Climate Change Exacerbated Dalbergia sissoo Dieback Under Water Stress and Ceratocystis fimbriata Infection

Dalbergia sissoo is a native tree species of the Indo-Pak and is one of the most important timber-producing species used in the agroforestry, fuelwood, and furniture industries. Historically widespread mortality of shisham due to dieback was observed during an El Niño cycle characterized by low rains and high temperatures. This is the first report that has successfully established the role of water deficit in shisham dieback under Ceratocystis fimbriata infection. Seedlings were either predisposed to water deficit for two weeks before fungal inoculation or subjected to both stresses i.e., biotic, and abiotic at the same time. The imposition of water deficit and the availability of water at the time of inoculation was determined by the rate of plant development, lesion growth, physiological parameters such as (stomatal conductivity, transpiration rate, photosynthesis rate, water potential, water use efficiency), chlorophyll contents, carotenoids, and oxidative enzymes such as POD, CAT, and H2O2. Water-stressed plants showed dieback symptoms and more susceptibility to fungal infection than well-watered plants clearly demonstrating water deficit is the primary cause of shisham dieback. Inoculated plants responded to stress by decreasing stomatal conductance, transpiration rate, and photosynthetic activity due to low water potential. The growth rate was also affected due to low chlorophyll and carotenoid content. D. sissoo reacts to stress by increased production of CAT and POD, enzymes. This study emphasizes the importance of exploring the interaction of drought x disease in shisham and the primary physiological responses involved in plant growth.