Quantitative Disease Resistance and Quantitative Resistance Loci in Breeding

Abstract

Quantitative disease resistance (QDR) has been observed within many crop plants but is not as well understood as qualitative (monogenic) disease resistance and has not been used as extensively in breeding. Mapping quantitative trait loci (QTLs) is a powerful tool for genetic dissection of QDR. DNA markers tightly linked to quantitative resistance loci (QRLs) controlling QDR can be used for marker-assisted selection (MAS) to incorporate these valuable traits. QDR confers a reduction, rather than lack, of disease and has diverse biological and molecular bases as revealed by cloning of QRLs and identification of the candidate gene(s) underlying QRLs. Increasing our biological knowledge of QDR and QRLs will enhance understanding of how QDR differs from qualitative resistance and provide the necessary information to better deploy these resources in breeding. Application of MAS for QRLs in breeding for QDR to diverse pathogens is illustrated by examples from wheat, barley, common bean, tomato, and pepper. Strategies for optimum deployment of QRLs require research to understand effects of QDR on pathogen populations over time.

High‐Density Mapping of Resistance QTL Toward Phytophthora sojae, Pythium irregulare, and Fusarium graminearum in the Same Soybean Population

“…6). All QTL detected in the current study can be classified minor QTL because they explained less than 15% of PV (St. Clair, 2010). Therefore, it seems more likely that there are several to many genes with small effects involved in these resistances, rather than few genes at a major QTL, as can be the case for other quantitative traits (Young, 1996).…”

“…Quantitative resistance is also effective against pathotypes (races) of biotrophic pathogens (Kou and Wang, 2010;Hulbert and Pumphrey, 2014;Parlevliet and Zadoks, 1977;Poland et al, 2009;St. Clair, 2010;Umaerus, 1970).…”

“…irregulare and F. graminearum (Glazebrook, 2005;Kou and Wang, 2010;Kou and Wang, 2012). Prior to cloning genes from resistant genotypes associated with quantitative disease resistance in plants, characterizing the type of resistance, identifying and mapping the loci, and narrowing the locus requires a population that is both advanced in generation and large in size to capture the greatest number of recombination events (St. Clair, 2010;Xu et al, 2013). There have been several advancements in this arena where genes associated with quantitative resistance have been cloned and identified.…”

Quantitative Resistance: More Than Just Perception of a Pathogen

“…A significant body of current plant pathology research has focused on examples of qualitative resistance, where the underlying genetic architecture relies on a few genes of large effect that are amenable to detailed molecular analysis (Figure 1). By contrast, the genetic architecture underlying quantitative resistance is thought to involve many genes with small to moderate effects ( Figure 1) (Poland et al, 2009;St Clair, 2010;Roux et al, 2014;Niks et al, 2015). However, quantitative resistance governs the outcome of the vast majority of host-pathogen interactions.…”

Discovery of genes affecting resistance of barley to adapted and non-adapted powdery mildew fungi

“…Durable and broad-range non-host resistance (NHR) to virtually all races of non-adapted pathogens appears to be an important manifestation of PTI in many cases [4,5] although there is also experimental evidence that NHR can -at least in grass species -be mediated by as little as one major R gene recognizing an indispensable Avr effector [6]. Race-specificity of NHR QTL to non-or only partially adapted fungal pathogens has also been described, similar to QTL for host quantitative resistance (QR) that is another manifestation of PTI [7] and QR is also referred to as race-non-specific or horizontal resistance [8][9][10]. However, in contrast to the very robust NHR response, QR is often not very efficient suffering from effector-triggered susceptibility (ETS) brought about by small secreted proteins or peptides from adapted pathogens that are active in the plant apoplast or inside host cells [11].…”