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Plant breeders have attempted to enhance yield by selecting for individual traits since the beginning of plant breeding. This approach has been broadened to encompass the breeding of model plants or ideotypes. An ideotype is a hypothetical plant described in terms of traits that are thought to enhance genetic yield potential. Ideotype breeding is defined as a method of breeding to enhance genetic yield potential based on modifying individual traits where the breeding goal (phenotype) for each trait is specified. The purposes of this paper are to elaborate on and evaluate ideotype breeding as a method to enhance genetic yield potential and to describe an ideotype for barley (Hordeum vulgareL.). Successes that have occurred in breeding to enhance yield with individual traits, the value of genetic diversity for individual traits, and benefits from goal setting are presented as arguments in support of ideotype breeding. Alternatively, information is presented on the requirement of symmetry in size among plant parts, compensation among plant parts, pleiotropy, and genetic background, all factors that may slow progress in ideotype breeding. Ranges of genetic diversity, heritability estimates, and introgression information are presented for 27 barley traits. A barley ideotype consisting of 14 traits and the target or goal for each trait are described. Ideotype breeding is recommended as a methodology to augment traditional plant breeding, when the breeding goal is enhancing genetic yield potential. Breeding experience and research to date suggest that ideotype breeding is not a suitable substitute for traditional yield breeding.

Production of tillers and their subsequent survival are important events in growth and development of barley (Hordeum vulgareL.) that affect the number of spikes produced per unit land area. Studies were conducted at St. Paul and Crookston, MN to evaluate tiller production, tiller mortality, and yield of 10 barley genotypes with different tillering capacities. In addition, these studies evaluated the influence of row spacing and seeding rate on tillering. The genotypes differed significantly in shoot and spike number. Shoot number for the highest tillering genotype was 42 to 71% greater than for the lowest, depending on the study, but the genotypes ranked consistently over years and locations. The high tillering genotypes tended to form tillers more frequently at the coleoptile node, in the axil of the third leaf, and from the primary tiller in the axil of the first leaf on the main shoot. In general, absolute shoot mortality (difference between maximum shoot number and spike number) was higher in the high tillering genotypes. Genotype M72‐269 was an exception to this generalization in having high shoot number and low shoot mortality. Row spacings of 7.5 and 15 cm had more shoots per unit area than the 30 cm spacing. However, narrower rows also had higher shoot mortality which led to similar spike numbers for the three row spacings. Higher seeding rates of 101 and 134 kg ha‐1increased shoot number and spike number compared to the 67 kg ha‐1rate. Changes in row spacing and seeding rate did not differentially affect shoot production or absolute shoot mortality among the genotypes. Grain yields of both low and high tillering genotypes were as high or higher than those of intermediate tillering cultivars. The extremely high and low tillering genotypes were not consistent in their yield performance at Crookston, suggesting a possible association between tillering capacity and yield stability. Small stem diameter and a tendency to lodge were characteristic of the high tillering genotypes. Identification of apparent genetic diversity for tiller mortality provides material for further study of the relationship between tiller mortality and yield.

The purpose of this research was to obtain information on the contribution of semidwarf stature, high head number, and high kernel number to increasing grain yield in barley (Hordeum vulgareL.) in Morocco. The three traits were selected because of their potential to enhance grain yield. Six populations, two for each character, were developed by crossing the Moroccan cultivar ‘Arig 8’ to six Minnesota lines and then backcrossing the F1's to Arig 8. This was followed by selection in the BC1F3generation in St. Paul, MN, and in the BC1F4generation in Morocco. Data were collected in Morocco from yield trials conducted in four field environments in 1981–1982 and 1982–1983. The procedure of introducing yield‐related traits via backcrossing to an adapted cultivar gave progenies that were superior to the relatively high‐yielding local cultivar, Arig 8. Eleven lines from the head number populations and eleven from the kernel number populations produced significantly higher grain yields than Arig 8. Two semidwarf lines were superior in yield to Arig 8. Semidwarf selections had increased lodging resistance and harvest indices, but were relatively taller in Morocco than in Minnesota. Generally, the highest yielding lines had modestly higher head number (differences not significant) or higher kernel number than Arig coupled with high kernel weight. Kernel weight was higher or near the high level of Arig 8 in most of the highest yielding lines. We could not determine whether the transgressive segregation for grain yield resulted from breeding for the three characters in question or from the reassortment of other genes from Arig 8 and the Minnesota parents. In this breeding effort the major limiting factor appeared to be an inability to consistently obtain uniform yield trials, and not available germplasm.

