QTL mapping of resistance to sorghum downy mildew in maize

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Title: QTL mapping of resistance to sorghum downy mildew in maize
Author: Sabry, Ahmed Mohamed-Bashir
Abstract: Sorghum downy mildew (SDM ) of maize is caused by the oomycete Peronosclerospora sorghi (Weston and Uppal ) C . G . Shaw . The disease can cause devastating yield losses in maize (Zea mays L . ) . Quantitative trait loci (QTLs ) mediating resistance to SDM were mapped using both restriction fragment length polymorphisms (RFLPs ) , and simple sequence repeats (SSRs ) in 220 F2 individual maize progeny derived from a cross between two extremes ; highly susceptible inbred parent SC -TEP5 -19 -1 -3 -1 -4 -1 -1 (white ) and highly resistant inbred P345C4S2B46 -2 -2 -1 -2 -B -B -B (yellow ) . The phenotypic expression was assessed on F2 :3 families in a wide range of environments under natural field infection and in a controlled greenhouse screening method . Heritability estimates of disease reaction ranged from 93 .3 % in Thailand sit 1 to 48 % in Thailand sit 2 . One hundred and thirty three polymorphic markers were assigned to the ten chromosomes of maize with LOD scores exceeding 4 .9 covering about 1265 cM with an average interval length between markers of 9 .5 cM . About 90 % of the genome was located within a 10 cM distance to the nearest marker . Three putative QTLs were detected in association with resistance to SDM in different environments using composite interval mapping . Despite environmental and symptom differences , one QTL on chromosome 2 bin 9 had a major effect in all trials and explained up to 70 % of the phenotypic variation in Thailand where the highest disease pressure was experienced . Two other QTLs on chromosome 3 bin 5 and chromosome 9 bin 2 had a minor effect , each explaining no more than 4 % of the phenotypic variation . These results revealed one major gene and two minor genes that control sorghum downy mildew resistance . These markers should be very useful in breeding programs in facilitating the introgression of the resistance genes into commercial varieties . Marker -assisted selection for these loci should be useful in incorporating SDM resistance genes in maize across environments , even in the absence of the pathogen .
URI: http : / /hdl .handle .net /1969 .1 /460
Date: 2004-09-30


QTL mapping of resistance to sorghum downy mildew in maize. Available electronically from http : / /hdl .handle .net /1969 .1 /460 .

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