Cultivar and seedling susceptibility to pecan bacterial leaf scorch caused by Xylella fastidiosa and graft transmission of the pathogen
The xylem-limited bacterium Xylella fastidiosa was detected in 20 cultivars and 4 seedling trees with pecan bacterial leaf scorch (PBLS) symptoms during a 2-year survey of commercial pecan (Carya illinoinensis) cultivars. The orchard survey and inoculation trials indicated that several of the currently recommended cultivars, as well as older, popular cultivars, are susceptible to infection by the bacterium and develop PBLS. The severity of disease development was variable between cultivars and within cultivars. Eight of 9 cultivars growing in pots that were needle-puncture inoculated with X. fastidiosa became infected and developed the disease. Currently, no cultivars have been identified that are not susceptible to infection and symptom development. All 6 seedling types that were inoculated became infected and developed PBLS. The frequency of infection of the seedlings was greater than the cultivars: 88% of the inoculated seedlings and 44% of the inoculated cultivar trees were infected. It was demonstrated that the pathogen could be transmitted through scion wood. Because pecan cultivars are clonally propagated, graft-transmission may represent a major source of pecan infection.