IDENTIFICATION OF FUNGI CAUSING POSTHARVEST DECAY OF IRISH POTATO (SOLANUM TUBEROSUM L.) AND THEIR CONTROL USING TRICHODERMA SPECIES

Post-harvest decay of Irish potato is a major disease occurring wherever Irish potatoes are stored or kept. The study investigated the in vitro potential of Trichoderma species on the fungi causing postharvest decay of Irish potato tubers. Samples of Irish potato tubers showing signs of decay were obtained from four markets in Makurdi namely; Wurukum, Wadata, Northbank and High Level markets. The decaying Irish potato tubers were taken to the Botany Laboratory of the Benue State University for isolation of fungi. Small sections were cut from decaying tubers and surface sterilized in 5% sodium hypochlorite (NaOCl) solution for 1 minute and rinsed in several changes of sterile distilled water. Soil samples from farmland within the premises of Benue State University, Makurdi were collected in polythene bags and taken to Botany Laboratory of the Benue State University for isolation of Trichoderma species. Potato Dextrose Agar (PDA) was prepared according to the manufacturer’s instruction and used for fungi isolation. The serial dilution technique was used in isolation of Trichoderma from soil samples. The effect of Trichoderma species on the radial growth of the isolated fungi was carried out using the dual culture technique. Data collected from the study was analysed using Analysis of Variance and means were separated using Fisher’s Least Significant Difference at 5% level of significance. The fungi isolated from decaying Irish Potato tubers were; Alternaria sp., Aspergillus niger and Phytophthora infestans while Trichoderma viride and Trihoderma harzianum were isolated from the soil samples. The results from the study revealed that there was no significant relationship in fungal occurrence based on locations (χ²= 0.980; df = 2; P= 0.613). Phytophthora infestans had the highest occurrence of 15(38.46%), followed by Aspergillus niger and Alternaria sp each with 12 (30.77%) respectively. Irish potato collected from NorthBank had the highest fungal occurrence with 12 (30.77%) followed by Wurukum 11 (28.21%), Wadata 10 (25.64%) and the least was observed in High Level 6 (15.38%). The biocontrol potential of Trichoderma viride paired with Aspergillus niger showed significantly reduced radial growth (0.37±0.06, 0.57±0.12, 0.83 ± 0.15, 1.10 ± 0.10)cm compared with the control (0.87±0.06, 1.47±0.06, 1.97±0.15, 2.63±0.12)cm at 48 hrs-120hrs respectively. Radial growth in the control was significantly higher (0.93 ± 0.06, 1.53 ± 0.06, 2.20 ± 0.10, 3.07 ± 0.06)cm from 48 hours-120 hours compared with the radial growth of A. niger paired with Trichoderma harzianum (0.57 ± 0.12, 0.90 ± 0.10, 1.37 ± 0.12, 1.67 ± 0.15)cm respectively. Similar trend was observed in radial growth of Alternaria species and Phytopthora infestans paired with T. harzianum and T. viride respectively compared with the control. The pathogenicity revealed that area of rot (cm²) induced by P. infestans (18.42 ± 7.49cm²) was significantly higher (P