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Soil microbes play a key role in the nutrient cycling by decomposing the organic material into plant-available elements and also by maintaining the soil health. The study of soil microbial hydrolytic activity (SMA) was carried out in a long-term crop rotation (barley undersown (us) with red clover, red clover, winter wheat, pea and potato) experiment in five different farming systems during 2014–2018. There were two conventional systems, with chemical plant protection and mineral fertilizers, and three organic systems, which included winter cover crops and composted manure. The aim of the present study was to evaluate the effect of the (i) cropping system and (ii) precrops in rotation on the soil SMA. The soil microbial hydrolytic activity was significantly affected by yearly weather conditions, farming system, and crops. In all farming systems, the SMA was the lowest after dry and cold conditions during early spring in 2018. In unfertilized conventional systems, the considerably lower SMA is explained by the side effects of pesticides and low organic residuals, and we can conclude that the conventional system with no added fertilizer or organic matter is not sustainable, considering soil health. In each year, the SMA of organic systems with cover crops and composted manure was 7.3–14.0% higher compared to all farming systems. On average, for both farming systems, the SMA of all the rotation crops was positively correlated with the SMA values of precrops. However, in conventional farming systems, the effect of undersowing on the SMA of the precrop was smaller compared to organic systems.

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 ...

Potato crop losses can be substantial when conditions for late blight (Phytophthora infestans) development and spread are favourable. In this study, drivers of differences between the P. infestans population structures in Latvia and Lithuania, two neighbouring countries with similar potato-growing traditions, were investigated. Genotypes of P. infestans and population genetic diversity were analysed using a 12-plex simple sequence repeat (SSR) marker assay. High genetic diversity was demonstrated in both populations, with population diversity being higher in Latvia. It would appear that local populations established from soilborne oospores early in the season are well adapted to the conditions in the region. However, somewhat greater spread and survival of local clones was detected in Lithuania, suggesting that potato cropping there is more vulnerable to clonal invasion than in Latvia. For effective disease management, current strategies should be adjusted according to the specific pathogen populations in the region, considering the reproduction and survival of the pathogen. Potato growers should implement late blight preventive measures such as longer field rotation to prevent oospore infections, especially in Latvia, and should use more disease resistant cultivars and high-quality seed potatoes.

International audience; 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.

The soil fungal community plays an important role in determining plant growth and health. In this study, we investigated the fungal diversity and community composition in the roots and soil of 21 potato (Solanum tuberosum L.) cultivars using high-throughput sequencing at three different time points across the growing season. In soil and roots, the fungal richness and relative abundance of pathogens and saprotrophs were mainly affected by sampling time. While sampling time affected fungal composition in soil, root fungal communities were also significantly affected by cultivar. The cultivar had the strongest effect on diversity of pathogens and abundance of particular pathogen species. Our results demonstrate changes in soil and root fungal communities of potato over the growing season, as well as highlighting the importance of potato cultivar on root fungal communities and abundance of pathogens.

The rhizosphere fungal community can play an important role in determining plant growth and health. In this study, using high-throughput sequencing, we investigated the fungal diversity and community composition in the roots and rhizosphere soil of 21 potato (Solanum tuberosum L.) cultivars. The samples were collected at three different sampling points. Furthermore, we assessed the differences in both diversity and composition of pathogen and saprotroph communities. In soil and roots, the fungal richness and relative abundance of pathogens and saprotrophs were mainly affected by sampling time. However, root fungal communities were also significantly affected by cultivar. The most substantial effect of cultivar was on root pathogen diversity. Moreover, the occurrence of most pathogens strongly varied among cultivars. Soil fungal community composition was primarily determined by sampling time; whereas in roots, the primary determinant was cultivar. Our results demonstrate changes in fungal communities over the potato growing season, as well as highlight the importance of potato cultivar on root fungal communities, and emphasise their importance in plant breeding.

Information about the root mycobiome may improve the overall quality of the plants and contribute to a valuable strategy to enhance sustainable agriculture. Therefore, we assessed differences in fungal community diversity and composition in the roots of potato, wheat and barley grown under mineral nitrogen fertilisation at five rates, with and without farmyard manure amendment. The same factorial combination of treatments has been used since 1989. Species richness and diversity, as well as community composition, of different fungal guilds were characterised using Illumina MiSeq sequencing of the ITS2 region. Crop species was the main factor determining overall fungal richness and diversity, with wheat showing the highest, and potato the lowest, richness and diversity. Pathogen diversity indices were highest in wheat plots amended with farmyard manure, whereas the lowest values were observed for potato roots. Fertilisation treatments and the interaction between crop species and fertilisation had the strongest impact on arbuscular mycorrhiza and saprotroph diversity. Crop species also determined the composition of the overall fungal community and that of fungal guilds, whereas fertilisation treatment had only a minor effect. This study highlights crop species as the main driver in shaping root fungal diversity and composition under the same environmental conditions.

