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Disease Detection and Losses

Symptomatology and Detection of Macrophomina phaseolina in Sunflower Plants Parasitized by Cylindrocopturus adspersus Larvae. S. M. Yang, Research plant pathologist, Conservation and Production Research Laboratory, Agricultural Research Service, U.S. Department Agriculture, P.O. Drawer 10, Bushland TX 79012; D. F. Owen, research scientist, Texas A&M University, Agricultural Research and Extension Center, Route 3, Lubbock 79401. Phytopathology 72:819-821. Accepted for publication 10 November 1981. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1982.. DOI: 10.1094/Phyto-72-819.

The typical symptoms and signs of charcoal rot of cultivated sunflower (Helianthus annuus L.) in the Texas High Plains areas are a gray discoloration of the stem and formation of many minute, black sclerotia on the surface of the stem and in the pith tissues. Sunflower stems infected with M. phaseolina and parasitized by C. adspersus (stem weevil) larvae have a black-to-brown discoloration with or without typical gray areas on the surface of the stem. Pith tissue may be black and partially or completely disintegrated. Portions of the lower stem are hollow. Mixtures of frass and fragments of pith tissue are observed in the lower stem and upper taproot. M. phaseolina was isolated from all plants with typical symptoms on potato-dextrose agar amended with antibiotics. The fungus was also detected in most plants parasitized by stem weevil larvae, even when the stems lacked gray discoloration. The pathogen was isolated from internal tissues of the taproots, stem epidermis, pith, stem weevil larvae, and frass, but not necessarily from all these in a given plant. Isolates of M. phaseolina from plants parasitized and unparasitized by stem weevil larvae, and from stem weevil larvae, caused brown-and-gray discoloration of charcoal rot in inoculated sunflower plants kept in a growth chamber.