Water extraction under terminal drought explains the genotypic differences in yield, not the anti-oxidants changes in leaves of pearl millet (Pennisetum glaucum (L.) R. Br.)

Abstract

Pearl millet (Pennisetum glaucum (L.) R. Br.) is a resilient crop suiting the harshest conditions of the semi-arid tropics, in which we assessed possible relationships between crop tolerance, anti-oxidative enzyme activity, and plant / soil water status. Biochemical acclimation and cell homeostasis traits have indeed been proposed as critical for the drought tolerance of crops, but their limited practical application in breeding so far suggests that the role of biochemical acclimation for drought tolerance is still unclear. A possible limitation of previous research may be in not having approached biochemical acclimation from the angle of plant water relations. Four pearl millet genotypes, contrasting for terminal drought tolerance, were evaluated (sensitive H77/833-2, tolerant PRLT2/89-33, and two near isogenic lines carrying a terminal drought tolerance quantitative trait locus) under water stress (WS) and well-watered (WW) conditions in a lysimetric system that simulates field-like conditions. We assessed the genotypic variation and relationship between photosynthetic pigments (chlorophylls a, b, carotenoids), antioxidative isoenzymatic spectrum (superoxide dismutase, ascorbate peroxidase, catalase), physiological traits (soil moisture available, normalized transpiration, stay-green, water extraction), biomass and yield. Investigated biochemical traits were tightly related among each other under WS conditions but not under WW conditions. Two major ascorbate peroxidase isoforms (APX6&7), whose variation in both water regimes reflected the presence/absence of the drought tolerance quantitative trait locus, were identified, but these did not relate to yield. Both, yield and biochemical traits under terminal drought stress were closely related to the traits linked to soil-plant water status (soil moisture available, normalized transpiration, stay-green, water extraction), while yield and the biochemical indicators were not correlated, except for one. It is concluded that there is no direct effect of biochemical traits on yield parameters since both are consequences of soil-plant water status and their putative relation appear to be secondary â through soil-plant water status