced in the USA, and commercial wet millers and hybrid seed companies are increasingly interested in hybrids which have enhanced milling properties. Because of the cumbersome nature of traditional laboratory wet-milling procedures, relatively little information is available regarding inheritance of wet-milling product fractions. In this study, the inheritance of maize wet-milling product fractions was evaluated in grain of 40 full-sib families from a Design I mating (20 males; two females per male) and a newly developed, rapid, laboratory milling procedure. The narrow-sense heritability estimate of male-family means for the starch fraction was 0.73. Predicted gain from selection with a conservative heritability estimate was 7.4 g kg -1 per cycle for the starch fraction. Phenotypic and genetic correlation coefficients between the wet-milling starch fraction and initial starch concentration, measured by near-infrared reflectance, were significant (0.79 and 0.89, respectively). Significant phenotypic and genetic correlation coefficients were observed between a wet-milling index and an index based on near-infrared reflectance. Relative rankings of check hybrids were significantly different between these two indices. Results from this study indicated product fractions from maize wet milling are heritable, and thus modifiable through selection. Genetic correlation coefficients suggested that selection for increased starch extractability from wet milling could be accomplished by using near-infrared reflectance to measure starch concentration. Changes in hybrid rank among wet-milling and near-infrared reflectance indices suggested that final selections of candidate hybrids for specific milling applications should be based on actual wet-milling evaluation.

Cuphea lanceolata forma silenoides Ait. (Lythraceae) is a self-compatible, insect-pollinated, allogamous annual oilseed crop. Our objectives were to develop a set of inbred lines from an open-pollinated population (LN-43), estimate inbreeding effects by using differences between an S 0 population (LN-43) and S 1 and S 2 lines, estimate heterosis effects by using differences between inbreds and single-cross hybrids, and rank inbred lines as sources of alleles for enhancing single-cross hybrids of C. lanceolata. Ten groups of S 1 and S 2 lines were developed by single-seed descent from the C. lanceolata population LN-43. All possible single-cross hybrids were developed among five S 5 lines from LN-43. Plant height, biomass, seed yield, seed oil content, and 500-seed weight decreased as inbreeding increased. Significant inbreeding depression was observed for every trait. Biomass and seed yield were more severely affected by inbreeding than the other traits. Significant heterosis was observed for every hybrid and trait. Heterosis was greatest for seed yield and least for 500-seed weight. Mean heterosis was 71.7% for plant height, 79.9% for biomass, 159.0% for seed yield, 36.7% for seed oil content, and 22.3% for 500-seed weight. A significant positive correlation of 0.72 was observed between line per se and hybrid seed yield, and the highest yielding inbred lines (LN-97 and LN-98) produced the highest yielding hybrid (LN-97 x LN-98). The seed yield of LN-97 x LN-98 might be increased by using LN-99 as a donor. Although seed yields can be maximized by using single-cross hybrids, a mechanism for producing hybrid seed has not yet been developed. The heterosis of this species can nevertheless be exploited by using synthetic cultivars.

Alfalfa (Medicago sativa L.) is the most important forage crop in the world, but with current breeding practices improvements in yield potential have been limited during the last 40 yr. The development of hybrid alfalfa cultivars would likely improve forage yield potential, but an efficient method to estimate outcrossing rates would be needed to confirm percentage hybrid seed. The objective of this research was to demonstrate the applicability of a RAPD nulliplex analysis to estimate outcrossing/selfing rates in autotetraploid alfalfa. Marker selection is based on polymorphism between a seed parent and its bulk open-pollination progeny. Polymorphic markers identify the seed parent as nulliplex (aaaa) for those particular loci, which allows the individual open-pollinated progeny from that seed parent to be classified as F 1 or S 1 progeny based on the presence/absence of these markers. Two alfalfa genotypes served as seed parents in crossing studies which differed in pollination control and number of pollen parents. Random amplified polymorphic DNA (RAPD) nulliplex analysis was conducted on these two seed parents and their progeny. Controlled crossing and selfing provided independent control over S 1 s and F 1 s. Five polymorphic markers were identified for both seed parents and these markers were sufficient to identify S 1 and F 1 progeny. The percentage S 1 seed was 7, 27, and 100% for crossing with emasculation, crossing without emasculation and self-pollination, respectively. In conclusion, RAPD nulliplex loci analysis can provide accurate identification of F 1 and S 1 progeny and an estimation of outcrossing rates in autotetraploid alfalfa.

