Pyramiding and Validation of Quantitative Trait Locus (QTL) Alleles Determining Resistance to Barley Stripe Rust

Abstract

The use of molecular and quantitative trait locus (QTL) analysis tools initially lent support to the idea that relatively few genetic factors were the principal determinants of complex traits, including quantitative resistance (QR) to plant diseases. However, there are concerns regarding bias in QTL estimation and reproducibility of QTL effects in different genetic backgrounds. We are interested in mapping determinants of QR, and pyramiding resistance alleles at QTL loci may lead to durable resistance as well as provide independent validation of QTL effects and estimation of QTL interactions. We used molecular marker information to validate effects of resistance alleles at three QTL conferring QR to barley stripe rust (caused by Puccinia striiformis West. f. sp. hordei). Two of the QTL [one on chromosome 4(4H) and one on chromosome 7(5H)] trace to one parent, while another QTL on chromosome 5(1H) traces to a different parent. The pyramids of these QR alleles provide independent estimates of QTL effects, influence of genetic background on QTL effects, QTL × QTL interaction, and QTL × environment interaction. Our results validate QTL effect estimates, showing that a small number of QTL explained 94% of the genetic variation in trait expression in a new genetic background. Original QTL estimates were quantitatively biased, but that did not preclude the achievement of selection responses. We also confirmed the additive effects of the QTL alleles, as well as the consistent effects of QTL alleles across environments.

Fractionation, Stability, and Isolate-Specificity of QTL for Resistance toPhytophthora infestansin Cultivated Tomato (Solanum lycopersicum)

“…As reviewed by St.Clair (2010), there are successful examples of pyramiding QTL alleles for increased disease resistance in crop plants, including resistance to common bacterial blight in bean (Mutlu et al 2005), Fusarium head blight in wheat (Wilde et al 2008), root rot and shoot blight in pepper (Thabius et al 2004), and stripe rust in barley (Toojinda et al 1998; Castro et al 2003; Richardson et al 2006). Previously, Brouwer and St.Clair (2004) observed that pyramiding QTL lb5b and lb11b (contained in the NIL parents of our sub-NIL populations) resulted in a higher level of P. infestans resistance (unpublished data).…”

Positioning of the major locus for Puccinia psidii rust resistance (Ppr1) on the Eucalyptus reference map and its validation across unrelated pedigrees

“…QTL validation for different rust diseases caused by Puccinia sp. has been carried out in wheat (Khlestkina et al 2007;Schnurbusch et al 2004), barley (Castro et al 2003), and sugar cane (McIntyre et al 2005) to name a few. In all cases a major locus conferring resistance to the rust disease was found and its presence validated across unrelated pedigrees.…”

Confirmation of Three Quantitative Trait Loci Conferring Adult Plant Resistance to Powdery Mildew in Two Winter Wheat Populations

“…vt-1BL explained proportionally less when compared to the values reported in the original BM mapping population (Liu et al 2001). Castro et al (2003) evaluated three QTL for APR to barley (Hordeum vulgare) stripe rust (Puccinia striiformis) in different genetic backgrounds and found that one QTL with a small genetic effect in the mapping population explained significantly more of the variation in a different genetic background. Therefore, it is likely that effects of QTL governing APR to powdery mildew will vary in different genetic backgrounds due to both positive and negative epistasis among genes affecting host resistance and susceptibility.…”