MANAGEMENT OF FUNGAL DISEASES OF PEPPER (Capsicum spp.) WITH HOST PLANT RESISTANCE AND SELECTED BIOPESTICIDES IN SOUTHWESTERN NIGERIA

Abstract

Pepper is an important vegetable crop used as a food condiment worldwide. However, Fungal Diseases (FD) reduce yield and limit pepper production. Synthetic pesticides are effective in managing FD but could be detrimental to the environment. Resistant crop varieties and biopesticides have been employed to manage FD on some crops, but there is limited information on their use in controlling pepper FD. Therefore, FD of pepper, and their management with host plant resistance and biopesticides were investigated.

Infected pepper leaves (n=450) were randomly collected from farmers’ fields in Oyo, Ogun, Osun, Ekiti and Ondo States where pepper were predominantly cultivated, and symptoms of FD were assessed. Fungi were isolated, identified and Frequency of Occurrence (FO) and their pathogenicity determined following standard procedures. On the field, ten pepper cultivars comprising three Capsicum annuum-CAN, three Capsicum frutescens-CFRand four Capsicum chinense-CCH were evaluated for resistance to Colletotrichum coccodes-CC, Colletotrichum capsici-CCA and Pyrenochaeta lycopersici-PL on a plot of 6 x 15m (40,000 plants/ha) area in a split-plot design replicated four times. Disease Severity (DS) was assessed using a rating scale of 1.0-2.0 (resistant), 2.1-2.5 (moderately resistant), 2.6-3.0 (susceptible), 3.0-5.0 (highly susceptible). On the field, eight biopesticides [dried powder of Thevetia neriifolia Leaf-TNL, Azadirachta indica Leaf-AIL and Seed-AIS, Tagetes erecta Shoot-TES and Root-TER each at 2.5g/100L of water and biocontrol agents; Trichoderma harzianum-TH, Trichoderma pseudokonnigii-TP each at 2.06 × 106 spores/mL, and Bacillus subtilis-BS at 2 × 108 CFU/mL] were evaluated separately on CAN-Tatashe (40,000 plants/ha) inoculated with the pathogens. Untreated and mancozeb treated plots served as controls. The experimental design was split-plot fitted into RCBD and replicated four times. Disease severity was determined at 12 weeks after sowing. Data were analysed using descriptive statistics and ANOVA at α0.05.

The FD symptoms identified were leaf spots, chlorosis, necrosis, blight and fruit rot. Six fungi (CC, TH, CCA, PL, TP and Penicillium sp) were isolated and identified. Colletotrichum coccodes had the highest FO of 81, 64, 60, 54% in Oyo, Ogun, Osun, and Ekiti States, respectively, while TP was highest in Ondo State (55.5%). Three isolates, CC, CCA and PL were pathogenic with 84.0, 72.0 and 50.0% levels of infection, respectively. Penicillium sp, TH and TP were not pathogenic (0.0%) on healthy pepper plants. Capsicum chinense cv. Batassa was resistant (2.0±0.1) to CCA and PL and moderately resistant (2.4±0.2) to CC. Other pepper cultivars ranged from susceptible (3.0±0.3) to highly susceptible (4.7±1.0) to the three pathogens, while uninoculated plants had the least DS of 1.0±0.0. Plants treated with TP had the least DS (1.5±0.0) which was significantly different from AIS (2.0±0.1), AIL (2.5±0.2) and TNL (2.5±0.2) powders. The DS of plants sprayed with TH (2.7±0.3) and BS (2.7±0.3) were significantly lower than TES (3.7±0.7), TER (4.0±0.9), and mancozeb (4.1±1.0).

Fungal diseases of pepper are prevalent in Southwestern Nigeria. Colletotrichum coccodes, Colletotrichum capsici and Pyrenochaeta lycopersici were pathogenic on all pepper cultivars. Capsicum chinense cv. Batassawas resistant to fungal diseases of pepper. Trichoderma pseudokonnigii at 2.06 × 106 spore/mL reduced fungal infection on pepper.