1985 Volume 51 Issue 2 Pages 159-167
Pythium spinosum, P. irregulare and P. sylvaticum were frequently isolated from diseased rice seedlings with symptom of root and stem rot. The disease was favored by low temperature at the early growth stage of rice seedlings grown in four different solis in nursery flats. In pathogenicity tests, all of the three Pythium species were strongly pathogenic to rice seedlings at emergence and produced symptoms similar to those characteristically seen in nursery flats, but were nonpathogenic to rice seedlings later than the first leaf stage. The severity of damping-off caused by the three Pythium species increased under low temperature of emergence time and on soil with a pH of 6. The additional pathogenicity tests also indicated that five other species (P. aphanidermatum, P. myriotylum, P. splendens, P. ultimum and P. vexans) from the different sources significantly reduced rice seedling emergence. From these results, P. spinosum, P. irregulare and P. sylvaticum are considered to be the causal agents of damping-off of rice seedlings grown in nursery flats. In addition, some other Pythium species appear to be involved in the rice seedling disease in nursery flats.