Manipulation of yeasts on field-grown wheat leaves and their antagonistic effect on Cochliobolus sativus and Septoria nodorum

Abstract

Different methods were compared to enhance the growth of the saprophytic mycoflora in field-grown wheat leaves to a population density high enough to be antagonistic to Septoria nodorum Berk. and Cochliobolus sativus (Ito & Kuribayashi) Drechsler ex Dastur. Cell suspensions of the common phyllosphere yeasts Sporobolotnyces roseus Kluyver & Van Niel and Cryptococcus laurentii var. flavescens Lodder & Van Rij, with or without nutrients, nutrients alone, or water, were sprayed on third leaves or on just unfolded flag leaves (leaf 1). Increase of population densities, from 100 to 10000 cells/cm2 leaf surface, within a week was only observed in the treatment with yeasts in combination with 2 % sucrose and o.1 % yeast extract; other treatments gave densities that did not differ much from those of water-sprayed leaves, remaining below 1000 cells/cm2. After the first treatment the flag leaves were inoculated at intervals with 5. nodorum or C. sativus. During the first 3 weeks, infection by both pathogens was about 50 % less on flag leaves with an artificially enhanced mycoflora than on the water-sprayed control leaves. Later on, this difference disappeared because the saprophytes on the control leaves had reached a density of c. 20 000 propagules/cm2, providing an antagonistic potential apparently equal to that of the manipulated mycoflora.