Search

Wild diploid goatgrass, Aegilops tauschiiCoss., is the D-genome donor to hexaploid bread wheat. Goatgrass has been crossed with tetraploid durum wheat (Triticum turgidumvar. durumL.) and hexaploid bread wheat (T. aestivumL. ssp. aestivum) to broaden the genetic base of bread wheat. We examined the contribution of main stem water-soluble carbohydrates (WSC) and current assimilates to grain yield in one goatgrass relative to those in one durum and four cultivars of bread wheat under well-watered and droughted field conditions across two years. Drought reduced grain yield and its components. Number of tillers per plant was higher in goatgrass, but 55% of tillers produced were sterile. Number of grains per spike was lower in goatgrass. Grain weight was the component severely limiting potential yield in goatgrass. Main stem WSC and concentration was lowest in goatgrass. Linear rate of grain growth in goatgrass was 20 and 17 mg spike-1day-1under well-watered and droughted conditions, whereas those in durum and bread wheats ranged from 55 to 73 and from 37 to 60 mg spike-1day-1, respectively. Current assimilates were the major source of carbon to fill the grains under both irrigation regimes. A large number of goatgrass accessions and adapted durum cultivars should be examined for grain yield and its components to identify promising accessions to be used in producing synthetics.

Grain filling in wheat crops grown in semiarid regions may depend more on stored water‐soluble carbohydrates (WSC) than on current photosynthesis. We evaluated the hypothesis that internode WSC content, specific content (WSC content/internode length), and concentration (WSC content/internode weight) of genotypes affect accumulation and mobilization of stem WSC. Genotypic variation for internode WSC‐related traits was measured on the main stem at 10‐d intervals in 11 diverse wheats grown under well‐watered and droughted field conditions across 2 yr. Relationships among internode WSC‐related traits were determined. Date of harvest was the most important factor affecting internode WSC‐related traits followed by genotype, irrigation, and year. Genotype × date of harvest was the most important interaction. Drought reduced WSC content, specific content, and concentration in different internodes, except WSC concentration in peduncles. Mobilized WSC from peduncle, penultimate, and lower internodes ranged from 70 to 244 mg, from 95 to 227 mg, and from 175 to 450 mg, respectively. The lower internodes provided 51% of the stem mobilized WSC. Mobilized WSC was higher in well‐watered than in droughted conditions for penultimate (164 vs. 135 mg) and lower internodes (274 vs. 244 mg). Drought improved mobilization efficiency in the peduncle, penultimate, and lower internodes by 33, 17, and 11%, respectively. Postanthesis maximum WSC content was highly correlated (r= 0.89 to 0.99) with the amount of WSC mobilized in different internodes, and could be used as a selection criterion to stabilize grain yield under stressful environments.

Wheat crops grown in dryland areas may depend more on stem reserves for grain filling than on current photosynthesis. We evaluated the hypothesis that internode length, weight, and specific weight of genotypes affect accumulation and mobilization of stem reserves. This knowledge might complement selection in stressful environments. Genotypic variation for internode characteristics and their effects on dry matter accumulation and mobilization were measured at 10‐d intervals in 11 diverse wheat cultivars grown under well‐watered and droughted field conditions across 2 yr. Relationships among internode characteristics and accumulation and mobilization of stem reserves were determined. The main effect of year, irrigation, genotype, and harvest date and genotype × harvest date interaction were significant. Internode length, weight, and specific weight were reduced under drought. Mobilized dry matter from peduncle, penultimate, and the lower internodes ranged from 43 to 171, 81 to 272, and from 198 to 474 mg, respectively. Mobilized dry matter was less in well‐watered than in droughted conditions for peduncle (93 vs. 110 mg) but not for penultimate (173 vs. 143 mg) and the lower internodes (331 vs. 304 mg). Drought increased mobilization efficiency, expressed as percentage of maximum dry mater mobilized, in the peduncle, penultimate, and the lower internodes by 65, 11, and 5%, respectively. Stem maximum specific weight was correlated (r= 0.64) with stem mobilized dry matter. Balanced partitioning of stem length into upper and lower internodes and internode maximum specific weight are important in genotypic accumulation and mobilization of stem reserves in wheat.

