Disease Note.

First Report of Macrophomina phaseolina Associated with Vine Decline of Muskmelon in South Australia. G. E. Walker, South Australian Research and Development Institute (SARDI), P.O. Box 411, Loxton, South Australia 5333, Australia. Plant Dis. 78:640. Accepted for publication 29 January 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0640B.

Local growers of muskmelon (Cucumis melo L., Reticulatus Group) commonly ascribe symptoms of declining vines and bleached, tan lesions on stems near the crown to the disease gummy stem blight caused by Didymella bryoniae (Auersw.) Rehm. Muskmelon plants (cv. Eldorado) from Waikerie with these symptoms were examined in January 1991, and abundant microsclerotia and, occasionally, pycnidia consistent with descriptions of Macrophomina phaseolina (Tassi) Goidanich were observed on stem lesions. Microsclerotia were also abundant in the pith of stems. M. phaseolina was consistently isolated from diseased tissue on potato-dextrose agar. Stem lesions grew larger with dark, water-soaked margins when stems were incubated under moist conditions at 24 C. Early spring planting in warm (11-25 C) Riverland soils kept excessively wet by drip irrigation is thought to favor infection by the fungus. Early root infection by M. phaseolina is an important causal agent of vine decline of muskmelon in the lower Rio Grande Valley of Texas (1,2). Surveys are required to establish the importance of this disease in South Australia.