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Identification of QTLs in Cotton Conferring Resistance to the Bacterial Blight Pathogen

R.J. Wright, P.M. Thaxton, A.H. Paterson and K.M. El-Zik


 
ABSTRACT

Bacterial blight of cotton (Gossypium hirsutum L) , incited by the pathogen Xanthomonas campestris pv. malvacearum (Smith) Dye (Xcm), is a disease that can cause substantial yield loss and reduced fiber quality. In the U.S., yield losses due to Xcm average 1.5% of the annual cotton crop. Yield losses in Asian and African countries can exceed 50%. The characterization,at the molecular level, of plant genes that confer resistance to pathogenic organisms is a giant step toward improving the effectiveness of breeding crops with durable resistance. This study was conducted to map genes in cotton that confer resistance to races of the bacterial blight pathogen. Mapping populations consisted of five parental cotton (G. hirsutum) lines representing different genetic backgrounds and gene combinations. Four parents are isogenic lines for Xcm resistance genes (Empire B2, B3, B2b6 , and B4) and a genotype (S295) containing the B12 resistance gene. These five populations segregating for resistance to Xcm were developed from crosses between the G. hirsutum parents and Pima S7, a G. barbadense parent, to ensure genetic polymorphism across the genome. To substantiate the association between marker data and conferred resistance to the pathogen, four Xcm races (1,4,7, and 18) were used to evaluate individual plants in the segregating F2 populations. To date, three QTLs have been identified of which all map to D-subgenome chromosomes. Several markers linked to the B12 gene have been identified in the S295 mapping population. The region containing the B12 locus has been defined to an interval of approximately 14 cM. The B2 gene was identified in both the Empire B2 and Empire B2b6 populations. Additional markers which map within this region are currently being used in both populations. These markers will enable the fine mapping of the B2 locus within this region. Two markers linked to the putative b6 locus were found in the Empire B2b6 population. Both markers identifying the b6 gene in this population, also identify the B12 in the S295 population. The alignment of conserved markers indicates that both genes map in the same region of the genome. The B12 and b6 genes may be alleles at the same locus or independent loci linked within this region. Additional markers that could more closely define this relationship are currently being studied. Continuing mapping experiments are currently being conducted on these and the Empire B3 and Empire B4 populations.



Reprinted from Proceedings of the 1997 Beltwide Cotton Conferences pg. 105
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998