Increased frequency of self-fertile isolates in Phytophthora infestans may attribute to their higher fitness relative to the A1 isolates

Abstract

Knowledge of population dynamics of mating types is important for better understanding pathogen’s evolutionary potential and sustainable management of natural and chemical resources such as host resistances and fungicides. In this study, 2250 Phytophthora infestans isolates sampled from 61 fields across China were assayed for spatiotemporal dynamics of mating type frequency. Self-fertile isolates dominated in ~50% of populations and all but one cropping region with an average frequency of 0.64 while no A2 isolates were detected. Analyses of 140 genotypes consisting of 82 self-fertile and 58 A1 isolates indicated that on average self-fertile isolates grew faster, demonstrated higher aggressiveness and were more tolerant to fungicides than A1 isolates; Furthermore, pattern of association between virulence complexity (defined as the number of differential cultivars on which an isolate can induce disease) and frequency was different in the two mating types. In A1 isolates, virulence complexity was negatively correlated (r = −0.515, p = 0.043) with frequency but this correlation was positive (r = 0.532, p = 0.037) in self-fertile isolates. Our results indicate a quick increase of self-fertile isolates possibly attributable to their higher fitness relative to A1 mating type counterpart in the field populations of P. infestans in China.

The dynamics of Phytophthora infestans populations in the major potato‐growing regions of Asia – A review

“…In contrast to the findings of Zhu et al (2016), studies of the P . infestans population in northern China (Heilongjiang) over a 14‐year period (2005–2019) found that while the A1 genotype SIB‐1/JP‐2 was dominant before 2010, the frequency of 13_A2 increased from 2011 to 2013, although it was not found in 2015–2016 (M. Guo, Heilongjiang Academy of Agricultural Sciences, China, 2020, personal communication).…”

“…Southern China (Guangxi, Guangdong, and Fujian provinces) accounts for 5% of the total area and both major hosts of P . infestans are cultivated, potatoes in the winter and tomatoes in the spring (Chen & Qu, 2008; Zhu et al, 2016). The differences in cultivation practices, together with movement of host material within the country and introduction of genotypes from external sources, impact the disease cycle as well as the population structure of P .…”

“…In the last 10 years (2009-2019), a number of studies have reported rapid changes in the P. infestans population, with an increase in the occurrence of A2 and self-fertile isolates in most regions except central China where the A1 mating type has remained dominant (Tian et al, 2015b(Tian et al, , 2016Zhu et al, 2015Zhu et al, , 2016. Tian et al (2016), in a study of 959 isolates, showed that in north-western China between 2009 and 2011, the frequency of first A2 and then selffertile isolates increased.…”

Rapid adaptation of the Irish potato famine pathogen Phytophthora infestans to changing temperature

“…Phytophthora infestans is considered to be a heterothallic oomycete with two mating types designated A1 and A2, despite the existence of self‐fertile isolates (Judelson, ). It can reproduce sexually, asexually, and/or parasexually (Billiard et al, ; Zhu et al, ) and has a potential for long distance wind dispersal (Granke, Windstam, Hoch, Smart, & Hausbeck, ). The pathogen has a large genome (~240 Mbp) rich in transposable elements (>75% of total genome) (Haas et al, ; Vetukuri et al, ).…”

Genome Analysis of Two Newly Emerged Potato Late Blight Isolates Sheds Light on Pathogen Adaptation and Provides Tools for Disease Management

“…The mating types of Phytophthora species, referred to as A1 and A2, do not signify the production of particular sex organs, as isolates of either mating type are hermaphroditic and thus capable of producing both antheridia and oogonia, the male and female reproductive organs, respectively (Judelson 1997). Each mating type secretes a specific hormone (a1 or a2) that induces sexual reproduction in isolates of the opposite mating type (Harutyunyan et al 2008), but the isolates of A1A2 mating type as self-fertile isolates can induced sexual reproduction with no other isolates (Zhu et al 2016). Mating type of each isolate was determined by the sputum culture method (Qi et al 2005).…”