Significant heterosis for seed yield in oilseed rape (Brassica napus L.) has created interest in the development of hybrid cultivars. The objective of this study was to determine the value of restriction fragment length polymorphism (RFLP) markers in predicting hybrid performance. The hybrids and parents of two sets of diallel crosses were evaluated at three environments for seed yield and other agronomic traits. The parents of the first diallel were seven oilseed rape cultivars and the parents of the second diallel were seven unselected S₆ lines derived from the cultivars. Genetic distances (GD) between the parents crossed in the diallels were estimated by RFLP data from 43 DNA clones. Both general combining ability (GCA) and GD estimates were significantly (P < 0.05) correlated with hybrid seed yield in both diallels, although GCA was more greatly correlated than GD. Genetic distance was significantly correlated with heterosis for seed yield only in the inbred diallei whereas GCA was significantly correlated with heterosis only in the cultivar diallel. Midparent yield was significantly correlated only with heterosis for the cultivar diallel. A multiple linear regression model that included both the GD and GCA of the parents was more greatly correlated with hybrid seed yield than any variable alone. The GCA values were significantly correlated with hybrid plant height, and seed oil and protein concentration in both diallels whereas GD was significantly correlated only with hybrid plant height. These results suggest that GD estimates alone do not identify high yielding hybrid combinations with the consistency to be useful in breeding programs. Contribution from the Dep. of Agronomy, Univ. of Wisconsin.

The discovery of two stable male-sterile genes and the prevalence of adequate insect-aided cross-pollination led to the development and release of the first pigeonpea [Cajanus cajan (L.) Millsp.] hybrid in India. Commercialization of this hybrid is constrained because of the labor intensiveness of seed production and concerns about seed purity. Cytoplasmic male-steriles would effectively circumvent these constraints and revolutionize the hybrid seed industry. This paper reports the development of cytoplasmically determined male-sterility, which was accomplished by two methods: wide hybridization involving conventional backcrossing of Cajanus sericeus van der Maesen and Cajanus cajan and multiple cross genome transfer. In these matings, two forms of reversion to fertility were noticed, one influenced by low temperature and high humidity, and the other probably determined by genetic factors alone. The influence of temperature on fertility restoration as reported for Viciafaba L. is different from that seen in species crosses of Cajanus. The multiple cross genome transfer method resulted in stable cytoplasmic-genic male sterility maintainable by the pigeonpea genotypes ICPL 85030 and ICPL 90035. These male-sterile lines are in agronomically desirable backgrounds.

Heat stress is an important production constraint of wheat (Triticum aestivum L.) affecting many plant biological activities in the cell membrane. This study determined the genetic control of heat tolerance through diallel analysis of selected wheat germplasm. Heat-induced damage of plant membranes was assayed by the membrane thermal stability (MTS) assay, which measures electrolyte leakage from leaf tissue after exposure to high temperature. Six wheat genotypes ('TAM 107', 'TAM 108', 'Arlin',' Kauz', 'Glennson 82', and 'Siete Cerros') were hybridized in a complete diallel, and MTS was measured on 12 d old F1 seedlings. The mean square for general combining ability (GCA) was four times that of specific combining ability (SCA), indicating the importance of additive gene effects in acquired thermal tolerance. Maternal effects accounted for 67% of reciprocal variation, suggesting that maternal seed-source effects may be important in hybrid seed. These results suggest that heat tolerance based on MTS can be improved using the existing genetic variability available within the germplasm evaluated in this study.

Manual cross-pollination to produce large quantities of hybrid soybean seed is difficult and time consuming. An environmentally stable sterility system is one of the necessary components to produce large quantities of hybrid seed. The objective of this study was to subject cytoplasmic male-sterile (CMS) BC5F1 plants, from a cross of a Chinese Glycine max wild-type soybean with a Chinese wild annual soybean G. soja (male parent) and controls, to a variety of different temperature and photoperiod treatments to test whether CMS is stable under various environmental conditions. Plants were grown in growth chambers under controlled temperature, photoperiod, and irradiance regimes until pod set, and then they were transferred to a glasshouse until they matured. Plants were evaluated for time of anthesis after photoperiod induction (13 h light/11 h dark) and fertility or sterility. Anther squash and pod set data showed that sterility of the CMS line was stable under all environmental conditions tested, whereas fertility-restored control plants remained fertile. Extreme environmental conditions led to delayed floral induction andlor stunted growth.

