Eve Runno-Paurson

Characterisation of Phytophthora infestans 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.

Current potato varieties are too susceptible to late blight to be grown without chemical control under North-East European conditions

Abstract 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.

The structure of Phytophthora infestans 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.

Population changes and phenotypic diversity of Phytophthora infestans isolates from Estonia and Finland.

In Estonia and Finland, 386 and 671 isolates, respectively, of Phytophthora infestans were collected during the growing seasons of 2001-2007. Collection was from groups of potato cultivars of different origin from field plots at two research institutions in eastern and northern Estonia and from variety trials at two locations and commercial potato fields in Finland. Mating type, pathotype based on virulence on a differential set of 11 R genes of Solanum demissum and response to the fungicide metalaxyl were determined in both countries by comparable methods. The diversity of the P. infestans populations in both countries over the monitoring period was high. In Finland, the proportion of A1/A2 mating types was almost equal throughout the monitoring period, while in Estonia the A1 population, dominating in 2001-2004, shifted towards an equal proportion of both mating types in 2005-2007. The diversity of the P. infestans population, as measured by virulence pathotypes and the number of avirulence factors per isolate, developed in opposite directions in Estonia and Finland from 2001-2004 to 2005-2007: the diversity decreased in Estonia and increased in Finland. Metalaxyl sensitivity in the Estonian P. infestans population increased while in Finland it decreased during the same period. Results clearly show differences between Estonian and Finnish populations of P. infestans in several aspects, which may derive from cropping practices. The high A2 mating type percentage during 2005-2007 in both countries points to soil contamination with oospores.

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.ResumenEn total, se obtuvieron 365 aislamientos de Phytophthora infestans de papas propagadas por tubérculo-semilla de alta (multiplicada por dos años en campo abierto después de la fase de meristemo) y baja (semilla certificada comercial multiplicada por varios años consecutivos en campo abierto) calidad fitosanitaria, a diferentes fases de progreso de la epidemia durante los ciclos de cultivo de 2001 a 2007 de lotes de campo en dos institutos experimentales en Estonia, Europa del Noreste. La calidad fitosanitaria alta o baja de la semilla de papa no tuvo efecto en la proporción de los grupos de compatibilidad o en la respuesta al metalaxil en poblaciones de P. infestans aisladas de estos dos diferentes grupos de material de papa. En contraste, la incidencia de ciertos factores de virulencia, así como la diversidad de patotipos, fue muy alta en poblaciones colectadas de papas propagadas de semilla de baja calidad en comparación con aquellas de semilla de alta calidad. La incidencia de variantes del grupo de compatibilidad A2 y completamente sensibles a metalaxil fue más alta con significancia estadística al inicio de la epidemia que más tarde, durante el progreso epidémico. La incidencia de factores de mayor virulencia y la diversidad de patotipo en general no se afectaron por el progreso temporal de la epidemia. Los factores de virulencia raros 5 y 9 fueron más frecuentes al estallamiento de la epidemia y declinaron en la población durante el transcurso de la misma.

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

The potato late blight pathogen Phytophthora infestans was collected from a region of Eastern Estonia during a period of seven years (2001–07). In total, 180 isolates were assessed for virulence, 133 for mating type and 171 for metalaxyl resistance. The average frequencies of mating types A1 and A2 were 59% and 38%, respectively. Considerable differences in the proportion of A1 and A2 between years were found. The data indicate that, in the Estonian population of P. infestans, both mating types occurred simultaneously within fields, with the potential for sexual recombination. The relatively rare virulence factors 5 and 9 and the less frequent virulence factors 2, 6, 8 were found in all studied years. Racial diversity, calculated with normalised Shannon diversity index, was high (0.71) but did not show significant differences between different collection years. The data showed that the response of isolates to metalaxyl did not depend on the year of collection. Still, the interaction was considerable between response to metalaxyl and the year, which means that the proportion of sensitive isolates increased and the proportion of intermediate isolates decreased notably compared to other concentration variants. By contrast, metalaxyl resistant isolates remained at a similar level during the seven year period.

High genotypic diversity found among population of Phytophthora infestans collected in Estonia

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.

Lithuanian Populations of Phytophthora infestans Revealed a High Phenotypic Diversity

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.

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.

Reliability of the entomovector technology using Prestop-Mix and Bombus terrestris L. as a fungal disease biocontrol method in open field

Botrytis cinerea Pers.:Fr. is a major plant pathogen, and a new approach is needed for its control in strawberry to minimise the increasing use of synthetic fungicides. The biofungicide Prestop-Mix, which contains Gliocladium catenulatum, is effective against Botrytis infections; however, the need for frequent applications increases the costs for farmers. Here, we demonstrate that bumble bees, Bombus terrestris L., effectively disseminate the preparation onto flowers in open field conditions. Over the course of three years, we found a highly significant decrease in the rate of Botrytis infection. Pathogen control was achieved with relatively low numbers of G. catenulatum spores per flower, even using flowers that are not highly attractive to bumble bees. An even distribution of spores was detected up to 100 m from the hives, either due to primary inoculation by bumble bees or secondary distribution by other flower visitors such as honey bees and solitary bees. We showed that the application of a biocontrol agent by bumble bees is reliable for the use of environmentally friendly pest control strategies in northern climatic conditions. This low cost technology is especially relevant for organic farming. This study provides valuable information for introducing this method into practice in open strawberry fields.