Effect of plant resistance and fongicide treatment on groundnut leaf spots

摘要

In groundnut (Arachis hypogaea L.), leaf spot caused by Cercospora arachidicola Hori (early leaf spot) and Cercosporidium personatum (Berk. & Curt.) Deighton date leaf spot) are major worldwide diseases. In Cameroon, losses of up to 53% have been estimated. This study was carried out during the 1991 and 1992 growing seasons in Dschang, Cameroon. The aim was to characterise the development of leaf spots on three varieties of different susceptibility, and to evaluate the effects of fungicide treatments on disease progress. A strip block design with three replicates was used. Eight foliar applications of benomyl (Benlate 50WP, 0.45 kg a.i./ha) or cupric hydroxide (Kocide 101 77WP, 3.85kg a.i./ha) were given according to a ten-day schedule. Leaf spot severity was rated at ten-day intervals on four randomly selected plants in the central line of each plot. The size and density of each lesion type and the total disease severity were assessed in each season. Epidemic rates and areas under the disease progress curves were also computed. Disease progress curves were better described by the Gompertz model (R 2 = 93-96%) than the logistic model (R 2 = 81-96%). Epidemic rate, lesion size, lesion density and area under the disease progress curves were low in the fungicide-sprayed plots, or in the control plots of Ewondo Baki or Southern Runner varieties, compared with the unsprayed susceptible variety Siksa. Benomyl limited disease progress more than cupric hydroxide. Lesion size and density of early leaf spot were both generally higher than those of late leaf spot. In both seasons, the size and density of the two lesion types were often higher in Siksa than in Ewondo Baki or Southern Runner. The lowest lesion size or density was always obtained in plots treated with benomyl. The above observations suggest that both host resistance and fungicide treatment effectively control groundnut leaf spot.