Paradoxes Surrounding Our Understanding of Plum Leaf Scald

Abstract

Xylella fastidiosaWells et al., a xylem limited bacterium (XLB) and the causal agent of plum leaf scald, has also been shown to be the causal agent of Pierce’s disease in grape, phony peach, and almond leaf scorch and has produced blight symptoms in citrus. Scientific and circumstantial evidence are presented for and against all 5 crop diseases being caused by the same XLB. This XLB has been transmitted among the 5 crops, but not in all combinations. The XLB has a wide host range, is transmitted by similar leafhoppers, is characterized by occlusions in the xylem with plant symptoms appearing most severely following stress (heavy crops), and results in decreased productivity and generalplant decline. Germplasm resistant to plum leaf scald is recommended for breeding programs in the southeastern U.S.