Abstract: Variation and heritability of seed mass in the Mesoamerican crop chia, Salvia hispanica L. was studied to examine the feasibility of selection for the trait. Genotypic variation in seed mass in wild/cultivated and domesticated accessions of chia from different origins was assessed. Broadsense heritability of seed mass was estimated using variances associated with parental and F2 generations derived from two crosses and from the response to one cycle of selection. Significant (P . 0.0001) genotypic variation was observed among accessions. Mean seed mass for domesticated accessions (14.84 mg/100 seeds) was greater than that of the wild accessions (11.29 mg/100 seeds) by 31%. The heritability of seed mass was relatively high in chia (0.75), suggesting that this trait is under strong genetic control. This conclusion was supported by a single selection cycle from the F2 to F3 generation that produced a 16% increase in mean seed mass. The realized heritability estimated based on this one cycle of selection also was 0.75. These observations indicate that gains from selection in chia seed mass are possible when mass selection is conducted in early generations. Basic information is thus provided for future breeding efforts in a species for which little or no knowledge of inheritance currently exists.

Aegilops neglectaReq. ex Bertol. is a forage goatgrass that has tetraploid and hexaploid forms. No morphological trait is known to distinguish between the two forms. Accessions of Ae. neglectarepresenting diverse germplasm were characterized for stomatal frequency and size on the adaxial surface of leaves. Stomatal frequency among tillers within a plant and among leaves on a tiller was measured. Significant variation was found in stomatal frequency between the ploidy levels for basal leaves 2 and 3 and the penultimate and flag leaves. Mean stomatal frequency for basal leaves ranged from 50.24 to 54.80 per mm2for tetraploid and from 39.24 to 40.50 per mm2for hexaploid accessions. For upper leaves, it varied from 52.88 to 53.50 per mm2for tetraploid and from 46.12 to 46.40 per mm2for hexaploid accessions. The two ploidy forms also exhibited clear differences for stomatal size on the basal and upper leaves of the main tiller. Mean stomatal size for the basal leaves ranged from 41.42 to 46.09 μm for tetraploid and from 53.59 to 54.97 μm for hexaploid accessions. For upper leaves, stomatal size varied from 47.29 to 53.29 μm in tetraploid and from 64.76 to 66.84 μm for hexaploid accessions. None of the individual accession ranges overlapped between the ploidy levels. Stomatal frequency and size were highly negatively correlated. Increased ploidy in Ae. neglectahas resulted in fewer but larger stomata per unit leaf area. Stomatal size and/or frequency on the adaxial surface of leaves could be used to distinguish tetraploid from hexaploid cytotypes in Ae. neglectain fresh material from Turkey collected in the field.

Positive performance is reported for centric translocations of chromosome 1 of rye (Secale cerealeL.) in bread wheat (Triticum aestivumL.). Objectives were to determine the effects of short arm translocations of rye chromosome 1 (1RS) derived from ‘Kavkaz’ winter wheat, in ‘Pavon’ spring wheat background, on root biomass, water‐use efficiency, and agronomic performance. Pavon and its translocations were evaluated in glasshouse pot experiments in 1997 and 1998 and in field experiments in 1999 and 2000 under well‐watered and droughted treatments. The 1RS translocations in Pavon delayed maturity, reduced plant height in some cases, and increased root biomass. Association between root biomass and grain yield was significant under droughted and under well‐watered conditions. The 1RS translocations increased grain yield and grain weight, especially under well‐watered field conditions. The overall mean grain yield was 4.066 Mg ha−1for Pavon, 4.895 Mg ha−1for 1RS.1AL, 4.503 Mg ha−1for 1RS.1BL, and 4.632 Mg ha−1for 1RS.1DL. The 1RS translocations, in general, were more tolerant to field environmental stresses than Pavon. These results encourage the development and use of the 1RS.1AL and 1RS.1DL translocations in wheat breeding programs.

