A Study on Specificity and Host Range of Wilsonomyces carpophilus, the Causal Agent of Shot Hole Disease of Stone Fruit Trees and Evaluation of Relative Resistance of some Peach Cultivars

To determine the specificity and host range of Wilsonomyces carpophilus isolates, some stone fruit seedlings (Prunus armeniaca, Prunus dulcis, Prunus reuteri, P. vulgaris, P. domestica, P. persica, P. avium and P. cerasus), pome fruits (Malus communis, Pyrus communis, Crataegus azarollus and Crataegus monogyna) as well as ornamental plants (Rosa persica, Rosa sp. and R. damascena) were selected for pathogenicity tests under greenhouse conditions. Five isolates from five different hosts (apricot, almond, plum, peach and sweet cherry) were taken for pathogenicity tests on ten leaf-seedlings under 20±2˚C and relative humidity of more than 75%, using atomized 105 conidial suspensions. The results showed that all isolates caused disease on Prunus seedlings. No specificity was observed between isolates and hosts. Pale brown to black lesions were observed on some of the pear leaves and twigs, and as well on apple and hawthorn leaves after 4 days past of inoculation. Lesions did not expand or abscise and there was no sporodochium observed on leaves even after 20 days past, so that, pear, apple and hawthorn were not determined as important hosts of the fungus. In addition, symptoms were not observed on the ornamental plants and on whitethorn, raising the expectation that the fungus is limited to stone fruits. Appearance of disease symptoms on almond, plum, peach and nectarine, and on apricot twigs in orchards, infection of plum and apricot twigs in greenhouse and isolation of fungus from these are the first reports from Iran. To evaluate the relative resistance of nine peach cultivars to tree fungus isolates, as based on the number of lesions per 10 cm2 of leaf surfaces, tests were carried out under greenhouse conditions (20±2˚C and relative humidity of more than 75%). The results indicated that there were significant differences among relative resistance of cultivars and among isolate's pathogenicity. Redtop, Springcrest and Early Elberta cultivars were resistant, whereas, Dixired cultivar was recorded as highly susceptible.