The importance of water potential range tolerance as a limiting factor onTrichodermaspp. biocontrol ofSclerotinia sclerotiorum

Abstract

Biological control of fungal phytopathogens is often more variable in efficacy compared with disease suppression achieved by conventional pesticide use. Matching the environmental range of a potential biocontrol agent with that of the target phytopathogen is necessary if consistent disease suppression is to be achieved under field conditions. Strains of Trichoderma that could parasitise sclerotia of Sclerotinia sclerotiorum had their spore germination and mycelial growth (five strains) and ability to parasitise sclerotia (two strains) tested under a range of water potentials under laboratory conditions. Relative mycelial growth and germination of all strains decreased with decreasing osmotic and matric potentials, with matric potential having a greater impact on growth and germination over the range examined. Trichoderma harzianum LU698 mycelial growth was the least affected by decreasing osmotic potential than the other isolates, and Trichoderma atroviride LU141 growth least affected by decreasing matric potential. The germination of LU698 and LU144 was also generally less affected by decreasing osmotic potential, although generally decreasing matric potential had the greatest affect on the germination of LU698 along with T. atroviride LU132. Soil treatments of LU698 and Trichoderma asperellum LU697 reduced sclerotial viability in all but the lowest soil water potential tested, with LU698 being most effective at −0.1 and −0.3 MPa after 28 days and LU697 most effective at −0.01 and −1.5 MPa after 28 days. We conclude that differences in the tolerance of potential biocontrol agents to changing water potential is an important experimental factor to consider when assaying biocontrol or making predictions of biocontrol efficacy in the field.