Weeds as alternative hosts of Xylella fastidiosa in Brazilian plum orchards.

Xylella fastidiosa is a generalist phytopathogen transmitted by several polyphagous species of sharpshooters. This bacterium is responsible for plum leaf scald disease (PLS), the main phytosanitary barrier for the culture in Brazil. As an aggravating factor, weed species present in orchards can be related to the epidemiology of the disease as a source of inoculum for the pathogen. Therefore, the objective of this study was to evaluate the natural infection by X. fastidiosa in weed species present in plum orchards with a high incidence of PLS in two producing regions of Brazil, as well as to determine the colonization capacity by three sequence types (STs 26, 67 and 71) of X. fastidiosa isolated from plum trees. A total of 12 prevailing weed species were collected, nine of which (Bidens pilosa, Lepidium ruderale, Lolium multiflorum, Plantago major, Parthenium hysterosphorus, Raphanus sativus, Rumex sp., Solanum americanum and Vernonia sp.) tested positive by PCR for X. fastidiosa infection. From these, L. ruderale and L. multiflorum had the highest infection rates of 70% and 90% in root and leaf samples of L. ruderale, respectively, and 100% in leaf samples of L. multiflorum. Mechanical inoculation allowed systemic infection of the bacteria in B. pilosa, L. ruderale, R. sativus and S. americanum. Our results indicate that several weed species in plum orchards are hosts of representative STs of X. fastidiosa that infect plum, and might play a role in the spread of the pathogen to plum trees. [ABSTRACT FROM AUTHOR]