VIEW ARTICLE

Genetics

The Role of the H Locus in Heterokaryosis in Rhizoctonia solani. J. E. Puhalla, Research Geneticist, Agricultural Research Service, U.S. Department of Agriculture, National Cotton Pathology Research Laboratory, Drawer JF, College Station, Texas 77840; W. W. Carter, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, National Cotton Pathology Research Laboratory, Drawer JF, College Station, Texas 77840, Present address: Market Quality Research Laboratory, Box 267, Weslaco, Texas 78596. Phytopathology 66:1348-1353. Accepted for publication 18 May 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1348.

Rhizoctonia solani grew as button-like colonies on a medium containing L-sorbose and polygalacturonic acid. Consequently, three auxotrophs were detected and isolated from basidiospores irradiated with ultraviolet light. These were used to determine the function of the two closely linked genes (together called H factor) that control heterokaryon formation in R. solani. When different monoauxotrophs were paired on minimal agar, strains with either the same H factor (H= ) or different H factors (H ≠) yielded heterokaryons. The H ≠ heterokaryons were considerably more stable than the H= heterokaryons. When fruited, H ≠ heterokaryons showed strict outcrossing between the two paired strains. The H= heterokaryons yielded progeny from both outcrossed and selfed basidia. The H locus, therefore, functions like incompatibility loci in other basidiomycetes, and controls the stability and outbreeding of the heterokaryon.