Rhizoctonia solani AG8 is a soilborne pathogenic fungus that causes Rhizoctonia bare patch of cereals in the low and medium rainfall zones of Southern and Western regions of Australia. It has a wide range of hosts, including grasses, broadleaf crops, and weeds. Currently, there are no fully effective resistant varieties, and alternative approaches such as in-furrow fungicides and crop rotation with non-cereal crops can partially help reduce the pathogen severity.
In Western Australia (WA), mechanical soil amelioration can enhance crop yields and soil health by addressing issues including subsurface compaction, acidic subsoil, and water-repellent topsoil. Strategic deep tillage techniques, such as soil inversion with mouldboard ploughs, thorough mixing with rotary spaders, and deep ripping are commonly used.
Enhancing soil suppressiveness against soilborne diseases is crucial for sustainable crop production. Application of organic amendments can help enhance disease suppression in soil, possibly by improving the overall diversity and activity of the soil biology. However, the impact of these soil amelioration techniques combined with soil amendments on R. solani AG8 inoculum levels, disease expression, and subsequently yield loss, remains unclear.
Two field experiments were conducted during the 2024 season, at Wongan Hills (WH) and Merredin (ME) DPIRD Research Facilities in WA to investigate the effects of soil amelioration and amendments on the incidence, severity of disease and yield loss caused by one R. solani AG8 isolate in the barley cv. Maximus CL. The study examined the effects of soil amelioration and amendments on the spatial distribution of R. solani AG8 at different soil depths and its relationship with disease expression. A total of 72 plots were included, with 36 serving as non-inoculated controls. Mouldboard ploughing and deep ripping were implemented in combination with two compost amendments, as well as untreated (Nil) plots. Soil samples were collected at different depths (0–40 cm) after sowing and harvest to assess R. solani AG8 inoculum level using PREDICTA®B. Surface soil (0–10 cm) was also analysed for nutrients and microbial catabolic diversity and potential (MCDP) with a customised MicroResp® method. Plant root infection, dry weight and yield loss were also assessed. PREDICTA®B data indicated that R. solani AG8 DNA was predominantly prevalent in the top 0–10 cm of soil. Furthermore, significant differences (p ≤ 0.05) in MCDP were observed across treatments, including amelioration, amendments and inoculum levels. The treatment effects varied between sites. The root disease severity results showed a significant ‘amelioration by inoculum’ interaction at ME (p = 0.021) and significant individual effects of amelioration and inoculum at WH (p ≤ 0.05). No significant differences were observed across treatments for the plant dry weight in either experiment.
The outcomes of this research will offer growers a better understanding of how mechanical soil amelioration and amendments directly contribute to managing R. solani AG8-induced disease impacts in the WA agricultural regions.