Seed coat structural and imbibitional characteristics of dark and light coloured Bambara groundnut (Vigna subterranea L.) landraces.

Bambara groundnut is cultivated using landraces of different seed coat colours. However, very few studies have associated the seed coat colour (morphological feature) with other physiological and biochemical processes as underlying the observed differences in seed quality among landraces. This research sought to investigate seed quality characteristics (viability and vigour) of landraces on the basis of seed coat colour with the hypothesis that; seed coat colour could be linked to other properties (physical, physiological, biochemical and ultra-structure) that may account for seed quality with respect to germination, vigour and storage potential. Four landraces were analysed for differences in seed coat colour and seed coat thickness using a scanning electron microscope (SEM). Seed imbibition, electrolyte conductivity, tetrazolium test, and standard germination tests were combined to evaluate the viability of seeds after deterioration through accelerated ageing (AA) at 42 °C and 100% relative humidity (RH) over 5 durations, namely 24, 48, 72, 96 and 120 hours. There were significant differences (P < 0.001) among landraces with respect to seed coat colour, seed coat thickness, electrical conductivity (EC), hydration rate, germination rate and length of the measured seedling axis. The light coloured landrace, Kazai, had the highest germination (66.9%) whereas the dark coloured landrace, G340A, had the lowest final germination (53.6%) after 120 hours of seed ageing. Likewise, G340A and Kazai had the highest (110.33 μS cm^-1 g^-1) and lowest EC (92 μS cm^-1 g^-1), respectively. Electron microscope revealed that dark and light seeds had the thickest (127 μm) and the thinnest (104.6 μm) seed coats, repsectively. This study highlighted that (1) seed coat thickness and colour alone do not account for hydration pattern of Bambara groundnut landraces and (2) Bambara groundnut seeds viability may not necessarily imply good seed vigour.