Validation of molecular markers for wheat breeding

Abstract

Five sets of markers were assessed for their usefulness in breeding, two linked to wheat stem rust gene Sr2, several markers linked to a chromosome segment conferring Yr17/Lr37/Sr38 resistance, two reported markers for the linked genes Lr35 andSr39, one for Lr28, and one linked to flour colour. The gene for Sr2 confers adult plant resistance to stem rust (Puccinia graminis f.sp. tritici) and was originally transferred to bread wheat from the tetraploid emmer (‘Yaroslav’) to the cultivars Hope and H-44. The gene is located on the short arm of chromosome 3B and confers a durable adult plant resistance to stem rust usually expressed only in the field. The chromosome segment carrying the Lr37, Sr38, Yr17 resistance genes is located on 2AS and was originally introduced into wheat through an Aegilops ventricosa Triticum persicum cross, followed by a cross to the cultivar Marne (VPM1). The flour colour quantitative trait locus was originally described in a Yarralinka Schomburg cross and is located on chromosome 7A. The primers as originally developed required optimisation for more routine use in a breeding program.

Confirmation of QTL mapping and marker validation for partial seedling resistance to crown rot in wheat line '2-49'

“…This attribute of the SSR markers highlights the necessity to test markers against the full range of pedigree sources prior to use in MAS even when a tightly linked pair of flanking markers (2.1 cM) has been identified in the original mapping study. Although single, tightly linked markers can still be effective for MAS in the absence of 'perfect' markers within a gene (Wilcox et al 2002;Zhou et al 2003), the identification of a 'window' or 'suite' of flanking markers is preferable for each QTL, since different pairs of flanking markers can be used in different backgrounds (Langridge et al 2001;Sharp et al 2001). However, in practice this level of marker density is not always available due to low polymorphism levels or to a lack of identified markers in critical regions.…”

“…'QTL confirmation' and 'marker validation' are critical stages prior to the deployment of molecular markers for MAS (Langridge et al 2001; Sharp et al 2001;Zhou et al 2003).…”

Molecular marker assisted selection as approach to increase the selection efficiency of drought tolerant genotypes

“…Simple sequence repeats (SSR) markers, however, combine reliability and genomic abundance with high levels of polymorphism and codominance [5]. Recently, there is increasing use of single nucleotide polymorphism markers (SNPs) in maize [26]. The main drawback of SSRs is the initial identification of primer sites to amplify SSR loci, a procedure which is time-and resource demanding.…”

“…In maize, about 148 QTLs for grain yield have been detected. However, fewer QTLs were identified under waterstressed conditions (about 20 QTLs) [26]. In maize, most research efforts have been directed toward the development of microsatellite marker systems for genetic mapping and germplasm analysis [8], [33].…”

“…Dubey et al (2009) in an effort to identify SSR markers of drought tolerance in 24 tropical maize lines with different responses to drought stress came to the conclusion that dupssr12, umc1042, bnlg1866, umc1056 ,dup13, umc1069, umc1962, bnlg1028 and c1344 markers were among those drought related markers in the susceptible and drought tolerant genotypes under investigation [17]. Despite numerous reports of QTLs in maize [26], including QTLs for adaptation to water-limited conditions, reviewed by Tuberosa et al(2002) and Sawkins et al (2006), little has been published on the implementation of MAS based on these QTLs in breeding programmes [22], [30]. Successful MAS applications have been reported for introgression breeding in maize, including introgressions of transgenes [20] and conversions involving simple [19] or complex traits [24].…”