Influence of the nitrogen source on the tolerance of actinidia chinensis to pseudomonas syringae pv. actinidiae

Nitrogen (N) can be supplied to plants as nitrate (NO3-) or ammonium (NH4+), which may influence plant nutritional status and predisposition for pathogen infection. Understanding how kiwifruit plants (Actinidia spp.) cope with Pseudomonas syringae pv. actinidiae (Psa) infection when grown under different N sources may improve our knowledge on how to manage N supply to mitigate this pathogen. Here, A. chinensis var. deliciosa plants were grown for 21 days in a complete hydroponic nutrient solution, differing in the source of N: 214 μM of NO3-, 214 μM NH4+ or a mixture of both (107 μM NO3- + 107 μM NH4+ - Mix), after which plants were inoculated with Psa. Fourteen days post-inoculation, plants grown with NO3- showed no visual disease symptoms and had a lower Psa endophytic population. In contrast, NH4+ led to the appearance of typical Psa-induced leaf spotting and lower total chlorophyll content. With NO3- supply higher P, K, Mg, Ca and Fe contents were observed in plant tissues, which possibly contributed to an improved mineral nutrition and increased tolerance to Psa. It is concluded that the N source affected plant mineral accumulation, leading to distinct infection outcomes, and should be taken into consideration for a more effective and sustainable Psa management.