Mapping and validation of quantitative trait loci for resistance to Cercospora zeae-maydis infection in tropical maize (Zea mays L.)

Abstract

Breeding for resistance to gray leaf spot, caused by Cercospora zeae-maydis (Cz) is paramount for many maize environments, in particular under warm and humid growing conditions. In this study, we mapped and characterized quantitative trait loci (QTL) involved in the resistance of maize against Cz. We confirmed the impact of the QTL on disease severity using near-isogenic lines (NILs), and estimated their effects on three major agronomic traits using their respective near isogenic hybrids (NIHs), which we obtained by crossing the NILs with an inbred from a complementary heterotic pool. We further validated three of the four QTL that were mapped using the Multiple Interval Mapping approach and showed LOD values>2.5. NILs genotype included all combinations between favorable alleles of the two QTL located in chromosome 1 (Q1 in bin 1.05 and Q2 in bin 1.07), and the allele in chromosome 3 (Q3 in bin 3.07). Each of the three QTL separately significantly reduced the severity of Cz. However, we found an unfavorable epistatic interaction between Q1 and Q2: presence of the favorable allele at one of the QTL allele effectively nullified the effect of the favorable allele at the other. In contrast, the interaction between Q2 and Q3 was additive, promoting the reduction of the severity to a greater extent than the sum of their individual effects. When evaluating the NIH we found significant individual effects for Q1 and Q3 on gray leaf spot severity, for Q2 on stalk lodging and grain yield, and for Q3 on grain moisture and stalk lodging. We detected significant epitasis between Q1 and Q2 for grain moisture and between Q1 and Q3 for stalk lodging. These results suggest that the combination of QTL impacts the effectiveness of marker-assisted selection procedures in commercial product development programs.

Bayesian inference to study genetic control of resistance to gray leaf spot in maize

“…In some of these reports, additive gene effects were linked with QTL regions mapped on chromosome 2 by Bubeck et al (1993), on chromosome 1 by Saghai-Maroof et al (1996) and also on chromosome 4 by Gordon et al (2004). Our results are consistent with most of the reports in the literature, in that previous studies revealed that additive effects account for more than 90% of the variability among generations and that GLS resistant could be: i) inherited additively, ii) controlled by additive gene action and presenting minor dominant and epistatic contributions, iii) associated with the general combining ability of inbred lines, and iv) controlled by few effective factors (Clement et al, 2000;Julliati et al, 2009;Pozar et al, 2009). The results and inferences about GLS genetic resistance obtained in this study would be different from previously reported studies if least square estimates were applied, since a high influence of epistasis was observed on scaling-test (data not shown).…”

<b>Effect of foliar fungicide and plant spacing on the expression of lipoxygenase enzyme and grain rot in maize hybrids

“…In research conducted by Pozar et al (2009) in Brazil, QTLs related to gray leaf spot resistance have been mapped and characterized through SNP and SSR markers.…”

“…This species is cultivated in many different environments and climates at different latitudes, from Russia to Argentina. The culture has a wide geographic range of cultivation and can be developed in many different soil and climate conditions; consequently, it is possible to use various commercial hybrids that have sundry tolerance levels to leaf and grain pathogens (Pozar, Butruille, Diniz, & Viglioni, 2009). The occurrence of these pathogens causes reductions in grain yield and grain health quality because infection by these fungi results in paralysis of the normal process of grain filling and reduces maize cob weight.…”

QTL mapping to anthracnose leaf blight resistance in tropical maize

“…However, the development of cultivars with genetic resistance to disease is costly and laborious, since it involves numerous selection cycles and favorable environmental conditions for the pathogen's development, as well as for the expression of resistance in segregating populations. Thus, QTL mapping (Quantitative Trait Loci) to disease resistance using molecular markers may accelerate the development of resistant genotypes, maximizing the yield potential of crops by means of marker-assisted selection (Pozar et al 2009). The literature indicates that a few genes with additive and dominant gene action control resistance to ALB (Badu-Apraku et al 1987).…”

“…Studies aiming to know the nature and magnitude of the effects of resistance genes are important to guide the breeding procedures in order to introduce new resistance alleles in susceptible germplasm, and maximize the use of genetic variability in populations under selection (Pozar et al 2009). Thus, determining the number, the nature of gene action, and the position of QTL in the maize consensus map can significantly contribute to the clarification of the genetic basis of resistance to ALB in tropical maize germplasm.…”