Fine mapping of qtl-qslb.pau-3.04 for southern leaf blight resistance in maize (Zea mays L.)

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Date
2019
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Punjab Agricultural University, Ludhiana
Abstract
Southern leaf blight (SLB) caused by Cochliobolus heterostrophus (Drechsler), is a serious disease throughout the world where maize is grown under warm and humid conditions, leading to enormous yield losses. Exploiting genes and quantitative trait loci (QTLs) related to SLB is helpful for improving fungal resistance. In earlier study at Punjab Agricultural University, Ludhiana a set of 325 F2:3 families and F4 progenies derived from the cross of CM139 as the resistant (female) parent and CM140 as the susceptible (male) parent were phenotyped for resistance to SLB under field conditions. A total of 172 polymorphic SSR markers were genotyped on F2 population.Three probable QTL viz. qSLB2.1, qSLB3.1, qSLB3.2 were detected for SLB resistance in bins of 2.05-2.08, 3.04 and 3.06-3.09. The marker interval phi099-umc1729 spanning qSLB3.1 was considered as major putative QTL. In present study, the QTL qSLB3.1 spanning region was saturated with more SSR markers on 298 RIL population of the same cross. The detected QTL region (13.7 cM) was fine mapped to 1.2 cM region flanked with marker MSSR1-MSSR20 explaining phenotypic variance of 15.1 per cent at log-likelihood of 6.9. The 1.2 cM region corresponds to 269.3 Kb and comprises only six candidate genes. The candidate gene based markers were designed, to study the differential expression patterns of candidate genes through quantitative real-time PCR (qRT-PCR). Two of the candidate genes viz. GRMZM2GO88371 and GRMZM5G862219 showed 3.48 and 6.40 fold higher expression in CM140 at 48h and 72h respectively. GRMZM2GO88371 and GRMZM5G862219 have their biological function in lipid metabolism and β oxidation respectively that is involved in the defense pathway and may be one of the potential candidate genes conferring resistance against C. heterostrophus. The SLB QTL linked flanking markers were employed for mobilization of qSLB3.1 QTL into the background of CM140 through marker assisted backcross breeding (MABB). The F1s of cross (CM139 X CM140) were backcrossed to recurrent parent to generate BC1F1 population. A total of 64 plants out of 420 were selected on the basis of foreground selection. Recombinant selection for the carrier chromosome was done to identify single and double recombinants. The plants having maximum recurrent parent recovery for carrier chromosome were selected and backcrossed with CM140 to generate BC2F1 generation. The data generated from this study can serve as valuable genomic resource for maize breeding programmes. It will enable the researcher to multi-thronged and focused approaches for sustainable development of new genotypes by pyramiding it with other desirable genes using MABB.
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