Moderate water stress improve resistance to anthracnose rot in Arbequina olive fruits

Olive anthracnose caused by Colletotrichum spp. is the most important olive fruit disease worldwide. We hypothesize that induced water deficit in olive trees generates anatomical and biochemical changes which contribute to anthracnose fruit rot resistance. A three-year experiment was conducted in Arbequina under two irrigation treatments: fully irrigated (no water stress) and non-irrigated (moderate water stress), from pit hardening until harvest. At harvest, fruits were inoculated both in planta and in vitro with an isolate of C. acutatum s.l. Our results showed that fruits grown under moderate water stress had significantly lower disease incidence and severity compared to those grown without water stress. Additionally, moderate water stress increased the activity of the enzymes related to hydrogen peroxide scavenging (Catalase and Peroxidase) and enhanced cuticle fruit thickness. Together, these factors contributed to a greater resistance to C. acutatum s.l. infection, both in vitro and in planta, reflected by different area under the disease progress curve (averaging 45% and 30% lower incidence and severity, respectively). These findings could explain differences in disease expression observed in olive orchards across seasons and managements practices.