The structure of mating type,virulence, metalaxyl resistance of Phytophthora infestans in a long-term phenotypic study in distinct location in Eastern Estonia

Journal of Plant Diseases and Protection - The potato late blight pathogen Phytophthora infestans was collected from a region of Eastern Estonia during a period of seven years (2001–07). In...     

Lithuanian Populations of Phytophthora infestans Revealed a High Phenotypic Diversity

Journal of Plant Diseases and Protection - This is the first characterisation of Lithuanian populations of Phytophthora infestans with mating type and virulence on a differential set of 11 R genes...     

The structure of <Emphasis Type="Italic">Phytophthora infestans</Emphasis> populations from organic and conventional crops

The characteristics of populations of Phytophthora infestans from organic farms, small conventional farms and large conventional farms were determined from isolates collected in northern Estonia in 2004 and 2005. For the population as a whole 41% were A2; all virulence factors to the 11 R genes from Solanum demissum were found; and more than 70% had high or intermediate resistance to metalaxyl. Isolates from organic farms tended to have more complex pathotypes than isolates from either large or small conventional farms, but there was a higher proportion of metalaxyl resistant isolates from large conventional farms than from small conventional farms or from organic farms.     

Distribution of major clonal lineages EU_13_A2, EU_2_A1, and EU_23_A1 of Phytophthora infestans associated with potato late blight across crop seasons and regions in Algeria

Potato is one of the most important agricultural crops in Algeria and worldwide. Each year, potato late blight, caused by Phytophthora infestans, is responsible for significant damage that leads to large production losses, and is thus a direct threat to food security in Algeria. In this study, 131 isolates of P. infestans and 92 DNA fingerprints captured on FTA cards were sampled from commercial and seed production fields in three major potato production regions (western, eastern, and central) during the main-season and late-season in Algeria over six cropping seasons (2010–2016). Genotypes of P. infestans and population genetic diversity were analysed using a 17-plex simple-sequence repeat (SSR) marker assay, and the mating type of all isolates was characterized. Both mating types (A1 and A2) were found, and often occurred in the same field. Differences in mating type proportion were observed between regions and between sampling periods. Analysis with SSR markers showed the prevalence of the EU_13_A2 lineage (70%) over EU_2_A1 (16%), EU_23_A1 (10%), and 4% of unknown multilocus lineage (MLL). The EU_13_A2 showed differentiation within the group. EU_23_A1 was found mainly in late-season crops. However, the cropping region did not influence the distribution of lineages due to the dispersal of the pathogen in Algeria by seeds. Genetic structure did not reveal a clear variation in distribution of the three lineages throughout the sampling regions. These data provide important new information on the composition and change over time of P. infestans populations in Algeria and open the way for a better understanding of the local epidemiology of this important pathogen.     

Foliar resistance to the late blight pathogen Phytophthora infestans (Mont.) de Bary in a backcross of potato (Solanum tuberosum L.) cultivar Ando

ABSTRACT

Regardless of variable environmental conditions and changing pathogen populations, the Estonian potato cultivar (cv.) Ando has shown elevated field resistance to Phytophthora infestans for over 40 years. One of cv. Ando’s parents, the Latvian cultivar Agra, is considered a cultivar of medium to low resistance, the other parent, line 382-48, has a well-known source of resistance, Solanum demissum, in its pedigree. Segregation of late blight disease severity in a population of 95 hybrid plants from cv. Ando’s backcross to cv. Agra (cv. Ando x cv. Agra BC1) in field trials of three consecutive years (2013?2015) and in a test of a single pathogen isolate fits a model of additive action of multiple unlinked race-specific resistance genes responsible for the field resistance of cv. Ando. At least some of the resistance genes in cv. Ando’s genome do not function in juvenile plants and are developmentally upregulated.     

Outcome of sexual reproduction in the <Emphasis Type="Italic">Phytophthora infestans</Emphasis> population in Estonian potato fields

In this study, the Estonian population of Phytophthora infestans was characterized with mating type, sensitivity to metalaxyl, virulence on 11 potato R-gene differentials and 12 SSR markers to show the outcome of potential sexual reproduction in the population. During the three years 2010–2012, 141 P. infestans isolates, collected from 23 potato fields, showed quite a high and stable frequency of the A2 mating type, 48% of the total population. In 87% of all sampled potato fields, both mating types were recorded, suggesting continuous sexual reproduction of P. infestans and possible oospore production. Metalaxyl-sensitive isolates prevailed in all three years (68 out of 99 isolates). Amongst the 95 isolates tested, 51 virulence races were found. The race structure was diverse, and most pathotypes were unique, appearing only once; the two most common pathotypes, 1.2.3.4.6.7.10.11 and 1.2.3.4.7.10.11, comprised 35% of the population. The P. infestans population was genetically highly diverse and most of the multilocus genotypes (MLGs) appeared only once. Furthermore, all of the MLGs appeared in only one of the three sampling years. Our results confirm that the high diversity in the Estonian P. infestans population is most likely the result of frequent sexual reproduction, which benefits the survival, adaptability and diversity of the pathogen in the climate of North-Eastern Europe.     

