Two Xylella fastidiosa genotypes associated with almond leaf scorch disease on the same location in California

• Published in: Phytopathology Vol. 95; no. 6; pp. 708 - 714
• Main Authors: Chen, J, Groves, R, Civerolo, E.L, Viveros, M, Freeman, M, Zheng, Y
• Format: Journal Article
• Language: English
• Published: St. Paul, MN American Phytopathological Society 01.06.2005
• Subjects: almonds; Biological and medical sciences; Fundamental and applied biological sciences. Psychology; fungal diseases of plants; genetic variation; genotype; leaves; molecular sequence data; nucleotide sequences; pathogenicity; pathotypes; Phytopathology. Animal pests. Plant and forest protection; plant pathogenic fungi; Prunus dulcis; scorch; sequence homology; symptoms; Xylella fastidiosa; California; United States; North America; America; Mixed infection; Multiplex polymerase chain reaction; Prunus dulcis; Rosaceae; Ribosomal DNA; Genotype; Identification; Strain; Restriction fragment length polymorphism; Dicotyledones; Morphology; Angiospermae; 16S-RNA; Bacteria; Genetics; Spermatophyta; Fruit tree; Single nucleotide polymorphism
• ISSN: 0031-949X; 1943-7684
• DOI: 10.1094/PHYTO-95-0708

Almond leaf scorch disease (ALSD) has recently reemerged in the San Joaquin Valley of California threatening almond production. ALSD is caused by Xylella fastidiosa, a nutritionally fastidious bacterium. Single nucleotide polymorphisms (SNPs) in the 16S rRNA gene (16S rDNA) of X. fastidiosa strains were identified to characterize the bacterial population in infected trees. Genotype-specific SNPs were used to design primers for multiplex polymerase chain reaction assays of early passage cultures. Two genotypically distinct types of X. fastidiosa strains, G-type and A-type, coexist simultaneously in the same infected almond orchard. This was substantiated by restriction fragment length polymorphism analysis of a different genetic locus, RST31-RST33, which has previously been used to identify and differentiate X. fastidiosa strains. Furthermore, unique bacterial colony morphology was consistently associated with the A-type X. fastidiosa strains. To our knowledge, this is the first report of a mixed genotype infection of X. fastidiosa disease on the same location under natural environmental conditions. The concept of mixed genotype infection could affect the current epidemiological study based on the assumption that one genotype causes ALSD on one location and, therefore, the disease management strategy.