Physiological and biochemical changes in wheat plants infected by Pyricularia oryzae caused by thermal oscillations

Abstract

Abstract Physiological and biochemical changes in plants exposed to high temperatures may lower their resistance to diseases. In this regard, this study investigated whether thermal oscillations could change wheat resistance to blast, caused by Pyricularia oryzae, considered one of the most important diseases affecting wheat production. Plants were kept in two growth chambers with temperatures of 19 and 28°C each for five days for thermal acclimatization and inoculated with P. oryzae after that. After inoculation, groups of plants were transferred to their original growth chambers (19 and 28°C) and switched to growth chambers with temperatures different from those used for acclimatization (from 19oC to 28°C and from 28°C to 19°C) during three days. Plants subjected to thermal condition (TC) of 19°C→19°C compared to TC of 28°C→28°C showed lower blast symptoms. Photosynthetic impairment (lower maximum photosystem PSII photochemical efficiency, effective PSII quantum yield, quantum yield of non-regulated energy dissipation and stomatal conductance values and high internal CO2 concentration) and lower concentrations of total chlorophyll a+b and carotenoids were noticed for plants subjected to 28oC before or after inoculation. Inoculated plants subjected to TC of 28oC→28oC showed higher superoxide dismutase and lower ascorbate peroxidase activities. Lower superoxide anion and high hydrogen peroxide concentrations occurred for inoculated plants subjected to TC of 28oC→28oC. Higher chitinase, phenylalanine ammonia-lyase, and peroxidase activities occurred for inoculated plants subjected to TC of 28oC→28oC and 19oC→28oC and lower polyphenoloxidase activity for inoculated plants subjected to 28oC after or before inoculation. Plants continuously subjected to 28oC, before or after inoculation, displayed remarkable damage to their photosynthetic apparatus, a less robust antioxidative system, and a minor contribution of defense-related enzymes to counteract the deleterious effect of P. oryzae infection.