| Popis: |
Linear regression analysis of data transformed according to several mathematical models showed no significant correlation between the inoculum density of Verticillium dahliae determined at sowing time in randomly chosen cotton fields and the incidence of plants with vascular discoloration, the incidence of plants with foliar symptoms, or a disease intensity index for Verticillium wilt of cotton calculated at the end of the crop season. Epidemic development of Verticillium wilt in cotton was investigated in field plots naturally infested with different inoculum densities of the defoliating and nondefoliating pathotypes of V. dahliae in 1986 and 1987. The straight line model adequately described the increase in the incidence of plants showing foliar symptoms and the disease intensity index over the accumulated physiological time from sowing. For similar levels of initial inoculum, the defoliating pathotype of V dahliae caused an earlier epidemic onset, a higher rate of increase in the incidence of foliar symptoms and the disease intensity index over physiological time, and a higher final amount of both disease measurements than the nondefoliating pathotype. Also, for the two disease measurements, the rate of progress increased with the initial inoculum density of the defoliating pathotype up to a threshold of 24 to 44 CFU/g of dry soil in 1986 and 44 to 75 CFU/g of dry soil in 1987. Differences in severity among Verticillium wilt epidemics were described more appropriately by the descriptive parameters of the increase in the disease intensity index over physiological time than by the corresponding parameters of the increase in the incidence of foliar symptoms. |
