EPIDEMIOLOGY OF COWPEA BROWN BLOTCH INDUCED BY COLLETOTRICHUM CAPSICI AND ASSESSMENT OF CROP LOSSES DUE TO THE DISEASE

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EPIDEMIOLOGY OF COWPEA BROWN BLOTCH INDUCED BY COLLETOTRICHUM CAPSICI AND ASSESSMENT OF CROP LOSSES DUE TO THE DISEASE

Abstract:

Colletotrichum capsici (Syd.) Butler and Bisby which induces brown blotch in cowpea was found to grow and sporulate between 20 and 3 5°C on potato dextrose agar incorporated with streptomycin, the optimum temperature being 25°C. When plants aged 1-6 weeks were inoculated with the conidial suspension of the fungus containing 4.16 x 1Q5 to 3.7 5 x 106 conidia/ml, plants aged 1 or 2 weeks at inoculation were more severely affected than older plants aged 3 to 6 weeks at the time of inoculation. There was a highly significant (P=0.01) interaction between plant age at inoculation and inoculum concentration. The incubation period was 2-3 days for all the aerial parts of the plants inoculated irrespective of age. C. capsici sporulated faster on relatively tender petiole tissues than on less succulent stem tissues. The latent period varied from 5 to 16 days, depending on the plant part. Cowpea sown early at the third week of July or first week of August (when there was high and frequent rainfall) had higher incidence of brown blotch than those sown late August. In addition the quality of the grain produced in the early sown crop was poor (being mostly wrinkled) while that of the late sown crop, was relatively high, being mostly wholesome and non-discoloured. It appears that both rainfall and relative humidity enhance the development of brown blotch in cowpea provided that there is enough rainfall and consequently, sufficiently high relative humidity for disease establishment, although among the two factors, the progress of the disease appears to depend more on relative humidity. Loss in grain yield of cowpea due to brown blotch ranged from 10% for variety IT83S-742-11 to 44% for Ife Brown

EPIDEMIOLOGY OF COWPEA BROWN BLOTCH INDUCED BY COLLETOTRICHUM CAPSICI AND ASSESSMENT OF CROP LOSSES DUE TO THE DISEASE

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