Verticillium Wilt On-Farm Cotton Cultivar Variety Evaluation

Abstract

Verticillium Wilt is caused by Verticillium dahliae, which colonizes the vascular cylinder of the plant and causes defoliation, stunting, and yield loss. Thirteen cotton varieties were planted and evaluated for resistance to Verticillium dahliae. The trial was planted on the Isbell farm in Northwest Alabama. Plots were six rows each, and approximately 500 feet long. The field was irrigated, when needed, with a center pivot irrigation system. Disease ratings were taken September 20. Ten feet sections of the third row in each plot were observed for total number of
plants and stems were cut longitudinally to assess disease incidence. Disease severity ratings of foliar symptoms were evaluated on a scale from 1-5 with 1 having no foliar wilting, 3 having interveinal chlorosis and necrosis of the leaves and 5 having completely defoliated plants. Four replications of each variety were counted. Petioles were taken from infected plants of each variety and re-isolated to confirm the presence of Verticillium dahliae.  In regards to disease severity, the top thirty percent of plants displaying the least amount of foliar symptoms and the most resistant varieties were BX 1347 GLB2, FM 1944 GLB2, PHY 339 WRF, and DP 1044 B2RF. None of these varieties received averaged scores exceeding 3. In terms of disease incidence, the resistant check FM 1944 GLB2 had the lowest number of plants with darkened vascular systems. PHY 339 WRF, DP 1044 B2RF, DP 1321 B2RF, ST 6448 GLB2, ST 4946 GLB2, DP 1133 B2RF, DPLX 12R224 B2R2, BX 1347 GLB2, and DP 1137 B2RF all displayed vascular staining and average percent of disease incidence ranged from 45.5-68.1. These percentages were statistically similar and performed better than the susceptible varieties but below the resistant check.