GENETIC NATURE, STABILITY, AND IMPROVED VIRULENCE OF HYBRIDS FROM PROTOPLAST FUSION IN BEAUVERIA

Genetic improvement of two different strains of the entomopathogenic f ungus Beauveria bassiana for more effective control of Ostrinia nubila lis and Leptinotarsa decemlineata was obtained by crosses with the ins ecticidal toxin-producing strain Beauveria sulfurescens. Protoplast fu sion between diauxotrophic mutants resulted in the recovery of some st able prototrophic fusion products. The low levels of virulence of the wild type strain B. bassiana 28 isolated originally from L. decemlinea ta were enhanced both on L. decemlineata and O. nubilalis for one of t he hybrids obtained (FP 8) from the cross B. bassiana 28 x B. sulfures cens 2. Fusion product 25 obtained from the cross between B. sulfuresc ens and the highly pathogenic strain B. bassiana 147 showed a three-da y reduction in the LT(50) towards O. nubilalis. Southern blot hybridiz ation with nine probe-enzyme combinations were conducted on genomic DN As from the original wild strains, parental mutant strains, and fusion products. Additive banding patterns or unique banding pattern of eith er parental strain was observed in five hybrids, indicating their stat us as recombinant and/or partially diploid. Combination of RFLP marker s indicative of both parental genomes was never observed with fusion p roduct FP 25. The stability of the virulence following passage through insect-host and stability of molecular structure for the fusion produ cts FP 8 and FP 25 suggest that asexual genetic recombination by proto plast fusion may provide an attractive method for the genetic improvem ent of biocontrol efficiency in entomopathogenic fungi.