ABSTRACT

Bacterial blight of cotton, caused by Xanthomonas campestris pv. malvacearum (Smith) Dye (XCM), is one of the most important bacterial diseases causing significant losses to cotton growers all over the world. Cotton disease resistance is the primary method of controlling bacterial blight of cotton. Studies were conducted in 2000, 2001 and 2002 to determine the resistance levels of present germplasm in west Texas. The main objective of this study was to differentiate resistant commercial cotton varieties from susceptible varieties. Plants for all experiments were inoculated with XCM (race 18) by spray application. The plots were rated for disease after the symptoms were clearly visible on both surfaces of the leaves. Differences in resistance to XCM were identified by analysis of variance (µ = 0.05) using the general linear model procedure of statistical analysis system. Mean separation between entries was performed with the Waller-Duncan k-ratio t-test at µ = 0.05. An arbitrary scale was developed for the range of ratings and used to group entries. Highly susceptible varieties were All-Tex (Atlas, Atlas RR, Atlas Plus, Excess Plus, Top-Pick), DeltaPine (2379, 458 B/RR), FiberMax (5013, 5024), Paymaster (183, 330, HS-26, 2266 RR, 2326 RR, 2326 BG/RR, 2344 BG/RR, 2379 RR, 2145 RR), Phytogen (355, GA 161, GA894, HS-12, 952, 14512), Stoneville (474, 4892 BR) and Texas 28 R. Less susceptible varieties were All-Tex Max-9, BXN 16, Paymaster 2200 RR, Stoneville 2454 R and SureGrow 501 BR. Moderately resistant varieties were All-Tex (Xpress RR, Xpress), Paymaster 2280 BG/RR, Stoneville 5599 BR, SureGrow 521 RR and Syngenta NK 2164 C. Highly resistant varieties were All-Tex Excess, FiberMax (819, 832, 958, 966, 989), Paymaster (280, 1218 BG/RR, 2167 RR), Stoneville (239, 239 BR), SureGrow (747, 215 BG/RR), Syngenta NK 2387 C and Tamcot (Sphinx, Pyramid).