C. E. Pankhurst

USE OF FATTY ACIDS FOR IDENTIFICATION OF AM FUNGI AND ESTIMATION OF THE BIOMASS OF AM SPORES IN SOIL

Abstract Fatty acid methyl ester (FAME) analysis performed on the spores of four arbuscular mycorrhizal (AM) fungi (Glomus coronatum, Glomus mosseae, Gigaspora margarita and Scutellospora calospora) showed 16:1ω5c to be the dominant fatty acid present. In addition, spores of Gi. margarita contained large quantities of 18:1ω9c and three 20-C fatty acids (20:1ω9c, 20:2ω6c and 22:1ω9c) that were not present in the spores of the other two species. Addition of a known number of spores of each AM species to soil demonstrated that the spore fatty acids could be readily detected and quantified against the background of soil fatty acids. Addition of different combinations and quantities of spores to soil gave the expected ratios of the marker fatty acids in the soil FAME profiles. The results confirm the use of 16:1ω5c as a marker fatty acid for AM fungi in controlled environments and suggest that 18:1ω9c, 20:1ω9c, 20:2ω6c and 22:1ω9c could be used as possible markers for the detection of Gi. margarita.

Effect of tillage and stubble management on chemical and microbiological properties and the development of suppression towards cereal root disease in soils from two sites in NSW, Australia

Different tillage and stubble management practices were compared at two sites in New South Wales, Australia, to determine their effect on soil chemical and microbiological properties and the development of suppression towards Gaeumannomyces graminis var. tritici (Ggt) and Rhizoctonia solani. At one site (Harden), the management practices were direct-drilling of crops with stubble retained (DD) and conventional sowing of crops with stubble burnt (CC) for 6 years prior to sampling. At the second site (Cowra), a stubble incorporated (SI) treatment (SI with a single cultivation prior to sowing) was compared with DD and CC treatments and the practices had been in place for 16 years. By comparing the difference in plant growth in γ-irradiated and natural (unsterilised) soil in the presence of added Ggt and Rhizoctonia inoculum, evidence of suppression towards Ggt was observed in soil from both the sites. The suppression was greater in the DD compared to the CC soils. This was associated with higher levels of organic C and total N in the DD compared to the CC soils at Cowra and with higher microbial biomass, CO2 respiration and populations of fungi (including cellulolytic fungi) in the DD compared to the CC soils at both the sites. There was less evidence of suppression towards Rhizoctonia but higher disease levels were obtained from the added Rhizoctonia inoculum in the CC soil compared to the DD soil at both the sites. The results showed that the DD practice augmented a build-up of organic C and microbial biomass in the surface soil and increased its suppressiveness towards two introduced fungal pathogens.

Influence of tillage and crop rotation on the epidemiology of Pythium infections of wheat in a red-brown earth of South Australia

Abstract Propagules of Pythium spp were concentrated in the top 10 cm and associated with soil aggregates >250 μm and 80% of isolates recovered from wheat seed and wheat roots.

Amendments of sugarcane trash induce suppressiveness to plant-parasitic nematodes in a sugarcane soil

In a field experiment at Bundaberg, Queensland, sugarcane trash was incorporated into soil with, or without, additional nitrogen supplied as either soybean residue or ammonium nitrate. The carbon inputs from plant material (lOtC/ha) were the same in all treatments, while both plus-nitrogen treatments received the same amount of nitrogen (210kgN/ha). Sugarcane was planted 23 weeks after amendments were incorporated, and 24 weeks later there were 95%fewer lesion nematodes (Pratylenchus zeae) in roots growing in amended soil than in roots from the unamended control. Populations of P. zeae and Tylenchorhynchus annulatus in amended soil were reduced by 85%and 71%, respectively. Bioassays in which forage sorghum was planted in soil collected during the experiment and inoculated with P. zeae indicated that amended soils were suppressive to the nematode at 20 weeks but not after 47 weeks. All amendments increased readily oxidisable carbon, microbial biomass, microbial activity and numbers of free-living nematodes, but had no effect on known predators of nematodes (i.e. dorylaimid and mononchid nematodes and three naturally occurring species of nematode-trapping fungi, Arthrobotrys conoides, A. thaumasium and Drechslerella dactyloides). However, an unidentified predatory fungus was found only in soil amended with sugarcane trash and was possibly involved in the suppression of plant-parasitic nematodes.