Present status of bacterial blight in cotton genotypes evaluated at Busia and Siaya counties of Western Kenya

Bacterial blight (BB) incited by Xanthomonas citri subsp. malvacearum (Xcm) is an important bacterial disease occurring in all cotton growing areas throughout the world, including parts of Western Kenya, that are characterized by a hot and humid climate. The disease causes seedling blight, angular leaf spot, boll rot and black arm on petioles and branches leading to a loss of fruiting branches with yield losses of up to 35 %. Fifty- one Kenyan cotton genotypes (Gossypium hirsutum L.) were established in the two counties of Siaya and Busia famous for their cotton cultivation in the western region. The BB symptoms caused by natural Xcm infection in the field were scored for each cotton accession. In addition artificial inoculation with the same strains was done to confirm the status under controlled greenhouse conditions. The results of BB disease scoring revealed that some accessions (e.g. T 24A and T 24B) possess a reasonable level of resistance. However, most of the Kenyan genotypes surveyed showed medium to severe symptoms of BB, including KSA 81 M, the only commercially grown cultivar in the region of Western Kenya. Overall, 71 % of the genotypes showed susceptibility and 29 % were classified as either resistant or moderately resistant. There is therefore need to improve the local commercial genotypes by introducing new genetic resources with a more durable BB resistance to ensure a successful revitalization of the Kenyan cotton sector. © 2014 Koninklijke Nederlandse Planteziektenkundige Vereniging.