Highly Diverse Phytophthora infestans Populations Infecting Potato Crops in Pskov Region, North-West Russia

There is limited understanding of the genetic variability in Phytophthora infestans in the major potato cultivation region of north-western Russia, where potato is grown primarily by small households with limited chemical treatment of late blight. In this study, the mating type, sensitivity to metalaxyl, and genotype and population genetic diversity (based on 12 simple sequence repeat (SSR) markers) of 238 isolates of P. infestans from the Pskov region during the years 2010–2013 were characterized. The aim was to examine the population structure, phenotypic and genotypic diversity, and the prevalent reproductive mode of P. infestans, as well as the influence of the location, time, and agricultural management practices on the pathogen population. The frequency of the A2 mating was stable over the four seasons and ranged from 33 to 48% of the sampled population. Both mating types occurred simultaneously in 90% of studied fields, suggesting the presence of sexual reproduction and oospore production in P. infestans in the Pskov region. Metalaxyl-sensitive isolates prevailed in all four years (72%), however, significantly fewer sensitive isolates were found in samples from large-scale conventional fields. A total of 50 alleles were detected in the 141 P. infestans isolates analyzed for genetic diversity. Amongst the 83 SSR multilocus genotypes (MLGs) detected, 65% were unique and the number of MLGs varied between locations from 3 to 20. These results, together with the high genotypic diversity observed in all the locations and the lack of significance of linkage disequilibrium, suggest that sexual recombination is likely responsible for the unique MLGs and the high genetic diversity found in the Pskov region population, resembling those of north-eastern European populations

The mating type proportion of potato late blight Phytophthora infestans in Estonian and Latvian populations and consequences of sexual reproduction

Kartuli-lehemädanikutekitaja Phytophthora infestans on üks enam kartuli saagikadu põhjustav patogeen nii Eestis kui mujal maailmas. Haigustekitaja on kahe paarumistüübiga (A1 ja A2) organism, mis võimaldab patogeenil mõlema paarumistüübi koosesksiteerimisel suguliselt paljuneda ja moodustada kaua säiluvaid oospoore. Töö eesmärgiks oli uurida P. infestans Eesti ja Läti populatsioonide paarumistüüpide proportsiooni ning hinnata kas need sarnanesid omavahel või mitte. Lehemädanikutekitaja tüved isoleeriti ühe tüüpilise haigustekitaja laiguga lehtedelt. Lehemädanikust nakatunud lehed (üks taime kohta) koguti haiguse erinevates epidemioloogilistes faasides kogu kasvuperioodi jooksul. Kõik kogutud isolaadid viidi iseloomustamiseks puhaskultuuri. Tulemused näitasid, et Eestis ja Lätis on P. infestans paarumistüüpide proportsioonid sarnased. Mõlemas riigis esines kõrge A2 paarumistüübi sagedus. Enamusel uuritud põldudest esinesid koos A1 ja A2 paarumistüüp, mis viitab patogeeni sugulisele paljunemisele nendel põldudel. Lätis pole varem P. infestans paarumistüüpide proportsioone uuritud, seega oleks oluline uurimistööga jätkata, et saada täielik ülevaade Läti kartulipõldudel toimuvast ning välja selgitada kas Eesti ja Läti populatsioonid sarnanevad / erinevad ka pikemaajalistes uurimistes. Kindlasti oleks vaja teha ka geneetilised analüüsid, et näha kas nendes riikides esineb domineerivaid genotüüpe. See annaks head eeldused tõrjesüsteemide väljatöötamiseks ja koostööks kahe naaberriigi vahel.Late blight caused by Phytophthora infestans is globally most important potato disease. Under favourable conditions it can destroy the whole potato haulm and cause considerable yield loss. Under favorale conditions such as frequent rain or dew and temperatures around 10 to 20 °C, pathogen can completely kill the foliage of a crop within a few weeks. The pathogen is heterothallic, with two mating types designated A1 and A2. The populations of P. infestans which consisting of both mating types, the sexual reproduction may occur and formation of oospores are detected. The aim of the research was to compare the mating type proportions of potato late blight pathogen P. infestans in Estonian and Latvian populations. P. infestans mating type proportions in Latvian populations are not previously studied. The hypothes of the research were: the late blight pathogen Phytophthora infestans in Estonian and Latvian populations are different from mating type proportions. Both mating types were detected in Estonian and Latvian populations in 2010 and 2011, also reare self-fertile A1A2 mating type were wound. The A2 mating type ratio was high in both countries. In Latvia, the A2 mating type proportion increased rapidly between 2010 and 2011. 2010 the A2 mating type frequance in Latvia were 31%, year later the A2 mating type ratio were 47%. In organic fields the A1 mating type prevalance was higher than A2 mating type. In conventional farm fields, the A1 and A2 ratio was close to 1:1, which may presume higher risk for sexual reproduction. Both mating types were wound together from most of the fields. In both countires 15 fields were studied. In Estonia A1 and A2 mating types coexisted in 13 fields and in Latvia 11 fields. These results may indicate to soil-borne infections with oospores. The mating type proportion of potato late blight pathogen P. infestans in Estonian and Latvian populations were similar.It is important to continue the reaserch to get a complete overview of the P. infestans populations in Latvian potato fields and to find out is the Estonian and Latvian populations similar also in longer-term investigations. Definitely need to do a genetic analysis to see whether these countries have a dominant genotypes. This would provide a good basis to cooperation between two neighboring countires for developing potato late blight control systems

