A screening method for antimitotic and antifungal substances using conidia of Pyricularia oryzae, modification and application to tropical marine fungi

A bioassay method detecting deformations of mycelia germinated from conidia of Pyricularia oryzae P-2b, has been modified to give quantitative estimations. The method was first developed using antimitotic agents which showed characteristic curling effect. Morphological deformations include curling, swelling, hyper-divergency, beads shape and so on, and inhibition of the germination was also observed. For quantitative estimations, indices were introduced for the hyphal growth inhibition and a quantity of conidia in each assay cell and concentration of test solutions were adjusted. Details of the modified method and the application to screening assay of marine fungi isolated in Yap Islands are described. Eight strains of 109 tested showed morphological deformations, and chaetoglobosin A was isolated from the broth filtrate of a strain assigned to Chaetomium sp. This bioassay is a cheap, quick and easy method to be applied to the primary screening for antimitotic and antifungal substances from natural sources.