Abstract:
Field, greenhouse and laboratory studies were carried out at the Department of Crop Science, University of Nigeria, Nsukka in order to evaluate the leaf spot disease of eggplant and its management with some botanicals. Field survey of diseased plants was conducted on eggplant farm. Solanum aethiopicum L. plants were sampled on every 1 m distance along the diagonal transects for disease incidence and severity. Pathogen isolation from severely infected leaves was carried out in the laboratory where the diseased leaves were plated on fresh Potato Dextrose Agar. Identification of the isolated fungi was carried out with the aid of identification scheme based on their cultural characteristics. Nursery preparation for raising eggplants used in the green house was also carried out on a sterilized soil. The five most abundant pathogens isolated were inoculated separately on the seedlings of eggplant in five replicates. The experiment was arranged in a completely randomized design. Phytochemical contents of the four plant extracts were determined in the laboratory. An in vitro control of the organism responsible for the leaf spots was carried out using plant extracts at 0.030 g/ml, 0.060 g/ml, and 0.120 g/ml and 0.250 g/ml concentrations. The experimental design was a 9x4 factorial in a completely randomized design (CRD). The data were analyzed using analysis of variance (ANOVA). Means were later separated using Fisher’s least significant difference (F-LSD). Helminthosporium infestans Dur. & Mont, Cladophialophora carrionii Trejos, Aspergillus niger van Tieghem, Rhizopus nigricans Ehrenb and Neurospora africana Huang & Backus were isolated from the diseased eggplant leaves. H. infestans recorded the highest percentage frequency (61.11 %) while A. niger had the lowest percentage frequency (5.56 %). H. infestans was pathogenic to eggplant seedlings. The Koch postulate test confirmed H. infestans as the causal organism of the spots symptoms. The qualitative phytochemical analysis on the test plants revealed the presence of tannin, soluble carbohydrate, hydrogen cyanide, steroids, flavonoids, alkaloids as well as glucosides in all the extracts analyzed. The effect of ethanolic extracts of the test plants significantly (P<0.05) reduced the incidence and severity of the pathogen. Anti-fungal activity of seed extracts of G. kola on H. infestans was highest at 0.0120 g/ml concentrations. G. kola could be used as fungicide to manage leaf spot in eggplant because of its availability and eco-friendliness.
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