Effect of a short and severe intermittent drought on transpiration, seed yield, yield components, and harvest index in four landraces of bambara groundnut

Drought is a major constraint to crop production worldwide and landraces are one of the important genetic resources to crop improvement in the dry areas. The objective of this study was to investigate transpiration and yield responses of bambara groundnut (Vigna subterranea L. Verdc.) landraces exposed to a intermittent drought spell at an early reproductive stage. The four landraces (S19-3, Uniswa Red, LunT, and Ramayana collected from Namibia, Swaziland, Sierre Leone, and Indonesia, respectively) were grown in pots in a climate-controlled greenhouse and were either well-watered (WW) daily to 90% of pot holding capacity until seed maturity or drought-stressed (DS) in the period from 76 to 85 days after sowing (flowering and early podding stage). During drought, although the total water use differed among the four landraces, transpiration rate and stomatal conductance (gs) responded similarly to soil drying. The high soil water thresholds for the reduction of transpiration rate and gs of bambara groundnuts indicate their great sensitivity in the stomatal control over plant water loss during soil drying. Even though the shoot dry weight at maturity was hardly affected by DS, seed yield, seed number, and harvest index were all significantly decreased in the DS plants. Among landraces, LunT and Ramayana were more susceptible to DS than S19-3 and Uniswa Red in terms of reduction of seed number and seed yield. The different responses of the landraces to DS may reflect their adaptation to their local climate at the site of collection being that landraces collected from wet regions were more vulnerable to DS than those collected from dry areas.