Transmission of Xylella fastidiosa through pecan rootstock
Xylella fastidiosa Wells et al., the pathogen that causes pecan [Carya illinoinensis (Wangenh.) C. Koch] bacterial leaf scorch disease, was demonstrated to be highly transmissible through graft unions from infected rootstock into new growth developing from scions. Infected rootstocks were obtained by inoculation of pecan seedlings in pots with in vitro cultures of the pathogen. If rootstock infection occurs in nature, transmission of the pathogen into tissue growing from scions could serve as a significant source of introduction of the disease into pecan orchards. Because symptom development in infected trees typically begins in midsummer and grafting takes place in the early spring, it would be difficult to identify infected rootstock before grafting. Commercial pecan growers sometimes attempt to eliminate bacterial leaf scorch from trees by regrafting to other cultivars. The high rate of transmission from infected rootstocks observed in this test and the lack of knowledge of cultivars with resistance to the disease makes this practice ineffective.