Improving Nematocidial Activity of Bacteria via Protoplast Fusion

Cucumber plants play an important role in economical field in Egypt. But they are infected by plant parasitic nematodes that leading to losses cucumber yield. This study attempted to construct more efficient bacterial strains may be able to controlling nematodes, as well as, maintenance the soil fertility using molecular biology method via induced protoplast fusion between different strains of Pseudomonas and Serratia to improve the biological control against the nematodes number in infected fields, in order to reduce the use of nematocidial agents. Four strains of Serratia and six Pseudomonas strains were used in this study. The results showed that more efficient strains in the production of indole acetic acid and antibiotic resistance were controlling plant parasitic nematodes such as Meloidogyne and some other type of nematodes. Mortality values were obtained by all strains of Serratia and Pseudomonas, as well as, the high values of mortality were obtained from Pseudomonas strains. Different bacterial strains could control the nematodes larva under green house condition which reduced the numbers of larva. per k.g soil, as well as, reduced galls formation and galling index. However, some bacterial strains were more efficient in controlling nematodes such as Serratia strains ESA.4, ESA12 and Pseudomonas strains NRRL-B 514, NRRL-B 694, NRRL-B.99, NRRL-B.51. On the other hand, fusants produced antibiotic chitinoltic enzymes, chitinases and bacteriocin which improved their ability to control the nematodes in the soil rhizosphere. Fusants induced high mortality levels against nematodes if compared with the parental strains, as well as, all the fusants obtained controlled nematodes and protected cucumber plants from nematode infection causing yield losses. This indicated that fusants evaluated against plant parasitic nematodes appeared high efficient nematocidial effect. The results of fusants documented using polyacrylamide gel electrophoresis and DNA fingerprinting appeared genetic variations between fusants and their parental strains.