Assessment of water deficit effects on agromorphological and physiological traits of six bambara groundnuts (vigna subterranea (l.) verdc.) landraces grown in Western and coastal regions of Kenya.

Abstract

Bambara groundnut (Vigna subterranea (L.) Verdc.) is one of the most neglected and under-utilized African legume with the potential to alleviate food insecurity and poverty in the tropical semi-arid regions of Africa. The crop is reported to be drought tolerant and produce reasonable yields in poor soils. However key morphological and physiological attributes that confer drought tolerance to different landraces is not well established. The main objective of this study was to assess the effects of water deficit on agro-morphological and physiological traits in six Bambara groundnut landraces commonly grown in western and coastal regions of Kenya. The study involved two greenhouse experiments conducted at University Botanic Garden, Maseno. Six commonly cultivated landraces in Kenya were collected from farmers. Six seeds of each landrace were planted in a 20-litre plastic pot and thinned to three plants 20 days after sowing. Greenhouse experiment 1 involved measurements of agro-morphological parameters (plant height, number of leaves per plant, plant leaf area, shoot: root biomass % and total dry matter), while experiment 2 involved measurements of physiological parameters (stomatal conductance, net photosynthesis internal CO2 concentration and transpiration rate, water use efficiency and leaf chlorophyll content). Soil moisture % was determined after every 10 days in both experiments till 80days after sowing. The experimental design was randomized complete block design with 4 replications and 4 treatments laid in a factorial set up. The main factor was water irrigation imposed after 20days after sowing at four levels (5, 10, 15 days intervals and no irrigation at all) while the sub-factor was six Bambara groundnut landraces. Data collected was subjected to analysis of variance and effects declared significant at 5% level. Least significance difference was used to separate the means. Linear correlation was conducted to determine the relationship between variables. Plant leaf area, shoot to root biomass%, total dry matter significantly (p<0.05) decreased as water deficit increased while stomatal conductance, transpiration rate and chlorophyll content significantly (p<0.05) decreased as irrigation frequencies decreased. The results obtained from this study demonstrated significant variation between the Bambara groundnut landraces in moisture stress, and also identified some important traits that are useful in selecting for drought tolerance in Bambara groundnut The traits include restriction of leaf area expansion, lowering stomatal conductance, decreased shoot to root biomass% and increasing water use efficiency in response to increasing water stress. Chlorophyll content also proved to be a useful index for evaluating Bambara groundnut responses to reduced water availability. Total dry matter which was the best indicator of yield was also found to reduce as water stress increased indicating that the effects of water stress on growth and physiology of Bambara groundnut ultimately results in reduced yields. Mombasa dark brown and Mumias light brown landraces were identified to have drought tolerant traits which could make them thrive in low rainfall areas hence recommended to farmers in areas prone to moisture stress. The results of this study therefore provided useful data that can be used in optimizing food productivity in drought prone regions.