Genetic Structure of the Norwegian Parastagonospora nodorum Population

Abstract

The necrotrophic fungal pathogen Parastagonospora nodorum causes Septoria nodorum blotch (SNB), which is one of the dominating leaf blotch diseases of wheat in Norway. A total of 165 P. nodorum isolates were collected from three wheat growing regions in Norway from 2015 to 2017. These isolates, as well as nine isolates from other countries, were analyzed for genetic variation using 20 simple sequence repeat (SSR) markers. Genetic analysis of the isolate collection indicated that the P. nodorum pathogen population infecting Norwegian spring and winter wheat underwent regular sexual reproduction and exhibited a high level of genetic diversity, with no genetic subdivisions between sampled locations, years or host cultivars. A high frequency of the presence of necrotrophic effector (NE) gene SnToxA was found in Norwegian P. nodorum isolates compared to other parts of Europe, and we hypothesize that the SnToxA gene is the major virulence factor among the three known P. nodorum NE genes (SnToxA, SnTox1, and SnTox3) in the Norwegian pathogen population. While the importance of SNB has declined in much of Europe, Norway has remained as a P. nodorum hotspot, likely due at least in part to local adaptation of the pathogen population to ToxA sensitive Norwegian spring wheat cultivars.

Identification and cross-validation of genetic loci conferring resistance to Septoria nodorum blotch using a German multi-founder winter wheat population

“…Alternatively, the isolate we used may not be representative of those responsible for the natural field infection conditions under which we investigated SNB resistance. Indeed, as our recent research finds the Norwegian P. nodorum population to be genetically diverse (lacking in obvious genetic populations substructure, and collectively containing all eight possible combinations for the presence/absence of the three cloned effector genes) (Lin et al 2020b ), it is likely that this latter hypothesis is correct. Future work investigating possible correlation between NE- Snn interactions and SNB in the BMWpop would therefore benefit from CF assessment using isolates obtained from the naturally infected experimental trials under study.…”

Hidden in plain sight: a molecular field survey of three wheat leaf blotch fungal diseases in North-Western Europe shows co-infection is widespread

“…Before this time, SNB was considered the most important wheat leaf blotch disease in Northern Europe, while STB was most prevalent in Mediterranean climates (Bayles, 1991;Bearchell et al, 2005;Scharen, 1999). Over the last 30-40 years there has been a focal shift in most North Western European countries from SNB to STB (Bearchell et al, 2005;Shaw et al, 2008;Torriani et al, 2015), although Scandinavia has remained a SNB hot spot (Lin et al, 2020).…”

“…The founder varieties of the multi-parental 'BMWpop' (Stadlmeier et al, 2018) and 'NIAB Elite MAGIC' (Mackay et al, 2014) populations were also included in the panel. Each cultivar was present in at least two replicate plots at each of the disease resistance screening trials in the four countries, as previously described (Lin et al, 2020;Stadlmeier et al, 2019). Different inoculation methods for the three diseases were applied depending on year and location (Supplementary Table 3).…”

“…Four effectors were cloned and characterized for their role in TS and SNB: ToxA (present in both Ptr and Pn), ToxB (Ptr), Tox1 (Pn) and Tox3 (Pn) (Faris et al, 2013;Friesen et al, 2007; reviewed by Downie et al, 2020). These four effectors explain a significant fraction of SNB and/ or TS disease levels in agricultural environments as different as Australia (Vleeshouwers & Oliver, 2014) and Norway (Lin et al, 2020;Ruud et al, 2017), and there are clearly more to be found. For STB, many resistance QTL have been reported (e.g.…”

Sensitivity genes in wheat and corresponding effector genes in necrotrophs exhibiting inverse gene-for-gene relationship

“…This was attributed to the biased sample from a single eld and may not represent the situation in whole of Australia (Oliver et al 2009). (ii) In a diverse sample of 165 P. nodorum isolates, from Norway and 9 isolates from other countries, SnToxA was found to occur with high frequency in Norwegian P. nodorum isolates relative to other parts of Europe, suggesting that SnToxA gene is the major virulence factor in Norway (Lin et al 2020). The disease reaction in interaction Snn1-SnTox1 has been observed to range from 0 to 58% and seems to depend on both, the genetic background of the host and that of the pathogen (Liu et al 2004a; Chu et al…”