Abstract
Plants being sessile are under constant threat of multiple abiotic and biotic stresses within its natural habitat. A combined stress involving an abiotic and a biotic factor reportedly increases susceptibility of the plants to pathogens. The emerging threat, collar rot disease of chickpea (caused by Sclerotium rolfsii Sacc.) is reported to be influenced by soil moisture condition (SMC). Hence, we studied the influence of differential SMC viz. upper optimum (100%), optimum (80%), lower optimum (60%), and limiting (40%) soil moisture conditions on colonization and collar rot development over the course of infection in two chickpea cultivars, Annigeri (susceptible to collar rot) and ICCV 05530 (moderately resistant to collar rot). Disease incidence was found to be directly proportional to increase in soil moisture (R2 = 0.794). Maximum incidence was observed at 80% SMC, followed by 100 and 60% SMC. Expression of genes (qPCR analysis) associated with host cell wall binding (lectin) and degradation viz. endopolygalacturonase-2, endoglucosidase, and cellobiohydrolase during collar rot development in chickpea were relatively less at limiting soil moisture condition (40%) as compared to optimum soil moisture condition (80%). As compared to individual stress, the expression of defense response genes in chickpea seedlings were highly up-regulated in seedlings challenged with combined stress. Our qPCR results indicated that the expression of defense-related genes in chickpea during interaction with S. rolfsii at low SMC was primarily responsible for delayed disease reaction. Involvement of moisture and biotic stress-related genes in combined stress showed a tailored defense mechanism.
Highlights
Chickpea (Cicer arietinum L.) is one of the most important and essential legumes crops for semi-arid tropical area
It was observed that once disease appeared, the disease progression was faster in upper optimum soil moisture condition as compared to optimum soil moisture condition and no significant effect of soil moisture on collar rot incidence was observed after a certain period of inoculation (48 and 72 hpi; Figure 1)
Under limiting soil moisture (40%) condition, no disease symptoms were observed in both chickpea cultivars even after 8 days of inoculation
Summary
Chickpea (Cicer arietinum L.) is one of the most important and essential legumes crops for semi-arid tropical area. Plants in fields are always exposed to multiple biotic and abiotic stresses where plants exhibit certain unique and convergent physiological and molecular responses that interact and impact each other to withstand the combined effect of these stresses (Choi et al, 2013; Padaria et al, 2015; Pandey et al, 2015). The molecular responses of different crops against several pathogen infection and combined low soil moisture stress have been reported (Choi et al, 2013; Ramegowda et al, 2013; Hatmi et al, 2015). Among soil borne diseases in chickpea, dry root rot and collar rot are predisposed by low and high soil moisture respectively. There are some reports of effects of soil moisture and temperature on dry root rot of chickpea but minimal work has been done with respect to collar rot
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