Prolific production of sclerotia in soil by Rhizoctonia solani anastomosis group (AG) 11 pathogenic on lupin

Rhizoctonia solani anastomosis group (AG) 11 causes serious damping-off and hypocotyl rot of narrow-leafed lupins (Lupinus angustifolius) in the northern grain-belt of Western Australia. R. solani AG-11 produced abundant sclerotia in sand overlaid on potato dextrose agar. Sclerotia were produced in larger numbers in natural Lancelin sand than in Geraldton loamy sand collected from the northern grain-belt of Western Australia. The majority of the sclerotia produced were in >250 to less than or equal to500 mum size range. The germination levels of sclerotia in the first two cycles of drying and germination were not significantly different. Sclerotia still retained 50% germination after four such cycles, indicating that they may have the ability to withstand the climatic cycles of the Mediterranean environment of southwestern Western Australia. The radial growth of the mycelium from sclerotia, however, declined with each drying and germination cycle. Inoculum potential of the pathogen increased with the size of sclerotia resulting in more severe lupin hypocotyl rot with larger sclerotia. The number of sclerotia produced in soil increased with increasing density of lupin seedlings. The results also indicate that R. solani AG-11 can produce sclerotia on infected plant tissues as well as in soil. This is the first report of the prolific production of sclerotia by AG-11 and their significant role in infection of lupins in soil in Western Australia.