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.     

Stability and variability of virulence of Phytophthora infestans assessed in a ring test across European laboratories

Determining virulence towards race‐specific resistance genes is a prerequisite to understanding the response of pathogen populations to resistant cultivars, and therefore to assess the durability of these resistance genes and the performance of resistance management strategies. In Phytophthora infestans, virulence testing began shortly after the introduction of R‐genes from Solanum demissum into S. tuberosum cultivars. However, the characteristics of R‐gene expression, the sensitivity of the phenotype to environmental and physiological parameters, and the diversity of experimental protocols make the comparison of data from different studies problematic. This prompted European teams working on P. infestans diversity to: (i) design a joint protocol, using detached leaflets from greenhouse‐grown plants of a shared set of differential cultivars inoculated with standardized suspensions of inoculum, and (ii) assess the performance of this protocol in a blind ring test involving 12 laboratories and 10 European isolates of the pathogen. A high level of consensus in the determination of virulence/avirulence to R1, R3, R4, R7, R8, R10 and R11 was achieved among the collaborators, showing that the protocol could be robustly applied across a range of laboratories. However, virulence to R2, R5 or R9 was detected more frequently in some laboratories, essentially from northern Europe; these genes are known to be highly sensitive to host and environmental conditions. The consensus determination was often markedly different from the original virulence phenotype of the isolates, suggesting virulence instability in stored P. infestans isolates. This indicates that creating reliable core collections of pathogen isolates with known virulences could be difficult.     

Environmental Evaluation of Metals in Sediments and Dragonflies Due to Sugar Cane Cultivation in Neotropical Streams

The use of fertilizers, containing different metals ions such as lead(II), chromium(III), cadmium(II), copper(II) and zinc(II), in the soil, for sugar cane cultivation, may cause impacts on the hydric resources of the adjacent areas. The scope of this study was to evaluate the impacts of sugar cane cultivation based on metal concentrations in sediments and dragonflies (Odonata). The bioavailability of such metals was determined in ten Neotropical streams. Six streams were located on areas with sugar cane cultivation, without riparian vegetation (classified as impacted area) and four streams were located on forested areas (reference sites). The results showed that there are high concentrations of metals in the sediments and dragonflies in streams located on impacted areas. The contamination by metals of aquatic insects of terrestrial adult life cycle, as Odonata organisms, represents a dangerous link for the transference of metals to upper trophic levels, as fishes, reptiles, birds and mammals.     

Application des méthodes ELISA et immunofluorescence pour la detection deCorynebacterium sepedonicum: réponses variétales de la pomme de terre au flétrissement bactérien

Résumé Une adaptation d'une méthode ELISA à la détection deCorynebacterium sepedonicum est présentée. Trois immunsérums (dont au moins deux d'origines animales différentes) sont nécessaires. Les sensibilité, spécificité, reproductibilité de la méthode sont discutées et comparées à l'immunofluorescence, en analysant des souches pures et des extraits de tubercules. La méthode décrite est utilisée pour suivre la contamination de la descendance de 15 variétés sur deux générations de tubercules. Une classification des ces variétés, en fonction de leur aptitude à transmettre l'agent pathogène à leur descendance, est proposée.

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Summary An ELISA method was developed to detectC. sepedonicum: three immunsera were needed, at least two from different animals. A relationship between bacterial suspension concentrations and optical density as determined by ELISA was established (Fig 1). The lower limit for detection was 10⁵ bacteria/ml which was similar to that obtained using IF. The relationship between ELISA and IF values determined simultaneously on different concentrations of the bacteria is given in Table 1. The specificity of ELISA and IF was tested on different bacteria pathogenic to Solanaceae species (Table 2). The optical densities obtained with healthy tuber extracts were 0; analyses of infected tubers showed not only the presence of whole bacterial cells but also of soluble antigens in the extracts (Table 3). When 1000 daughter tubers obtained from plants grown from inoculated seed tubers were examined, similar results were obtained using ELISA or IF in c. 90% of the tests (Table 4). The ELISA method was used subsequently to determine over two years the reaction of 15 potato cultivars initially inoculated withC. sepedonicum and planted in the soil. The cultivars could be divided on the basis of the percentage of contaminated daughter tubers into 11 susceptible to the pathogen, 2 slightly susceptible and 2 tolerant (Table 5).

