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Aphanomyces euteiches Drechsler is an oomycete pathogen of leguminous crops that causes root rot, a severe disease of pea ( Pisum sativum L.) worldwide. An improved understanding of the genetic structure of A. euteiches populations would increase knowledge of pathogen evolution and assist in the design of strategies to develop pea cultivars and germplasm with stable disease resistance. Twenty six primers pairs were used to amplify Sequence Related Amplified Polymorphisms (SRAP) among 49 A. euteiches isolates sampled from pea. A total of 190 polymorphic SRAP bands were generated, of which 82 were polymorphic between all the A. euteiches isolates. The percentage of polymorphic bands per primer pair ranged from 22 to 75%. According to the PIC value estimated for each marker, 60% of the SRAP markers were highly to reasonably informative (PIC > 0.25). Genetic structure of A. euteiches populations sampled in different American and French locations showed low to high genetic diversity within populations. The largest variation occurred within countries, with a total estimated genetic diversity of 0.477 and 0.172 for American and French populations, respectively. This was particularly evident from a principal component analysis (PCA) and a Minimum Spanning Networks (MSN) based on genetic profiles of isolates, which generated two different clusters, one corresponding to the French isolates and four American isolates (MV1, MV5, MV7, Ath3), and the other to American isolates. A. euteiches populations from cultivated pea in France appeared as a single unstructured population, whereas American isolates of A. euteiches diverged into three different populations. [ABSTRACT FROM AUTHOR]

Controlling bacterial plant diseases remains a challenge, as direct chemical control is usually not possible. Obtaining new biocontrol methods, in particular efficient biomolecules able to boost defence reactions and limit infection or symptom development, is therefore of major importance. This study screened extracts from leaves of two Mediterranean plants rich in bioactive phenolic compounds, olive and carob, for their ability to reduce soft rot severity and to trigger phenylalanine ammonia-lyase (PAL) activity in potato tuber slices. Extracts from olive leaves significantly reduced disease severity caused by Pectobacterium atrosepticum or Pectobacterium carotovorum, whereas carob leaf extracts significantly increased it. Olive extracts and its main phenolic components, oleuropein and hydroxytyrosol, also significantly increased PAL activity 7.5 h after application. None of the extracts or purified molecules reduced bacterial growth in vitro. Furthermore, the effect of these extracts varied according to potato cultivars. These data therefore open new ways for the biological control of soft rot bacteria, but stress the importance of understanding the causes of response difference in different potato varieties in order to obtain optimal efficacy. [ABSTRACT FROM AUTHOR]

The Concerted Action on potato late blight ‘Eucablight’ ( ) was launched in 2003 to promote collaboration between researchers across Europe and to collate the previously fragmented data on host resistance to late blight and characterization of populations of its causal agent, Phytophthora infestans. Fundamental to the project was the development of standardized protocols, databases and data collection tools with which data from across Europe could be centralized. The ultimate aim was to capitalize on the vast resource of data available in order to allow a pan-European analysis to be conducted. The P. infestans database is currently populated with information relating to over 15 000 isolates from 20 European countries. The host resistance database holds primary disease data, and derived statistics, from more than 50 field trials assessing mainly foliage blight resistance. The use of five standard cultivars in these trials facilitated the comparison of resistance information across years and regions. The host database is structured, and made accessible, in such a way that DSS builders can access the model parameters they need to construct locally adapted forecasting systems. In this presentation we describe the database and the data analysis tools that have been developed in this project and how they are directly applicable to other host-pathogen systems. [ABSTRACT FROM AUTHOR]

1. Selection during interepidemic stages is crucial for the evolution of pathogen populations. Trade-offs involving aggressiveness (quantitative pathogenicity) have rarely been explored in pathogens with a life cycle requiring the disease-causing organism to change organs within the same host. 2. We investigated the existence of a trade-off between aggressiveness and survival in Phytophthora infestans, the pathogen causing potato late blight. In France, P. infestans behaves as an obligate biotroph, surviving in infected tubers. Aggressive isolates, which are favoured during the epidemic, may exhaust their nutrient supply too quickly to bridge seasons, resulting in a possible trade-off between the two life stages. 3. We inoculated tubers with isolates possessing different aggressiveness levels, let them overwinter as outdoor piles at three different sites, and scored the proportion of live tubers the following spring. 4. At two sites, infection caused early tuber sprouting, which can be seen either as a manipulation of the host by the pathogen, or as an attempt by the host to escape. 5. Overwinter survival was higher for control than for inoculated tubers, but did not differ between tubers inoculated with different isolates. This suggests that aggressiveness should gradually increase in P. infestans populations, unless a trade-off occurs at another stage of the life cycle. [ABSTRACT FROM AUTHOR]

