Multi-environment multi-QTL mixed models were used in a GWAS context to identify QTL for disease resistance. The use of mega-environments aided the interpretation of environment-specific and general QTL. Diseases represent a major constraint for barley (Hordeum vulgare L.) production in Latin America. Spot blotch (caused by Cochliobolus sativus), stripe rust (caused by Puccinia striiformis f.sp. hordei) and leaf rust (caused by Puccinia hordei) are three of the most important diseases that affect the crop in the region. Since fungicide application is not an economically or environmentally sound solution, the development of durably resistant varieties is a priority for breeding programs. Therefore, new resistance sources are needed. The objective of this work was to detect genomic regions associated with field level plant resistance to spot blotch, stripe rust, and leaf rust in Latin American germplasm. Disease severities measured in multi-environment trials across the Americas and 1,096 SNPs in a population of 360 genotypes were used to identify genomic regions associated with disease resistance. Optimized experimental design and spatial modeling were used in each trial to estimate genotypic means. Genome-Wide Association Mapping (GWAS) in each environment was used to detect Quantitative Trait Loci (QTL). All significant environment-specific QTL were subsequently included in a multi-environment-multi-QTL (MEMQ) model. Geographical origin and inflorescence type were the main determinants of population structure. Spot blotch severity was low to intermediate while leaf and stripe rust severity was high in all environments. Mega-environments were defined by locations for spot blotch and leaf rust. Significant marker-trait associations for spot blotch (9 QTL), leaf (6 QTL) and stripe rust (7 QTL) and both global and environment-specific QTL were detected that will be useful for future breeding efforts.
Intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth and D.R. Dewey], bred for high grain yield, has become the first perennial grain in North America and is commercialized under the tradename Kernza. The expansion of this crop from the U.S. Midwest to areas with milder winters would require an understanding of its vernalization requirements for flowering and the availability of genetic diversity for this trait. The goal of this research was to determine the length of the cold period required for vernalization in Kernza intermediate wheatgrass. Two treatment factors (population and length of cold incubation period) were evaluated. Seeds from eight breeding populations from Kansas and Minnesota were evaluated in growth chambers at 5 ˚C and 10 h light for cold periods from 3 to 9 wk. The percentage of plants that flowered increased from 30 to 96% as the length of the cold incubation period increased from 3 to 7 wk following a sigmoid model. For most yield components, no changes were observed after 7 wk of cold incubation. There were no differences among populations for most traits and there was large within-population phenotypic diversity. These results confirm that Kernza intermediate wheatgrass populations have moderate vernalization requirements. Further research is needed to confirm the feasibility of breeding Kernza with lower vernalization requirements. INTRODUCTIONAnnual crops dominate global production of grain, occupying two-thirds of the arable land and they are associated with soil erosion, water contamination, high input use, and biodiversity loss (Cox et al., 2006;Tilman et al., 2001). Perennial species can have more-developed root systems, provide continuous ground cover year-round, and use nutrients more efficiently than annual species (Glover et al., 2010). Although many species have shown potential for domestication as perennial grain crops, intermediate wheatgrass [Thinopyrum intermedium (Host) Barkworth and D.R. Dewey] stands out because it has moderate shattering and its grains are easy Abbreviation: GDD, growing degree days.
Expansion of perennial grain and forage Kernza intermediate wheatgrass to temperate regions may be limited by its vernalization requirements. We compared vegetative and reproductive traits of Kernza plants grown in greenhouse under four environmental treatments of temperature and daylength for a 7 week induction period. Percent of plants which flowered and spikes per plant decreased from 83% and 8.2 at 4°C and 10 h to 15% and 0.4 at 26°C and 15 h, respectively. The variability observed suggests that there is potential for selection for reduced vernalization requirements in Kernza populations.
We used the ‘Baronesse’/‘Full Pint’ doubled haploid population to analyse the genetic factors controlling flowering date under South American conditions. Both parents have similar heading dates, but the population shows transgressive segregation. Two genes, eps2S on chromosome 2H and sdw1 on chromosome 3H, explained most of the phenotypic variation for anthesis date, with the later allele carried by ‘Baronesse’ and ‘Full Pint’ , respectively. Both effects were completely additive with no interaction. We studied three plant developmental periods: seedling emergence to tillering (Z10–Z20), tillering (Z20–Z30) and end of tillering to anthesis (Z30–Z49) under field conditions at three contrasting planting dates. Z10–Z20 was also measured under semi‐controlled conditions. eps2S controlled Z30–Z49 periods, while sdw1 controlled Z20–Z30. Each of the two genes for the end‐point phenotype—anthesis date—was a determinant of flowering at a different developmental stage. No gene x planting date interactions were detected.
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