Germination of individual microsclerotia ofVerticillium dahliae

Viability of individual microsclerotia (MS) ofVerticillium dahliae of different sizes (<37 μm, 37–74 μm, 75–125 μm) was studied throughout repeated transfers in a moist chamber. Germination rate and number of germinating hyphae were positively correlated with the size of the MS. After 13 transfers, some MS of the above size ranges still germinated; some MS germinated until they lost their viability; others did not germinate for a while and then started germinating again. The length of germination time of MS on a synthetic medium was 8 days, with slight differences between MS originating from soil and those from one-year-old potato stems. Fresh MS from potato stems, however, completed their germination after 36 hours. Fewer MS (size <37 μm) were isolated from soil by the wet-sieving than by the dry-sieving technique. This finding and microscopic observations lend further support to the assumption that MS exist in soil partly in clusters.