THE MECHANISM OF HETEROKARYOTIC GROWTH IN VERTICILLIUM DAHLIAE

John E. Puhalla ¹ and John E. Mayfield ¹

¹ U.S. Department of Agriculture, Agricultural Research Service, Southern Region, Oklahoma-Texas Area, National Cotton Pathology Research Laboratory, P. O. Drawer JF, College Station, Texas 77840

Heterokaryons of Verticillium dahliae, forced between complementary auxotrophs, were stable at 21° 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° because the high temperature prevents hyphal anastomosis. Heterozygous diploids sector out from heterokaryons after 8-12 days at 30°. Interhyphal anastomosed cells are apparently the site of karyogamy.