Root system attributes, morphology and yield of cowpea (Vigna unguiculate L. Walp.) under moisture stress

Cowpea is an important grain legume crop and inexpensive plant protein source cultivated year around in Sri Lanka. Tolerance to moisture stress is a critical factor for getting high production of cowpea growing in the Dry Zone (mean annual rainfall < 1,750mm). The present study consisting of three experiments was conducted in a protected house and laboratory conditions to determine the relationship of root traits with plant morphology and yield among eight cowpea varieties grown in Sri Lanka under moisture stress conditions. The eight cowpea varieties and two moisture stress levels were used as experimental factors and set up as a two-factor factorial completely randomized design. The interaction effect between the two factors were not significant for morphological traits such as the number of branches, plant height, number of leaves and basal stem diameter, but some of those traits significantly influenced by the main factors. The yield and root attributes such as the pod length, 100 seed dry weight and root dry weight at maturity were significantly influenced by the interaction while the number of flowers per plant, the number of pods per plant, the number of seeds per pod and the above-ground biomass per plant were not significantly affected by the interaction. However, those parameters varied significantly with variety and moisture stress levels. Furthermore, the interaction effect was significant for the water use efficiency of the mature plants. The basal root growth angle, taproot diameter at 5cm level and length of the taproot at maturity were significantly affected by the interaction. Additionally, seedlings grown in cotton wool culture reported a significant interaction effect of main factors on the length of the taproot, the total root length and root dry weight except for the number of lateral roots. However, the Interaction effect of variety and moisture stress was significant for the majority of root attributes such as length of the taproot, total root length and the number of lateral roots of the seedlings grown in sand media. A positive correlation found between the total root length of the mature plant and the above-ground biomass. All seedling root traits measured in cotton wool culture showed a negative correlation with the above-ground biomass of mature plants while none of the seedling root traits in sand media had an association with above-ground biomass. All root traits recorded in mature plants showed a significant negative and positive correlation with important yield attributes of cowpea. Therefore, identified favourable root attributes related to morphology and yield components of cowpea could be used as screening parameters of cowpea populations at the seedling stage to identify efficient genotypes under moisture stress levels and introduce them to breeding programs.