Stripe rust caused by Puccinia striiformis Westend. f. sp. tritici Erikks. is an economically important disease of wheat (Triticum aestivum L.). Hexaploid spring wheat landrace PI 480035 was highly resistant to stripe rust in the field in Washington during 2011 and 2012. The objective of this research was to identify quantitative trait loci (QTL) for stripe rust resistance in PI 480035. A spring wheat, “Avocet Susceptible” (AvS), was crossed with PI 480035 to develop a biparental population of 110 recombinant inbred lines (RIL). The population was evaluated in the field in 2013 and 2014 and seedling reactions were examined against three races (PSTv-14, PSTv-37, and PSTv-40) of the pathogen under controlled conditions. The population was genotyped with genotyping-by-sequencing and microsatellite markers across the whole wheat genome. A major QTL, QYr.wrsggl1-1BS was identified on chromosome 1B. The closest flanking markers were Xgwm273, Xgwm11, and Xbarc187 1.01 cM distal to QYr.wrsggl1-1BS, Xcfd59 0.59 cM proximal and XA365 3.19 cM proximal to QYr.wrsggl1-1BS. Another QTL, QYr.wrsggl1-3B, was identified on 3B, which was significant only for PSTv-40 and was not significant in the field, indicating it confers a race-specific resistance. Comparison with markers associated with previously reported Yr genes on 1B (Yr64, Yr65, and YrH52) indicated that QYr.wrsggl1-1BS is potentially a novel stripe rust resistance gene that can be incorporated into modern breeding materials, along with other all-stage and adult-plant resistance genes to develop cultivars that can provide durable resistance.
Wheat (Triticum aestivum L.) is a major cereal crop grown across a wide range of environments, but its productivity around the world is challenged by various biotic and abiotic factors. Wheat landraces from around the world are a source of unexploited genetic diversity that can be essential for modern wheat-breeding programs in search of resistance to abiotic stresses like freezing tolerance. This genetic diversity study of 553 winter wheat landraces based on single-nucleotide polymorphisms (SNPs) revealed separate clusters of landraces related to the latitude of origin. Linkage block analysis revealed genomic regions with specific alleles skewed towards landraces from higher latitudes, suggesting that migration to higher latitudes resulted in the fixing of specific alleles. Electrolyte leakage was used to measure the tolerance of freezing to −14 • C, −16 • C, and −18 • C of 192 landraces. There was a significant negative correlation between latitude and electrolyte leakage, with an R 2 value of 0.14, (p < 0.0001), in a regression analysis indicating greater freezing tolerance in landraces from higher latitudes. Genome-wide association studies identified regions in chromosomes 4A and 6A associated with higher latitudes and freezing tolerance, respectively. Landraces with freezing tolerance may be useful in developing new germplasm as novel sources of greater cold hardiness.
Weigela (Caprifoliaceae) is a genus of ornamental plants popular for its phenotypic variation and hardiness, that includes species hybridized to produce the commercially available cultivars. Despite its popularity, limited genetic resources exist for the genus. Twenty genomic simple sequence repeat (gSSR) markers distributed across the genome were developed using low coverage whole-genome sequencing data of Weigela Spilled Wine®. A cross-amplification evaluation with these 20 gSSR markers on a collection of 18 Weigela cultivars revealed a total of 111 unique alleles, including 36 private alleles. A diagrammatic key was constructed to identify cultivars using only six of the gSSR markers, demonstrating the newly developed gSSR markers are immediately useful for cultivar identification. Future uses could include breeding with marker-assisted selection, determining the history of hybridization of the current cultivated lines, aiding in the construction of genetic maps, and assessing the patterns of population genetic structure of Weigela spp.
Spring mix is a popular packaged salad that contains lettuce (Lactuca sativa L.) as one of its main ingredients. Plants for baby leaf lettuce (BLL) production are grown at very high densities, which enhances the occurrence of bacterial leaf spot (BLS) caused by Xanthomonas hortorum pv. vitians (Xhv), a disease that can make the crop unmarketable. The market demands disease-free, high-quality BLL all year round. Growing highly BLS-resistant cultivars will reduce loss of yield and quality thus minimizing economic detriment to lettuce and spring mix growers. The research objectives were to identify lettuce accessions resistant to BLS and associated quantitative trait loci (QTL). A total of 495 lettuce accessions were screened with six isolates (BS0347, BS2861, BS3127, L7, L44, and Sc8B) of Xhv. Accessions showing overall high level resistance to all tested Xhv isolates were ‘Bunte Forellen’, PI 226514, ‘La Brillante’, ARM09-161-10-1-4, ‘Grenadier’, ‘Bella’, PI 491210, ‘Delight’, and ‘Romana Verde del Mercado’. Genome-wide association studies of BLS resistance by mixed linear model analyses identified significant QTLs on four lettuce chromosomes (2, 4, 6, and 8). The most significant QTL was on Chromosome 8 (P = 1.42 x 10-7) that explained 6.7% of total phenotypic variation for the disease severity. Accessions with high level of resistance detected in this study are valuable resources for lettuce germplasm improvement. Molecular markers closely linked to QTLs can be considered for marker-assisted selection to develop new BLL lettuce cultivars with resistance to multiple races of Xhv.
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