Effects of exogenous application of methyl jasmonate and salicylic acid on the physiological and molecular response of ‘Dusa®’ avocado to Rosellinia necatrix

Abstract

Abstract Background: Elicitors are compounds that induce defense responses in plants similar to those induced by pathogens. Methyl jasmonate (MeJA) and salicylic acid (SA) are two of the most used elicitors due to their importance in mediating plant responses to abiotic and biotic stresses. Elicitor recognition involves the triggering of various biochemical mechanisms and physiological responses that can provide plants with long-term protection against a wide range of pathogens. In this sense, exogenous application of MeJA and SA could protect susceptible avocado plants, such as 'Dusa®' rootstock, against white root rot (WRR) disease caused by the necrotrophic fungus Rosellinia necatrix, one of the main biotic stresses affecting avocado orchards in southern Spain and other countries. Thus, this work evaluated the effects of MeJA or SA on the physiological and molecular response of 'Dusa®' plants, and their ability to provide some protection against R. necatrix. Results: MeJA and SA application in ‘Dusa®’ plants 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 in avocado 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 harsh environments, such as water scarcity and WRR disease. In addition, MeJA upregulated a greater number of defense-related genes than SA, most notably overexpression of a glu protease inhibitor, a key gene in avocado defense against R. necatrix. The overall effects of MeJA on ‘Dusa®’ avocado rootstock improved its performance after R. necatrix inoculation, as indicated by delayed WRR disease progression. In all plants, R. necatrix infection led to impaired rubisco carboxylation activity in the early stages of disease progression. Conclusions: MeJA increased avocado tolerance to the necrotrophic pathogen R. necatrix by inducing a primed state that delayed WRR disease symptoms in susceptible avocado ‘Dusa®’. These findings point towards the use of MeJA application as an environmentally friendly strategy to mitigate the impact of this disease on susceptible rootstocks in avocado orchards.