Effects of position of seed perforation by cowpea weevils, Callosobruchus maculatus (F.), on viability and vigour of cowpea (Vigna unguiculata L. Walp) seed

Cowpea, Vigna unguiculata, is a high-protein legume crop that is often susceptible to pest damage. The cowpea weevil, Callosobruchus maculatus, predates on cowpea seeds in storage which renders grain unsuitable for human consumption. In the larval stage, cowpea weevils consume food reserves from the seed endosperm and may deter seed germination. The problem is more pervasive among resource-poor farmers in Sub-Saharan Africa, who grow cowpea for subsistence and keep the surplus grain for sale and use it as seed in the subsequent growing seasons. Unsuitable storage structures and ineffective methods of weevil control may increase weevil infestation of cowpea seeds in storage which constrains the production of cowpeas. The aim of the study was to determine if the position of seed perforation by cowpea weevils affects seed viability and growth of cowpea seedlings. Undamaged cowpea seeds ‘black-eyed peas’ were infested with cowpea weevils and stored for three months to allow for infestation. Thereafter, seeds with a single perforation or hole were selected from the infested seed lot and sorted into groups of damage according to the position of the hole on the seed. Five categories of potential damage were identified namely seeds with holes on the top, bottom, side, back or hilum area of the seed as presented schematically in the paper. The positions of holes on seeds served as treatments for the study and undamaged seed served as control. Data on germination and seedling height were collected and analysed statistically. Results reveal that the positions of damage on seed affects seed germination and seedling height. Seed germination on day two was significantly poorer for seeds damaged at the top, relative to both undamaged seeds and the alternative sites of damage. The results of top damaged seed being inferior than other treatments, remained consistent for germination on day seven and for seedling height at two weeks after the first emergence. Small holder farmers should therefore refrain from planting top damaged cowpea seed.