GENETICS OF ECTOMYCORRHIZAL SYMBIOSIS .2. FUNGAL VARIABILITY AND HERITABILITY OF ECTOMYCORRHIZAL TRAITS

Seedlings from three open-pollinated families of Pinus elliottii Engel m. var. elliottii were inoculated with 16 dikaryotic progenies of Piso lithus tinctorius (Pers.) Coker and Couch obtained from controlled cro sses between monokaryotic cultures with a tetrapolar mating system. Ni nety days after inoculation mycelial strand growth, number of ectomyco rrhizas and percentage ectomycorrhizal colonization were assessed. Hal f-sib host families and full-sib fungal progenies differed significant ly in all these respects. There were no significant interactions betwe en different genotypes of the two symbionts. The largest proportion of fungal genetic variability was attributable to the non-additive genet ic component. The additive genetic component was significant only for percentage ectomycorrhizal colonization. Mycelial strand growth, numbe r of ectomycorrhizas and percentage colonization had broad-sense herit abilities of 0.19, 0.29 and 0.23, and narrow-sense heritabilities of 0 .03, 0.00 and 0.15 respectively. These results show that selected Piso lithus strains, obtained from specific crosses, could be used with sel ected host plants to improve mycelial strand growth and ectomycorrhiza formation in a combined fungal and tree breeding programme.