Estimation of Tolerance Levels of Thirty - One Upland Cotton Cultivars to Bacterial Blight (Xanthomonas campestris pv. malvacearum).

ABSTRACT

Bacterial blight of cotton caused by the gram-negative bacterium Xanthomonas campestris pv. malvacearum (Xam) is potentially one of the most destructive diseases of cotton. Under favorable conditions serious epidemics are possible wherever susceptible cultivars are grown. Hence, use of a bacterial blight resistant cultivar is critical to minimize potential loss of yield and fiber quality. However, there is very limited information available about the blight resistance capacity of many commercial cultivars. The objective of this study was to evaluate tolerance levels of 31 cotton cultivars to bacterial blight. Thirty one cotton cultivars developed by five different entities were grown in greenhouse for this study. Randomize complete block design with four replications was used for the experiments. Plants were inoculated with freshly grown culture of Xanthomonas campestris pv. malvacearum (Xam) race 18 at two growing stages (30 and 90 days after planting). After 21 days of inculcation plants were graded and classified according to the morphological symptoms observed. Cultivars showed significant (P<0.05) variations in the disease reaction toward bacterial blight. In 30 days old plants, four cultivars received disease grade value of 0, which were classified as immune, 11 cultivars were scored in three grades of  0.1, 0.2, and 1 which were classified as resistant, and 16 cultivars received grade values of 1.2 and 2.3, which were classified as moderately susceptible. In 90 days old plants, seven cultivars were classified as immune, 10 cultivars were classified as resistant, and 14 cultivars were moderately susceptible. Our study shows sufficient genotypic variation among cultivars to improve bacterial blight resistance in cotton through breeding programs.