Interactive effects of Bacillus subtilis and elevated temperature on germination, growth and grain quality of cowpea irrigated with acid mine drainage

Abstract

This study’s main goal was to evaluate Bacillus subtilis inoculation and mine water irrigation effect on germination, growth, nodulation, physiology and shoot/grain quality of cowpea genotypes exposed to extreme climatic conditions (elevated temperatures). The first experiment evaluated the interactive effect of Bacillus subtilis (BD233) inoculation and elevated temperature on germination indices and plumule lengths of three genotypes (Asetanapa, Soronko and Nyira) of cowpea. The results showed that interaction between B. subtilis (BD233) and temperature significantly (p<0.05) influenced the germination indices (germination percentage (G%), germination index (GI) and germination rate index (GRI)) and plumule length of cowpea seedlings and genotype responses were significantly different. At elevated temperature (35oC), inoculation with B. subtilis (BD233) enhanced seed germination and growth of cowpea. The second experiment evaluated the effect of temperature on growth and nutritional content of cowpea incubated for seven days in a growth chamber. The results showed that when cowpea genotype, Soronko, was incubated at different temperature regimes, the whole plant biomass, shoot carbon and crude protein contents were significantly affected with temperature increases at all three stages of the plants’ life cycle. The results suggest that the pre-flowering (40 DAP) and flowering (90 DAP) stages of cowpea compared to post-flowering (123 DAP) are more susceptible to elevated temperatures (30-35oC). The third experiment evaluated Bacillus subtilis inoculation and mine water irrigation effect on growth, nodulation, physiology and nutritional content of cowpea under glasshouse conditions. The results revealed that the interaction of B. subtilis (BD233) inoculation and mine water (75% AMD) irrigation was significant for the growth, nodulation, stomatal conductance, chlorophyll contents and shoot/grain nutritional quality of cowpea genotypes. In comparison with control, generally, B. subtilis inoculation enhanced the growth, nodulation and yield of all tested cowpea genotypes and irrigation with mine water significantly influenced the mineral contents in both shoot and grain of cowpea. Taken together, findings in this study have implications for cultivation of cowpea, an important candidate for food/nutrition security in Africa, under future climate change scenarios.