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The development of functional root nodules resulting in N2fixation in soybean [Glycine max(L.) Merr] can be induced by two strains of rhizobia, Bradyrhizobium japonicum(B. japonicum) and Bradyrhizobiumspp. (cowpea‐type). Genetic control of response to each type has been recognized in soybeans with two categories identified after inoculation with cowpea‐type rhizobial strains: (i) promiscuous, which produces functional nodules, N2fixation, and green leaves; and (ii) nonpromiscuous, which forms no or nonfunctional nodules and yellow leaves. Using leaf color, segregation patterns indicated that nonpromiscuity was dominant with two alleles segregating at each of two independent loci. With this genetic model, the expression of promiscuity requires the presence of both recessive alleles at each locus. Since the cowpea strain is indigenous to the soils in many tropical areas, especially Africa, the development of promiscuous soybean cultivars would greatly increase soybean production without commercial seed inoculation.

The dwarfing alleles in wheat (Triticum aestivumL.) are associated with shorter coleoptile length that can produce unacceptable and erratic stands. The combined effect of temperature (2, 10, 18°C) and five gibberellic acid (GA) concentrations [0, 5, 50, 100, 500 mg L−1of potassium gibberellin A3(C19H21O6K)] in the germination medium on the coleoptile length of four homozygous isolines [normal or T‐0 (Rht‐B1a/Rht‐D1a), semidwarf‐1 or SD‐1 (Rht‐B1b/Rht‐D1a), semidwarf‐2 or SD‐2 (Rht‐B1a/Rht‐D1b), dwarf or D‐12 (Rht‐B1b/Rht‐D1b)] in ‘Marfed’ (spring) and ‘Burt’ (winter) was studied. With each decrease in temperature, the coleoptile length in each isoline and cultivar increased, with the increase greater in those isolines and cultivars having the shortest length at 18°C and containing at least one dwarfing allele (Rht‐B1band/or Rht‐D1b). At 2°C, higher GA concentrations increased coleoptile length over 0 GA mg L−1in all isolines, with the greatest increase at the 500 mg L−1concentration. The three midconcentrations (5, 50, 100 mg L−1) resulted in an intermediate but almost equal increase. Increasing temperatures decreased the response to GA so that at 18°C, only T‐0 and SD‐1 responded to GA applications. The reported “GA insensitivity” was found to be highly temperature dependent, with the Rht‐B1ballele having a wider temperature response range than Rht‐D1bThe results suggested that differences in genetic background, possibly related to the winter–spring growth habit, could influence the effect of the dwarfing alleles.

In the subtropical lower latitudes, rye (Secale cerealeL.) is used primarily for late fall‐winter‐early spring forage and, secondarily, for grain. Diploid and tetraploid forms are available, with tetraploids having many advantages over diploids in the amount, distribution, and quality of forage. Information on grain production is essential to develop appropriate breeding strategies for forage and grain types at each ploidy level. Various grain production traits (grain yield GY, seed weight = SW, test weight = TW, percent fertility = %F) of five adapted diploid (2x) cultivars (‘Florida Black,’ ‘Gator,’ ‘Elbon,’ ‘Explorer,’ ‘Wrens Abruzzi’) and their colchicine‐derived tetraploid (4x) forms were examined. Tests were conducted in three seasons (1981–1982, 1982–1983, 1983–1984) at two Florida locations (Gainesville—29°4′0 N Lat; Quincy‐30°3′ 5N Lat) at two seeding rates (0.5 and 1.0 viable seeds per linear centimeter of row). Over all environment(ss easons, locations, seeding rates), highly significant differences amongc ultivars within each ploidy level were found for GY, SW, TW, and %F. The environmental stability values (means, bvalues, deviation mean squares) at each ploidy levels were inconsistent, indicating that ploidy level influenced the environmental response. Over all cultivars and environments, the tetraploid‐diploid relationship [(tetraploid/diploid ✕ 100)] was 59% for GY, 116% for SW, 89% for TW, and 84% for %F. However, substantial differences in this relationship resulting from genetic background( cultivars) were found for GY (range = 41–101%), SW (range = 98–134%), TW (range = 82–93%), and %F (range = 77–95%). Apparently, genetic background as well as environment influenced ploidy level differences. The results indicate that selection within each ploidy level should be effective in improving various grain characteristics, but testing and selection in a number of seasons and locations would be necessary.