Insect tripping might enhance seed production in common bean (Phaseolus vulgarisL.). The effect of flower visits by insects on seed production was studied during 3 yr, 1992 to 1994, in Riverside, CA, using four cultivars with different growth habits: Linden, Pindak, PI 164778, and Ferry Morse 53 (FM 53). Each year, a factorial experiment in a randomized complete block design with four replicates was used. Each cultivar was grown under three treatments: (i) exposed to open visitation by all insects, (ii) in insect‐proof cages, and (iii) in cages with bumblebees. All pods produced by bean plants were collected and counted, and seed yield was determined. Year‐to‐year variation had signiticant impact on cultivar performance and treatment effects. The bean lines were significantly different for seed yield. The treatment effects were not consistent across years. The old cultivar FM 53 and line PI 164778 had no clear trend for seed yield response to insect visits across years, whereas Linden and Pindak showed a more defined and positive response to visits. Seed yield of Linden was similar in the open visitation and caged‐with‐bumblebees treatments but was significantly higher than that of caged plants, by 13% in 1992 and by 35% in 1994. Pindak showed a 9% increase in seed yield when plants were visited by insects in the open or in caged treatments compared with caged plants in 1992. The results indicate that cultivars such as Linden and Pindak, which behave as determinate plants, may respond to bumblebee tripping by increasing seed yield.

Parents, F1, F2, and backcross generations (BC1and BC2) of a cross of safflower, Carthamus tinctoriusL., were planted at two locations in Iran (Safiabad and Ahvaz). Data were collected on yield/plant, heads/plant, seeds/head, seed weight, flowering time, and height. Location effects were either significant or highly significant for all traits except for heads/plant. Generation differences were either significant or highly significant for all traits except for heads/plant and seeds/head. Location ✕ generation interaction was significant only for seed weight. Genetic analysis of the generation means were carried out at each of the two locations for those traits that showed significant differences among generaions. Dominance played a major role in the variation of yield/plant and seeds/head at Safiabad. For the remaining traits at either location, in addition to different degrees of additive and dominance effects, significant interallelic interactions were obtained. The full model analysis for seed weight showed, in addition to highly significant additive and dominance effects, a highly significant additive ✕ location interaction. Dominance ✕ location was not significant for seed weight

The tepary bean (Phaseolus acutifoliusA. Gray) is reputed to be heat and drought tolerant, but the literature contains little information on yield performance of tepary in different conditions. To fill this void, replicated field studies were conducted to measure and compare yield, seed protein concentration, and seed weight of 16 domesticated and eight wild tepary lines at the hot, dry location of Riverside, CA. Well‐watered and drought‐stressed conditions were set up in the summer of 1978. The experiment was repeated with six of the domesticated lines in the spring and summer of 1979. Significant differences were found among the wild lines and among the domesticated lines for the three traits measured. Mean yield and seed weight of wild teparies were 40 and 75% lower than those of domesticates, but mean protein concentration of the two groups was the same (27.6%). Moderate drought‐stress reduced the mean yield of teparies by 55%, but did not reduce protein concentration or seed weight. Seed yield showed a positive correlation with seed weight (r= 0.78), but a negative correlation with seed protein concentration (r= −0.75) in domesticated teparies.

