The role of mycorrhizal associations in the growth and survival of the native hills daisy, Ixodia achillaeoides: interactions with root-pathogenic nematodes

Summary of final report on the Australian Flora Foundation funded project:

Paul Dalby1, Evelina Facelli1, and Greg Walker2
1 Department of Soil Science, University of Adelaide, Waite Campus, Glen Osmond 5064 SA Australia.

2 SARDI, Plant Research Centre , Adelaide, SA 5001
Grant Details   Final Report

Although mycorrhizal associations are widespread in Australian ecosystems (McGee 1986; Logan et al. 1989; Bellgard 1991; Brundrett 1991) and some studies have shown an improved growth of native plants due to the presence of the symbiosis (Barrow 1977; Jasper & Davy 1993), there is scant information on the ecological significance of the symbiosis in these systems. However, there is consensus that mycorrhizas not only play an important role in the nutrient acquisition of native plants but also may increase the resistance/tolerance of the host plant to root diseases as in some cultivated plants (Fitter & Garbaye 1994).

The initial aim of the project was to determine whether the degree of nematode infection found in Ixodia plants under commercial production was similar to that of plants from natural populations found in stringybark forests and to assess if there was a negative correlation between mycorrhizal infection and nematode infection in the forest or commercial environment. However, at the time of the field surveys all commercial plantations had been pulled out in the area of the Adelaide Hills. The only one left was a plantation established at SARDI, Lenswood Research Centre with research purpose. There were few commercial plantations in Nelson, VIC. However, the assessment of these plantations would have increased the cost of the project over the limit of the available funds. Therefore, we decided to survey the experimental plantation and three other natural populations established in eucalyptus forests with different fire history to assess the effect of fire on the potential mycorrhizal and nematode soil infectivity. Fire (together with disturbance) is one of the most important determinants of the establishment of Australian plants (Bell et al. 1993; Bonnet 1993). However, there is no information about its effect on the mycorrhizal infectivity of the soils, or on the population of nematodes associated with native plants.

• Mycorrhizal infection was not affected by cultivation and it may be higher in plants growing on soils exposed to fire. However, more sites should be sampled to test this hypothesis.
• The site without previous fire has only one species of nematodes whereas the two sites with fire history have higher specific diversity (in number of species). It is important to highlight that these are trends and that due to the extreme patchiness of the distribution of the nematodes, more sites should be sampled before confirm any hypotheses.
• Nematode populations were different between the plantation and the wild sites. Meloidogyne and Pratylenchus, present at the plantation, are likely to be of economic importance on cultivated plants and are found worldwide as well as Criconemella, Helicothylenchus and Rotylenchus (Siddiq 2000). In contrast Morulaimus spp, is confined to Australia (Siddiq 2000). Different species of this genus were found associated with several native plants (Austin et al. 1985; McLeod et al. 1994) but, to our knowledge, this is the first report of its association with Ixodia .
• This survey provides with basic information for future work on the effect of fire on the diversity of nematode populations and mycorrhizal infectivity.