Interactions between fusarium oxysporum and meloidogyne arenaria as root pathogens of subterranean clover affected by soil sterilisation and inoculum substrate

Abstract

Pot experiments were conducted to examine the effects, on the root health and growth of subterranean clover, of Fusarium oxysporum and Meloidogyne arenaria applied singly or in combination. The effects of the sterilised ryegrass seed substrate used for the growth of F. oxysporum, and of live and dead inoculum of this fungus were also investigated. In autoclaved soil, F. oxysporum was a virulent pathogen, causing severe root rot and seriously affecting plant growth. No nematode galls were formed in this soil when F. oxysporum and M. arenaria were inoculated together. But in pasteurised soil, although the fungus was the main cause of the root necrosis observed, it was only a weak or non-pathogen, and had little or no effect on M. arenaria root infection. In pasteurised soil, in addition to the fungus and nematode, the sterilised ryegrass seed, either colonised with the fungus or uncolonised, was also a contributing factor to the reduction in plant growth. The effects by these factors were independent of one another. But, in the absence of microorganisms in autoclaved soil, this detrimental effect resulting from the ryegrass seed inoculum was not evident, indicating that its cause is biological. M. arenaria had no effect on root necrosis in both the pasteurised soil and autoclaved soil. In the absence of the nematode in pasteurised soil, the fungal inoculum with live fungus produced greater total root length and dry shoot weight than inoculum containing killed fungus. This increase in plant growth with live fungus however, was negated when M. arenaria was added in combination with the live fungus. © 1992 Taylor & Francis Group, LLC.