Ten institutions in nine countries joined together to test the stability of resistance of 14 potato genotypes to the oomycete pathogenPhytophthora infestansin three separate trials. Seven of the genotypes were tested in one trial involving seven locations, and all 14 were tested in two subsequent trials, each involving eight locations. Stability of resistance was tested with nonparametric tests and with an additive main effects and multiplicative interaction (AMMI) model. Overall, resistance toP. infestanswas robust; resistant genotypes were consistently resistant in all locations and trials. The nonparametric analysis indicated that specific genotypes were basically stable across sites for resistance. In trial 3, theZstatistic for overall stability was significant at 0·05%, indicating a significant level of interaction across the trial, but there were no significant interactions for specific genotypes in this trial. The genotype by environment (G × E) effect of the AMMI model was highly significant in both trials, but the mean square of G × E was less than 10% of the genotype effect in each trial. The first two principal components (PCA1 and PCA2) of the AMMI analyses together explained 75 and 80% of the interaction effects in trials 2 and 3, respectively. Based on both nonparametric and AMMI analyses, Ecuador and Argentina were locations of relatively high interaction effects for both trials 2 and 3, although in Ecuador this interaction was not associated with any particular potato genotype. Other locations also had high interaction effects, but these occurred in only one trial. The genotypes Chata Blanca and, to a lesser extent, Torridon were relatively unstable in trials 2 and 3, but in the case of Torridon, resistant, this did not represent a significant loss of resistance. [ABSTRACT FROM AUTHOR]

Leaf segments from seedlings of 68 old barley varieties and 38 more recent cultivars of past or current importance in France were infected with 6--9 powdery mildew isolates in order to identify race-specific resistance genes. No resistance gene was apparent in the 21 old winter varieties, 43 of 47 old spring varieties, 10 recent winter and 3 recent spring cultivars. Two old spring varieties (`Colmar S 142' and `Johanna') were postulated to have Mlg and Ml(CP), and two others (`Pontrieux' and `Finistère 62-5') had an unidentified, weakly effective gene. Mlg, Ml(CP), Mlb, Mla6 and Mla13 were the only genes detected in recent winter cultivars. Recent spring cultivars presented the greatest diversity; the presence of one or several genes among Mla1, Mla6, Mla9, Mla12, Mlg, Ml(CP), Ml(La), Mlk and mlo was postulated in several lines. [ABSTRACT FROM AUTHOR]

Comparisons of the pathotype composition in random samples of barley mildew populations collected in 1985 and 1986 in several European regions were made in an attempt to quantify the influence of migration on population structures. In each of the situations studied (northern France 1986 and eastern Lower Austria 1985 and 1986), evidence was obtained from influx of spores from at least two remote areas. Depending on year and location, 48 to 87% of the resulting composite samples consisted of 'foreign-type' isolates. Implication of long-distance dispersal for studies on population dynamics and for control strategies relative to mildews and other wind-spread pathogens are discussed. [ABSTRACT FROM AUTHOR]

Random samples of spores of wheat powdery mildew were collected from the atmosphere by means of a jet spore sampler while driving through selected wheat growing areas in Europe in 1986. Their single colony progenies were tested in the laboratory for virulence against wheat differential varieties with powdery mildew resistances Pm2, Pm4b, Pm8, Mli and the combinations Pm2+Pm6, Pm4b+Pm8 and Pm2+Pm4b+Pm8. There were regional differences in virulence frequencies. Virulence on Pm2, Pm2+Pm6 and, less expressed, on Pm4b was most frequent in England and decreased mainly to the east, whereas the reverse was true for Pm8. Virulence to Mli was generally high, and to the combined genotypes generally low. The results suggest that large parts of Europe are an epidemiological unit. The data are discussed with respect to selection caused by the varieties grown, as well as to the influence of wind distribution on the composition of the pathogen population. [ABSTRACT FROM AUTHOR]

