Change of Mating Type in an EU1 Lineage Isolate of Phytophthora ramorum

Abstract

All Phytophthora ramorum EU1 lineage isolates tested are of A1 mating type, except for three rare isolates from 2002 to 2003 from Belgium, which were originally assigned the A2 mating type. In one of these isolates (2338), a switch from A2 to A1 mating type was observed in 2006. This observation initiated a larger study in which all cultures and subcultures of the original three EU1 A2 isolates, maintained in three laboratories under different storage conditions, were checked for mating type change. The A2 to A1 mating type switch was observed in four of seven independently maintained isolates that were derived from isolate 2338 in two laboratories, using different transfer regimes and storage conditions. Following the mating type switch to A1 in these four derived isolates, no reversion back to A2 mating was observed, even after up to 5 years of additional isolate maintenance and several more subculturing events. The three other isolates that were derived from isolate 2338 as well as the other EU1 A2 isolates collected in 2002 and 2003 and stored in the same conditions did not display such mating type change. The potential causes of the mating type conversions as well as their epidemiological implications are discussed.

The Destructive Tree Pathogen Phytophthora ramorum Originates from the Laurosilva Forests of East Asia

“…The IC1 isolates did however have significantly different growth rates. Hence, over time IC1 has probably accumulated genetic changes via mutation or genome rearrangement, as already well documented for the introduced lineages [ 13 , 17 , 18 , 19 , 20 , 128 , 129 ]. The same may also apply to the IC2 lineage.…”

“…In its introduced form, P. ramorum is known to occur as four anciently divergent clonal lineages, of which NA1 and NA2 were initially detected in North America and EU1 and EU2 in Europe [ 14 , 15 , 16 , 17 , 18 ]. Only the A1 mating type has been found in the EU1 and EU2 lineages (an exception in EU1 is probably due to somatic recombination [ 19 ]), and NA1 and NA2 are exclusively of A2 type. In culture, the lineages exhibit differences in colony patterns, temperature-growth responses and pathogenicity similar to those usually seen between Phytophthora species [ 20 , 21 , 22 ].…”

In planta detection used to define the distribution of the European lineages of Phytophthora ramorum on larch (Larix) in the UK

“…The NA1 and NA2 lineages are exclusively of A2 mating type, but are absent from the UK, whilst limited testing of isolates of EU1 and EU2 lineages from the UK have shown them all to be A1 (Brasier & Kirk, 2004;Van Poucke et al, 2012). More intensive testing of EU1 isolates from elsewhere in Europe has confirmed all are A1 mating type, with the exception of three rare EU1 A2 isolates from Belgium that are believed to be genetic segregants from the dominant A1 (Vercauteren et al, 2011;Chandelier et al, 2014). Most probably therefore, only the A1 mating type of P. ramorum is present in the UK, with outcrossing between isolates unlikely to occur due to the lack of a compatible mating partner (Brasier & Kirk, 2004;Goss et al, 2009).…”