Early blight destroys potato foliage in the northern Baltic region

In recent years, potato early blight [Alternaria solani (Ellis & G. Martin) L.R. Jones, A lternaria alternata (Fr.) Keissl.] has occurred with increasing frequency in European potato fields, including those in northern regions. In our study, early blight was evaluated during the two years 2010–2011 on potato plants in a conventional farming experiment. Both growing seasons were very favourable for early blight development and evaluation. Our study indicates that, despite chemical treatments, potato early blight is a great problem for potato growers in conventional farming systems in the North-East region in years when temperatures are higher than average. In 2011, early blight damage was particularly high on the untreated (N0P0K0) treatment plots where severity increased abruptly from an initial 2% to 91%, and killed the potato haulms within five weeks. In 2010, the most severely infected plants were also recorded on the untreated (N0P0K0) plots, where 70% of foliage was destroyed by the end of the growing season. Results showed that a more efficient chemical strategy is needed against this disease on susceptible cultivars. Breeding and growing more resistant cultivars of potato is considered the most efficient, cost effective and environmentally friendly control method for sustainable cultivation in conventional growing systems. As an increase in the frequency of warmer summers is predicted, greater problems from this pathogen are to be expected in Northern Europe.     

Impact of Phytosanitary Quality of Seed Potato and Temporal Epidemic Progress on the Phenotypic Diversity of Phytophthora infestans Populations

Altogether 365 isolates of Phytophthora infestans were sampled from potatoes propagated from seed potatoes of high (multiplied for two years in open field after meristem phase) and low (commercial certified seed multiplied for several consecutive years in open field) phytosanitary quality at different phases of epidemic progress during the growing seasons of 2001–2007 from field plots at two experimental institutes in Estonia, North-East Europe. High or low phytosanitary quality of seed potatoes had no effect on mating type ratio or response to metalaxyl in populations of P. infestans isolated from these two different groups of potato material. In contrast, the incidence of certain virulence factors, as well as the diversity of pathotypes, was very high in populations collected from potatoes propagated from low-quality seed in comparison to those from high-quality seed. The incidence of A2 mating type and fully metalaxyl sensitive strains was statistically significantly higher at the epidemic outbreak than later during epidemic progress. The incidence of most virulence factors and overall pathotype diversity were not affected by the temporal progress of the epidemic. Rare virulence factors 5 and 9 were more frequent at the outbreak of the epidemic and declined in the population during the course of epidemic.     

Characterisation of <Emphasis Type="Italic">Phytophthora infestans</Emphasis> isolates collected from potato in Estonia during 2002–2003

A collection of 101 isolates of Phytophthora infestans, obtained from seven sampling sites representing central, east and south-east Estonia during 2002 and 2003 were assessed for several phenotypic and genotypic markers. All 101 isolates were assessed for virulence and resistance to metalaxyl. Virulence to each of the 11 classic resistance genes was found among the tested isolates. The mean number of virulences per isolate was 6.3, with a very low frequency of virulence against resistance genes R5 (5%) and R9 (14%). The most common pathotypes were 1.3.4.7.8.10.11 and 1.3.4.7.10.11, representing altogether 12% of the studied strains. In terms of metalaxyl resistance, 30 resistant, 52 intermediate and 19 sensitive isolates were found. A subgroup of 50 isolates was assessed for mating type, allozymes [glucose-6-phosphate isomerase (Gpi) and peptidase (Pep)], DNA fingerprints with probe RG57 and mtDNA haplotype. Of this subset, 30 were A1 and 20 were A2. Collections from three of the seven fields contained both mating types. Allozyme analysis did not reveal any polymorphism. However, 19 diverse RG57 fingerprints were detected, and two mitochondrial DNA haplotypes, Ia and IIa, were detected. By combining the mating type, mtDNA haplotype and RG57 fingerprint data, 26 multilocus genotypes were identified, of which 18 were detected only once. Genotypic diversity measured by the normalised Shannon diversity index was high (0.76). The large number of multilocus genotypes and the presence of both mating types in some fields indicate that sexual reproduction may take place in Estonian populations of P. infestans.