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

Abstract

The host range of Ustilago bullata includes important forage crop and grassy weed species that germinate and establish under a wide range of temperature and salinity conditions. Previously, two subgroups (pathotypes 1 and 2) were identified from collections across the prairies, which had no host species in common. When germination of teliospores from these collections was assessed, the two pathotypes differed substantially in the stage of development reached at 20 h of incubation. This study was initiated to determine if differences between the pathotypes were consistent and if they corresponded with factors affecting the host environment during seed germination and establishment. Individual teliospores from representative collections of each 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 development and sporidial doubling was similar for both pathotypes. Four teliospore collections of pathotype 1 and six of pathotype 2 were assessed for percentage germination and rate of growth on potato dextrose agar (PDA) at temperatures from 15 to 30°C and osmotic potentials from -5 to -85 bars (1 bar = 100 kPa) on PDA amended with NaCl. Teliospore germination in pathotype 1 was more tolerant of high and low temperatures and high osmotic potentials than pathotype 2. These results are discussed in relation to the tolerance of U. bullata pathotypes to extremes of temperature and salinity and their adaptation to their respective host species in nature.