Transmission and distribution of Xylella fastidiosa subsp. pauca in olive trees as a parameter for managing olive quick decline syndrome

Abstract

AbstractSystemic bacteria such as Xylella fastidiosa can be vertically transmitted by using diseased propagative material during nursery tree production. We tested the hypothesis that X. fastidiosa is not transmitted by symptomless olive tree sprouts. In addition, we investigated the distribution of bacteria in olive plants (different parts of canopy and root system) with initial leaf scorch symptoms and with symptoms spread throughout the canopy. In both studies, the presence of bacteria was tested by quantitative real‐time PCR (qPCR). For the first hypothesis, sprouts from a symptomless olive tree were rooted and checked for X. fastidiosa infection 32 months later. A total of 57.7% (41 of 71) of rooted seedlings were positive for X. fastidiosa (Ct from 24.25 to 31.82) but only one plant had scorched leaves. Regarding the distribution of the bacteria in the diseased plants, results based on qPCR showed that X. fastidiosa was systemically distributed through the olive plant canopy (30% to 77% of sampled tissues, with Ct values from 19.56 to 31.59). Samples from trees showing symptoms of olive quick decline syndrome (OQDS), taken 3 m above the lateral branch with symptoms, were positive for the presence of X. fastidiosa, as was the root system. The results demonstrate that vegetative material from olive plants used for rooting must be carefully selected for the absence of X. fastidiosa. Also, based on the qPCR‐positive results, pruning may have a limited effect on eliminating the bacteria from diseased plants, even from the ones showing few OQDS symptoms.