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Effects of individual and combined heat and drought stress during seed filling on the oxidative metabolism and yield of chickpea (Cicer arietinum L.) genotypes differing in heat and drought tolerance
Drought and heat stress are two major constraints that limit chickpea (Cicer arietinum L.) yield, particularly during seed filling. The present study aimed (i) to assess the individual and combined effects of drought and heat stress on oxidative metabolism during seed ﬁlling, and (ii) to determine any genetic variation in oxidative metabolism among genotypes differing in drought and heat tolerance and sensitivity. The plants were raised under outdoor conditions with two different times of sowing, one in November [normal-sown; temperatures below 32 °C/20 °C (day/night) during seed filling], and the other in February [late-sown; temperatures above 32 °C/20 °C (day/night) during seed filling]. Plants were regularly irrigated to prevent any water shortage until the water treatments were applied. At both sowing times, the drought treatment was applied during seed filling (at ~75% podding) by withholding water from half of the pots. Water was withheld until the relative leaf water content (RLWC) of leaves on the top three branches reached 42-45%, while those in the fully-irrigated control plants were maintained at 85-90%, and then were rewatered and maintained under fully-irrigated condition until maturity. In the combined heat + drought treatment, water stress was applied to the late-sown plants, when the temperatures were higher than 32 °C/20 °C during seed filling. At the end of the stress treatments, a number of biochemical parameters were measured on the leaves and seeds, while the seed yield and aboveground biomass were measured at maturity. Individual and combined stresses damaged membranes, decreased PSII function and leaf chlorophyll content; more so under the combined stress treatment. The levels of oxidative molecules [malondialdehyde (MDA) and hydrogen peroxide (H2O2)] markedly increased compared with the control plants in all stress treatments, especially across genotypes in the combined stress treatment (leaves, MDA: 5.4- to 8.4-fold increase; H2O2: 5.1- to 7.1-fold increase; seeds, MDA: 1.9- to 3.3-fold increase; H2O2: 3.8- to 7.9-fold increase). The enzymatic and non-enzymatic antioxidants related to oxidative metabolism increased under individual stress treatments, but decreased in the combined stress treatment. Leaves had higher oxidative damage than seeds, which likely inhibited their photosynthetic efficiency. Yields were reduced more by the drought-stress than by the heat-stress treatment, with the lowest yields in the combined heat + drought treatment. Heat- and drought-tolerant genotypes suffered less damage and had higher yields than the heat- and drought-sensitive genotypes under the individual and combined stress treatments, suggesting partial cross-tolerance in these genotypes. A drought-tolerant genotype ICC8950 produced more seed yield under the combined heat and drought stress than other genotypes, and this was associated with low oxidative damage in leaves and seeds.
CP17028 Accepted 06 September 2017
© CSIRO 2017