Environment and genetics influence the process of nodulation in soybean [Glycine max(L.) Merr.]. To select for increased N2fixation in soybean, plant breeders need to identify those morphological traits associated with the fixation process. The objectives of this study were to classify cultivars (Maturity Groups V through IX) and breeding lines for nodule weight, nodule number, and shoot and root weight at the R3 to R4 stage of development under field conditions in Gainesville, FL. Of the 100 soybean genotypes screened in 1983, 17 were selected for more detailed study in 1984 and 1985. ‘Hardee’, ‘Centennial’ and F81‐7313 ranked among the genotypes with the greatest nodule weight and number; and these rankings were consistent across years and locations tested. Environmental stability analyses showed that those lines with the greatest mean nodule weight also had the greatest positive response to favorable environments. Nodule weight and number were highly correlated traits (r> 0.84). Root and shoot weight had moderately positive correlations with nodule number and nodule weight.

Red clover (Trifolium pratenseL.) is an important forage species grown in temperate climates around the world. Most genetic transformation methods require regeneration of whole plants from single undifferentiated cells, but one of the major problems encountered in red clover tissue culture is low frequency of plant regeneration. Nine genotypes of red clover, with a range in the level of callus formation and plant regeneration [low (01L, 04L, 30L), intermediate (231, 641, 741), and high (34H, 54H, 71H)] on a B5 basal salts medium protocol, were used in a combining ability study of in vitro callus formation and plant regeneration. Hypocotyl sections from 40 progeny from each of 36 F1crosses were evaluated on a B5 medium protocol for callus formation at 4 wk of culture and plant regeneration at 12 wk of culture. Analysis of variance showed significant effects of crosses, general combining ability (GCA), and specific combining ability (SCA). Results obtained from diallel analysis (Griffing's Method 4, Model I) showed that crosses with 34H, 54H, or 71H as one parent were among the combinations showing the highest callus diameter and regeneration capacity. Those crosses with OIL, 04L, or 30L as one parent were among the lowest in callus diameter and regeneration response. A highly significant positive relationship (r= 0.91, df = 34) was found to exist between callus diameter and regeneration capacity. Although both general and specific combining ability (SCA) were significant sources of variation for callus diameter and plant regeneration, SCA effects were significant for only a few crosses. The results are in agreement with our previous research showing that red clover regeneration from tissue culture can be improved using recurrent selection methods which exploit additive genetic effects. Initial selection for large callus size should result in improved regeneration capacity.

The late fall planting season for rye in the southeastern USA is typically characterized by an extreme range of temperature conditions. The potential for selection of diploid and tetraploid rye (Secale cerealeL.) populations possessing superior seedling growth characters over a broad range of temperatures was assessed by examining the effect of genetic background on various seeding growth characters at three temperatures (12, 20, 28°C). Diploid populations, and their colchicine‐derived tetraploid counterparts from five genetic backgrounds (‘Elbon’, ‘Explorer’, ‘Florida Black’, ‘Gator’, ‘Wrens Abruzzi’) were compared. The seedling characters included shoot and primary root growth day−1, root cross‐sectional area at the meristematic region, and primary root bluntness ratio (distance from the plane of maximum root diameter at the meristematic region to the root tip divided by the maximum root diameter at the meristematic region). Highly significant ploidy level (PL), genetic background (GB), and temperature (T) main effects were obtained for both shoot and primary root growth day−1. A highly significant T✕GB✕PL interaction was found for shoot growth day−1, but this effect was not significant for root growth day−1. The T ✕ PL interaction was significant for primary root growth day−1at the 0.05 level. Highly significant ploidy level (PL) and temperature (T) main effects were obtained for root cross‐sectional area. A highly significant ploidy level (PL) main effect was found for the bluntness ratio. The lower ratios obtained for the tetraploid populations indicated that the tetraploid root tips were blunter than those of diploids, which may be a factor in soil penetration and root proliferation. The results indicated that substantial genetic variation for seedling growth characters was present among genetic backgrounds as well as within populations at both ploidy levels over a wide temperature range. It was concluded that selection for diploid as well as tetraploid rye populations possessing superior seedling growth characters over a broad range of temperatures would be successful.

Autotetraploids differ from their diploid counterparts in many morphological, physiological, cytological, and ecological characteristics. The tetraploidy effect on the amount and environmental stability of rye (Secale cerealeL.) forage production was examined in this study. Six populations consisting of three diploid (2x) cultivars (‘Florida Black’, ‘Gator’, ‘Explorer’) and their autotetraploid (4x) derivatives were grown in two late fall‐winter‐early spring forage seasons (1979–1980, 1980–1981) at Gainesville (29°40′ N Lat) and Quincy (30°35′ N Lat), Fla., at two seeding rates (0.5, and 1.0 viable seeds/linear cm of row). Forage weight was obtained at a total of 16 clipping dates among seasons and locations (Gainesville—four dates in both seasons, Quincy—three dates in 1979–1980 and five dates in 1980–1981). The direction and magnitude of the differences between the forage production of the 2x and corresponding 4x populations were not consistent and were influenced by genetic background (2x cultivar source) and clipping dates within season and location. Apparently, the tetraploid effect was altered by genetic factors and many interacting environmental forces. Significantly higher production from the higher seeding rate was obtained primarily at the earlier clipping dates within each season and location but seeding rate interactions with all genetic and environmental variables were not significant. No differences among populations in environmental stability were found.

