EFFECT OF SUGARCANE CULTIVAR SUSCEPTIBILITY ON SPREAD OF RATOON STUNTING DISEASE BY THE MECHANICAL HARVESTER

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.