Effects of combined abiotic and pathogen stress in pomegranate (Punica granatum L.)

Plants are often challenged by stresses acting in combination and the response to combinatorial stress differs from that triggered by each factor individually. Pomegranate cultivation in Italy is currently limited by the emerging Coniella granati and Phytophthora palmivora pathogens. It is ignored if they benefit from previous stress caused in pomegranate by periods of heavy rainfall or intense drought. We hypothesized that drought and waterlogging experienced by plants will increase damage caused by subsequent infection. In June 2022, two-year-old plants were subjected to regular watering (C), drought (D) and waterlogging (W) conditions and stem-inoculated, individually or simultaneously, with C. granati and P. palmivora (n=10) or with a PDA plug as control (n=10). Lesion length in the stem was assessed and used as a proxy of plant susceptibility. W prior to C. granati infection significantly increased lesion length (140%), and D prior to P. palmivora infection significantly decreased lesion length (60%), in relation to C-infected plants. Lesion length caused by C. granati significantly increased if plants were co-infected by P. palmivora and this was dependent on conditions experienced by plants before infection (ca. 100, 50 and 30% for C, D and W plants, respectively). Lesion length caused by P. palmivora was not altered if plants were co-infected C. granati irrespective of the conditions experienced by plants before infection.