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Disease Note.

Lasiodiplodia theobromae and Fusarium proliferatum Causing Storage Rots of Taro on Guam. G. C. Wall, College of Agriculture & Life Sciences, University of Guam, Mangilao 96923. F. J. Cruz, College of Agriculture & Life Sciences, University of Guam, Mangilao 96923. Plant Dis. 75:1186. Accepted for publication 5 July 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-1186D.

Both AG-2-2 and AG-4 of Rhizoctonia solani Kuhn were problems on tobacco (Nicotiana tabacum L.) seedlings produced under plastic in 1991 in Georgia. The AG-4 type is endemic and causes dampingoff and stem lesions in tobacco seedbeds. The AG-2-2 type causes a foliar spot and was first identified on tobacco in Georgia in 1989. The foliar spot may have been misdiagnosed as anthracnose, caused by Colletotrichum gloeosporioides (Penz.) Penz. & Sacco in Penz., before that time; both disease organisms cause small, water-soaked spots on leaves of seedlings. Large necrotic areas developed on leaves of seedlings inoculated with agar plugs of R. solani AG-2-2 and maintained at or near 100% humidity in a greenhouse. Within a week, adjacent uninoculated seedlings showed water-soaked symptoms typically found in vivo on lower leaves as a result of infections by basidiospores (1). Lesions allowed to develop showed the typical target spot symptom (1), which has been verified on field tobacco in Georgia this year. The appearance of these two fungi may be related to environmental conditions. March 1991 rainfall in Tifton was 23.5 cm (66- yr mean = 11.7 cm), and average daily temperatures were 18.2 C (66-yr mean = 15.3 C).

Reference: (1) H. D. Shew and C. E. Main. Plant Dis. 74:1009, 1990.