The Mechanism of Heterokaryotic Growth in VERTICILLIUM DAHLIAE.

Heterokaryons of Verticillium dahliae, forced between complementary auxotrophs, were stable at 21 degrees and resembled the wild type morphologically. In such heterokaryons the hyphal cells were predominantly uninucleate, and no nuclear migration from cell to cell was observed. Heterokaryosis was apparently confined to binucleate, interhyphal, anastomosed cells that arose 1-2 mm behind the colony front. Such anastomosed cells thereby fed and maintained large homokaryotic areas including the colony edge. This stable mosaic colony is in sharp contrast to the heterokaryon of Neurospora.-Heterokaryons of V. dahliae cannot continue growth at 30 degrees because the high temperature prevents hyphal anastomosis. Heterozygous diploids sector out from heterokaryons after 8-12 days at 30 degrees . Interhyphal anastomosed cells are apparently the site of karyogamy.