Growth and Physiological Responses of Bambara Groundnut to Sodium Chloride Salinity

Abstract

Bambara groundnut is one of the most neglected and under-utilized indigenous African legume with potential to alleviate food insecurity, malnutrition and poverty in tropical semi-arid regions of Africa. The crop is drought tolerant, resistant to pests and diseases, produces reasonable yields in low fertile soils and has high nutritional value. Salinity affects plant growth, development and productivity in agricultural soils world wide. It is caused by the accumulation of soluble salts especially sodium and chloride ions in the root zone. This crop may be grown in some semi-arid areas or under irrigation, both of which offer potentially saline conditions. There is limited research on the effect of salinity on growth and physiology of this plant, more so the landraces cultivated in Kenya. The study investigated the effects of NaCI salinity on growth and physiological responses of Bambara groundnut grown in Western Kenya, Kakamega 2 (Kk) and Mumias 2 (Mm).The experiments were laid out in the laboratory and greenhouse at Maseno University botanic garden as a completely randomized design consisting of 5 treatments and 3 replica. Seeds and plants were exposed to NaCI concentrations of electrical conductivity: 0 mm ho em", 6.96 mm ho em", 12.93 mm ho em", 19.89 mm ho cm' and 25.86 mm ho ern" in the growth media. Germination percentage was determined, shoot and root length measured using a meter rule, seedling root and shoot fresh and dry weights measured using an electronic weighing balance, leaf growth, root to shoot biomass ratio, and percentage water content in shoots and roots were determined. Net photosynthesis was measured using an infra-red gas analyzer, chlorophyll fluorescence parameters measured using chlorophyll fluorescent monitoring system, leaf chlorophyll content measured using spectrophotometer and nitrogen content determined using the soil plant analysis device. Data was subjected to analysis of variance using Costat statistical computer package to determine whether the treatment effects were significant or non-significant at 5% level. Least significant difference was used to separate the means. NaCl salinity significantly (P<O.Ol) decreased and delayed germination. Plant growth parameters were significantly (P<O.Ol)reduced by salinity in both landraces however, Mm landrace was more salt tolerant. Salinity significantly (P<O.Ol) reduced chlorophyll and nitrogen content, and net photosynthesis. The Mm landrace had significantly (P<O.05)higher chlorophyll a, band t compared to Kk landrace. Salinity significantly (P<O.05)decreased the FvIFm ratio and electron transport rate inthe two landraces hence decreased plant growth and ultimately productivity, however there were no significant (P>O.05)differences inthe Fv/Fm values for Mm as compared to the control indicating the ability of its PSI! system to function under stressful conditions and thus may contribute to salt tolerance. The Mm landrace seeds seemed to be more salt tolerant at higher salinity (12.93 mm ho em" and 19.89 6.96 mm ho cm') as Kk landrace was at lower salinity (6.96 mm ho ern"). Both landrace seeds may be tried in saline soils with electrical conductivity as indicated.