The two most commonly used dwarfing genes of bread wheat (Triticure aestivumL.) are Rhtland Rht2. The Rht3gene is also a potent dwarfing gene. Information in the literature is limited as to the comparative effects of these genes on transpiration efficiency (TE) and wateruse efficiency (WUE). Carbon isotope discrimination (Δ) has proposed as a criterion to select for improved TE. Four near‐isogenic lines, rhtrht, RhtlRhtl, Rht2Rht2, and Rht3Rht3, in ‘Maringa’ bread wheat background and four of their near‐isogenic F1hybrids derived from crossing the original lines were used to determine the effects of dwarfing genes on plant height, root dry matter, shoot dry matter including grains, grain yield, total dry matter (TDM), TE (TDM/water transpired), WUE (grain yield/water used), and Δ in well‐watered droughted pot experiments in the glasshouse. The near‐isogenlc lines and their six F1hybrids were also grown in well‐watered and droughted field conditions. Plant height ranged from 60 to 124 cm and from 53 to 121 em in well‐watered and droughted pot experiments, and it varied from 50 to 94 cm and from 49 to 90 cm in well‐watered and droughted field experiments, respectively. Total dry matter, grain yield, TE, and WUE declined with plant height in well‐watered glasshouse conditions. No significant relationships were found between plant height and these traits in droughted glasshouse conditions. Carbon isotope discrimination was negatively correlated with TE, but significantly so only in the well‐watered pot experiment. Plant height was negatively associated with Δ in both well‐watered and droughted pot and field experiments. Grain yield and shoot dry matter also declined with plant height in field conditions. Negative correlations were observed between Δ and grain yield and Δ and shoot dry matter in well‐watered field conditions. In most cases, the dwarfing genes reduced shoot dry matter more than grain yield and, therefore, harvest index of the semidwarf and dwarf lines was higher than that of the tall standard fine. The dwarfism caused by RhH, Rht2, and Rht3genes had, in general, depressing effects on TE, WUE, TDM, and grain yield.

Drought and heat stress are major environmental factors reducing grain production of rainfed wheat (Triticum aestivumL.) in semiarid regions. The objective of this research was to identify bread wheats with improved adaptation to hot, dry environments. Field studies were conducted to measure effects of terminal drought and heat stress on duration of developmental phases, grain yield, and yield related traits of day‐length insensitive spring wheats. Fifteen genotypes, including lines from landraces of southwestern Iran and improved cultivars from Iran and California, were grown in a nonstress and three artificially imposed stress environments at Moreno Valley, CA, in 1986. Genotype ✕ environment interactions were significant for grain yield and its components. Stress susceptibility of each genotype was estimated using a calculated index based on grain yield. Landrace genotypes and improved cultivars that were evaluated exhibited a wide range in stress susceptibility and adaptation to stress environments. Landrace genotypes and cultivars did not vary for mean stress‐susceptibility index values. Landrace genotypes generally had lower yield potential than the cultivars. The stress‐susceptibility index identified some genotypes that did not have outstanding yield performance per se in stress environments due to low yield potential and others that had high average yield in stress conditions. Stress susceptibility and yield potential were not associated, indicating that they may be independent components which both contribute to adaptation to stress environments. The stress‐susceptibility index was negatively correlated with number of grains per head, grain weight, grain yield, and harvest index under stress conditions, indicating selection for these characters in stress environments might result in decreased susceptibility to stress.

Two models have been suggested to facilitate the study of genetic variation for seasonal water‐use efficiency (WUE) and its components in spring bread wheat (Triticum aestivumL.). These models were used to estimate the contribution of each component trait to variation in WUE. Eight diverse bread wheat cultivars were grown in replicated pot and field experiments under well‐watered and droughted conditions. Significant genotypic variation was observed for WUE (ratio of grain yield to water used), evapotranspiration efficiency (ETE, ratio of total dry matter to water used), and harvest index (HI, ratio of grain yield to total dry matter). Modern short cultivars, on average, had higher WUE than old tall cultivars in well‐watered (1.225 vs. 0.984 g kg−1) and droughted (1.198 vs. 0.860 g kg−1) pot conditions, due mainly to higher HI. Two old tall cultivars exhibited highest values for ETE. Harvest index and ETE accounted for 85 and 15% and for 81 and 19% of variation in WUE in well‐watered and droughted conditions, respectively. Harvest index had a higher direct effect and was more highly associated with WUE than ETE. The negative correlation between HI and ETE was not significant. Carbon isotope discrimination (Δ) showed negative correlation with ETE in well‐watered ( − 0.82) and droughted ( − 0.68) treatments. Grain yield and HI of modern short cultivars, on average, were higher than those of old tall cultivars under field conditions. Mean Δ was lower in droughted (17.9%o) than in well‐watered (18.9%o) field conditions. Plant growth rates estimated at boot stage and at anthesis were negatively associated with a drought susceptibility index based on grain yield. Drought susceptibility index was not correlated with Δ. Water‐use efficiency in wheat could be improved by improving either transpiration efficiency or ETE.