Breeding for erect leaf angle has been suggested as a method for increasing grain yield in cereal crops. This study was designed to investigate the effect of erect leaf angle on grain yield in barley (Hordeum vulgareL.). Five cycles of crossing and selection were used to incorporate the erect leaf of C16146 into adapted Minnesota barleys. Subsequently, erect leaf lines from five populations were evaluated in yield trials. In addition, the yield response of erect leaf lines was compared to check cultivars at planting rates of 56, 94, and 132 kg ha−1. No significant difference was found for grain yield between erect leaf lines and check cultivars in three populations. Comparisons of erect and horizontal leaf progeny in two other populations showed no difference in one population; however, the horizontal leaf group was higher yielding in the second. The yield responses of erect and horizontal leaf‐types to the three planting rates were similar, although significant interaction was observed for kernel number and weight, suggesting that canopy type may influence these components. Erect leaf lines had less culm flex, more erect spikes, lower head number, later maturity, and greater lodging resistance than horizontal leaf lines. These associations with the erect leaf trait, which likely resulted from pleiotropy, were confounded with the effect of erect leaves and likely reduced the chances of finding a positive grain yield response. Although the potential of increased lodging resistance and the leaf‐type density interaction for kernel number and weight offer some encouragement for continuing research, results from our study provide little or no evidence that erect leaf angle enhances grain yield in barley.

The presence of genetic information in organelles of the cytoplasm suggests that certain nucleus‐cytoplasm combinations may be superior in terms of crop productivity or crop quality. The objective of this study was to examine cytoplasmic effects on eight agronomic and seven malting quality traits in six‐rowed malting barley (Hordeum vulgareL.). Backcrossing was used to incorporate the nuclear genome of two malting cultivars, ‘Conquest’ and ‘Dickson’, into six diverse cytoplasms represented by three H. vulgarecultivars and three other Hordeumspecies. Backcross derived lines and Conquest and Dickson were evaluated in field trials at two Minnesota locations in 1978 and 1983. In all, 15 traits were examined in 12 different nucleus‐cytoplasm combinations. There was little evidence of cytoplasmic effects on the agronomic traits and none for the malting quality traits. The six cytoplasms failed to influence any of the traits in combination with the Conquest nuclear genome. In the Dickson backcrosses, ‘Betzes’ cytoplasm resulted in a slightly earlier heading date, and H. spontaneumvar. spontaneumcytoplasm resulted in an earlier heading date and fewer plump kernels. The different performance of the Conquest and Dickson backcross derived lines may indicate a failure to rid the Dickson derived lines of nuclear genes from the cytoplasm donors or be evidence of nuclear‐cytoplasm genotype interaction.

Five to six cycles of crossing and selection have resulted in well‐adapted semidwarf barleys (Hordeum vulgareL.). The original semidwarf stock was a radiation mutant obtained in the Norwegian cultivar, ‘Jotun.’ This report provides a comparison of the performance of these semidwarf barleys and their normal‐height counterparts. Lines from five populations were compared in field environments for yield and 10 other characters. Inheritance information also was obtained using five populations. The semidwarf lines had higher mean yields than the normal lines in four of the five populations, but the yield difference was modest, amounting to 3% for the average of the five populations. Lodging did not influence yield in these experiments. The semidwarf lines had 7% more tillers, 10% more heads, and a 14% higher harvest index than the normal lines based on the mean of five populations. The semidwarfs also had 10% longer coleoptiles than the normal lines, based on the average of four populations. The normal lines were 5% higher in total dry matter and 8% higher in kernel weight. From the results of this study, it appears that the lengthy breeding program has resulted in semidwarf barleys that have potential for direct use as cultivars and as parental material. If so, the effort illustrates an important principle, i.e., capitalizing on "new germplasm" may require a prolonged breeding effort. Results of this study plus our experience in the semidwarf breeding program indicate that a single gene controls the semidwarf character in this material. The symbol suggested for this gene is sdw.

Three preanthesis growth periods were studied in barley (Hordeum vulgareL.) in order to identify genetic variation and estimate heritability for the three periods. Duration of the three periods, leaf initiation, spike initiation, and spike growth, was determined in a field experiment by dissecting and observing shoot apices. In a comparison of 10 cultivars, mean duration of the leaf initiation, spike initiation, and spike growth periods was 10.2, 9.6, and 20.6 days, respectively. Genetic diversity was found for each of the three periods with cultivar means ranging from 4.9 to 13.6, 7.3 to 12.2, and 17.1 to 23.5 days. Cultivars with similar duration of the vegetative period exhibited modest but significant differences in duration of the three periods. Cultivar means for rate of spike initiation ranged from 1.8 to 2.5 nodes per day; these differences were not significant. Duration of leaf initiation was correlated with leaf number; duration of spike initiation with leaf area, spikelet primordia number, and kernel number; and duration of spike growth with leaf area, height, spikelet primordia number, spikelet primordia survival, and kernel number. Parent‐offspring heritability estimates were 0.43, 0.60, and 0.68 for duration of the leaf initiation period in three segregating populations. Inconclusive evidence was obtained for a major gene affecting duration of the leaf initiation period in two of the three populations. Genetic variation was nonsignificant for duration of the spike initiation period in the three populations and heritability estimates were not different from zero. Estimates of heritability for duration of the spike growth period were 0.59, 0.23, and 0.74. The correlations involving leaf and kernel number with duration of two of the growth periods indicate possible benefits from breeding for optimum duration. While conjecture on the optimum duration of the three growth periods is probably not warranted, genetic variation in duration of the growth periods might be used in breeding for increased yield via obtaining durations better suited to specific environments.