High Temporal Variability in Late Blight Pathogen Diversity, Virulence, and Fungicide Resistance in Potato Breeding Fields: Results from a Long-Term Monitoring Study

Long-term site-specific studies describing changes in the phenotypic variability of Phytophthora infestans populations allow quantitative predictions of pathogen spread and possible outbreaks of epidemics, and provide key input for regional resistance breeding programs. Late blight samples were collected from potato (Solanum tuberosum) breeding fields in Estonia during a twelve-year study period between 2001 and 2014. In total, 207 isolates were assessed for mating type and 235 isolates for metalaxyl resistance and 251 isolates for virulence factors. The frequency of mating types strongly fluctuated across the years, whereas the later period of 2010–2014 was dominated by the A2 mating. Despite fluctuations, both mating types were recorded in the same fields in most years, indicating sustained sexual reproduction of P. infestans with oospore production. Metalaxyl-resistant and intermediately resistant strains dominated in the first years of study, but with the progression of the study, metalaxyl-sensitive isolates became dominant, reaching up to 88%. Racial diversity, characterized by normalized Shannon diversity index decreased in time, varying from 1.00 in 2003 to 0.43 in 2013. The frequency of several virulence factors changed in a time-dependent manner, with R2 increasing and R6, R8, and R9 decreasing in time. Potato cultivar resistance background did not influence the frequency of P. infestans mating type, response to metalaxyl, and racial diversity. However, the diversity index decreased in time among isolates collected from resistant and susceptible cultivars, and remained at a high level in moderately resistant cultivars. These data demonstrate major time-dependent changes in racial diversity, fungicide resistance, and virulence factors in P. infestans, consistent with alterations in the control strategies and popularity of potato cultivars with different resistance

Alternaria Black Spot (Alternaria brassicae) Infection Severity on Cruciferous Oilseed Crops

The increase in the cultivation area of cruciferous oilseed crops and the use of short crop rotation has resulted in the enhanced spread of several major pests in Northern latitudes. There is currently limited information about incidence and severity of Alternaria black spot disease (Alternaria brassicae) on the main oilseed crop, spring oilseed rape (Brassica napus), in the Northern Baltics. Thus, spring oilseed rape and five alternative cruciferous oilseed crops were selected and their resistance to black spot disease was evaluated in field conditions during two growing seasons. We hypothesized that spring oilseed rape is more susceptible to Alternaria black spot disease than other alternative cruciferous oilseed crops. Both growing seasons were warmer and drier compared to the long-term average, and were thus suitable for A. brassicae development and assessments. In both years, incidence of Alternaria black spot infection was recorded on all cruciferous species, yet the disease development differed considerably among the crops. During both growing seasons, black mustard (B. nigra) plants were the most infected. Based on our observations during warm growing seasons we conclude that alternative oilseed crops such as Sinapis alba, Eruca sativa and Raphanus sativus are more resistant to the Alternaria black spot infection than the traditional oilseed crops and thus, possess a great potential to grow with limited chemical disease control in Northern Baltic conditions

The variability of Phytophthora infestans isolates collected from Estonian islands in the Baltic Sea

Knowledge of a pathogen's genetic variability and population structure is of benefit to effective disease management. In this study, 193 isolates of Phytophthora infestans collected from three Estonian islands, were characterized over three years using SSRs marker data complemented by information on their mating type and resistance to metalaxyl. In combination with SSR marker data from samples in the neighbouring Pskov region of north west Russia, the impact of regional and landscape structure on the level of genetic exchange was also examined. Among the Estonian islands 111 P. infestans isolates, forty-nine alleles were detected among twelve SSR loci, and 59 SSR multilocus genotypes (MLGs) were found, of which 64% were unique. The genetic variation was higher among years than that among islands, as revealed by AMOVA. The frequency of metalaxyl-resistant isolates increased from 9% in 2012 to 30% in 2014, and metalaxyl resistant was most frequent among A1 isolates. The test for isolation by distance among the studied regions was not significant, and coupled with the absence of genetic differentiation revealed gene flow, and the absence of local adaptation. The data are consistent with a sexual population in which diversity is driven by an annual germination of soil-borne oospores. The absence of shared genotypes over the years has important implications when it comes to the management of disease. Such population diversity can make it difficult to predict the nature of the outbreak in the coming year as the genetic makeup are different for each year.</p