Root biomass and genotypic response in bread wheat (Triticum aestivum L.) under well-watered and drought field conditions

An optimum root system in wheat might enhance water and nutrient uptake under drought-prone environments without depleting soil moisture, thus improving grain yield. Two experiments were carried out at the University of California, Riverside, under well-watered and droughted field conditions; receiving 412 and 268 mm of water and rain, respectively. Five recombinant inbred lines with root biomass ranging from 1.175 to 7.850 g plant-1 plus a check parent variety, Yecora Rojo, with root biomass of 1.820 g plant-1 were used. Phenological, morphological and agronomic characters were measured. Covariate analysis between grain yield (GY) with number of days from sowing to anthesis (DTA) and to physiological maturity (DTM), grain filling period (GFP), and plant height (PH) were not significant under both irrigation regimes indicating GY was not confounded with these traits. The main effect of irrigation on DTM, GFP, PH, number of tillers (NT) and spikes (NS) per 50 cm, thousand grain weight (TGW), GY, and shoot biomass (SB) was either significant or highly significant, but not on days to anthesis (DTA), number of grains per spike (NGS), and harvest index (HI). The main effect of genotype on the traits measured was highly significant. The effect of genotype × irrigation interaction was relatively low. The mild drought before anthesis and severe drought after anthesis reduced DTM by 5%, GFP by 10%, NS per 50 cm by 24.6%, and TGW by 11% which resulted in 25% and 27% reduction in GY and SB, respectively. Stress tolerance index (STI) of the genotypes calculated based on GY ranged from 0.52 to 0.88. A quadratic pattern of relationship was observed between root biomass measured under well-watered (soil water-holding capacity) glasshouse conditions with GY measured under well-watered (R2 = 0.62) and droughted field conditions (R2 = 0.93). The relationship between root biomass and STI also followed a quadratic pattern (R2 = 0.60). According to the quadratic equations, GY under well-watered and droughted field conditions maximized at 5.806 and 4.575 t ha-1 when root biomass was 1.630 and 3.975 g plant-1, respectively, and STI was highest when root biomass was 3.500 g plant-1. These results indicated that wheat lines with vigorous root system might be better adapted to drought-prone environments.  However, over-sized root biomass might reduce grain yield under both well-watered and drought conditions.

Root biomass and genotypic response in bread wheat (Triticum aestivum L.) under well-watered and drought field conditions Keywords:

Bread wheat , Correlation coefficient , root system , optimum root biomass , stress tolerance