Abstract

Two field experiments were conducted in April and August, 2007 cropping season at the Department of Crop Science research farm, University of Nigeria, Nsukka, to evaluate the pollen germination potentials and the pollen tube growth of thirteen bambara groundnut cultivars. The harvested pollen grains were exposed for 0, 5, 10 and 15 min durations to ambient conditions before in vitro germination. Pollen germination and pollen tube growth were tested using a medium containing 10 g sucrose, 100 mg/l boric acid and 300 mg/l calcium nitrate made up to 100 ml with deionized water. The results showed that cultivars, had significant effect on the pollen germination only at the late planting. The early and late planting results showed that pollens incubated immediately after harvest had the highest germination percentage,while pollen exposed for five minutes prior to germination showed very poorgermination. Pollens exposed beyond five minutes after harvest did not germinate. The cultivars significantly (P < 0.05) affected the pollen tube growth at both early and late planting dates. The pollen tube growth decreased drastically with increase in duration of pollen exposure. The pollen tube had an exponential growth rate at the on set of the pollen tube growth, followed by lag and stationary growth phases in the pollen tube growth curves. The exponential, logistic and Gomperzt growth models were used to estimate the best fit model for the pollen tube growth in bambara groundnut cultivars. In the early planting, the average straightness (R²)  value of these models for growth estimate were 98.4, 98.6 and 98.5%, respectively. During the late planting,  the average R² values were 91.5, 96.6 and 96.6%, respectively. The three models are therefore considered suitable for the computation of the pollen tube growth rates. The principal component and cluster analyses were used to groupthe cultivars in relation to the levels of pollen survival under ambient conditions. At early planting, cultivar Bg-01 had moderate surviving pollen grains while Bg-08, Bg-09, Bg-10 and Bg-11 were found to have poor surviving pollens. At late planting, cultivar Bg-04 and Bg-07 had high survival pollens while Bg-01 had poor pollen survival.

Key words: Pollen behaviour, pollination, fertilization, Bambara groundnut, Vigna subterranea (L.) Verdc.