Abstract
The cotton cultivar DELTAOPAL is resistant under field as well as under glasshouse conditions to the Brazilian isolates of Xanthomonas axonopodis pv. malvacearum (Xam). Segregating populations derived from the cross between this cultivar and one susceptible cv. BRS ITA 90, were utilized to identify molecular marker linked with the resistance gene to Xam by “Bulk Segregant Analysis (BSA)”. Two hundred and twenty microsatellite (Single Sequence Repeat—SSR) primers were tested. The amplification products were visualized in polyacrylamide gels stained with silver nitrate. Only one primer was informative and showed polymorphism between the DNA of the parents and their respective bulks of homozygous F2 populations contrasting for resistance and susceptibility, and hence was used to analyze DNA of 120 F2 populations. The microsatellite primer yielded one band of 80 bp linked with the resistance locus, which was absent in the susceptible parent as well as in the bulk of the homozygous susceptible plants of the cross. The segregation ratio as determined by phenotypic analysis was 3R:1S. It is believed that the microsatellite marker was linked with the resistance locus and hence may offer new perspectives for marker assisted selection against the angular leaf spot disease of cotton. It is however, felt necessary to repeat the microsatellite analysis and make sure that the primer is tightly linked with the resistance locus and at the same time verify the genetic distance between the marker and the resistance locus.
Highlights
The angular leaf spot of cotton, known as “bacterial blight” and “black arm” of cotton, caused by Xanthomonas axonopodis pv. malvacearum (Xam) is economically important in several cotton growing areas of Asia, Africa, USA and the Latin America, including Brazil
It is believed that the microsatellite marker was linked with the resistance locus and may offer new perspectives for marker assisted selection against the angular leaf spot disease of cotton
Analysis of the F2 populations derived from the cross DELTAOPAL × BRS ITA 90, yielded a segregation ratio of 3R:1S suggesting the presence of a single dominant gene for resistance to Xam [3]
Summary
The angular leaf spot of cotton, known as “bacterial blight” and “black arm” of cotton, caused by Xanthomonas axonopodis pv. malvacearum (Xam) is economically important in several cotton growing areas of Asia, Africa, USA and the Latin America, including Brazil. The angular leaf spot of cotton, known as “bacterial blight” and “black arm” of cotton, caused by Xanthomonas axonopodis pv. The pathogen is seed transmitted and can cause appreciable yield losses. In the USA the estimated annual losses could be between 0.1% and 2.3% [1]. In Brazil, the disease is reported to cause heavy yield losses under favorable weather conditions [2]. The angular leaf spot disease can be controlled through varietal resistance. Nineteen races of the pathogen currently are recognized in the USA [1,3]. DELTAOPAL, EPAMIG LIÇA and FIBERMAX 986, are available, breeding for resistance against this disease is difficult. Conventional breeding strategies for disease resistance which involve pyramiding of resistance genes are time consuming, expensive and require artificial inoculations under glasshouse and field conditions.
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