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Disease Note.

Occurrence of Pestalotiopsis microspora on Torreya taxifolia in Florida. M. W. Schwartz, Center for Population Biology, University of California, Davis 95616. D. J. Porter, Center for Population Biology, University of California, Davis 95616; S. M. Hermann, Tall Timbers Research Station, Tallahassee, FL 32312; and G. Strobel, Department of Plant Pathology, Montana State University, Bozeman 59717. Plant Dis. 80:600. Accepted for publication 10 March 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0600A.

Torreya taxifolia Arnott is an endangered conifer endemic to 400 km2 of ravine habitats along the Apalachicola River located in northern Florida. A population decline in the 1950s reduced the species to 1,000 to 1,500 immature individuals. The failure to recover since this decline poses a significant threat of extinction for T. taxifolia and is thought to be a result of low light conditions and foliar pathogens causing decreased net photosynthetic capacity and premature needle loss (2). Field symptoms of disease at present in T. taxifolia (needle spotting and stem cankers) are consistent with Pestalotiopsis spp. infections in a variety of conifers (E. F. Guba, Monogr. Monochaetia Pestalotia, 1961). P. microspora, isolated from T. taxifolia, was identified by- the characteristic five-celled spores, with three dark center cells surrounded by two outer hyaline cells. Spores are also characterized by one basal and with three to four apical appendages. The frequency of P. microspora was examined in 62 (among 51 needle and 25 twig samples of multiple ages) plants across the indigenous distribution of T. taxifolia. The fungus was cultured on potato dextrose agar at 23C for up to 7 days. Isolates of P. microspora were found on 56 (90%) plants on both twig (85%) and needle (88%) tissue. Twig age was not related to probability of infection as 84 and 83% of first and second year twigs were infected, respectively, compared with 88% of 3- to 9-year-old twigs combined. No geographic pattern to the distribution of infection was observed. These results suggest that virtually the entire T. taxifolia population is infected with P. microspora. While typically considered saprophytes and secondary pathogens, Pestalotiopsis spp. have been identified as pathogens in conifers (E. F. Guba, Monogr. Monochaetia Pestalotia) (1). Ten replicated stems of T. taxifolia were inoculated with P. microspora mycelial plugs producing cankers on stems and necrotic areas and chlorosis on terminal leaves. P. microspora was reisolated from all the inoculated and symptom-bearing stems. The fungus was never isolated from control stems inoculated with sterile water agar, thus fulfilling Koch's postulates.

References: (1) Z. Madar et al. Phytoparasitica 19:79,1991. (2) M. W. Schwartz et al. Ecol. Applic. 5:501, 1995.