Comparison of Diagnostic Techniques for Determining Incidence of Ratoon Stunting Disease of Sugarcane in Florida
and J. L. DEAN, USDA, ARS, U.S. Sugarcane Field Station, Canal Point, FL 33438 commercial plantings of sugarcane in ABSTRACT Florida. This was viewed as a first step in Davis, M. J., and Dean, J. L. 1984. Comparison of diagnostic techniques for determining incidence determining the importance of RSD in of ratoon stunting disease of sugarcane in Florida. Plant Disease 68:896-899. Florida. Also, effective diagnosis is essential to other areas of RSD research. Fluorescent-antibody staining was
... dy staining was more accurate for detecting the RSD bacterium in xylem sap extracts from sugarcane than was phase-contrast microscopy or isolation in culture. Concentration MATERIALS AND METHODS of fluorescent antibody-stained bacteria on the surface of polycarbonate membrane filters (0.2-A.m Mat s of MeTcon S pore-size) by filtration before examination by epifluorescent microscopy resulted in a sevenfold to Plants of sugarcane clone CP 53-1 were eightfold increase in sensitivity of detection compared with the usual method of staining dried sap grown from cuttings that had been samples on the surface of microscope slides. When phase-contrast microscopy, isolation in culture inoculated with crude juice from RSDby the dilution-plate technique, and fluorescent-antibody stains on membranes (FASM) were infected sugarcane (10). Plants were compared, 95 of 120 (79%) samples from 20 commercial sugarcane fields were determined to be grown in plastic pots in a greenhouse for infected with the ratoon stunting disease (RSD) bacterium by at least one of these diagnostic 6-8 mo before use in preliminary techniques, and about 20% more infections were detected by FASM than by the other two comparisons of diagnostic techniques. techniques. The frequency of detection of the RSD bacterium in the commercial fields by FASM Further tests were made with sugarcane was 18% greater on 26 October 1982 than on 1 September 1982, with 53 of 60 (88%) samples having bacteria in October. Only plant crops were examined and the RSD bacterium was detected in plants samples from experimental or commercial from all fields. Both incidence of RSD and the average population of the RSD bacterium in sap fields. Only the first crop of each field extracts varied among sugarcane clones, planting was sampled.