Guayule (Parthenium argentatumGray) is a promising alternative to the rubber tree (Hevea brasiliensisMuell. Arg.) for domestic production of natural rubber in semiarid regions. Guayule is not yet a crop and its commercialization will depend on the development of high rubber‐yielding cultivars. The objectives of this study were to determine if individual plant selection has been effective in improving rubber yield; to determine the suitability of California selections for rubber and resin production in Arizona; and to examine the extent of genotype‐by‐environment (G ✕ E) interactions in improved guayule selections. Plant height, width, dry weight, rubber content, resin content, rubber plus resin content, rubber yield, resin yield, and rubber‐plus–resin yield were measured for 24 guayule genotypes planted at Riverside and Palmdale, CA, and Maricopa, AZ, from 1986 to 1989. Genotypes were significantly different for all traits except for plant width and dry weight at Maricopa. The highest rubber yields were 743 kg ha−1yr−1at Riverside, 172 at Palmdale, and 564 at Maricopa. Genotype A9 at Riverside and Genotype A22 at Maricopa exceeded the mean rubber yield of two standard varieties by 163 and 66%, respectively, indicating that selection for increased rubber yield within heterogeneous germplasm has been successful. The highest resin yield was 1405 kg ha−1yr−1at Riverside, 668 at Palmdale, and 1006 at Maricopa. With rubber plus resin yields of 2085 and 1579 kg ha−1yr−1, Genotypes A4 and A22 appear acceptable for large‐scale production at Riverside and Maricopa, provided economic markets are found for guayule resin. The G ✕ E interaction effects were significant for all traits. Analyses of data suggested that both quantitative and qualitative differences in performance of genotypes in different locations were responsible for the observed G ✕ E interactions.

Carbon isotope discrimination (?) has been suggested as a selection criterion to improve transpiration efficiency (W) in bread wheat (Triticum aestivum L.). Cultivars ‘Chinese Spring’ with low A (high W) and ‘Yecora Rojo’ with high ? (low W) were crossed to develop F1, F2, BC1, and BC2 populations for genetic analysis of ? and other agronomic characters under well-watered (wet) and water-stressed (dry) field conditions. Significant variation was observed among the generations for ? only under the wet environment. Generation x irrigation interactions were not significant for ?. Generation means analysis indicated that additive gene action is of primary importance in the expression of ? under nonstress conditions. Dominance gene action was also detected for ?, and the direction of dominance was toward higher values of ?. The broad-sense and the narrow-sense heritabilities for ? were 61 % and 57% under the wet conditions, but were 48% and 12% under the draughted conditions, respectively. The narrow-sense heritabilities for grain yield, above-ground dry matter, and harvest index were 36%, 39%, and 60% under the wet conditions and 21%, 44%, and 20% under dry conditions, respectively. The significant additive genetic variation and moderate estimate of the narrow-sense heritability observed for ? indicated that selection under wet environments should be effective in changing ? in spring bread wheat.

Adaptation reactions of 33 genotypes of safflower Carthamus tinctorius L. were studied under 7 different climatic conditions. The genotpyes were divided into two sets. Set I consisted of 15 genotpyes selected from the local populations. Set II had 15 introduced and local varieties. Three control genotpyes, Ute, Ferio, and Local Arak, were common to both sets.

