Temperature and water potential effects on growth and pathogenicity of Rhizoctonia solani AG-11 to lupin

Rhizoctonia solani anastomosis group (AG) 11 causes serious damping-off and hypocotyl rot of lupins (Lupinus angustifolius L.) and is wide-spread in the northern grain-belt of Western Australia. We compared growth of AG-11 to AG-8, which causes bare-patch of grain crops including lupin. AG-11 grew significantly faster than AG-8 on potato dextrose agar (PDA) at several temperatures (10, 15, 20, 25, or 30 degrees C) and also grew best within the pH range of 4-7. Growth of AG-8 was best at pH 7. There was no difference in the linear growth in soil of both AGs at 10 degrees C, but AG-11 grew at a significantly faster rate at 20 degrees C: Reduction in growth of AG-11 on osmotically adjusted PDA at temperatures between 10 and 30 degrees C was more pronounced than that of AG-8. AG-11 caused very little lupin pre-emergence damping-off and hypocotyl rot at 10 degrees C, and most severe hypocotyl rot was recorded at 20 and 25 degrees C. Severity of hypocotyl rot caused by AG-11 at soil water potentials of -0.1, -0.07, and -0.05 MPa was higher than at -0.03 MPa. It appears that AG-11 is well suited to the environmental conditions of the relatively small area in Western Australia from which it is readily isolated.