Autotetraploids differ from their diploid counterparts in many vegetative, reproductive, and ecological traits. The effect of tetraploidy on the forage quality of rye (Secale cerealeL.) grown in the lower latitudes was examined in this study. Six populations consisting of three diploid (2×) cultivars (‘Florida Black’, ‘Gator’, ‘Explorer’) and their autotetraploid (4×) derivatives were grown in two late fall‐winter‐early spring seasons (1979–1980, 1980–1981) at Gainesville (29°40′N Lat) and Quincy (30°35′N Lat), Florida. Two forage quality traits (in vitro organic matter digestion or IVOMD, crude protein or CP) were measured at a total of 16 clippings (Gainesville—four dates in each season, Quincy—three dates in 1979–1980 and five dates in 1980–1981). Over all clippings and genetic backgrounds, the IVOMD and CP of the tetraploids. No significant genetic background ✕ ploidy level interaction for either trait was present suggesting that autotetraploidy per se was the prime factor. Highly significant interactions for ploidy level ✕ cliping within season and location were found for both IVOMD and CP. The diploid‐tetraploid differences were more pronounced at the later clippings within each season and location but considerable variation in this pattern was observed among the various season‐location combinations. The genetic background ✕ ploidy level ✕ clipping within season and location (GB✕PL✕C/SL) interaction was significant for IVOMD but not CP. Regression analysis indicated that ploidy level altered the environmental stability of IVOMD but not CP. In general, the results of this study showed that the tetraploids, regardless of their genetic background, had a higher IVOMD, higher CP and a more uniform environmental response than their diploid counterparts.

Three varieties of diploid rye, ‘Florida Black,’ ‘Gator,’ and ‘Wrens Abruzzi,’ were crossed reciprocally to obtain six F1populations. The parental varieties and the F1populations were compared for plant weight and grain production under space‐planted conditions in 2 years at Gainesville, Florida. The plant weight of the F1population ranged from 99.2 to 120.4% of the higher parent, with 5 of the 6 F1populations exceeding the higher parent. The variability in plant weight ranged from 86.8 to 104.0% of the higher parent, with 3 of the 6 F1population surpassing the higher parent. The grain production of the F1populations ranged from 60.7 to 112.4% of the higher parent, with 3 of the 6 F1populations exceeding the higher parent. The variability in grain production ranged from 19.3 to 415.3% of the higher parent, with 3 of the 6 F1populations surpassing the higher parent. Appreciable differences in combining ability between the parental varieties were obtained. However, the magnitude of the heterotic response was also considerably influenced by the direction of the cross and the year tested.

Three diploid rye varieties, their 3 F1populations, and 6 composite populations were compared for forage and grain production at 3 levels of population density in 2 years at Gainesville, Florida. Each composite population contained equal numbers of viable seeds from one F1population mixed with one of its parents. Heterosis for forage and grain production was obtained in certain F1populations, with indications that differences in combining ability between the varieties were present. The production of the composite populations could not be accurately predicted from the production of the F1population and the parental variety involved. However, the presence of the parental variety in the composite populations did not appreciably lower and, in some cases, substantially increased production in comparison to the F1population involved. In some instances, the presence of one of the parents in the composite population reduced environmental variability and altered the percentage contribution of various environmental components, thus making possible more flexibility in selection for specific environmental response patterns.

F1hybrids between Secale montanum(P1253956) and three varieties (‘Florida Black,’ ‘Gator,’ and ‘Wrens Abruzzi’) of S. cerealewere made with S. montanumthe female parent in each cross. F2populations were produced by interpollination within each F1population. Forage production and plant weight after final clipping were measured on plants from each population grown under space‐planted conditions in 1965–66 and 1966–67 winter seasons. or both characters, substantial heterosis was obtained in certain F1populations with the amount depending on the S. cerealevariety involved and the year tested. Heterosis for forage production in all hybrid populations was expressed late in the vegetative development of the plant. The response of the hybrid populations to yearly differences in environment was variable and associated with the character being measured. In comparison to the parents the variation within the hybrid populations was low. In general, the differences between the F1and F2populations were small.

