Quantitative trait locus (QTL) main effects and QTL by environment (QTL × E) interactions for seven agronomic traits (grain yield, days to heading, days to maturity, plant height, lodging severity, kernel weight, and test weight) were investigated in a two-row barley (Hordeura vulgare L.) cross, Harrington/TR306. A 127-point base map was constructed from markers (mostly RFLP) scored in 146 random double-haploid (DH) lines from the Harrington/TR306 cross. Field experiments involving the two parents and 145 random DH lines were grown in 1992 and/or 1993 at 17 locations in North America. Analysis of QTL was based on simple and composite interval mapping. Primary QTL were declared at positions where both methods gave evidence for QTL. The number of primary QTL ranged from three to six per trait, collectively explaining 34 to 52% of the genetic variance. None of these primary QTL showed major effects, but many showed effects that were consistent across environments. The addition of secondary QTL gave models that explained 39 to 80% of the genetic variance. The QTL were dispersed throughout the barley genome and some were detected in regions where QTL have been found in previous studies. Eight chromosome regions contained pleiotropic loci and/or linked clusters of loci that affected multiple traits. One region on chromosome 7 affected all traits except days to heading. This study was an intensive effort to evaluate QTL in a narrow-base population grown in a large set of environments. The results reveal the types and distributions of QTL effects manipulated by plant breeders and provide opportunities for future testing of marker-assisted selection. M OLECULAR MAPS of plant genomes, used in conjunction with phenotypic measurements, can provide information about chromosome regions that affect quantitative traits. Although knowing whether such regions represent individual quantitative trait loci (QTL)

Winter wheat (Triticum aestivum L.) –fallow is the predominant cropping system in low‐precipitation regions (<250 mm annually) of the inland Pacific Northwest (PNW) in the USA. Wind erosion is a recurrent problem during and after fallow periods when inadequate crop residue amounts are retained on the soil surface. Management options that optimize both grain yield and straw production are needed. A 3‐yr field study was conducted to determine sowing rate and sowing date effects on straw and grain yield, and grain yield components of winter wheat cultivars with semidwarf, standard height, or tall growth habit. Four winter wheat cultivars were evaluated at three sowing rates (65, 130, and 195 seeds m−2) and three sowing dates in August, September, and October. A split plot design was used, with sowing dates as main plots and sowing rate × cultivar combinations as subplots. The greatest effect of sowing date was on straw production. Straw biomass from mid‐August sowing averaged 6.70 Mg ha−1 compared with 4.65 and 2.78 Mg ha−1 from mid‐September and mid‐October sowing, respectively. Grain yield was highest for mid‐August sowing during two years and lowest for mid‐October sowing all years. Averaged across years, the semidwarf cultivar produced the highest grain yield on all sowing dates and was equal to the standard height and tall cultivars for straw production. Path coefficient analysis showed that variation in grain yield was due primarily to differences in spikes per unit area (SPU) and kernels per spike (KPS). Late sowing resulted in a large reduction in SPU and, therefore, grain yield. For cropland susceptible to wind erosion in east‐central Washington, early sowing results in increased wheat straw production and generally higher grain yield compared with mid‐to‐late sowing dates.

Improvement of expansion volume, defined as the volume of popped corn per gram of unpopped corn, generally is considered the most important objective of popcorn (Zea mays L.) breeding programs. Popcorn, however, generally is inferior to dent corn with respect to yield and other agronomic characteristics. Detailed information on the inheritance of expansion volume and grain yield in popcorn ✕ dent corn crosses was not available in the literature. The objective of this study was to determine the inheritance of expansion volume and grain yield, including yield components, in two popcorn ✕ dent corn crosses. Generation means analysis was used to quantify genetic effects in the popcorn ✕ dent crosses Ia53 ✕ B73 and Ia28 ✕ Mo17. Significant additive genetic effects were detected for ail traits in both crosses. Significant dominance genetic effects were detected for expansion volume in the cross Ia28 ✕ Mo17, and for grain yield, ear length, ear diameter, and 5O‐kernel weight in both crosses. Dominance effects resulted in reduced expansion volume, and increased grain yield, ear length, ear diameter, and 5O‐kernel weight. Significant epistatic effects for grain yield were detected in the crosses Ia53 ✕ B73. Expansion volume was negatively correlated with all yield components except for number of kernel rows. Thus, relative to other yield components studied, selection for high kernel row number would appear to result in the least reduction of expansion volume. Results from this study indicate that breeding methodologies which exploit additive genetic variation assoicated with expansion volume and dominance variation associated with grain yield are most likely to result in concurrent improvement of these two traits.

The model most widely used for path analysis of grain yield in small grains assumes bidirectional causal pathways between yield components; however, because yield components develop sequentially, it is questionable from a biological standpoint whether a yield component could influence others that develop earlier. The purpose of this research is to describe the theory and application of an alternative model for path analysis of grain yield that takes into account the sequential development of yield components. Path analysis was performed assuming bidirectional and unidirectional causal relationships among yield components of eight spring barley (Hordeum vulgare L.) cultivars grown at Palmer and Fairbanks, AK, in each of two years. Yield and the yield components spikes per square meter, kernels per spike, and kernel weight were estimated. The unidirectional model seems to reflect operative causal pathways more realisitically, and results in simpler estimates that present a clearer picture of the relationships among grain yield and yield components. Of the three yield components, spikes per square meter resulted in the greatest positive contribution to yield, while the effect of kernels per spike on kernel weight was the most negative compensatory response among yield components.

Expansion volume, defined as the volume of popped corn per gram of unpopped corn, is considered the most important quality trait in popcorn (Zea mays L.). The increasing popularity of microwave popcorn has necessitated the development of cultivars for use in both conventional and microwave popping. Information on expansion volume of popcorn genotypes using both popping methods is not available in the literature. This study investigated the presence of a genotype ✕ popping method interaction for expansion volume and its components in popcorn. Eleven commercial popcorn hybrids, one flint corn ✕ popcorn inbred line cross, and one open‐pollinated popcorn variety were grown in isolation in 1988. Seed harvested from each genotype was divided equally into large‐ and small‐kernel samples that were evaluated for expansion volume, popped kernel (flake) size, and percent unpopped kernels in conventional and microwave popping. All genotypes performed better in conventional popping than in microwave popping. Significant differences existed among genotypes for expansion volume and flake size. A significant genotype ✕ popping method interaction was detected for expansion volume, flake size, and percent unpopped kernels. Therefore, breeders utilizing germplasm similar to that which we studied with the dual objective of developing cultivars for conventional and microwave popcorn markets should conduct evaluations for expansion volume using both popping methods.