Intraspecific Competition and Mating Between Fungal Strains of the Anther Smut Microbotryum Violaceum From the Host Plants Silene Latifolia and S. Dioica

Abstract

Abstract. We studied intraspecific competition and assortative mating between strains of the anther smut fungus Microbotryum violaceum from two of its host species, Silene latifolia and S. dioica. Specifically, we investigated whether strains from allopatric host populations have higher competitive ability on their native host species and show positive assortative mating. In general, strains isolated from S. latifolia outcompeted strains isolated from S. dioica on both host species, but in female hosts, heterotypic dikaryons (i.e., dikaryons composed of a haploid strain originating from S. latifolia and a haploid strain originating from S. dioica) were most successful in competition. Furthermore, the latency period was significantly shorter for heterokaryons that contained at least one strain originating from S. latifolia, compared to heterokaryons that only contained strains originating from S. dioica. The frequencies of conjugations between strains originating from S. latifolia were much higher than conjugation frequencies between strains originating from S. dioica. A significant positive correlation was detected between the relative success of strains in competition and in conjugation, suggesting that success of a strain in competition might be partly determined by its swiftness of mating. In addition, reciprocal differences within heterotypic crosses revealed a significant effect of fungal mating type, with mating type a 1 being the main determinant of mating pace. The observed differences in infection success, conjugation rate, and latency period in favor of strains from S. latifolia relative to strains from S. dioica on both host species are discussed in an evolutionary context of opportunities for the maintenance of differentiation between different formae speciales upon secondary contact.Key words. Competition success, conjugation, formae speciales, mating success, mating type, smut fungus.Received December 19, 2001. Accepted December 26, 2002 Plant parasites are often capable of infecting more than one host species and show intraspecific variation in host use. Understanding the origin and maintenance of such variation and the conditions under which this may lead to host race formation and speciation are central questions in evolutionary biology. Differences in performance of pathogens on different host species and positive assortative mating are expected to play an active role in processes of divergence between strains or in the maintenance of host related differentiation.

Population genetics of ectomycorrhizal fungi: from current knowledge to emerging directions

“…EM taxa deserve more studies combining intersterility tests and evaluation of gene flow by tools of population genetics between potential trans-or inter-continental CBSs. In particular, it is unclear whether dikaryons produced by mating between allopatric haploids are more or less fit than those issuing from mating between sympatric haploids: this question, which is central to gene flow in nature, has received conflicting answers for fungal pathogens (Van Putten et al 2003;James et al 2008) and can be expected to vary among species complexes. Lastly, the distinction between allo-and sympatric CBSs is not always straightforward: Geml et al (2006) found three geographic clades within A. muscaria sensu lato that coexist (perhaps secondarily) in parapatry in Northern America (Geml et al 2009); European CBSs detected in T. scalpturatum complex are also sympatric (Carriconde et al 2008a, 2008b, Jargeat et al 2010.…”

Experimental hybridization and backcrossing reveal forces of reproductive isolation in Microbotryum

“…Generally, most Microbotryum species have high selfing rates [24], thus limiting the probability of interspecific gene flow [26-28]. Mechanisms of pre-mating barriers in the form of assortative mating have been investigated but not found [29,30]. When hybridization is achieved experimentally, it often leads to the production of unbalanced meiotic products with limited growth and reduced infection ability [30].…”

Multiple Infections by the Anther Smut Pathogen Are Frequent and Involve Related Strains

“…The M. violaceum–S. latifolia system is an important biological model for the study of host–parasite evolution [8,15–18]. The fungus sterilizes the hosts by destroying ovaries and replacing pollen with fungal spores that are then dispersed by natural pollinators of the plant (Figure 1).…”

“…latifolia after experimental inoculation by several genotypes of M. violaceum [18,19] and in experimental populations [20], with different fungal genotypes segregating in different stems of the plant. Even more interestingly, experimental inoculations showed that sequential inoculations with more related genotypes led to a higher frequency of multiple infections than sequential inoculation with less related genotypes even though the different strains inoculated alone yielded similar levels of infection [8].…”