For finding more sustainable cropping systems, this study on how the farming system influences the yield and quality of potato tubers was carried out with long-term crop rotation experiment. The long-term five-field crop rotation field trial was established with the following farming system treatments: organic farming system treatments: Org I (organic control), Org II (organic crop rotation with winter cover crops) and Org III (organic crop rotation with winter cover crops and the addition of composted cattle manure); conventional farming system treatments: N0 (conventional system without fertilizers), N50 (conventional system with fertilization, N50P25K95), N100 (conventional system, N100P25K95) and N150 (conventional system, N150P25K95). The average yield (based on 3 trial years) of conventional systems was 25% higher, compared to organic systems. However, in organic systems, the yield was the most stable. The most fluctuating cropping system was the most intensively managed N150. In each trial year, the yield differed statistically and it varied from 4.7 t ha−1 up to 10.9 t ha−1. Org I had the same dry matter yield as the N0 system, where chemicals were used, meaning that using chemicals for plant protection but no fertilizer for growth improvement had no positive effect. In each year, the yield in Org III system was similar to N50 system. Regarding the tubers per plant, there were no differences between farming systems but there was a significant difference between the trial years. The tubers in conventional systems had a lower starch content than the organic systems. It is possible to conclude that if cover crops and manure are used, organic farming practices provide just as good results as the conventional farming with low nitrogen level.

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.

Potato late blight, caused by the oomycete pathogen Phytophthora infestans, is one of the most important diseases of potato worldwide. This is the first study characterising Estonian P. infestans population using the SSR marker genotyping method. 70 P. infestans isolates collected during the growing season in 2004 from eight potato fields in three different regions of Estonia were characterised with nine polymorphic SSR markers. A1 and A2 mating type isolates were detected from every studied field indicating the high potential for sexual reproduction, which raises the genotypic diversity in P. infestans population. Results revealed highly diverse P. infestans population in Estonia resembling the Northern European populations. Most of the multilocus genotypes were detected only once among the collected isolates. Subpopulations collected from different geographical regions of Estonia showed no differentiation from each other but instead formed one highly diverse group.

A study was conducted which aimed to investigate the effect of farming systems (FS) (four conventional with increasing mineral N fertilizer amounts 0–150 kg of N ha−1) vs. two organic with catch crops (CC) and cattle manure (CC + M)) under the same five crop rotation system on the occurrence of tuber diseases such as common scab (Streptomyces spp.), silver scurf (Helminthosporium solani), dry rot (Fusarium spp.), and soft rot (Pectobacterium spp.). As the average of the first rotation years 2009–2011, the FS had a significant effect on the occurrence of silver scurf, dry rot and common scab (surface cover

Potato late blight, caused by the oomycete Phytophthora infestans (Mont.) de Bary, is one of the most serious potato (Solanum tuberosum L.) diseases, causing considerable yield loss in potato production worldwide, including Latvia. At present, the data on the population characteristics of P. infestans in Latvia is sparse. Therefore, the main aim of this study was to collect new data on Latvian isolates of P. infestans, to determine the main characteristics of the pathogen, particularly mating types, metalaxyl resistance and virulence with Black’s differential set of potato genotypes containing resistance (R) genes R1–R11. During 2010–2012, 181 isolates of P. infestans were collected from 23 potato fields, from 13 locations in Latvia. Out of 181 isolates tested, 52.5% were A1, 43.1% – A2 and 4.4% – self-fertile mating type. Of 116 isolates screened for resistance to metalaxyl, 25.9% were resistant, 19.8% – intermediate and 54.3% – sensitive. More than 80% of isolates were virulent to R1, R3, R4, R7, R10 and R11, while 33% or fewer isolates were virulent to R5, R8 and R9. The least frequent was virulence against R9 in 24% of isolates. Our study revealed that the Latvian population of P. infestans is diverse. The proportion of mating types and the occurrence of both A1 and A2 in the same field indicate the possibility of sexual recombination in Latvian fields. Thus, it is very important to keep the crop rotation system, to prevent soil contamination with long-living oospores. The Latvian population of P. infestans shares many similarities with other European populations, which suggests gene flow between populations.

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.

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.

The main aim of this research was to evaluate foliar resistance of the potato varieties of Dutch breeding company Agrico to find those most resistant to late blight in order to diminish the number of fungicide sprays required while obtaining a high yield in North-East European conditions. In the trial at the Einola Farm in 2010 and 2011, 10 potato varieties and 2 breeding lines were included. The disease scores of different varieties varied from 2.1 to 7.6 points. Nine of the varieties grown were susceptible and two varieties very susceptible to late blight. The most resistant variety was Toluca (foliar blight estimated mean value 5.9), which is immune to foliar blight in its land of origin. On the basis of two years data, we can conclude that most of the tested varieties are too susceptible to late blight to be grown without chemical control against this pathogen in North-East European conditions.