PATHOGENIC AND MOLECULAR CHARACTERIZATION OF 3 PHOMOPSIS ISOLATES FROM PEACH, PLUM, AND ASIAN PEAR

Three isolates of Phomopsis, causing shoot blight of peach, shoot tiss ue necrosis of plum, or bud death of Hosui Asian pear, respectively, w ere evaluated for their pathogenicity on apple, pear, peach, and plum. Current year's shoots of 1-year-old Stayman Winesap apple, Barlett pe ar, Babygold-7 peach, and Bruce plum trees were inoculated with each i solate by wounding a bud and applying agar blocks bearing young hyphae . The length of cankers on shoots was measured 10, 17, and 24 days aft er inoculation. Cankers developed on shoots of all hosts inoculated wi th the peach isolate and on peach shoots inoculated with plum and Asia n pear isolates. No cankers developed on apple, pear, or plum shoots i noculated with plum and Asian pear isolates. In the first experiment, 10 days after inoculation, the length of cankers on apple trees (56.0 mm) inoculated with the peach isolate was not significantly different (P greater than or equal to 0.05) from that on peach (42.8 mm), but wa s significantly greater than that on plum (25.3 mm) and pear (13.1 mm) . The cankers on peach were significantly longer than those on pear, b ut not on plum. Cankers on all four hosts were significantly different from one another 17 and 24 days after inoculation. There was no signi ficant difference between the length of cankers on peach shoots inocul ated with plum and Asian pear isolates, and they were significantly sm aller than those inoculated with the peach isolate. None of the contro l trees developed cankers. The three isolates differed in colony morph ology, and appearance of conidiomata, conidiogenous cells, and alpha-c onidia on potato-dextrose agar. None of the isolates produced beta-con idia in culture. Multi-locus DNA fingerprint analysis and internal tra nscribed spacer sequence comparisons revealed similarities between the plum and Asian pear isolates but a significant difference between the se two and the peach isolate. The results indicate that the Phomopsis sp. that causes shoot blight of peach has the potential to cause disea se on other stone and pome fruits, and peach may also be susceptible t o isolates of Phomopsis from different tree fruit hosts.