Production of hybrid seed is an important component of hybrid wheat (Triticum aestivum L.) utilization. A recurrent selection program was initiated using gridded mass selection to select for increased seed set on individual plants that had ben treated with a chemical hybridizing agent (CHA). Four cycles of selection with recombination were completed using the spring wheat random-mating population NDP1. To determine the effectiveness of this selection procedure, 32 random half-sib selfed families from both the CO and the C4 cycles of selection, 32 random inbreds from the original NDP1 population, and 32 inbred lines from several wheat breeding programs were compared for both fertile seed yield (no CHA) and hybrid seed yield (0.6 kg ha −1 CHA) in replicated tests at two location in 1986

Self-incompatibility provides a useful mechanism for pollination control in alfalfa, Medicago sativa L. Five hundred randomly selected seedlings from each of two well-adapted multiple pest-resistant alfalfa populations (W10 AC3 and BMP8 AC3) were screened for self-incompatibility. Twenty-eight plants were selected following three evaluations in the greenhouse. Unemasculated hand pollinations of the self-incompatible plants, using plants with the single-gene, completely dominant red-root character as the pollen source, resulted in the production of 98.6% hybrid seed. Plants were intercrossed in the greenhouse using honey bees, Apis melifera L. Growth chamber forage-yield trials of half-sib progenies indicate that certain combinations of self-incompatible plants exist that will yield significantly better than the parent populations. Twelve elite self-incompatible plants selected after the initial screening produced (i) 30% viable pollen, and (iii)>3 seeds floret −1 when used as the male or female in crosses with other plants. Pollen-pistil interaction studies of the self-incompatible plants showed that the pollen had normal viability and either failed to germinate upon self pollination or pollen tube growth was abnormal. Pollen tubes that grew near the ovules either formed bulbous structures and terminated, or formed several branches, or continued to grow past all of the ovules resulting in the failure of fertilization. However, normal fertilization and good seed set were obtained when the self-incompatible plants were used both as male and female in crosses with other plants. The 12 elite self-incompatible plants were shown to have the capacity to produce somatic embryos in vitro, indicating that these plants could be propagated utilizing artificial seed technology. Evidence to date indicates that the use of the self-incompatibility system may provide a mechanism for successfully producing high-yielding hybrid alfalfa cultivars

Pearl millet (PM), Pennisetum glaucum (L) R. Br., x napiergrass (NG), P. purpureum Schum., interspecific hybrids (PMN) have the potential to extend production of high quality forage into the late summer and fall in the USA. The objective of this study was to determine if interspecific hybrid seed could be produced on a commercial scale at Kunia, HI, and to identify production problems. Although one block yielded 1145 kg ha -1 PMN seed in 1986, seed yields in most years averaged 300 to 600 kg ha -1 if birds were controlled. Rain storms during November and December, when seed was maturing, reduced both seed yields and seed quality. Observations in this study indicated that PMN seed may be more successfully produced if flowering of plants is manipulated to mature seed in March in Hawaii or if produced in a tropical climate with a dry winter season.

The development of an interspecific hybrid cotton has been hampered by a serious problem with pollination. A field study was conducted to compare Pima Cotton (Gossypium barbadense L.) with upland cotton (G. hirsutum L.) as a pollen source for hybrid seed production using male-sterile upland seed parents. Male-sterile cotton flowers were hand pollinated with either upland or Pima cotton pollen. The number of pollen grains per stigma and the resulting number of seeds per boll were evaluated using covariance analysis. In each of 3 yr the bolls produced from pollen of upland cotton produced more seeds per boll than did those produced from Pima pollen. Adjusted least square means indicate an advantage of four to seven seeds per boll with upland polle

There is increased interest in using a dwarf, spontaneously self-pollinated accession (U389) of annual, white-flowered sweetclover (Melilotus alba Desr.) for studying N 2 fixation and for characterizing the photosynthetic apparatus. Genetic analysis of this accession may therefore be required. In a study of the inheritance of 10 nonmodulating U389 mutants, >2000 crosses made in the late bud stage were unsuccessful, probably because florets were mishandled during the crossing procedure. Development of an improved crossing technique resulted in production of hybrid seed from 10% of the emasculated and pollinated florets. This succesful technique is described in detail for future use by researchers making crosses with spontaneously self-pollinated sweetclovers similar to U389

