Sporobolomyces roseus Kluyver et Van Niel developed on green wheat leaves equally well in simulated dew as under conditions of high ambient relative humidity. Relative humidities varying from 65–95% had differential effects on the Sporobolomyces population. At 65% r.h. the population decreased but resumed growth when exposed to 95% r.h. Under optimum humidity the population reached a steady state at densities between 5 × 103 and 104 cells/cm2. Spraying leaves with nutrients resulted in additional growth of the population, reaching a steady state again within 10 days, at a density of ca. 5 × 105 cells/cm2. Nutrients were equally available under dew as under high r.h. Sporobolomyces could only profit from the nutrients if exposed to relative humidities of at least 90% during part of the day. Susceptibility to low r.h. and the ability to consume exogenous nutrients were similar in populations of individual cells and established colonies.
A temperature of 32 °C during part of the day interfered with the growth rate but was not as detrimental as earlier field observations suggested.