Abstract
A variety of stress situations may affect the activity and survival of plant-beneficial pseudomonads added to soil to control root diseases. Pseticlomonas fluorescens strain CHAO produced extracellular proteases and caused substantial mortality of the juveniles of Meloidogyne javanica, the root-knot nematodes, in vitro while strain CHA211, a highly mucoid (exopolysaccharide overproducing) derivative of the strain CHAO, did not. In general, the both the bacterial inoculants exhibited osmosensitivity of a similar degree upon exposure to NaC1 or sorbitol, strain CHA2I I survived better than CHAO when growing cultures of the bacteria were exposed to sorbitol at 1.2 M concentration. Whereas both the bacterial strains were equally susceptible to paraquat and NaOCI, strain CHA211 was more tolerant to H202 than CHAO. Likewise, mutant withstood thermal stress (42 and 50°C) better than its wild type counter part CHAO. Application of strains CHAO or CHA211 to sandy loam soil resulted in a significant reduction of nematode population densities in roots but only strain CHAO reduced root-knot infection due to M. javanica. The bacterial strains did not differ markedly in their colonization in tomato rhizosphere. Strain CHAO caused systemic reduction of nematode penetration greater than CHA211.