Cold soil temperatures, seedling diseases, and soil crusting may limit stand establishment of early-season muskmelons (Cucumis melo L.). We tested the ability of seed and soil treatments to overcome these factors and improve seedling emergence. The seed treatments were seed priming (6 d at 25 °C in aerated 0.3 M KNO₃ solution followed by drying) to improve the rate of germination at low temperatures, and metalaxyl [N-(2,6-dimethylphenyl)-N-(methoxyacetyi) alanine methyl ester] fungicide (Apron 25W) to prevent damping- off diseases. The soil treatments were spot applications of soil drenches containing metalaxyl fungicide (100 μg L⁻¹ Ridomil 2E), an anticrostant [2% Naico 2190, (Nalco Chemical Corp, Carson, CA)] or both fungicide and anticrustant. In laboratory tests at 18 °C, both germination rate and final germination were markedly improved by seed priming in ‘PMR 45’, ‘Magnum 45’, ‘Topmark’, and ‘Topscore’ plants. Seedling emergence from sterilized soil in flats under ambient outdoor temperatures (7-23 °C) was also improved by seed priming. Seed priming resulted in more rapid emergence or increased final emergence in five of seven field trials in two locations. Anticrustant applications to the soil covering the seed consistently improved stand establishment, particularly in badly crusted soils. Metalaxyl application to the seed or soil generally improved emergence, but the effect varied with cultivar, location, and planting method. None of the treatments significantly influenced final fruit yield. The combination of seed priming, fungicides, and anticrustants could allow lower seeding rates of expensive hybrid seed while achieving earlier emergence and adequate plant densities in earlyseason muskmelon crops. Supported in part by an allocation to K.J. Bradford through Regional Res. Project W-168 and by grants from the Melon Research Board, Dinuba, CA.