Research was initiated in 1965 to identify and incorporate genes for high tiller number into midwestern six‐rowed barley, Hordeum vulgareL. The objective of this paper is to report on the performance, especially yield, of barleys with high tiller and head number from this program. Cyclic crossing, primarily backcrossing, and selection were used to develop high tillering lines that had agronomic promise. When the source of high tiller number was a two rowed barley, XH‐263, lines were evaluated after four cycles (Exp. 1) and seven cycles (Exp. 2) of breeding and when the source of high tiller number was six rowed Sel. 6194‐63, lines were evaluated after four Cycles of breeding (Exp. 2). Good progress in incorporating the genes for high tillering into a good genetic background was achieved using cyclic crossing and selection. High tillering lines developed in Exp. 1, had better agronomic performance than XH‐263, but they were lower yielding than the checks. However, in Exp. 2, the high tillering parents, Minn 73‐129 and Minn 75‐61, were nearly equal to the checks, Minn 34 and Minn 38, in yield and mean yields of individual high tiller number lines exceeded the checks, although not significantly. In Exp. 2, four groups of lines which differed in tiller number had similar yields. In both experiments, high tillering lines were high in head number and tiller mortality, low in kernel number per head and kernel weight, and susceptible to lodging. Because of high tiller mortality, breeding for increased tiller number was only 36% effective in terms of adding additional heads. We plan to continue this breeding effort since improvement in yield was achieved in the high tillering lines during the several cycles of breeding.

Several studies of various crop species have suggested the possibility of identifying an optimum grain‐filling duration for improving grain yield. Accordingly, a research program on grainfilling duration and its relationship to grain yield in barley (Hordeum vulgareL.) was initiated at the University of Minnesota, St. Paul in 1970. Two and three cycles of crossing and selection were used to incorporate variability for grain‐filling duration into improved genetic backgrounds. Ultimately, lines from four populations were grown in field trials in 1979, 1980, and 1982 to study the relationship between grain‐filling duration and grain yield. These lines were selected to assure diversity for grainfilling duration, while having similar maturity. Significant differences among genotypes for grain‐filling duration were found in all populations. Long duration lines spent an average of 3 to 7 days longer in the grain‐filling period than short duration lines. Although grain‐filling duration varied with environment, the long and short duration classes remained distinct. In spite of the consistent differences in grain‐filling duration there was no significant association between grain‐filling duration and yield in these populations. Failure to detect a yield advantage due to differences in grain‐filling duration in lines with similar maturity suggests that any advantage derived from alteration of the grain‐filling period may have been outweighed by the coincident change in length of the vegetative period. Genetic differences among lines for traits other than grain‐filling duration, such as synchrony of anthesis, may have limited our ability to find an association between grain‐filling duration and yield. Based on our research, selection for an optimum grain‐filling duration to improve grain yield does not appear to be a worth while objective for upper midwestern‐type barleys.

We studied inheritance of Stomatal frequency in five barley (Hordeum vulgareL.), populations and the effect of Stomatal frequency on photosynthesis, transpiration, and Stomatal resistance to diffusion. The latter studies were done using barley lines high and low in Stomatal frequency from two backcross populations. Heritabilities, estimated by the parent‐progeny regression method, ranged from 22 to 74%. These estimates were for the F2and F3generations on the individual plant basis. Realized heritabilities based on simulated high and low selection were in good agreement with the regression estimates, although the estimates were consistently higher for the high than for the low selection. For plants pretreated to assure open stomata, Stomatal diffusive resistances and transpiration rates differed statistically among lines, but photosynthesis did not. Lines having low Stomatal frequencies had higher Stomatal resistances, and transpired less water than lines with more stomata. A 25% decrease in frequency of stomata reduced transpiration rates by about 24%. Stomatal frequency did not influence the rate of photosynthesis, however. Hence, the possibility exists of altering transpiration without altering photosynthesis by selecting varieties with fewer stomata.