Combined application of endophytic «Fusarium solani» and «Pseudomonas aeruginosa» for the suppression of «Meloidogyne javanica» in tomato

Abstract

The impact of two application rates of Fusarium solani strain Fs5 (3.5 106 and 2.2 107 cfu ml-1) and Pseudomonas aeruginosa strain IE-6S+ (2.8 107 and 1.3 108 cfu ml-1) on various population densities of Meloidogyne javanica in tomato was tested in pots under greenhouse conditions. Whilst combined applications of F. solani and P. aeruginosa caused a marked suppression of root knot 6 and 12 weeks after nematode addition, F. solani alone failed to inhibit root-knot infection after 6 weeks, and P. aeruginosa alone was ineffective after 12 weeks. Both biocontrol agents were frequently isolated from the inner root tissues of tomato without any detrimental effect on plant growth. High inoculum levels of M. javanica not only increased root knot but also promoted inner root colonization by F. solani and P. aeruginosa. Inner root colonization by F. solani was greatly reduced when high inoculum levels of the bacterium and low application rates of the fungus were used together. Likewise, P. aeruginosa at low inoculum levels in the presence of high dosages of F. solani led to the complete absence of the bacterium from the inner root tissues. F. solani parasitized eggs and females of M. javanica but P. aeruginosa did not. Egg parasitism increased with increasing fungal inoculum levels. Six weeks after nematode inoculation, F. solani at the low inoculum level and P. aeruginosa at both dosages greatly reduced fungal egg parasitism rates, whereas 12 weeks after nematode inoculation, both organisms used together promoted fungal parasitism. Under field conditions at Karachi and Gharo, combined application of P. aeruginosa and F. solani caused greater suppression of root-knot development due to M. javanica than either antagonist alone. Inner root colonization by F. solani and P. aeruginosa was higher in Karachi than in Gharo. When the microorganisms were applied alone, egg parasitism rates by F. solani were similar in both localities, but when they were applied together, the egg parasitism rate was slightly higher in Karachi than in Gharo.