Two field studies involving different groups of germplasm were conducted to compare sorghum-sudangrass, Sorghum bicolor (L.) Moench X S. sudanense (Piper) Stapf, hybrid seed production of male-sterile FI's with their component A·lines. The FI's yielded 45 and 82% more grain than their A·line counterparts in Study I and 2, respectively, with the increase attributable to more seeds per panicle and a greater threshing percentage. Mean values of nine traits measured on nine groups of eight FI's in Study I and seven groups of six FI's in Study 2 were compared with their respective A·lines. All groups of FI's significantly outyielded their A·line counterparts in both studies except for A·line N35 in Study 1. Phenotypic correlations of yield and seeds per panicle were high in both A·lines and FI's in both studies, as were the correlations of yield and threshing percentage except for the FI's in Study 1. Application of these findings should facilitate the production of higher yields of sorghum-sudangrass hybrid seed at reduced cost per unit of seed. The best FI's to use and the magnitude of their superiority over A·lines will be influenced by the location in which seed is produced. Additional indexwords:Sorghum bicolor (L.) Moench, Sorghum sudanense (Piper) Stapf, Single-cross hybrids, Three-way hybrids. SORGHUM-SUDANGRASS, Sorghum bicolor (L.) Moench X S. sudanense (Piper) Stapf, hybrids are grown extensively to provide supplementary forage for animals as pasture, silage, or greenchop. These hybrids play an important role in the management plans of many livestock producers, particularly in drouth-prone regions such as the Great Plains. In a 1977 survey by Harvey (I), 81.5% of the commercially produced sorghum-sudangrass hybrids in the United States were F I 's, with 'Redlan' grain sorghum being the preferred male-sterile and 'Greenleaf sudangrass the most often used pollinator. Also, three-way cross hybrids made up I I% of the total seed production of sorghums and sudangrasses used for forage compared with less than 2% in grain sorghum (I). Despite this rather extensive use of three-way crosses in forage and sudangrass hybrids, only two preliminary reports were found in which the seed production of three-way and single cross hybrids was compared. In a I-year study of seed production of sorghum-sudangrass hybrids in Hungary (3), seed yields of F I male steriles were greater and production was more dependable than for Alines because the F1's matured earlier, but comparative seed yields of three-way and single cross hybrids were not presented. In Japan (6), four grain sorghum A-lines, six grain-sorghum male-sterile F I 's and six sorgo male-sterile F I 's were used in a comparative I Contribution of USDA-ARS and the NebraskaAgric. Exp. Stn. Published asPaper no. 7415, Journal Series, Nebraska Agric. Exp, Stn., Lincoln. Research was conducted under Nebraska Project no. 12-114. Received 29 Feb. 1984. 2 Supervisory research geneticist, USDA-ARS; research technologist inagronomy;George Holmes professorof agronomy; and research geneticist, USDA-ARS, Lincoln, NE68583, respectively. study of seed production of forage sorghum hybrids. Seed weight per head on the grain-sorghum malesterile F I 's was slightly lower than for the A-lines, while seed weight per head on the sorgo male-sterile F I 's was substantially greater than on either of the other two female types. Seed yield per land area was not given. The A-lines used differed in each of the three groups of material, and seed weights of F I 's could not be compared with those of their component A-lines. Although published information on comparisons of three-way with single cross forage-type hybrids is limited, more extensive literature is available for grain sorghums as indicated in a recent report (2). The objectives of this study were to I) compare seed yield and other agronomIC traits between malesterile F I seed parents and their component A-line seed parents in the production of sorghum-sudangrass hybrids in two different groups of germplasm, 2) determine phenotypic correlations among traits within parental groups, and 3) relate the findings to hybrid seed production. Evaluation of the hybrid seed produced in terms of forage production will be reported in a subsequent paper. MA TERIALS AND METHODS The seed parents used in Study 1 were nine combineheight cytoplasmic male-sterile A-lines and their 36 malesterile AX B-line crosses (FI'S) that were identical to those used in a similar study with grain sorghum hybrids (2). The A-lines included KS4, KS23, 'Martin', N30, N35, N36, N38, WD4, and 'Wheatland'. In Study 2, the seed parents were seven A-lines and their 21 male-sterile F t's. The A-lines were KS5 and KS9, described by Ross et al. (4); N38 and N48, described by Ross et al. (5); N4692, described by Webster et al. (7); N50I3, an experimental line; and the cultivar Redlan. The pollen source was produced from a composite of equal seed weights of the sudangrass cultivars Greenleaf and 'Piper', Nebraska 7035, and experimentallow-dhurrin strains of Greenleaf and Piper. This heterogeneous pollen source assured continuous and adequate pollen dispersal to the female parents over the range of their stigma receptivity. The sudangrass composite was seeded in double rows, with six rows of male-sterile sorghums being grouped between each pair of sudangrass rows. The outside rows of each group of six male-steriles were seeded to cytoplasmic male-sterile 'Combine Kafir-60', which served as unharvested border rows to minimize any effect of the taller sudangrass rows on the four randomly assigned male-sterile lines and F I hybrids that were harvested in each group. The experiments were planted 29 May 1979 and 27 May 1980 at the University of Nebraska Field Laboratory, Mead, in a medium textured Sharpsburg silty clay loam soil (fine, montmorillonitic, mesic Typic Argiudoll) to which 112 kg haI of N had been applied. Four replications of singlerow plots 7.6 m long and 0.76 m apart in a randomized complete block design were used each year. All plots were overseeded and thinned to 15 em between plants, giving a plant population of about 87 000 plants ha1• The exper1134 Published in Crop Science (November-December 1984) v.24, no. 6

A study was conducted at Perugla, Italy in 1981 to evaluate the importance of intra-specific competition in alfalfa (Medicago sativa L.) and to investigate the consequence of different percentages of inbred seeds on forage yield. Three seed mixtures having ratios of inbred seed to hybrid seed (S₁/F₁) of 1/9, 3/7, 1/1 were sown, seed by seed, in micro-plots (50 ✕ 30 cm) at a seeding rate of 1600 seeds/m². Data were collected on establishment, green matter yield per plant of inbred or hybrid origin, dry matter yield per plot at first, second, and third cut, height and number of stems per plant at the third cut, and number of plants alive in the fall season. The results are summarized as follows: 1) yield of S₁ plants was much lower than that of F₁ in each of the three mixtures; the inbreeding effect was higher than that usually shown in spaced plant trials; 2) since no differences were observed in dry matter yield per plot among mixtures, differences in S₁ seed percentage would not seem important to productivity of alfalfa in the 1st year; and 3) no differences were observed in establishment between S₁ and F₁ seedlings but fall survival percentages of S₁ plants were significantly lower than those of F₁ in all mixtures. This confirms that selective elimination of S₁ plants begins during the seeding year. The selection against S₁ plants increases over time and suggests that 1 year after seeding few S₁ plants will survive irrespective of their percentage in the initial seed lot.

