Influence of seed size on the germination of four cowpea (Vigna unguiculata (L) Walp) varieties

A study was conducted to investigate how seed size affects germination and vigor of cowpea seeds. Four cowpea varieties, (Asontem, Nhyira, Soronko and Tona), were obtained from Crops Research Institute of the Centre for Scientific and Industrial Research (CSIR-CRI). The seeds were grouped in two sizes (large and small), by manually sorting by length, width and thousand seeds weight. Laboratory experiments were carried out at the Department of Horticulture, Kwame Nkruma University of Science and Technology, in 2012. Results of the study showed that seed germination was not affected by the variety and the seed size. However, variety x seed size interaction was significant. Nhyira large and Asontem small seed sizes had significant higher germination (P≤0.01) than Soronko and Tona. For seed vigor, first count, seedling dry weight and electrical conductivity were used. First count among varieties and seed sizes used as a vigor indicator, were not significant. Variety x seed size interaction was not also significant. Seedling dry weight was not affected by varieties but by seed sizes, the large seed size produced seedling dry weight (8.91 g) significantly higher than the small sized seeds (7.66 g); variety x seed size interaction were not significant. Small seed size had higher value (28.72 μ S/cm.g) significantly different from large seed. Among the varieties, there were no differences for conductivity value. Variety x seed size interaction did not affect seed electrical conductivity. It can be concluded that seed size did not have effect on the germination of cowpea seeds. Therefore, sorting it out will be of no economic return but time consuming except, for market grade purpose. Key words: Seed size, germination, vigor.