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There is limited understanding of the genetic variability in

The main aim of this study was to evaluate foliar late blight resistance and yield of selected foreign and Estonian potato cultivars to determine the most promising cultivars for the northern Baltic region. We hypothesized that local cultivars have higher late blight (Phytophthora infestans) resistance and yield due to higher blight resistance. Potato late blight observation field trials were carried out in 2012 and 2013 in Einola Farm, Tartu County, Estonia. In both growing seasons, 12 potato cultivars were compared, nine from the Dutch Breeding Company Agrico and three from the Estonian Crop Research Institute. They comprised four early cultivars: Ranomi, Esmee, Romie and Maret, four early-medium cultivars: Toluca, Mariska, Madeleine and Teele and four medium-late/late cultivars: Excellency, Bellefleur, Manitou and Anti. Of these, only two, Anti and Toluca, qualified as highly foliar late blight resistant. This research clearly indicates that, despite unfavourable conditions for the pathogen, late blight is able to destroy potato foliage in most of these cultivars before the end of the growing season in northern Baltic conditions. This reflects local genetic heterogeneity of populations of P. infestans, probably associated with the presence of strains adapted to a wide range of humidity conditions. In 2012 that had late blight favourable weather, the cultivar Toluca showed high foliar blight resistance, as it reached the maximum yield compared to most other cultivars which were susceptible or very susceptible to late blight and had drastically reduced yield. However, although the late blight infection was not recorded in the growing season 2013, the cultivar Toluca did not tolerate the dry weather well and its tuber yield remained significantly lower than that in all other cultivars. Additionally, in 2013, a potato early blight (Alternaria solani) outbreak was recorded with the two most susceptible cultivars being the local cultivar Teele and the Dutch cultivar Excellency.

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.

The main aim of this study was to evaluate foliar late blight resistance and yield of selected foreign and Estonian potato cultivars to determine the most promising cultivars for the northern Baltic region. We hypothesized that local cultivars have higher late blight (Phytophthora infestans) resistance and yield due to higher blight resistance. Potato late blight observation field trials were carried out in 2012 and 2013 in Einola Farm, Tartu County, Estonia. In both growing seasons, 12 potato cultivars were compared, nine from the Dutch Breeding Company Agrico and three from the Estonian Crop Research Institute. They comprised four early cultivars: Ranomi, Esmee, Romie and Maret, four early-medium cultivars: Toluca, Mariska, Madeleine and Teele and four medium-late/late cultivars: Excellency, Bellefleur, Manitou and Anti. Of these, only two, Anti and Toluca, qualified as highly foliar late blight resistant. This research clearly indicates that, despite unfavourable conditions for the pathogen, late blight is able to destroy potato foliage in most of these cultivars before the end of the growing season in northern Baltic conditions. This reflects local genetic heterogeneity of populations of P. infestans, probably associated with the presence of strains adapted to a wide range of humidity conditions. In 2012 that had late blight favourable weather, the cultivar Toluca showed high foliar blight resistance, as it reached the maximum yield compared to most other cultivars which were susceptible or very susceptible to late blight and had drastically reduced yield. However, although the late blight infection was not recorded in the growing season 2013, the cultivar Toluca did not tolerate the dry weather well and its tuber yield remained significantly lower than that in all other cultivars. Additionally, in 2013, a potato early blight (Alternaria solani) outbreak was recorded with the two most susceptible cultivars being the local cultivar Teele and the Dutch cultivar Excellency.

This is the first characterisation of Lithuanian populations of Phytophthora infestans with mating type and virulence on a differential set of 11 R genes of Solanum demissum. The sensitivity to metalaxyl was also determined. In 2010–2012, 93 Phytophthora infestans isolates, collected from all over Lithuania, showed quite high and stable frequency of A2 mating type. On 45% of all studied potato fields, both mating types were recorded, suggesting sexual reproduction of P. infestans and possible oospore production in Lithuanian potato fields. Fourteen metalaxyl-resistant isolates were found among 71 isolates in the current study period, and sensitive isolates prevailed in all three years. Amongst the studied 70 isolates, 38 avirulence pathotypes were found. The Lithuanian race structure was highly diverse and complex (the average number of missing avirulence factors per isolate was 7.2). Most pathotypes were unique, appearing only once, and the four most common pathotypes comprised only 34% of the population.

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 growin...

Nowadays, organically produced products have become more popular than ever and interest in them is still growing fast. The early blight causal pathogen Alternaria solani has not been considered a great threat to potato in northern climate conditions in the past and has not been routinely sprayed against. During our study early blight was evaluated in 2010 and 2011 on the plants of a potato cultivar ‘Reet’ in an organic farming experiment. In our study, both growing seasons were very favourable for early blight development. Significant differences between the two cultivation technologies were found (F1,12 = 4.84, p = 0.048). In 2010, the area under disease progress curve (AUDPC) value was 303 on cover crop (CC) plots and 990 on CC + M (manure) plots that is three times higher, whereas in 2011, the AUDPC value was 967 on CC plots and 1195 on CC + M plots. Our results confirm that potato early blight has become a serious problem in North-East European organic potato fields and thus susceptible potato cultivars cannot be recommended for growing in an organic farming system. However, it is possible to influence the development severity of early blight by selecting the proper growing technology. Since, in the changing climate conditions and in susceptible cultivars, early blight is a potato disease that can cause early defoliation of plants and crop death, there is a need for resistant potato cultivars.