Role of light, temperature, and method of propagation in cultural variability of Fusarium oxysporum f. sp. apii race 2

Development of mycelial cultures of wild-type Fusarium oxysporum f. sp. apii race 2 (FOA2) isolates was inhibited under incubation with 12- or 24-h photoperiods on chloramphenicol-amended potato dextrose agar (CPDA) plates. Development of pionnotal cultures from FOA2 isolates was favored under these conditions. Darkness and diffuse sunlight favored development of mycelial cultures. Transfer of mycelial cultures from dark to light resulted in cultures with an inner mycelial zone and an outer pionnotal zone. Pionnotal cultures produced in light assumed a dual morphology (inner pionnotal zone and an outer mycelial zone) after transfer to the dark and subsequent growth in the dark. Single microconidial transfers from 1-2-, 6-, 12-, and 24-day-old pionnotal cultures to fresh CPDA plates and growth in darkness resulted in mycelial cultures. Incubation temperature did not affect overall cultural variability. Transfer of single microconidia to CPDA plates followed by incubation in darkness reduced cultural variability more than either single microconidial transfer with light incubation or mycelial plug transfer with dark incubation.