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Red Spot (Helminthosporium rostratum) of Sweet Sorghum and Sugarcane, a New Disease Resembling Anthracnose and Red Rot. N. Zummo, USDA-ARS, Crop Science Research Laboratory, Mississippi State University, Mississippi State 39762. Plant Dis. 70:800. Accepted for publication 16 April 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-800c.

Leaf midrib lesions resembling anthracnose (Colletotrichum graminicola (Ces.) Wilson) were observed on anthracnose-resistant sweet sorghum (Sorghum bicolor (L.) Moench ‘Theis’) at Meridian, Mississippi, and lesions resembling red rot (C. falcatum Went) were found on the midribs of red-rot-resistant sugarcane (Saccharum officinarum L. ‘CP 67-500’). The disease, red spot, was incited by Helminthosporium rostratum Drechsler. On sweet sorghum, red spot lesions of the leaf midrib are red-brown to black with tan or brown centers, irregular, and longitudinal (8–12× 50 mm). On sugarcane, the lesions are bright red and 15–25 × 20–35 mm. Unlike anthracnose or midrib red rot lesions, red spot lesions are not sunken. Red spot is believed to be of little economic importance, but a major concern is that symptoms could be mistaken for those of red rot in breeding programs that screen for anthracnose and red rot resistance.