Evidence for recombination and segregation of virulence to pine in a hybrid cross between Gibberella circinata and G. subglutinans

Two species associated with the Gibberella fujikuroi species complex, G. circinata (the cause of pitch canker in pines) and G. subglutinans (avirulent on pine), were found to have limited interfertility in hybrid crosses. MAT idiomorphs, polymorphisms in the histone H3 gene, vegetative compatibility, and virulence phenotypes were used to verify recombination. The MAT idiomorphs appeared to be assorting independently, but the histone H3 haplotype was disproportionately represented by that of the G. subglutinans parent. Ninety-eight percent (45/46) of the progeny tested were vegetatively incompatible with both parents. All F1 progeny were avirulent to pine, but a wide range of virulence was restored through a backcross to the virulent parent (G. circinata). Attempts at hybrid crosses using other isolate combinations were rarely successful (1/26). This limited interfertility supports retention of G. circinata and G. subglutinans as separate species, but offers opportunities to characterize the inheritance of virulence to pine.