[20] Strain CBS 346.36 yielded low numbers of zygospores with members of both varieties; zygospore production between members of the varieties arrhizus and delemar have been described previously.[15, 20] Using the arrhizus tester strain CBS 346.36

contrasts with the following delemar strains were positive: CBS 285.55,[15] CBS 329.47,[15, 19] NRRL 1548, and NRRL 1550.[20] buy Metformin All strains belong to the basal ITS type C of Abe et al. [19] which also holds true for the two positive delemar strains in the present study (CBS 372.63 and CBS 131498) (Fig. 2). Thus far no positive mating has been reported within the variety delemar, which can perhaps be explained by the exclusive use of arrhizus tester strains in previous studies[15, 20]; all mating in R. arrhizus is dependent on the highly competent strain CBS 346.36. The absence of matings between variety arrhizus and the ITS type D of var. delemar might be interpreted as a partial mating barrier between BMN-673 var. arrhizus and type D of var. delemar, while var. arrhizus and delemar type C are still compatible. To our knowledge,

germination of zygospores has never been shown in Rhizopus arrhizus. Therefore biological species boundaries of the species are based only on the presence of zygospores as an indication of the absence of a mating barrier; this is an established method for species recognition in the Mucorales.[15] Gryganskyi et al. [20] argued against this method because Schipper et al. [34] claimed to have observed zygospore production between different Rhizopus species. However, the two species studied by these authors, R. microsporus Venetoclax datasheet and R. rhizopodiformis are now synonymized in R. microsporus.[22] Recent studies on species recognition in other members of the Mucorales [35, 36] have demonstrated that interspecific zygospores can be differentiated from their intraspecific counterparts by their size, color,

ornamentation and number. However, the low numbers of mature zygospores obtained in our study did not allow such a differentiation. In one of the positive matings between var. arrhizus and var. delemar small, pale colored zygospores were formed. The zygospores of the other two matings are in the range of 120–140 (180) μm as given by other authors.[15, 37] However, the two zygospores formed within the var. arrhizus were larger. Schipper [15] did not mention any differences in the number and the characters of the zygospores produced between the varieties. In a study on the mating locus of R. arrhizus, Gryganskyi et al. [20] observed a lower number of zygospores in matings between var. arrhizus and var. delemar than in matings within var. arrhizus. The percentage of fully developed zygospores was higher in mating within var. arrhizus (A. Gryganskyi, pers. comm.).