Nine pure lines of bread wheat collected from landraces of southwestern Iran and one local Iranian cultivar from the same area were used to estimate genetic variation and heritability for 12 developmental and yield component characters. Path-analysis was used to partition the genetic correlations between some of the characters into direct and indirect effects. Mean values for these lines were also compared with those of five improved cultivars from Iran and California. The goal of the experiment is to breed improved landraces and/or modern cultivars for areas of low input agriculture in southern California, southwestern Iran, and regions with similar environmental and agronomic conditions.

Drought stress is one of the most limiting factors to crop production in semiarid regions. Improved water‐use efficiency (WUE) could provide breeding programs with a means to improve adaptation to drought‐prone environments. Carbon isotope discrimination (Δ) has been proposed as a criterion to select for improved WUE. This study evaluates differences in total dry matter (TDM), WUE (TDM/transpiration), and Δ of flag leaves of landrace and modern wheat (Triticum aestivumL.) genotypes grown in pots in a well‐watered (wet) and in a drought‐stressed (dry) experiment for 2 yr. The wheat genotypes were also grown in wet and dry field conditions. In the pot experiments, average WUE of the genotypes varied from 2.85 to 4.41 g dry matter kg−1water in the wet experiment and from 3.08 to 4.53 in the dry experiment. The mean values of Δ were 21.7 ✕ 1O−10for the wet pot experiment and 21.6 ✕ 10−3for the dry pot experiment. The tall landrace genotypes had greater TDM and WUE, but were later in maturity than the modern dwarf and semi‐dwarf genotypes. Values of Δ associated with different genotypes were negatively correlated with WUE. Broad‐sense heritabilities for WUE and Δ were 93 and 90%, respectively, in the pot experiments. In the dry field experiments, Δ was positively associated with above‐ground dry matter and grain yield in both years. In the wet field experiments, there was a positive correlation between Δ and grain yield only in 1988. Broad‐sense heritabilities for Δ were 72% for wet field conditions and 74% for dry field conditions. These observations indicate that selection for C isotope discrimination, under either wet or dry conditions, can improve water use efficiency in wheat.

Abstract: Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is an important pest of wheat (Triticum aestivum L.) in the United States of America. Developing adapted wheat cultivars with genetic resistance to RWA is an effective control strategy. Genetic studies were conducted to determine the mode of inheritance of gene(s) conferring resistance to RWA in an Iranian landrace wheat line, G 5864. For the inheritance study, G 5864 was crossed with the susceptible wheats ‘Yecora Rojo’ and ND 2375. Seedlings of F1, reciprocal F1, F2, BC1 to the susceptible parent (BCS), and BC1 to the resistant parent (BCR) were screened for RWA reaction. Several phenotypic segregation ratios were tested in the F2 populations for goodness of fit; the 9:3:3:1 ratio (resistant: rolled leaves: stunted plants: susceptible) was an acceptable fit in all cases. Thus, resistance in G 5864 seemed to be controlled by two independent dominant genes with additive gene effects. The allelic relationships of gene(s) in this line with genes in other resistant lines, PI 137739 (Dn1), PI 262660 (Dn2), PI 372129 (Dn4), PI 294994 (Dn5), and PI 243781 (Dn6), were also studied. Segregation patterns observed in G 5864 × resistant (R × R) F2 populations were inconclusive. However, no susceptible plants were observed in these F2 populations. If previous reports concerning the number of resistance genes present in the other resistant lines are correct, then given the high manifestation of resistance observed in G 5864, and given the absence of susceptible plants in the R × R F2 populations, it is indicated that RWA resistance in G 5864 is either controlled by different alleles at the same loci as the other resistance genes, or that G 5864 shares a resistance gene with each of the other resistant lines.

