Heterokaryon self-incompatibility in Gibberella fujikuroi ( Fusarium moniliforme)

Abstract

Some isolates of Gibberella fujikuroi were unable to form a heterokaryon when complementary mutants were paired. The basis of this heterokaryon self-incompatibility (HSI) phenotype in two wild-collected strains was examined. The structural basis of HSI was determined microscopically by counting hyphal fusions. The HSI strains averaged 0·2 and 1·1 hyphal fusions per mm2 compared with 6·9 and 8·1 fusions per mm2 for heterokaryon self-compatible (HSC) strains (which form heterokaryons normally). The physiological basis of HSI was examined by observing heterokaryon formation by HSC and HSI strains on media containing compounds known to alter hyphal branching and/or hyphal fusion in other fungi. None of the compounds tested altered the ability of either the HSC or the HSI strains to form heterokaryons. Meiotic progeny of a cross between an HSC strain and an HSI strain segregated 1:1 for the HSI phenotype, suggesting that this trait is under the control of a single nuclear gene. Female infertility co-segregated with HSI among the cross progeny. We concluded that the HSI phenotype results from a mutation at a nuclear gene designated hsil that governs the ability of the fungal hyphae to anastomose.