Water stress and Verticillium wilt severity on eggplant (Solanum melongena L.)

Verticillium wilt is one of the most destructive diseases of eggplant (Solanum melongena L.). Some researchers have reported that wilt was encouraged by sufficient soil humidity, while others stated that it was encouraged by drought. This study investigated the water stress effect on the severity of Verticillium wilt on eggplant, as it is reflected on yield, agronomic traits and fruit quality. Thus, eggplant seedlings cv. 'Tsakoniki' were transplanted in three rows, each with 20 plants, during the summer of 1995 and 1996 in a plastic greenhouse, at the Agricultural Research Center of Macedonia and Thrace. Ten of the plants in each row were inoculated with the fungus Verticillium dahliae, while the other 10 were used as controls. Rows were irrigated every 2, 4 or 6 days. Soil humidity was calculated before every irrigation in each row. The disease severity was estimated by the disease index (DI) as the combination product of leaf symptom index (LSI) and vascular discoloration index (VDI). In addition. the plant height, early and total commercial yields, fruit numbers of early and total commercial yields, plant weight, the above-ground plant weight, root weight, pH, total soluble solids and fruit brilliance plus colour intensity were measured. The effect of Verticillium wilt on plants irrigated every 2, 4 or 6 days was estimated by the correlation coefficient (r) between LSI and DI and the aforementioned characteristics. Verticillium wilt had a significant but negative effect on all of the measured or calculated characteristics. This effect, however, was independent of the irrigation applied. On average, the early commercial yield was reduced by 40.8% and the final commercial yield by 39.4%. The only quality characteristic that was affected significantly by irrigation was the fruit brilliance and colour intensity (r = -0.640 to -0.727, P less than or equal to 0.01). Finally, the irrigation frequency (every 2, 4 Or 6 days) had a significant but negative effect on all of the characteristics measured on the control plants. The only exception was fruit quality. In conclusion, the combined effect of irrigation and Verticillium wilt infection significantly reduced the early and total production of eggplant and spoiled the fruit quality.