Pathotypes of Ustilago bullata differ in response to temperature and salinity conditions during spore germination

The host range of Ustilago bullata includes important forage crop and grass y weed species that germinate and establish under a wide range of temperatu re and salinity conditions. Previously, two subgroups (pathotypes 1 and 2) were identified from collections across the prairies, which had no host spe cies in common. When germination of teliospores from these collections was assessed, the two pathotypes differed substantially in the stage of develop ment reached at 20 h of incubation. This study was initiated to determine i f differences between the pathotypes were consistent and if they correspond ed with factors affecting the host environment during seed germination and establishment. Individual teliospores from representative collections of ea ch pathotype were monitored throughout the germination process over a 16-h period. Teliospores of pathotype 1 initiated germination much more quickly than those of pathotype 2, but the time required for metabasidial developme nt and sporidial doubling was similar for both pathotypes. Four teliospore collections of pathotype 1 and six of pathotype 2 were assessed for percent age germination and rate of growth on potato dextrose agar (PDA) at tempera tures from 15 to 30 degrees C and osmotic potentials from -5 to -85 bars (1 bar = 100 kPa) on PDA amended with NaCl. Teliospore germination in pathoty pe 1 was more tolerant of high and low temperatures and high osmotic potent ials than pathotype 2. These results are discussed in relation to the toler ance of U. bullata pathotypes to extremes of temperature and salinity and t heir adaptation to their respective host species in nature.