Identification of QTLs for Resistance to Fusarium Head Blight Using a Doubled Haploid Population Derived from Southeastern United States Soft Red Winter Wheat Varieties AGS 2060 and AGS 2035

Fusarium head blight (FHB), caused primarily by the fungus Fusarium graminearum, is one of the most damaging diseases of wheat, causing significant loss of yield and quality worldwide. Warm and wet conditions during flowering, a lack of resistant wheat varieties, and high inoculum pressure from corn stubble contribute to frequent FHB epidemics in the southern United States. The soft red winter wheat variety AGS 2060 is moderately susceptible (as opposed to susceptible) to FHB and regularly found in pedigrees of resistant breeding lines. AGS 2060 does not carry any known resistance genes or quantitative trait loci (QTL). A QTL mapping study was conducted to determine the location and genetic effect of its resistance using a doubled haploid mapping population produced from a cross between wheat varieties AGS 2060 and AGS 2035 (FHB susceptible). The population was genotyped using the Illumina iSelect single nucleotide polymorphism (SNP) array for wheat and phenotyped in Baton Rouge and Winnsboro, Louisiana and Newport, Arkansas in 2018 and 2019. The effect of genotype was significant for Fusarium damaged kernels (FDK) and deoxynivalenol (DON) content across all locations and years, indicating genetic variation in the population. The study detected 13 QTLs (one each on chromosome 1A, 1B, 1D, 2A, 2B, 6A, 6B, 7A, and 7B, and two each on 5A and 5B) responsible for the reduction of FDK and/or DON. Of these, nine QTLs for FHB resistance were identified in Winnsboro, Louisiana, in 2019. QTLs on chromosomes 2A and 7A could be valuable sources of resistance to both DON and FDK over several environments and were likely the best candidates for use in marker-assisted selection. Consistently expressed QTLs on chromosomes 5A, 6B, and 7A were potentially newly identified sources of resistance to FHB in soft red winter wheat

Reducing the generation time in winter wheat cultivars using speed breeding

Reducing generation time is critical to achieving the goals of genetic gain in important crops like wheat (Triticum aestivum). Speed breeding (SB) has been shown to considerably reduce generation times in crop plants. Unlike spring wheat cultivars, winter wheat varieties require typically 6–9 weeks of cold treatment, called vernalization, for flowering which extends the generation time for the development of improved winter wheat cultivars. Here, we optimized the SB method using a set of 48 diverse soft red winter wheat (SRWW) cultivars by testing vernalization duration, light and temperature requirements, and the viability of seeds harvested after different durations post-anthesis under extended daylight conditions. We have found that using a 22-h setting (22 h day/2 h night, 25°C/22°C) in high-density 50-cell trays results in rapid generation advancement. We used genotypic data for a panel of soft red winter wheat varieties from the regional programs to determine the impact of photoperiod and vernalization alleles on the efficiency of the SB approach. Using a set of 48 SRWW cultivars and germplasm from Maryland and four other public breeding programs, we establish that this protocol can allow for the advancement of four generations per year in controlled conditions for winter wheat varieties, experimental lines, or emerging cultivars. Our work shows the potential to reduce generation time by ∼30 days per generation faster than what had been reported in the SB strategies for winter wheat, thus allowing for a quicker turnaround time from original cross to genetically stable experimental genotypes that can be tested in field settings.https://doi.org/10.1002/csc2.2098

Haplotype diversity of stem rust resistance loci in uncharacterized wheat lines

Stem rust is one of the most destructive diseases of wheat worldwide. The recent emergence of wheat stem rust race Ug99 (TTKS based on the North American stem rust race nomenclature system) and related strains threaten global wheat production because they overcome widely used genes that had been effective for many years. Host resistance is likely to be more durable when several stem rust resistance genes are pyramided in a single wheat variety; however, little is known about the resistance genotypes of widely used wheat germplasm. In this study, a diverse collection of wheat germplasm was haplotyped for stem rust resistance genes Sr2, Sr22, Sr24, Sr25, Sr26, Sr36, Sr40, and 1A.1R using linked microsatellite or simple sequence repeat (SSR) and sequence tagged site (STS) markers. Haplotype analysis indicated that 83 out of 115 current wheat breeding lines from the International Maize and Wheat Improvement Center (CIMMYT) likely carry Sr2. Among those, five out of 94 CIMMYT spring lines tested had both Sr2 and Sr25 haplotypes. Five out of 22 Agriculture Research Service (ARS) lines likely have Sr2 and a few have Sr24, Sr36, and 1A.1R. Two out of 43 Chinese accessions have Sr2. No line was found to have the Sr26 and Sr40 haplotypes in this panel of accessions. DArT genotyping was used to identify new markers associated with the major stem resistance genes. Four DArT markers were significantly associated with Sr2 and one with Sr25. Principal component analysis grouped wheat lines from similar origins. Almost all CIMMYT spring wheats were clustered together as a large group and separated from the winter wheats. The results provide useful information for stem rust resistance breeding and pyramiding

Haplotype diversity of stem rust resistance loci in uncharacterized wheat lines

Stem rust is one of the most destructive diseases of wheat worldwide. The recent emergence of wheat stem rust race Ug99 (TTKS based on the North American stem rust race nomenclature system) and related strains threaten global wheat production because they overcome widely used genes that had been effective for many years. Host resistance is likely to be more durable when several stem rust resistance genes are pyramided in a single wheat variety; however, little is known about the resistance genotypes of widely used wheat germplasm. In this study, a diverse collection of wheat germplasm was haplotyped for stem rust resistance genes Sr2, Sr22, Sr24, Sr25, Sr26, Sr36, Sr40, and 1A.1R using linked microsatellite or simple sequence repeat (SSR) and sequence tagged site (STS) markers. Haplotype analysis indicated that 83 out of 115 current wheat breeding lines from the International Maize and Wheat Improvement Center (CIMMYT) likely carry Sr2. Among those, five out of 94 CIMMYT spring lines tested had both Sr2 and Sr25 haplotypes. Five out of 22 Agriculture Research Service (ARS) lines likely have Sr2 and a few have Sr24, Sr36, and 1A.1R. Two out of 43 Chinese accessions have Sr2. No line was found to have the Sr26 and Sr40 haplotypes in this panel of accessions. DArT genotyping was used to identify new markers associated with the major stem resistance genes. Four DArT markers were significantly associated with Sr2 and one with Sr25. Principal component analysis grouped wheat lines from similar origins. Almost all CIMMYT spring wheats were clustered together as a large group and separated from the winter wheats. The results provide useful information for stem rust resistance breeding and pyramiding