Uneven Distribution of Mating‐Type Alleles Among Togninia minima Isolates, One of the Causal Agents of Leaf Stripe Disease on Grapevines in Northwest Iran

Abstract

Togninia minima is the main fungal species associated with grapevine leaf stripe disease worldwide. This species is mainly known from its asexual state in nature; nevertheless, a biallelic heterothallic mating strategy has been confirmed for this species based on in vitro crossing studies. There are no data available on the incidence of an active sexual cycle within the populations of this species in many grapevine-producing countries as well as Iran. The possibility of a clandestine sexual cycle within the Iranian isolates of T. minima was evaluated by analysing the distribution and frequency of the mating-type alleles on a microspatial and a macrogeographical scales. Towards this aim, a total of 90 T. minima isolates were recovered from grapevines with esca disease from the vineyards in north and north-western Iran. A multiplex PCR method previously designed by authors was applied for simultaneous identification and determination of the mating-type alleles in T. minima populations. The results on the screening of mating-type alleles using multiplex PCR method revealed the mating-type identity of 77 isolates as Mat1-2 and 23 isolates as Mat1-1. Our results showed that both Mat1-1 and Mat1-2 isolates are present in a single vineyard and even on single vines. The distribution of mating-type alleles in the sampled area skewed from the 1 : 1 ratio (77 : 23); however, co-occurrence of both mating types in a single vineyard and even on single vines is suggestive for the presence of an active sexual cycle for T. minima in north-western Iran.

The rate of facultative sex governs the number of expected mating types in isogamous species

“…In Chlamydomonas, bouts of asexuality frequently sweep single mating types to fixation [4], as a result of hitch-hiking on beneficial mutations and asexuality maintaining the linkage. Similar dynamics occur in fungi [46,63], where amongst pathogenic species [8,39,49] there is also evidence for fitness differences between mating type alleles [14].…”