INFECTION OF ADVENTITIOUS ROOTS OF AGROSTIS-PALUSTRIS BY PYTHIUM SPECIES AT DIFFERENT TEMPERATURE REGIMES

Pathogenicity of several isolates of Pythium species to the adventitious roots of Agrostis palustris was evaluated at high (35:24, light:dark) and low (24:13 degrees C, light:dark) temperature regimes. Isolates of P. graminicola-arrhenomanes, P. rostratum, P. torulosum, P. vanterpoolii, and one unclassified species were evaluated. All isolates of all species infected roots. Some isolates of P. graminicola-arrhenomanes (PGA-5), P. torulosum (PT-1, PT-2, PT-3, PT-5), P. vanterpoolii (PV-1), and an unclassified species (UP-I) infected roots and decreased dry weight at both the high and low temperature regimes. Other isolates of P. graminicola-arrhenomanes (PGA-1, PGA-2, PGA-4, PGA-6, PGA-7) and P. torulosurn (PT-4) infected roots and decreased dry weight only at the high temperatures. Isolate PGA-7 of P. graminicola-arrhenomanes also stimulated plant growth at low temperatures. The remaining isolates of P. graminicola-arrhenomanes (PGA-3), P. rostratum (PR-1), and P. vanterpoolii (PV-2) infected roots and decreased dry weight only at the low temperatures. Infection of roots was limited to root hairs, root tips, and epidermal and cortical tissues. The observations are discussed relative to the function of Pythium species as minor root pathogens and their potential function in disease complexes.