VIEW ARTICLE

Studies on Heterokaryosis and Virulence of Rhizoctonia solani. Hasan A. Bolkan, Department of Plant Pathology, University of California, Davis 95616, Present address of senior author: Department of Plant Pathology, Massey University, Palmerston North, New Zealand; Edward E. Butler, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 64:513-522. Accepted for publication 25 October 1973. DOI: 10.1094/Phyto-64-513.

Heterokaryotic field isolates of Rhizoctonia solani Kuehn [=Thanatephorus cucumeris (Frank) Donk] ('Praticola type' AG-4) interacted with each other to produce new heterokaryons. Naturally occurring genetic markers were employed to show the occurrence of heterokaryosis. The same genetic markers were used to obtain evidence for the formation of heterokaryons between homokaryons. Heterokaryons synthesized from field isolates were avirulent; whereas, heterokaryons synthesized from homokaryons were either as virulent as the parent isolates or were less virulent than the parent isolate with the higher virulence. The basidiospore progeny of all synthesized heterokaryons tested yielded a high percentage of highly virulent cultures even if one parent was weakly virulent. Virulence of Rhizoctonia solani appears to be recessive and is determined by multiple factors; avirulence is determined by the cumulative effect of dominant genes.