Phyllosphere yeasts antagonize penetration from appressoria and subsequent infection of maize leaves by Colletotrichum graminicola

Abstract

In growth cabinet experiments, the common phyllosphere yeasts Sporobolomyces roseus and Cryptococcus laurentii var. flavescens were sprayed as a mixture (1:1) onto the fourth leaves of maize plants (Zea mays) two-three days prior to inoculation with Colletotrichum graminicola. In four experiments the average yeast population of the treated leaves at the time of pathogen inoculation varied between 5 x 10 4 and 8 x l0 s cells cm - 2 leaf, whereas on the untreated leaves the yeast population varied from < 103 to 10 4 cells cm - 2 leaf. The yeasts reduced lesion density and necrosis from C. graminicola infection by approximately 50%. Contrary to findings with other necrotrophic pathogens, conidial germination, superficial mycelial growth and appressorium formation were not affected. Instead, the reduction of infection could only be explained by a reduced number of penetrations from the normally formed appressoria, a site of interaction not previously recorded.