Control of Verticillium wilt of cotton by means of soil solarization and tolerant cultivars in southern Spain

Abstract

Eight field experiments (I‐VIII) were conducted in clay soils naturally infested with a cotton‐defoliating pathotype of Verticillium dahliae in the lower Guadalquivir Valley of Andalucia, southern Spain, during the period 1986‐90. Experiments I‐VI aimed to determine the efficacy of soil solarization in reducing populations of the pathogen in soil and eventually contributing to the control of Verticillium wilt of cotton. The population of V. dahliae in the 0‐to 40‐cm soil layer was reduced to undetectable or very low levels after solarization for 6 to 10 weeks. The final incidence of Verticillium wilt in the cotton crop following solarization was reduced to 13% or less in solarized plots, compared to 55–90·5% in unsolarized controls. The onset of disease incidence in the solarized plots was delayed by 2–7 weeks, increased at a lower rate, and had a smaller area under the disease progress curve, compared to that in unsolarized plots. Seed cotton yields in solarized plots increased by 11·3‐130·9% depending upon experiments, cultivars and years. Experiments VII and VIII aimed to determine the use of the highly wilt‐tolerant cotton cv. Acala GC 510 for control of the disease that had been cropped to susceptible cotton cultivars the year before in solarized soils. Solarized or unsolarized plots were first sown to susceptible cotton cvs Acala SJ2 and Coker 310, and the following year were sown to cv. Acala GC 510. The inoculum density of V. dahliae at the time of sowing cv. Acala GC 510 in previously solarized plots had increased to moderate levels, but remained considerably lower than that in unsolarized plots. The final disease incidence in cv. Acala GC 510 grown in unsolarized plots was lower than that in susceptible cultivars grown in the same plots the year before. Furthermore, the disease incidence in cv. Acala GC 510 grown in solarized plots was as high as that in susceptible cultivars grown the year before with much less initial inoculum.