Postmeiotic mitosis in the basidia of Suillus granulatus: Implications for population structure and dispersal biology

Abstract

Recent studies indicate that numerous tetrasporic Suillus species have both binucleate and uninucleate spores. If the binucleate spores are homokaryotic, resulting from postmeiotic mitotic divisions in the spores, then the breeding system is primarily determined by the heterothallic mating system of the fungus, be that bipolar or tetrapolar. Alternatively, if the postmeiotic mitoses occur in the basidia prior to nuclear migration, then some proportion of the spores could also be secondarily homothallic (heterokaryotic), this proportion being determined by the pattern of nuclear migration into the spores. The secondary mycelia of many Suillus species do not regularly produce clamp connections, thus complicating the determination of the genetic constituencies of the binucleate spores. In this paper we report the results of genetic analyses using randomly amplified polymorphic DNA markers which suggest that the binucleate spores of Suillus granulatus from eastern North America may result from postmeiotic mitotic divisions in the basidia, prior to nuclear migration into the spores. Binucleate spores of S. granulatus are thus potentially secondarily homothallic. The implications of a functionally diverse mating system, resulting from heterothallic uninucleate spores and secondarily homothallic binucleate spores, are discussed for this cosmopolitan ectomycorrhizal basidiomycete.

Key Words:

• binucleate spores
• RAPD marker analysis
• secondary homothallism
• Suillus granulatus