Effects of exogenous application of MeJA and SA on the physiological and molecular response of 'Dusa' avocado to Rosellinia necatrix.

Abstract

Methyl jasmonate (MeJA) and salicylic acid (SA) are important in mediating plant responses to abiotic and biotic stresses and can act as elicitors by triggering plant defense responses similar to those induced by pathogens and may even provide long-term protection against them. Thus, exogenous application of MeJA and SA could protect susceptible avocado plants against white root rot (WRR) disease caused by the necrotrophic fungus Rosellinia necatrix, one of the main diseases affecting avocado orchards. This work evaluates the effects of MeJA or SA on the physiological and molecular response of susceptible 'Dusa' avocado rootstock, and their ability to provide some protection against WRR. MeJA and SA application in avocado increased photoprotective mechanisms (NPQ) and upregulated the glutathione S-transferase, suggesting the triggering of mechanisms closely related to oxidative stress relief and reactive oxygen species (ROS) scavenging. In contrast to SA, MeJA effects were more pronounced at the morpho-anatomical level, including functional traits such as high leaf mass area (LMA), high stomatal density, high root/shoot ratio, closely related to strategies to cope with water scarcity and WRR disease. Moreover, MeJA upregulated a greater number of defense-related genes than SA, including a glu protease inhibitor, a key gene in avocado defense against R. necatrix. The overall effects of MeJA increased 'Dusa' avocado tolerance to R. necatrix by inducing a primed state that delayed WRR disease symptoms. These findings point towards the use of MeJA application as an environmentally friendly strategy to mitigate the impact of this disease on susceptible avocado orchards.