Genetic variation of nitrate reductase activity in mono- and dikaryotic populations of the ectomycorrhizal fungus, Hebeloma cylindrosporum Romagnési.

Intraspecific variability in the activity of nitrate reductase (NR) has been studied in the ectomycorrhizal fungus Hebeloma cylindrosporum Romagnési at the interstrain and intrastrain levels, the latter within a population of 11 wild dikaryotic strains collected in'Les Landes'(SW France) at four locations less than 100 km away from one another. An attempt was made to determine whether variability within the monokaryotic and dikaryotic progeny of the HC1 fruiting strain could be used as a basis for an improvement programme involving breeding between selected monokaryons. The NR activity of the wild strains ranged from 201 to 700 nmol NO synthesized h mg fungal protein whilst that of 20 sib-monokaryons (5 per mating type) of the HCl strain varied from 51 to 510 nmol NO synthesized h mg fungal protein. Fifty controlled dikaryotic myeclia were obtained from all the compatible fusions with these monokaryons. In these, variation of NR activity was of the same order of magnitude as that recorded at the interstrain level, ranging from 72 to 689 nmol NO synthesized h rag fungal protein. Analysis of the components of the variation of NR activity in these controlled dikaryons demonstrated that the additive component of this variation accounted for less than 1 % of the total observed variation. The NR activity of any one controlled dikaryon could not therefore be predicted from the activity of its parental monokaryons However 14 of the 50 controlled dikaryons e8hibited an NR activity higher than that of the HCl parental dikaryon. These results indicate that breeding with sib-monokaryons can be used as a basis for an improvement programme of NR activity in this ectomycorrhizal Basidiomycete.