Black dot, caused by Colletorrichum coccodes, is of potential concern to potato production in France as part of the tuber-blemishing disease complex. The lack of information about the actual distribution of the pathogen in potato-producing areas led to a survey of the occurrence of the disease. Black dot symptoms were observed on roots, stems and/or tubers of the 82 potato cultivars examined in 1994. A baiting bioassay, using cuttings of potato cultivars Bintje and Urgenta, revealed the presence of the pathogen in all 37 soil samples tested, which had been collected throughout the main French potato growing areas. In vitro, growth of five C coccodes isolates recovered from diseased potatoes grown in western and southern France was severely affected by imazalil, tolchlofos-methyl and, to a lesser extent, mancozeb and thiabendazole. Conversely, iprodione. flutolanil and pencycuron were ineffective in reducing the growth of these isolates These data indicate that C. coccodes is widespread in French potato cropping areas, that currently popular cultivars are susceptible to the disease, and that at least some of the fungicides commonly applied to seed tubers arc ineffective against the pathogen. A better diagnosis of the disease, but also the insensitivity of the pathogen to several chemicals frequently used on seed tubers for controlling black or silver scurfs, might thus provide explanations for the apparent increase in black dot occurrence in recent years. [ABSTRACT FROM AUTHOR]

A critical review of available historical and scientific evidence related to the question of the origin of the first European populations of the potato late blight pathogen Phytophthora infestans is presented. It shows that the bases for the current theories of a direct introduction of the fungus into Europe and North America from either a Mexican or an Andean centre of origin and of diversity are questionable. An alternative theory, involving a three-step process: (i) migration from central Mexico to South America several centuries ago; (ii) migration from South America to the US in 184 1--1842, and (iii) migration to Europe from either South America, US or both in 1843-1844, is in good agreement with both the historical records and with the genetics and structure of current populations. [ABSTRACT FROM AUTHOR]

Isolates of the potato late-blight pathogen Phytophihora infestans, collected in several French regions from 1988 to 1992, were characterized in order to determine the structure and pathogenicity of French populations and to compare them with other European samples. All 254 French isolates tested were of the Al mating type, as were two Sicilian, five Portuguese and one Spanish isolate. Metalaxyl sensitivity of 157 isolates was investigated. The frequency of resistance to this chemical decreased in western France front 1989 to 1992. Two glucose phosphate isomerase phenotypes (90/100 and 90/90) were detected among the 46 isolates tested; the former largerly predominated (75-80%) in the samples investigated. Both phenotypes corresponded to the population recently introduced into Europe. A third genotype (86/100), typical of the former European population, was found in one isolate from Picardy, originating from an artificially infected field trial. Five isolates from Portugal and Italy were of the 100/100 phenotype. Race patterns among 26 isolates from western France were very similar, and could not be explained by local selection. The unusual composition of the Brittany population. consisting of `new' genotypes but all belonging to the Al mating type, is possibly related to the metapopulation type of structure of P. infestans in Europe. [ABSTRACT FROM AUTHOR]

The evolution of race patterns in three French regional populations of the barley powdery mildew pathogen Erysiphe graminis f.sp. hordei over a 5-year period showed rapid adaptation to newly introduced host resistance genes. In all three regions, the main change consisted of the replacement of initially abundant races by pathotypes differing markedly from them by their virulence gene combinations. This explained the increase in diversity during the first 3 years of the survey, when the second group of pathotypes became more common in the populations, and its subsequent decrease due to the decline of the first group of races. The mean number of virulence genes per isolate did not vary noticeably over time in the three populations, remaining at about four out of 12 genes tested. However, the distribution of the isolates into virulence complexity classes was greatly modified, fitting a binomial distribution by the end of the study, although significant deviations were apparent in the first 2 years (1986 and 1987). The data indicate that selection, migration and recombination are the most important factors shaping face structure and evolution in powdery mildew populations, and that mutation is of fruited significance. No convincing evidence was obtained for the existence of stabilizing selection sensu Underlain as the mechanism limiting virulence complexity. Implications regarding spatial and temporal deployment of race-specific resistance genes to control powdery mildew are discussed. [ABSTRACT FROM AUTHOR]

Nineteen races were found among 116 isolates of Phytophthora infestans recovered from French potato and tomato crops during 1991-1993. The most common races were 1.3.4.7.11. 1.3.4.7.8.11 and 1.3.4.7.10.11 in 1991, race 1.3.4.7.11 in 1992, and race 1.3.4.7.10.11 in 1993. None of the isolates was virulent to either R2 or R6, and only one to R5. The mean number of virulences per isolate was 5.78 in 1991, 4.35 in 1992 and 4.53 in 1993. The P. infestans population from Brittany showed mainly quantitative changes in the frequencies of major races over the period investigated, but races identified were almost the same in all 3 years. No geographical substructure was apparent, since variation between locations accounted for only 13-22% of the total racial diversity within the Brittany population. This is interpretated as evidence for limited gene flow in this population, which is believed to have evolved from a few founding genotypes. [ABSTRACT FROM AUTHOR]