Factors influencing the effectiveness of non-pathogenic Fusarium solani strain Fs5 in the suppression of root-knot nematode in tomato

Abstract

Four experiments were carried out under greenhouse conditions to evaluate the effectiveness of Fusarium solani strain Fs5 against the root-knot nematode Meloidogyne javanica. The effect of population densities of M. javanica, various application rates of F. solani, moisture regimes and levels of benzaldehyde, a volatile compound of plant origin affecting the plant-nematode-fungus interaction, were also studied. F. solani parasitized eggs and females of M. javanica and thereby reduced root-knot severity in tomato. Although the fungus was frequently isolated from root tissues, it did not produce phytotoxic symptoms; instead, there was enhanced plant growth. At higher nematode densities, inner root colonization by the fungus increased. The rates of fungal infection on M. javanica eggs and females also increased with increasing nematode densities and fungal inoculum levels. Nematode invasion and subsequent root-knot increased with increasing soil moisture, in both F. solani-treated and untreated plants. However, root-knot development was lower at all moisture regimes when F. solani was applied to the soil. Root colonization by F. solani and parasitism on female nematodes was highest at 50% moisture holding capacity (MHC) whereas egg parasitism by the fungus was greatest at 75% MHC. With increasing concentration of benzaldehyde in soil, nematode penetration and subsequent root-knot infection were progressively reduced. Root colonization by F. solani was greatest in soil treated with benzaldehyde at 2 µg g-1 of soil in the presence of M. javanica. Increasing benzaldehyde concentrations resulted in increased parasitism of M. javanica females by F. solani but in lower parasitism of the eggs. Treatments with F. solani led to better plant growth when they were combined with benzaldehyde at 2 µg g-1 of soil.