F1hybrids between Secale montanum(P.1.253956) the female parent and three varieties (‘Florida Black,’ ‘Gator,’ and ‘Wrens Abruzzi’) of S. cerealewere made. F2populations were produced by interpollination within each F1population. Under natural daylength and space‐planted conditions, 40% of the S. montanumplants produced seed in 1965‐66 and 10% in 1966‐67, whereas 100% of the plants in the S. cerealevarieties and 70 to 100% of the F1and F2plants produced seed. For number of seeds, seed weight, and grain yield, the F1populations were generally intermediate to the parents with S. montanumthe lower parent in all combinations. The F2populations tended to produce a larger number of seeds than the corresponding F1. Substantial differences resulting from the S. cerealevariety involved and year tested were observed. The variability of both the F1and F2populations as a result of differences in years and the variation within the F1populations were greater than the higher parent. However, the S. cerealevariety involved was a major factor. With 16‐hr daylength, the F1populations were generally below or equal to the mid‐parent in percent stainable pollen with S. montanumthe lower parent in all combinations. However, the corresponding F2populations were higher in percent stainable pollen with two out of three combinations exceeding the S. cerealeparent. The pollen diameter of the F1and F2populations was generally intermediate to the parents with S. montanumthe lower parent in all combinations.

Narrow sense heritability values were determined from actual selection response and in standard units using 94 populations grown in replicated trials in 1964, 1965, 1966, 1967, 1968, and 1969 at Gainesville, Florida. Eighty‐nine of the populations were homogeneous and homozygous lines with diverse genetic backgrounds derived from crosses involving Avena sativaL. and A. byzantinaC. Koch. Five were recommended varieties. Heritability values by selection response were determined using three levels (upper 10, upper 25 and upper 47 of the 94 populations) of selection and the mean of the 94 populations as a reference point for response. Over all levels of selection, the values ranged from _.55 to .76 for individual year comparisons. When individual years were compared to the 6‐year mean, the range was _.05 to .87. No consistent differences were found as a result of selection level although in a few cases selection of the upper 25 instead of the upper 10 resulted in higher values. Heritability values determined in standard units ranged from _.05 to .63 when individual years were compared and from .11 to .67 when individual years were compared to the 6‐year mean. In general, values between individual years and the 6‐year mean were equal to, or higher than, those between individual years. A hypothetical selection and testing procedure was designed in which the yields of 1, 2, 3, 4 and 5 years were combined at random to determine the effect of the number of years tested on the heritability values relative to the 6‐year mean. No substantial or consistent changes in values were obtained as the number of years tested was increased.

A positive relationship between crown traits of greenhouse‐grown plants and crown development in the field would allow for the efficient evaluation of large populations of bahiagrass (Paspalum notatumFlügge) for rapid stand establishment. The objective of this study was to determine if young plants exhibiting greater crown vigor (expressed as rapid crown area growth and profuse tillering) in the greenhouse would result in larger, more vigorous plants when grown in the field. Fifty young bahiagrass plants, from each of four cycles (C0, C4, C9, and C23) resulting from recurrent restricted phenotypic selection (RRPS), were evaluated in the greenhouse for plant vigor, crown width, crown wet weight, and tiller number. Plants were transplanted to the field and crown area was determined at 6 and 15 mo after establishment. Crown vigor of greenhouse plants was greatest for C4 and C9 plants. Vigor ratings for C9 plants were smaller (P< 0.05) than C4 in Exp. 2, but larger than C0 and C23. Crown area, crown wet weight, and tillering of the greenhouse plants favored plants from C4 populations. Greenhouse plants of C23 generally had smaller crowns and less tillering. Crown area of individual plants from greenhouse plants, for all cycles, was positively correlated with crown area in the field after 6 mo following transplanting (r= 0.74 to 0.87 for Exp. 1 and 0.75 to 0.93 for Exp. 2). At 15 mo after transplanting to the field, bahiagrass crowns had filled the area between spaced plants. Selecting young superior bahiagrass plants in the greenhouse should aid breeders in developing germplasm that could hasten field establishment.

The yield of 94 populations consisting of 89 homozygous and homogeneous lines and five recommended varieties was tested for 6 years at Gainesville, Fla. The r values between the yield of the 94 populations and their variability in yield over the 6 years were as follows: 1964 = −.24*; 1965 = −.79**; 1966 = .03; 1967 = −.39**; 1968 = −.47**; 1969 = −.37**; and six year mean = −.60**. Selection for high yield generally resulted in selecting populations with low environmental variability.