INCIDENCE OF LEAF BLIGHT DISEASE OF EGUSI MELON AND ITS MANAGEMENT WITH BIOPESTICIDES IN SOUTHWESTERN NIGERIA

Abstract

Egusi Melon (EM) is an important vegetable crop grown for its edible seed and oil, but Leaf Blight Disease (LBD) limits its productivity. Knowledge about LBD incidence and its Causal Pathogens (CP) is crucial in managing the disease. Synthetic chemicals applied to control LBD cause harzards, however biopesticides are environment friendly and have been successful in managing some crop diseases. Information on LBD incidence on EM, its CP and management with biopesticides is scanty in Nigeria. Hence, incidence and management of LBD of EM in southwestern Nigeria with botanicals and Biocontrol Agents (BA) were investigated. In Ogun, Oyo, Osun, Ekiti and Ondo States, thirty farms were randomly selected/state and 20 EM leaf samples were randomly collected/farm. Disease incidence (DI) was estimated and CP were isolated and identified using standard procedures. Samples (5.0, 7.5, 10.0, 12.5g) of Passiflora foetida Leaves (PfL), Thevetia neriifolia Leaves (TnL), Costus afer Leaves (CaL), Costus afer Stem (CaS), Costus afer Rhizome (CaR) and Phyllanthus amarus Leaves (PaL) were air-dried and each soaked in 100mL of water to obtain aqueous extracts (w/v). The aqueous extracts and BA [Trichoderma pseudokoningii (Tp), Trichoderma harzianum (Th), Bacillus subtilis (Bs), Pseudomonas fluorescens (Pf)] were screened against CP in vitro using agar poisoning and dual culture methods, respectively. Colony Diameter Reduction (CDR) was determined. In screenhouse, PfL, CaL, CaR, PaL (each at 5.0%, 10.0% and 50.0% w/v/50 seeds) and four BA (Tp and Th at 1g of mycelia/50 seeds and Bs and Pf at 1mL of 108cfu/mL/50 seeds) were evaluated as Seed Treatment (ST) on seeds inoculated with CP using seed coating method in a completely randomised design. Mancozeb treated seeds served as control. Data were collected on DI (%). Data were analysed using descriptive statistics and ANOVA at ᾳ0.05. Disease incidence ranged from 45.7±3.2 in Osun to 61.8±8.7 in Ondo States. Colletotrichum truncatum (Ct), Colletotrichum gloeosporioides (Cg) and Lasiodiplodia theobromae (Lt) were identified and noted to cause LBD. Costus afer leaves at 5.0% had CDR of 44.5±0.9%, while PaL at 12.5% w/v had the least (0.5±0.1%) on Ct. Highest CDR was obtained from Cg (33.3±2.5%) and Lt (40.8±5.1%) treated with PfL (7.5%), while the least was on Cg (24.2±3.3%) and Lt (26.7±6.3%) treated with PaL (10%). Trichoderma pseudokoningii caused highest CDR of 72.4±9.6%, 81.6±14.3% and 80.9±7.6% on Ct, Cg and Lt, while Bs had the least CDR of 16.2±4.6%, 32.1±9.2% and 47.6±15.4%, respectively. Among botanicals, the most effective ST that resulted in zero DI was Cal at 10.0% and 50.0%, while other ST had DI ranged from 16.7±16.7% (PaL at 10 and 50%) and 83.3±33.3 % (CaR at 10%). Inoculated seeds of Lt treated with Pf had DI of 83.3±16.7% which was significantly higher than Ct (0.0±0.0%, Cg (16.7±6.7%) and Lt (16.7±0.0%) treated with Tp. There was high variation in incidence of leaf blight disease in southwestern Nigeria. Aqueous extracts of Passiflora foetida and Costus afer leaves each at 10.0% w/v/50 seeds, and Trichoderma pseudokoningii (1g/50seeds) reduced leaf blight disease.