Study of interspecific SSR polymorphism among 14 species from Triticum-Aegilops group

In the present study, using in-gel hybridization and PCR based approaches, interspecific SSR polymorphism was studied among 14 species of Triticum-Aegilops group. The material represented seven different genomes and three ploidy levels (2x,4x,6x). In-gel hybridization involved 13 probe-enzyme combinations (four SSR oligonucleotide probes in combination with 2-4 enzymes) and resolved 5 to 20 bands (0.40kb to > 23kb) in each of the 14 individual species. This suggested ubiquitous distribution and interspecific polymorphism of SSRs among different species of Triticum-Aegilops group. The available polymorphism also proved helpful in discriminating not only the species with different ploidy levels and possessing different genomes, but also those possessing similar or very closely related genomes. The amplification of SSR loci using 15 primer pairs derived from hexaploid wheat was also carried out in all the 14 species. The primer pairs, each amplified SSR loci not only in species containing A, B and D genomes, but also in 2 to 10 of the remaining species that contained other genomes. This suggested that wheat SSRS might have been derived from the corresponding SSRs in an ancestral genome and are conserved across a number of species in the Triticum-Aegilops group. Also, two pairs of SSRs (one consisting of WMC243 and WMC415 and the other consisting of WMC35 and WMC404) each discriminated all the 14 species examined during the present study. Therefore, one can infer from the present study that SSR primers can be used in studies on DNA polymorphism, genetic diversity, gene mapping and synteny conservation across different species of Triticum-Aegilops group

Genetic analysis and molecular mapping of a new fertility restorer gene Rf8 for Triticum timopheevi cytoplasm in wheat (Triticum aestivum L.) using SSR markers

A study on mode of inheritance and mapping of fertility restorer (Rf) gene(s) using simple sequence repeat (SSR) markers was conducted in a cross of male sterile line 2041A having Triticum timopheevi cytoplasm and a restorer line PWR4099 of common wheat (Triticum aestivum L.). The F1 hybrid was completely fertile indicating that fertility restoration is a dominant trait. Based on the pollen fertility and seed set of bagged spikes in F2 generation, the individual plants were classified into fertile and sterile groups. Out of 120 F2 plants, 97 were fertile and 23 sterile (based on pollen fertility) while 98 plants set ≥5 seeds/spike and 22 produced ≤4 or no seed. The observed frequency fits well into Mendelian ratio of 3 fertile: 1 sterile with χ2 value of 2.84 for pollen fertility and 2.17 for seed setting indicating that the fertility restoration is governed by a single dominant gene in PWR4099. The three linked SSR markers, Xwmc503, Xgwm296 and Xwmc112 located on the chromosome 2DS were placed at a distance of 3.3, 5.8 and 6.7 cM, respectively, from the Rf gene. Since, no known Rf gene is located on the chromosome arm 2DS, the Rf gene in PWR4099 is a new gene and proposed as Rf8. The closest SSR marker, Xwmc503, linked to the Rf8 was validated in a set of Rf, maintainer and cytoplasmic male sterile lines. The closely linked SSR marker Xwmc503 may be used in marker-assisted backcross breeding facilitating the transfer of fertility restoration gene Rf8 into elite backgrounds with ease

Genetic dissection of grain weight in bread wheat through quantitative trait locus interval and association mapping

Genetic dissection of grain weight in bread wheat was undertaken through both genome-wide quantitative trait locus (QTL) interval mapping and association mapping. QTL interval mapping involved preparation of a framework linkage map consisting of 294 loci {194 simple sequence repeats (SSRs), 86 amplified fragment length polymorphisms (AFLPs) and 14 selective amplifications of microsatellite polymorphic loci (SAMPL)} using a bi-parental recombinant inbred line (RIL) mapping population derived from Rye Selection111 × Chinese Spring. Using the genotypic data and phenotypic data on grain weight (GW) of RILs collected over six environments, genome-wide single locus QTL analysis was conducted to identify main effect QTL. This led to identification of as many as ten QTL including four major QTL (three QTL were stable), each contributing >20% phenotypic variation (PV) for GW. The above study was supplemented with association mapping, which allowed identification of 11 new markers in the genomic regions that were not reported earlier to harbour any QTL for GW. It also allowed identification of closely linked markers for six known QTL, and validation of eight QTL reported earlier. The QTL identified through QTL interval mapping and association mapping may prove useful in marker-assisted selection (MAS) for the development of cultivars with high GW in bread whea

Identifying quantitative trait loci for lodging-associated traits in the wheat doubled-haploid population Avalon × Cadenza

Lodging affects grain quality and grain yield in wheat (Triticum aestivum L.) and is difficult to breed for because its sporadic incidence and laborious protocols to measure lodging traits. Thus, developing molecular markers for these traits can increase selection efficiency in breeding programs. The aim of this article is to identify quantitative trait loci (QTL) associated with stem/anchorage strength and leverage traits (lodging traits) in a doubled-haploid population of UK bread wheat Avalon× Cadenza. Field experiments were conducted in the UK during 2012–2013 near High Mowthorpe and during 2013–2014 at Sutton Bonington. Phenotypic and genetic analysis indicated significant genetic variation for all traits. Stem strength (diameter, wall width, and material strength) and leverage (plant height) traits were highly heritable (0.64–0.95), whereas anchorage strength traits (root plate spread and structural rooting depth) and ear number per plant (leverage trait) were less heritable (0.21–0.33). This study identified 18 QTL for lodging traits and grain yield in chromosomes 1D, 2B, 2D, 3A, 3B, 4A, 4D, 5B, and 6B. Two QTL for stem strength on chromosome 1D and 3B explaining 49.6% of the total phenotypic variation (PVE) are estimated to reduce stem lodging risk and shortening the plant height by 12cm. One QTL for root plate spread on chromosome 5B explaining 22.4% of the PVE could increase root lodging resistance