Abstract
Two self-inhibitors were found in germination fluids of uredospores of Puccinia coronata var. avenae. Major one identified in the previous paper as methyl cis-3, 4-dimethoxycinnamate (MDC) was released in the germination fluid as soon as the uredospores were floated on water and mostly liberated from uredospores within 40min, before protrusion of germ tubes. On the other hand, a minor inhibitor (unidentified) became detectable in the germination fluid when germ tubes had mostly germinated, and increased thereafter. MDC strongly inhibited the germination, but exhibited little effect on the germ tube growth and differentiation of infection structures at the concentration giving complete inhibition of germination. MDC decreased its activity in the presence of sodium pelargonate. Characteristic behaviors of germination and infection structure formation of P. coronata var. avenae were different in various respects from those of rust fungi producing MDC, but rather resembled those of Puccinia graminis var. tritici which produced another self-inhibitor, methyl cis-ferulate. It is proposed that the hypothesis that rust species producing the same self-inhibitors are closely related to each other in the characteristics of germination and differentiation should be reexamined.
