Interspecific variability of indole-3-acetic acid (IAA)-synthesizing activity was examined within 12 wild strains of different Hebeloma species. Interstrain variability was studied within 11 wild strains of Hebeloma cylindrosporum (Romagnési) and intrastrain variability was considered by using 20 homokaryotic and 50 controlled dikaryotic mycelia belonging to the progeny of one laboratory fruiting strain of this species.
The range of variation of IAA-synthesizing activity was of the same order of magnitude within the four groups considered. No correlation was detected between, on one hand, the IAA-synthesizing activity of the mycelia and, on the other hand, their taxonomic position, their geographic origin, or their host plant.
Within the progeny of one H. cylindrosporum fruiting strain, 15 of the 50 controlled dikaryons presented an activity higher than that of the original dikaryon. The variation among dikaryons could not be strictly related to the variation in parental homokaryons, indicating that genetic control of this activity probably involves a nonadditive component. Significant additive and nonadditive components of the genetic variation were detected, each of them representing about 50% of the total variation. The nonadditive heritable component could not be explained by a model involving only dominance.