MORPHOGENESIS IN VERTICILLIUM: EFFECTS OF LIGHT AND ULTRAVIOLET RADIATION ON MICROSCLEROTIA AND MELANIN

Abstract

Delay or total suppression of microsclerotia and melanin formation by light seems general among Verticillium isolates of the microsclerotial form. White, fluorescent light delayed or prevented production of microsclerotia and melanin in 14 of 16 microsclerotial isolates on agar, and in 30 of 31 isolates which produced at least some microsclerotia and melanin in liquid culture. Most isolates produced more melanin and microsclerotia on a complex medium (potato dextrose agar) than in a defined medium (sucrose–nitrate liquid). Near-ultraviolet radiation (peak 3650 Å) suppressed melanin and microsclerotia production in one isolate (H-13) of Verticillium in both liquid and solid media. On agar, colonies of isolate H-13 grew larger in near-UV than in darkness. Isolate H-13 retained its ability to produce melanin and microsclerotia during 21 days suppression by near-UV. On some media, near-UV inhibits all steps in microsclerotia development. On others it inhibits only the final steps. There appear to be at least two places in the chain of events leading to melanin and microsclerotia production where near-UV can inhibit the process.