Effect of Sugarcane Cultivar Susceptibility on Spread of Ratoon Stunting Disease by the Mechanical Harvester. Kenneth E. Damann, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, LSU Agricultural Center, Baton Rouge, 70803. . Plant Dis. 76:1148-1149. Accepted for publication 19 May 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-1148.

The spread of ratoon stunting disease by the mechanical harvester was followed in disease-free sugarcane plants of cultivars susceptible, intermediate, or resistant to the disease. Incidence in a 12-m row of susceptible cultivar L 62-96 preceded by one, two, or four diseased plants was 30, 60, and 75%, respectively, after one harvest and 84, 98, and 99%, respectively, after two harvests. Incidence in intermediate cultivar CP 65-357 was 10, 11, and 9% in the first ratoon and 26, 24, and 44% in the second ratoon. No spread was detected in resistant cultivar L 60-25. Gradients were apparent in consecutive 3-m segments of rows. Little spread occurred beyond the first segments in CP 65-357. In contrast, incidences with L 62-96 were 4, 38, and 43% in the fourth 3-m segment of rows preceded by one, two, or four diseased plants, respectively.