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EFFECT OF SOIL TYPES ON RHIZOCTONIA ROOT ROT OF WHEAT
EFFECT OF SOIL TYPES ON RHIZOCTONIA ROOT ROT OF WHEAT J. S. GILL, K. SIVASITHAPARAM AND K. R. J. SMET-FEM Dept. of Soil Science and Plant Nutrition, University of Western Australia, Nedlands, WA, 6907, Australia Background and Objectives Rhizoctonia bare patch disease caused by Rhizoetonia solani Kuhn (anastomosis group 8) is the major problem in the no till farming system in southern Australia. The problem of this disease is more severe in sandy soils in Australia but in the USA Rhizoctonia root rot is also a problem in loamy and heavy soils. De beer (1965) reported that in South Australia there were eight times as many patches in a light soil compared to a heavier soil nearby. The aim of this glasshouse study was to investigate the effect of physical properties of soils associated with different soil types on root growth of wheat plants and the severity of disease. Material and Methods Bulk soil samples were collected from three sites having different texture (sandy, loamy and clay). Soils were air dried sieved through 2mm sieve and analyzed for their physical and chemical properties. Twelve PVC pipe pots (8.7 cm diam. and 40 cm deep) were filled with each soil type for the two inoculation treatments (inoculated and control) with four replications and remaining four pots were sacrificed to measure root growth during the experiment. Twenty-one days after applying the treatments, five wheat seeds were sown into each pot. In a second experiment nine pots were made from 8.7-cm diam. PVC pipe cut into 2.5 tall pieces and sixteen pieces were stuck together with PVC tape. These pots each filled with one of the three soils were used to measure soil moisture levels and root penetration resistance at various depths during the experiment. Growth of fungus in soil was studied in seedling trays (40cm x 30 cm 10cm) using toothpicks as bait. Pots were watered with 4OmI of water every second day to keep the soil near field capacity. Plants were harvested 24 days after sowing and root and shoot growth measured. Results and conclusions The reduction in root and shoot biomass production following inoculation with AG-8 is more in sand than in loam or clay soils. Dry root weight of wheat in sand, loam and clay soil inoculated with AG-8 was 91% 55% and 28% less than in uninoculated. There was better moisture retention in loam and clay soil as compared to sand in the upper 4-5 cm. The root penetration resistance was more in loam and clay than sand. Root growth in the uninoculated soil column was faster in sand than in the loam and clay soils. Radial growth of the pathogen was very fast in sand in comparison to loam and clay soils, this behaviour may be related to more sever disease in sand as compared to loam or clay soil. Reference 1. De Beer, J. F. 1965. Ph.D. Thesis. Study on the ecology of Rhizoctonia solani Kuhn. University of Adelaide, S.A., Australia