In trials at several sites in 1972-4, average yield of hybrid seed when a male fertility restorer and several male-sterile wheat lines were sown in male:female ratios of 1:1, 2:1 or 3:1 in strips 3.1-11 m wide were 1.37, 1.0 and 0.84 t/ha, respectively, or 0.69, 0.67 and 0.64 t/ha when adjusted for the area occupied by the restorer. Decreasing the width of strips to reduce pollen travel distances did not increase yields. Higher yields were obtained by sowing the earlier restorer line 44 growing degree days (growing degree day = average of maximum and minimum temperature - growth threshold temperature in this case 4.4 deg C) before sowing the later male sterile lines than with 0, 22 or 66 growing degree day differences. Hybrid seed yields were highly correlated with restorer yields indicating that hybrid seed production was much more likely to succeed at high than at low yielding sites.

Cytoplasmic-nuclear male steriles are used as female parents in the production of hybrid seed of sorghum, Sorghum bicolor (L.) Moench. A single male-sterility inducing cytoplasm is most often used in the female parents, resulting in uniformity of cytoplasm in hybrids and also a restriction on nuclear diversity. The purpose of the present study was to identify diverse malesterility inducing cytoplasms. Seed set and other characteristics of hybrids of sorghum were studied to determine differences in fertility response and related characteristics among the cytoplasms of male-sterile female parents. Thirteen near-isonuclear female parents with cytoplasms from diverse introduced sources were crossed by eight male parents, and the progeny were grown at eight locations. From seed-set, anther, and pollen characteristics five groups were identified. Cytoplasms from IS6271C, IS2266C, IS3579C, IS7502C, and IS6705C were not distinguished from milo cytoplasm. Cytoplasm from IS12662C differed from milo in degree of fertility restoration in hybrids and was somewhat similar to IS3063C, IS1056C, and IS2801C. Another group, composed of IS1112C and IS12565C, was distinct in that most male parents produced highly sterile hybrids when crossed with these male steriles. Another cytoplasm, from IS7920C, differed from all the other cytoplasmstudied in its effects on seed-set, anther, and pollen characteristics. It is concluded that among these cytoplasms there are at least four distinct groups in their effects on fertility characteristics. They have potential for providing diversity among parents and hybrids in sorghum, but their utility for such purposes remains to be tested.

The interspecific relationships among several Trifolium spp. in the section Calycomorphum were studied. Crosses involving T. israeliticum, T. globosum, and T. pauciflorum failed to produce hybrid seed. Crosses among T. subterraneum, T. eriosphaerum, and T. pilulare gave varying results. Complete interspecific sterility was most common; however, 3 F₁ plants (1 plant from the T. eriosphaerum ✕ T. subterraneum cross and 2 plants from the T. pilulare ✕ T. subterraneum cross) survived till after flowering. The F₁ plants had morphological characteristics of both parents. F2 seeds were formed, probably through backcrossing, in two male sterile interspecific hybrids, T. subterraneum ✕ T. eriosphaerum and T. pilulare ✕ T. subterraneum. Fertility was partially restored in the F₃ and F₄ lines, although several fertile F₃ plants produced sterile progenies. The results suggest that this group is young and shares common morphogenetical and physiological systems because interspecific hybrids can be obtained by conventional methods. Morphological specialization is more advanced than the reproduction barriers because the taxa involved are self-fertilized annuals and are isolated spatially.

Mean performance and within-plot variability of parents and hybrids of grain sorghums [ (L.) Moench] were evaluated from the results of experiments conducted during 2 years in Iowa. Analyses of the data combined over years indicated that fertile single crosses and three-way hybrids did not differ significantly for mean grain yield, 100-seed weight, seeds/head, heads/plant, plant height, and days to midbloom. Mean within-plot standard deviations for plant height and days to midbloom of the three-way hybrids were significantly greater (P < 0.01) than those of single-crosses, but the differences do not seem large enough to be important agronomically.Mean grain yields of single and three-way crosses and within-plot standard deviations for the other characters were not highly correlated. Neither the differences between parents of male-sterile single crosses nor heterogeneity within parental lines was closely associated with level of variability within three-way hybrids. Male-sterile single crosses yielded significantly more (19%) than sterile lines as parents for the production of hybrid seed. Superiority of the single crosses resulted primarily from larger numbers of seeds/head.