Abstract

The Fusarium wilt caused by Fusarium oxyspoum f. sp. cubense (Foc) is a major biotic constraint for banana production. The characteristics of F. oxyspoum f. sp.cubense isolates were investigated using electrophoretic studies of isozyme and whole-cell protein. The morphological characteristics of the isolates were very similar to each other. All the Foc isolates were pathogenic to banana cultivar ‘Nanjangud Rasabale’ but they did not induce any disease symptoms on cultivar ‘Cavendish’. F. oxyspoum (Isolate 6) did not induce wilt symptoms on either ‘Nanjangud’ or ‘Cavendish’ cultivar. Isozyme banding patterns showed 46 scoreable markers and cluster analysis with UPGMA using genetic distance showed that the isolates belonged to three main groups. Group 1 contained isolates 1, 2, 4, 5, 7 and isolate 3 and 6 were placed in group 2 and 3. Results indicated that the estimated intra-specific variation may be more pronounced with isozyme analysis than with protein markers. The level of isozyme variability detected within F. oxysporum f.sp. cubense suggested that it is reliable, efficient and effective in determining genetic relationships among Foc isolates.

Key words: Fusarium wilt, Fusarium oxysporum f. sp. cubense, polyacrylamide gel electrophoresis, isozyme analysis.

Abbreviation

Abbreviations: UPGMA, Unweighted pair-groups method using arithmetic mean;NRN, ‘nanjangud rasabale’; PDA, potato dextrose agar; PDB, potato dextrose broth; EDTA, ethylene diamine tetraacetic acid; POX, peroxidase; SOD, superoxide dismutase;  GDH, galactose dehydrogenase; G, β- 1,3-glucanase; SDH, Succinate dehydrogenase; CAT, Catalase; VCG, vegetative compatibility group; SDS-PAGE,sodium dodecyl sulfate-polyacrylamide gel electrophoresis; DNA, deoxyribonucleic acid; RAPD, random amplified polymorphic DNA; IGS, intergenic sequence.