Genetic and Physiological Analyses of Yield and Yield-Related Traits in West Africa Rice Germplasm under Induced Drought Stress

Abstract

Drought is the single most important factor limiting upland rice production in Africa and is aggravated by climate change leading to a serious food security threat in the continent. This study aimed to assess the impact of drought stress on morpho-physiological, biochemical traits and transcripts abundance of drought-responsive genes among the rice genotypes and select drought-tolerant genotypes. Furthermore, the study sought to understand the genetic basis and inheritance behind the expression of tolerance of the rice breeding lines to drought stress. To achieve these objectives, 100 genotypes were screened under drought stress in field conditions using 10×10 alpha-lattice design. Out of the 100, selected 14 genotypes were further screened under drought stress in the greenhouse using randomized complete-block design. Out of the 14, four genotypes were chosen for gene expression analysis. Furthermore, two drought-sensitive genotypes (CRI-Agrarice and Jasmine 85) were crossed with a drought-tolerant rice (APO) to develop six populations (F1, F2, BC1, BC2, P1 and P2) for each of the two crosses among which a generation mean analysis was conducted. Data were collected on grain yield and yield-related traits, leaf gas exchanges (stomatal conductance, transpiration rate), relative water content, leaf reflectance and biochemical traits (malondialdehyde and proline content). Drought yield-QTL profiling was used to assist in the selection. Under the field screening, for all the investigated traits, a general reduction was observed among the genotypes under drought stress compared to non-drought conditions. Grain yield was positively correlated with most yield-related traits under both water-regimes. Under the greenhouse screening, in general, the mean performance of all the genotypes was reduced notably under 11, 18, 27 days and reproductive stage drought stress compared to the non-drought conditions for stomatal conductance, transpiration rate for most genotypes except APO, UPLR-17 and Togo Marshall. Increase in malondialdehyde of >45% for all genotypes was observed, except in CRI-Enapa (25.15%), APO (39.37%) and UPLR-17 (43.65%). Grain yield had a significant negative correlation with delay-in-flowering and a significant positive correlation with renormalised difference vegetative index (RDVI). The genes osBHLH6 and Cytokinin-O-glucosyltransferase-1 were upregulated in all the genotypes evaluated under drought conditions in growth chambers. Under the screenhouse evaluation, among both crosses and water-regimes, additive x additive gene interaction was predominant even though the scaling tests were not significant indicating the effectiveness of selection in early generations. Based on the correlation and the multi-trait genotype-ideotype distance index (MGIDI) using relative trait values: grain yield, biomass, spikelet fertility score, grain length, malondialdehyde and RDVI are recommended for monitoring during the selection of drought-tolerant genotypes. Overall, Viwonor short, UPLR-17, APO and CRI-Enapa were selected in chronological order as genotypes with enhanced tolerance to drought and are recommended to be used as drought-tolerant donors or possibly released for commercial purposes.