Relationship Between Resistance to Clavibacter xyli subsp, xyli Colonization in Sugarcane and Spread of Ratoon Stunting Disease in the Field. J. C. Comstock, USDA-ARS, Sugarcane Field Station, Canal Point, FL 33438. J. M. Shine, Jr., Florida Sugar Cane League, Canal Point 33438; M. J. Davis, University of Florida, Tropical Research-Education Center, 18905 S.W. 280th St., Homestead 33031; and J. L. Dean, (USDA-ARS, Retired) Sugarcane Field Station, Canal Point, FL 33438. Plant Dis. 80:704. Accepted for publication 21 March 1996. 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, 1996. DOI: 10.1094/PD-80-0704.

The spread of ratoon stunting disease (RSD)' of sugarcane resulting from hand-cutting was monitored in plots of six different cultivars that varied in RSD resistance. Cultivar resistance influenced the disease spread. Very little spread was observed among plants of an RSD-resistant cultivar that had low numbers of Clavibacter xyli subsp. xyli-colonized vascular bundles (cvb) determined in 1 -cm-diameter core sample of stalk tissue; whereas the rate of spread and incidence were highest in the most susceptible cultivar, which had approximately 20 cvb per core sample. Disease spread followed the direction of hand harvest within rows from infected source plants (inoculated) to test plants (uninoculated). The incidence of RSD in test plants increased with the number of ratoon crops harvested.