Comparison of diagnostic techniques for determining incidence of ratoon stunting disease of sugarcane in Florida.
Fluorescent-antibody staining was more accurate for detecting the RSD bacterium in xylem sap extracts from sugarcane than phase-contrast microscopy or isolation in culture. Concn of fluorescent antibody-stained bacteria on the surface of polycarbonate membrane filters (0.2 µm pore-size) by filtration before examination by epifluorescent microscopy resulted in a 7 to 8-fold increase in sensitivity of detection compared with the usual method of staining dried sap samples on the surface of microscope slides. When phase-contrast microscopy, isolation in culture by the dilution-plate technique and fluorescent-antibody stains on membranes (FASM) were compared, 95 of 120 (79%) samples from 20 commercial sugarcane fields were determined to be infected with the RSD bacterium by at least one of these diagnostic techniques. The frequency of detection by FASM was 18% greater on 26 Oct. than on 1 Sept. 1982, with 53 of 60 (88%) samples having bacteria in Oct. Only plant crops were examined and the RSD bacterium was detected in plants from all fields. Both incidence of RSD and the average population of the RSD bacterium in sap extracts varied among sugarcane clones.