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Zusammenfassung Der entwickelte ELISA-Test zur Bestimmung vonC. sepedonicum erfordert drei Immunoserums, wovon mindestens zwei von verschiedener Tierarten stammen. Es wird eine Relation zwischen der Konzentration der Suspensionen und ihrer optischen Dichte aufgestellt (Abb. 1). Die Bestimmungsgrenze befindet sich bei 10⁵ Bakterien/ml: diese ist identissch mit der Immunofluoreszenz-Methode (IF). Suspensionen von bekannten Konzentrationen welche simultan mit ELISA und IF bestimmt werden, ergeben die in der Tabble 1 aufgeführten Resultate. Die Spezifizit?t der ELISA und IF-Methoden wird bestimmt durch die Prüfung von verschiedenen pathogenen Bakterienarten auf Solanaceen (s. Tabelle 2). Tabelle 3 zeigt, dass die gesunden Knollen optische Dichten von null ergeben; die Analyse von befallenen Knollen ergibt nicht nur ganze Bakterien, aber auch aus den Extrakten aufl?sbare Antigenen, Einen auf 1000 Tochterknollen durchgeführten Test, von künstlich befallenen Mutterknollen stammend, gibt ann?hernd 90 Prozent übereinstimmung der ELISA und IF-Ergebnisse (s. Tabelle 4). Dieser ELISa-Test wird danach benützt um das Verhalten von 15 Kartoffelsorten zu testen, welche mitC. sepedonicum inokuliert und in Erde ausgepflanzt wurden. Der Versuch wurde auf zwei Jahre bezogen. Eine Klassierung nach prozentualem Befallsgrad der Tochterknollen wird aufgestellt: elf Sorten werden als anf?llig, zwei wenig anf?llig und zwei tolerant gegenüber dem Pathogen beurteilt (s. Tabelle 5).

     

Adaptation of Phytophthora infestans to Partial Resistance in Potato: Evidence from French and Moroccan Populations

ABSTRACT The use of partially resistant cultivars should become an essential component of a sustainable management strategy of potato late blight, caused by Phytophthora infestans. It is therefore important to determine to what extent P. infestans populations can be selected for increased aggressiveness by potato cultivars with different levels of partial resistance. To this end, we sampled P. infestans populations from France and Morocco, chosen as locations where late blight occurs regularly but which differ in the distribution of potato cultivars. Cross-inoculation experiments were used to determine the aggressiveness of all populations to potato cvs. Bintje (prevalent in France but not grown in Morocco) and Désirée (popular in Morocco but cultivated to a very small extent in France). French populations were more aggressive on cv. Bintje than on cv. Désirée, irrespective of the site they were sampled from. Their aggressiveness increased between early and late samplings, suggesting that both cultivars selected for increased aggressiveness during epidemics. By contrast, Moroccan populations were more aggressive on Désirée, regarded as partially resistant in Europe, than on Bintje, highly susceptible under European conditions. These data indicate that P. infestans populations adapt to locally dominant cultivars, irrespective of their resistance levels, and can therefore overcome polygenic, partial resistance. This adaptive pattern may render partial resistance nondurable if not properly managed.     

Multiphasic Approach for the Identification of the Different Classification Levels Of Pseudomonas savastanoi Pv. Phaseolicola

