Effect of storage conditions on incidence of seed-borne fungi if cowpea (Vigna unguiculata (L.) walp) and their control with botanicals

Abstract

Seed-borne fungi cause deterioration of stored cowpea resulting in significant postharvest yield loss. Cowpea grains of three varieties stored for 12 months at varying temperatures, 28±2°C, 5°C and -20°C were collected from traders' warehouse across three prominent markets in three major towns, Southwest, Nigeria, while three cowpe~ accessions, TVU 10111, 10204 and 10305 in cold storage were obtained from Gene Bank of the International Institute of Tropical Agriculture (IITA), Ibadan). A total of 2700 grains were collected from Ibadan, Saki and Ogbomoso using random sampling method, while 600 were obtained from IITA. Infecting fungi were isolated using the blotter method and isolates purified on Potato Dextrose Agar. Cold water extracts of A Ilium sativum and Syzygium ""romaticum were bioassayed for their inhibitory· effect on mycelial growth, sporulation intensity and conidial germination·ofthe fungal isolates. Four extract concentrations were prepared by blending 5 g, 10 g, 15 g, and 25 g of each plant part in 100 ml of sterile distilled water. Fifteen fungal isolates were associated with cowpea stored at room tern perature with Aspergillu1flavus and A. niger having the highest incidences of 40.7% and 96.7% at room temperature and cold storage respectively. Extracts of A. sativum significantly (p=0.05) reduced mycelial growth, sporulation intensity and conidia germination of the test pathogens. Syzygium aromaticum was more effective with a minimum inhibitory concentration of25% w/v and will, therefore, be very useful in the protection of stored cowpea grains against spoilage by seed-borne fungi.