First report of Pestalotiopsis versicolor causing leaf-tip blight on Acacia in China

Acacia melanoxylon is one of more than ten species of Acacia used for timber production, that were introduced from Australia to southern China in the 1990s. In Guangxi, it is grown on over 160 hectares of land. In 2004, a leaf-tip blight was found there on 80-92% of trees, causing defoliation and stunting. This blight was angular, initiating at the leaf tip and extending to the middle of leaf. Diseased tissues became distorted and brown (Fig. 1). A fungus producing numerous acervuli with black, slimy spore masses was observed on diseased tissues and consistently isolated onto potato dextrose agar (PDA). Conidia were 5-celled, narrow fusiform, with a tapering base. Dimensions were 20-27 × 6.8-9.2 (mean 24.5 × 7.9) µm. The three intermediate cells of conidia were versicolorous, the two upper cells fuliginous, usually opaque and the lowest cell olivaceous-brown. Three apical appendages were hyaline, 16-28 µm long, with a short straight basal pedicel (Fig. 1). The fungus was identified as Pestalotiopsis versicolor, based on Steyaert (1949) and Guba (1961).

Two-year-old trees of A. melanoxylon were used for pathogenicity test. A conidial suspension of the fungus (1×10⁶ conidia per ml) taken from a PDA culture was sprayed on 1-year-old leaves. Leaves on control trees were sprayed with the same volume of sterilised, distilled water and all inoculated leaves were covered with polyethylene bags during incubation to maintain high moisture. Disease symptoms were observed on inoculated leaves after 13-17 days. Control leaves remained symptomless. The same fungus was re-isolated from diseased leaves, confirming Koch's postulates.

Pestalotiopsis versicolor is a pathogen of many different plants (Steyaert, 1949; Guba,1961; Prakash & Singh, 1975; Thakur & Sastry, 1981). This is the first record of the fungus as a pathogen on A. melanoxylon in China.