STRAIN VARIATION IN TOLERANCE OF WATER-STRESS BY IDRIELLA-(MICRODOCHIUM)-BOLLEYI, A BIOCONTROL AGENT OF CEREAL ROOT AND STEM BASE PATHOGENS

Three randomly chosen isolates of Idriella bolleyi differed markedly i n tolerance of water stress down to - 5 MPa in vitro. The differences were seen with respect to osmotic potential of media adjusted with KCl or matric potential of media adjusted with polyethylene glycol 8000. They were consistent when assessed by linear extension of colonies, sp ore germination, biomass production in liquid culture and sporulation in liquid culture. In comparative tests, one strain of I. bolleyi show ed similar stress tolerance to that of Fusarium culmorum, noted as a p athogen of cereals in dry conditions, whereas another strain of I. bol leyi showed low tolerance equivalent to that of the take-all fungus Ga eumannomyces graminis and a Phialophora sp. from maize. The extreme va riation in water stress tolerance of I. bolleyi might be used to selec t strains for biocontrol of different cereal root- and foot-rot pathog ens or strains might be combined in seed-applied inocula for consisten cy of biocontrol in different site or seasonal conditions.