Abstract:
BACKGROUND : White root rot (WRR) disease caused by Rosellinia necatrix is one of the most important threats
affecting avocado orchards in temperate regions. The eradication of WRR is a difficult task and environmentally
friendly control methods are needed to lessen its impact. Priming plants with a stressor (biotic or abiotic) can be a
strategy to enhance plant defense/tolerance against future stress episodes but, despite the known underlying
common mechanisms, few studies use abiotic-priming for improving tolerance to forthcoming biotic-stress and
vice versa (‘cross-factor priming’). To assess whether cross-factor priming can be a potential method for enhancing
avocado tolerance to WRR disease, ‘Dusa’ avocado rootstocks, susceptible to R. necatrix, were subjected to two
levels of water stress (mild-WS and severe-WS) and, after drought-recovery, inoculated with R. necatrix. Physiological
response and expression of plant defense related genes after drought-priming as well as the disease progression
were evaluated.
RESULTS : Water-stressed avocado plants showed lower water potential and stomatal limitations of photosynthesis
compared to control plants. In addition, NPQ and qN values increased, indicating the activation of energy
dissipating mechanisms closely related to the relief of oxidative stress. This response was proportional to the
severity of the water stress and was accompanied by the deregulation of pathogen defense-related genes in the
roots. After re-watering, leaf photosynthesis and plant water status recovered rapidly in both treatments, but roots
of mild-WS primed plants showed a higher number of overexpressed genes related with plant defense than severe-
WS primed plants. Disease progression after inoculating primed plants with R. necatrix was significantly delayed in
mild-WS primed plants.
CONCLUSIONS : These findings demonstrate that mild-WS can induce a primed state in the WRR susceptible avocado
rootstock ‘Dusa’ and reveal that ‘cross-factor priming’ with water stress (abiotic stressor) is effective for increasing
avocado tolerance against R. necatrix (biotic stressor), underpinning that plant responses against biotic and abiotic
stress rely on common mechanisms. Potential applications of these results may involve an enhancement of WRR
tolerance of current avocado groves and optimization of water use via low frequency deficit irrigation strategies.
