Factors Relating to Induced Systemic Resistance in Watermelon by Plant Growth-Promoting Pseudomonas spp.

The plant growth-promoting Pseudomonas strains, WR8-3 (Pseudomonas fluorescens), WR9-11 (Pseudomonas sp.) and WR9-16 (P.putida), which induced resistance systematically in watermelon to gummy stem rot were investigated on their induced systemic resistance(ISR)-related characteristics. The pyoverdine production was repressed in the standard succinate medium by increasing the concentration of $\textrm{FeCL}_3$. But the iron-binding ability on chrome azurol S agar media (CAS) was observed only in the strains, WR8-3 and WR9-16. When the two strains were mutated, the resulting iron-binding siderophore-negative mutants, WR8-3m and WR 9-16m, failed to promote the growth of watermelon and to induce resistance. The strains, WR8-3 and WR 9-16, slightly inhibited the growth of Didymella bryoniae at a low concentration of $\textrm{FeCL}_3$ on Kong's medium B, but not to exert control dffect. The strain WR9-11 showed antagonism in the concentration of $\textrm{FeCL}_3$ from 0 to $1,000\mu\textrm{M}$. When the crude lipoplysaccharide of each strain was treated in the rhizosphere of watermelon, mean lesion area was similar to that of the untreated control. The strains, WR9-11 and WR9-16 produced some level of hydrogen cyanide (HCN). Salicylic acid production was not detected in all of the strains.