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

Verticillium wilt is one of the most destructive diseases of eggplant (Sola num 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 trai ts and fruit quality. Thus, eggplant seedlings cv. 'Tsakoniki' were transpl anted in three rows, each with 20 plants, during the summer of 1995 and 199 6 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 i rrigated every 2, 4 or 6 days. Soil humidity was calculated before every ir rigation in each row. The disease severity was estimated by the disease ind ex (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, plan t weight, the above-ground plant weight, root weight, pH, total soluble sol ids and fruit brilliance plus colour intensity were measured. The effect of Verticillium wilt on plants irrigated every 2, 4 or 6 days was estimated b y the correlation coefficient (r) between LSI and DI and the aforementioned characteristics. Verticillium wilt had a significant but negative effect o n 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 on ly quality characteristic that was affected significantly by irrigation was the fruit brilliance and colour intensity (r = -0.640 to -0.727, P less th an or equal to 0.01). Finally, the irrigation frequency (every 2, 4 Or 6 da ys) had a significant but negative effect on all of the characteristics mea sured on the control plants. The only exception was fruit quality. In concl usion, the combined effect of irrigation and Verticillium wilt infection si gnificantly reduced the early and total production of eggplant and spoiled the fruit quality.