Growth, phenological and yield responses of a bambara groundnut (Vigna subterranea (L.) Verdc.) landrace to imposed water stress under field conditions

Bambara groundnut (Vigna subterranea (L.) Verdc.) is an underutilised species with potential to contribute nutritional and food security in marginal areas. Growth, phenology and yield of a local bambara groundnut landrace from Jozini, KwaZulu-Natal, characterised into three selections according to seed coat colour, namely Brown, Red and Light Brown, were evaluated under irrigated and rain-fed field conditions at Roodeplaat, Pretoria, over two seasons (2010/11 and 2011/12). Trials with three replicates were planted under rain-fed and irrigated conditions with seed colour as a subfactor. Emergence (up to 35 d after planting), plant height, leaf number, leaf area index, chlorophyll content index and stomatal conductance were measured in situ. Yield and components of yield were determined at harvest. The Red, Brown and Light Brown landrace selections emerged well (84%, 81% and 51%, respectively). Plant physiological and growth parameters of stomatal conductance, chlorophyll content index, plant height, leaf number, leaf area index and biomass accumulation were lower under rain-fed relative to irrigated conditions. Adaptations were landrace selection-specific, with the Brown and Red landrace selections showing better adaptation to rain-fed conditions. Under rain-fed conditions, bambara groundnut landrace selections flowered, senesced and matured earlier relative to irrigated conditions. Consequently, there were lower yields under rain-fed compared with irrigated conditions. The Red and Brown landrace selections may have drought-avoidance mechanisms. Seed colour may be used as a selection criterion for drought tolerance in bambara groundnut landraces.