The relationships between strains of Pseudomonas savastanoi pv. phaseolicola (P. sav. phaseolicola), P. syringae pv. tabaci (P. syr. tabaci) and P. syr. syringae which all cause disease on bean; the related species P. sav. glycinea and P. syr. actinidiae, and reference bacteria, were evaluated by studying the phenotypic and genetic diversity of a collection of 62 strains. All the P. sav. phaseolicola strains tested produced characteristic watersoaked lesions on bean pods. Other pathovars produced varying combinations of symptoms including necrotic lesions, with or without watersoaked centres and sunken tissue collapse of the lesion (P. syr. tabaci) and necrotic lesions with or without sunken collapse (P. syr. syringae). At the genomospecies level, all the strains of P. sav. phaseolicola, P. sav. glycinea and P. syr. tabaci, belonging to genomospecies 2, could be separated from P. syr. syringae strains (genomospecies 1) and P. syr. actinidiae strains (unknown genomospecies) by BOX-PCR and DNA/DNA hybridisation. To distinguish P. sav. phaseolicola, within genomospecies 2, from P. sav. glycinea and P. syr. tabaci, it was necessary to perform nutritional characterisations myo-inositol negative and p-hydroxy benzoate positive for P. sav. phaseolicola strains), PCR with specific primers designed from the tox region (positive for all of the P. sav. phaseolicola strains) and serotyping, as 71% of the P. sav. phaseolicola strains reacted as O-serogroup PHA1. Important intrapathovar variation was seen by genomic fingerprinting with REP and ERIC primers, as well as with RAPD primers (AE7 and AE10) and esterase profilings. While RAPD fingerprinting detected variability correlated with two race-associated evolutionary lines, REP, ERIC and esterase profiles revealed intrapathovar variation linked to some host origins, that separated the kudzu isolates, and the mungbean isolates, from the other P. sav. phaseolicola strains.     

Phenotypic and genotypic changes in French populations of Phytophthora infestans: are invasive clones the most aggressive?

The main objective of this investigation was to test the ‘always more aggressive’ hypothesis, often advocated to explain lineage replacements in clonal populations of the potato late blight oomycete Phytophthora infestans. To this end, genotypic and pathogenicity data on 1274 French isolates of P. infestans, collected over the period 2001–2008, were analysed. Overall, the populations sampled showed limited genetic diversity, with four multilocus lineages (1_A1, 2_A1, 8_A1 and 13_A2) accounting for over 80% of the isolates collected. As in other West European countries, drastic changes in these dominant clonal lineages were observed over the course of the 8 years, particularly in the appearance and propagation of the clone 13_A2. However, invasiveness of clones was not associated with higher aggressiveness; on the contrary, dominant clones had generally low or moderate aggressiveness relative to others present at the same time within the same populations. This finding challenges the link between invasive behaviour and increased aggressiveness often assumed for this biotrophic pathogen, and could reflect the existence of a trade‐off between intra‐season and inter‐season transmission. This would be consistent with the concept of inclusive fitness, which involves the abilities to both reproduce and survive.     

Resistance to late blight and soft rot in six potato progenies and glycoalkaloid contents in the tubers

Glycoalkaloids are anti-nutritional compounds commonly found in wildSolanum species used as resistance sources to major potato pathogens. It is therefore important for breeding purposes to know whether selecting for resistance using such species necessarily selects also for high glycoalkaloid contents in the tubers. To test this hypothesis, we used six partial progenies from crosses betweenSolanum tuberosum and accessions ofS. andigena, S. berthaultii, S. phureja, andS. vernei to investigate the possible correlation between resistance toPhytophthora infestans and/or toErwinia carotovora subsp.atroseptica and the concentration of glycoalkaloids in tubers. Concentrations of α-solanine and α-chaconine in the tubers segregated in each progeny, as did resistance to each pathogen. Some, but not all, clones from each progeny showed hypersensitive reactions to the isolate ofP. infestans used. Furthermore, clones within each progeny also differed for components of partial resistance toP. infestans, suggesting that all four wild species could be used as sources of both race-specific and partial resistance to late blight. With the exception of low, but statistically significant, correlations between concentration of α-solanine and two late blight resistance components (incubation period and spore production per unit lesion area) in progenies derived fromS. vernei, and despite a trend towards higher glycoalkaloid concentrations in the tubers of the clones most resistant to soft rot within progenies derived fromS. berthaultii andS. vernei, no consistent relationship between resistance to either disease and concentrations of α-solanine and/or α-chaconine was observed. These results indicate that neither race-specific nor partial resistance to late blight and soft rot in the accessions used as progenitors of resistance depend on high solanine or chaconine concentrations. These resistance sources could thus prove useful in breeding programs for improved behaviour againstP. infestans and/orE. carotovora.