Screening The Resistant Mutants To Banana Vascular Wilt Using The Crude Toxins Of Fusarium Oxysporum F.sp. Cubense

Co-cultivation technique was developed for in vitro selection of banana mutants, which crude toxins were extracted from Fusarium oxysporum f.sp.cubense were used as selection factor.The characters of physiological and biochemical of regenerated mutants and their parents were determined.To aimed at determining an appropriate concentration of the crude toxin for mutants screen,the banana multiple bud clumps were cultured on the modified MS medium supplemented with crude toxins.The results showed that the survivability and differentiation of banana buds were inhibited by crude toxins.There was a correlation between dose of the crude toxins which added to the MS medium and the survivability of banana buds.When the inhibitorytoxicity does was 36.3.38μg·mL^-1, which caused 50% of banana buds wilt.One step and multiple steps screen methods were established and banana mutants were obtained.The survivability of differentiated buds and the resistance identification were assessed.The results demonstrated that the multiple steps screen method was to be optimal.The differentiated buds were transferred to the MS medium with progressively increased dose of toxins, after two generations of banana buds were screened on half lethal dose toxins.The results of resistance identification indicated that the resistant levels of the banana mutants resistant to both crude toxins and fungus were increased significantly compared with their parents.And the banana mutants were more tolerance to crude toxins than fungus. Further more the tolerance of regenerated mutants to cruds toxin not complete accord to fungus.The experimental results indicated that in vitro selection of banana mutants resistant to the crude toxins seems to be a viable approach of obtaining Fusarium Will resistant banana plants.The mutants differentiated buds were transferred to toxin free MS medium successive 5 generations,the resistance identification of banana mutant differentiated buds was determined.The results showed that the survival probability of the mutant differentiated buds was above 80%, it was significantly higher than the control's.The results demonstrated that the resistant levels of the mutant differentiated buds screened by multiple steps selection were higher and stabilities.The dynamic activities of protective enzymes caused by F.oxysporum f.sp.cubens and its toxins in tissues of regenerated mutants and their parents while inoculated 0, 1, 3, 5, 7 days were sludied.The activities of superoxide dismutase(SOD),catalasc(CAT) and phenylalanine ammonialyase (PAL) were increased first and then decline after being treated with fungus and the crude toxins.The protective enzymes in tissues of regenerated mutants were more active than control's all the time.In contrast the malondiakiehyde (MDA) of regenerated mutants were in reversed way compared with protective enzymes.The cell membrane permeability of differentiated buds of regenerated mutants were lower than the control's,the tolerance of regenerated mutants cell membrane to crude toxins was improved.The electrophoretic analysis of the POD isozyme indicated that there were no new isozyme bands in the regenerated mutants,but the colour of some isozyme was deeper than their parents' and some isozyme bands became wider. The results demonstrated that the activities of POD isozyme of the regenerated mutants were enhanced after the banana multiple bud clumps were screened by crude toxins.