Growth, biomass distribution, gas exchange and chlorophyll fluorescence in cowpea (Vigna unguiculata (L.) Walp.) under drought conditions

Abstract

Drought modifies plant development and generates losses in agricultural production. The aim of this study was to analyze the growth, biomass distribution, gas exchange, and chlorophyll fluorescence in nine cowpea (Vigna unguiculata) genotypes under drought conditions in the greenhouse condition. A completely randomized experimental design with four replicates was used. The following genotypes (treatments) of LC-006-016, LC-029-016, LC-036-016, LC-021-016, LC-005-016, LC-009-016, LC-014-016, LC-002-016, and Caupicor-50 (control) were evaluated with irrigation for 21 days (after sowing) and 38 days of drought (DD) for a total duration of 59 days. In a simultaneous experiment, other plants of the same genotypes were irrigated for 59 days after sowing (DAS) with replacement of evapotranspirated water every three days. Measures of plant height and number of leaves were taken every four days, biomass at 59 days, gas exchange every seven days and chlorophyll fluorescence at 17, 21 and 38 DD. Moisture losses were quantified by recording the loss of soil weight every three days. The results showed that plant height reached 72.2% lower in plants under drought, while the vegetative biomass decreased by 76.3%. The photosynthesis, stomatal conductance, and transpiration were decreased 64.6%, 93.1%, and 86.9% under drought, respectively. Furthermore, intrinsic water use efficiency (A/gs) was increased almost six times. However, it was decreased when drought progressed towards the soil water content loss more than 0.0827 g.g-1. The quantum yield of photosynthesis (ΦPSII) was decreased 28.4%, 40.3% and 43.5% at 17, 21 and 38 DD, respectively, under drought condition. The principal component analysis (PCA) suggests that the genotypes with higher A/gs and those with higher biomass production show greater resistance to drought.