Abstract
A weakly virulent Fusarium sp. strain HPF-1 isolated from a Cymbidium leaf was suppressive to the occurrence of Cymbidium yellow spot on small plants of Cymbidium spp. Fusarium sp. strain HPF-1 was weakly virulent to Zygopetalum spp. and Cymbidium spp., and avirulent to rice, strawberry and asparagus. The strain caused small, irregular dark brown spots on Cymbidium spp. that were distinguishable with the naked eye, but it caused no damage to the production of Cymbidium. Yellow spot disease on Cymbidium spp. was suppressed by pre-inoculation with some other pathogenic Fusarium spp., but not by pre-inoculation with nonpathogenic Fusarium moniliforme. Strain HPF-1 was the most suppressive among the pathogenic Fusarium spp. tested. Spraying with a bud-cell suspension at a concentration of 105cells/ml was sufficient to reduce yellow spots. The suppressive effect was seen by 3 days after spraying and continued throughout the growing period. Strain HPF-1 spread over new leaves and lead leaves by systemically infecting the plant. An effective control of Cymbidium yellow spot can thus be made by pre-infection with strain HPF-1 of small mericloned plants.