Abstract: Little is known of genes that influence root development and drought resistance in bread wheat. The evapotranspiration efficiency (ETE = ratio of vegetative dry weight to total water used) of spring bread wheat tall landrace ‘Chinese Spring’ is relatively high. We used 42 ditelosomic and dimonotelosomic lines of Chinese Spring to identify chromosome arms that influence plant characters and ETE. Multiple regression analyses indicated that 96% of the variation observed in ETE was explained by variation in vegetative dry weight and total water used. Variation in plant height, number of spikes (tillers), root dry weight and shoot dry weight (excluding grains) together explained 88% of the variation observed in plant vegetative dry weight. Chromosome arms involved in expression of days to heading and maturity, plant height, number of spikes, root dry weight, shoot dry weight, number of grains, grain weight, and carbon isotope discrimination (Δ) were identified. Specifically, both arms of chromosome 2A, the long arm of chromosome 2B, and the short arm of chromosome 2D might carry genes with positive effects on number of spikes, root dry weight, and shoot dry weight. None of the aneuploids produced grain yield greater than Chinese Spring. The short arms of chromosomes 6A and 4D might carry genes that suppress Δ. Chromosome 1D might carry genes that increase relative water loss. The chromosome arms belonging to homoeologous group 2 might carry genes with positive effects on ETE. The genetic basis of ETE in modern wheats could be broadened by substituting specific chromosome arms of landrace wheats carrying desired characters into their genomes.

Abstract: There is renewed interest in wheat landraces as important sources of genetic variation for agronomic characters. Fifty-three pure lines of bread wheat (Triticum aestivum L.) derived from seven landraces collected from southeastern Iran were used to estimate genetic variation and heritability for 13 developmental and quantitative characters. Path-analysis was used to partition the genetic correlations between grain yield and six grain yield-related traits. Mean values of landraces were also compared with three improved cultivars from California and Iran. Genotypic differences among the landraces and among the pure lines collected from the landraces were highly significant for all characters considered. Compared with the modern cultivars, the landrace genotypes were, on average, later in days to heading and taller than the cultivars but had lower values for number of grains per spike, 1000-grain weight, grain yield and harvest index. Some landrace genotypes were similar to the modern cultivars for grain yield. Moderate to high genetic variation was displayed by number of grains per spike, number of spikes per plant, 1000-grain weight, and harvest index. The heritability estimates ranged from 59% for grain yield to 99% for days to anthesis. Expected genetic advance (as % of the mean) was ≈34% for number of spikes per plant, number of grains per spike, and 1000-grain weight. Days to heading and to anthesis correlated positively with number of spikes per plant, shoot biomass, and straw biomass but negatively with number of grains per spike and harvest index. The strong direct effect of number of spikes per plant on grain yield was completely counterbalanced by its indirect negative effects via number of grains per spike and 1000-grain weight. Number of grains per spike and 1000-grain weight were positively correlated with grain yield, and they had large direct effects. These two characters, however, were negatively correlated and exhibited a substantial counterbalance effect via one another and via number of spikes per plant. The landraces could be improved by intercrossing the promising genotypes identified in this study, with simultaneous selection for earliness, fewer number of spikes per plant, greater number of grains per spike and heavier grains. For further improvement, crossing programs between the landraces and introduced germplasm may be necessary.

Computer simulation was used to compare Hallauer's cyclic single cross selection (CSCS) with reciprocal recurrent selection (RRS). Three epistatic and three non-epistatic models with 60 loci determining a single character provided the genetic base. The rate of advance over seven cycles was always greater for CSCS than for RRS on either a cycle or generation basis. No genetic conditions were found where CSCS failed to respond. The advantages of CSCS increases as the proportion of non-additive genetic variance increases. Genetic advance of the hybrid population was shown to result from the joint effects of an average change in gene frequency and complementary effects (nicking) of selection. Nicking effects accounted for most of the advance for some starting conditions. RRS generally had higher selection limits with no epistasis or low gene frequency of the dominant allele. CSCS generally had higher limits with epistasis or high frequency of the dominant allele. We suggested that CSCS begin with divergent genetic populations and strong selection intensity for three cycles. Final selection of superior single crosses was indicated when the lines were completely inbred.