Looking for olive XF-resistance under high natural selective pressure in Salento

Several success stories in plant pathology indicate that the use of plant genetic resistance is the most effective, durable and environmentally/economically sustainable protection system for the coexistence with harmful organism whenever curative methods lack. In the epidemic of Xylella fastidiosa ST53 in Salento, the cultivars Leccino and FS17 showed interesting resistant traits. This important finding, even if allowed the replanting of olives in infected areas, is considered a starting point being highly desirable to find a wider range of varieties to avoid a dangerous genetic uniformity and to offer alternatives to the growers and oil producers. For this purpose in Salento, a large-scale program for testing the susceptibility of Italian and Mediterranean olive germplasm started and the first long-lasting breeding activities for the resistance/tolerance were initiated. Due to the urgency, the selection of productive plants derived from uncontrolled pollination and seed dissemination was identified as a third approach aimed to save the time of long olive juvenile period and enlarge the genetic variability to be explored looking for resistance or tolerance directly under high selective pressure of inoculum in the infected area. Furthermore, each seedling plant, derived mainly from parentals of the local cultivars, is potentially a new candidate “autochthonous” variety. After 3-years of activity in the framework of the regional project ResiXO and thousands of plants observed/tested, the activities of morphological/technological characterization, as well the pathogenicity tests by pathogen inoculation in controlled conditions started on a panel of candidate potentially resistant genotypes. Positive feedbacks are also coming from a newborn initiative called Xylor (Xylella Olive Resistance), contrived as a citizen science approach launched in September 2019 to involve the local community in the exploration of a huge territory to find plants asymptomatic or with mild symptoms in the abandoned and dying olive orchards.