Pathogenicity of a Species of Phomopsis Causing a Shoot Blight on Peach in Georgia and Evaluation of Possible Infection Courts

Abstract

A species of Phomopsis was isolated consistently from blighted shoots of peach trees in Georgia and Alabama. Isolates of the fungus caused characteristic cankers on current season's shoots of Babygold-7 peach trees when wounded or nonwounded dormant buds, breaking buds, and natural or artificially-created leaf scars were inoculated with conidia of the fungus. Mean canker length for the isolates was 35 mm 30 days after inoculation. No disease developed on control trees. There was no significant difference between the canker length on inoculated wounded dormant buds (59 mm) and nonwounded breaking buds (54 mm). However, cankers from both sites of inoculation were significantly longer than those resulting from inoculated artificially-created leaf scars (33 mm), natural leaf scars (33 mm), and non-wounded dormant buds (30 mm). There was no significant difference in virulence among the 5 isolates of Phomopsis sp. tested, and multi-locus DNA fingerprint analysis resulted in a similarity coefficient of 0.94 among the isolates. Additionally, results of the internal transcribed spacer (ITS) regions sequence comparisons for the isolates were consistent with the multi-locus polymerase chain reaction profiles, and the nucleotide sequences of the ITS region were identical for all 5 isolates. This is the first documentation of the pathogenicity of a Phomopsis sp. associated with shoot blight of peach in Georgia. Rapid development of disease in breaking buds indicates that they may be the primary site of invasion by the fungus. Natural leaf scars and dormant buds may also serve as possible infection courts.