A Trade-Off Between Sporangia Size and Number Exists in the Potato Late Blight Pathogen Phytophthora infestans, and Is Not Altered by Biotic and Abiotic Factors

The negative relationship between offspring size and number is a classic example of trade-off between life-history traits, reported many times in animal and plant species. Here, we wanted to ascertain whether such a trade-off occurred in the oomycete Phytophthora infestans, and whether it was impacted by biotic and abiotic factors. We thus conducted three infection experiments under controlled conditions and measured the number and the size of sporangia (asexual propagules) produced on potato by different P. infestans isolates. In all experiments, we observed a negative relationship between sporangia size and number, demonstrating the existence of a trade-off. Moreover, although the potato host cultivar, temperature and host of origin (tomato or potato) all affected sporangia number, sporangia size or both, none of these biotic and abiotic factors did change the trade-off. Therefore, the trade-off between sporangia size and number could maintain the polyphenism for these traits in P. infestans populations, and favors the coexistence of distinct reproductive strategies within this species. Our results emphasize the relevance to focus on the relationship between offspring size and number in other fungal plant pathogens, as well as to study the impact of offspring size on fitness-linked traits (virulence and disease lesion development) in these organisms

Souches de Phytophthora infestans : que nous apprennent les marqueurs génétiques ?

National audienceLes populations européennes de Phytophthora infestans ont été marquées par des modifications importantes avec l'arrivée des souches A2 à partir des années 1980. Avec le développement des marqueurs génétiques tels que les microsatellites, les chercheurs disposent aujourd'hui de puissants outils pour suivre l'évolution des populations afin d'adapter les méthodes de lutte

Pied chétif du blé, ré-émergence d'une virose : Etat des connaissances sur le fonctionnement de cette maladie transmise sur céréales par des cicadelles du genre Psammotettix

BGPI : équipe 6National audienc

Projet IPMBlight 2.0: L'épidémiosurveillance pour une meilleure aide à la décision

International audienceContrôler efficacement et durablement le mildiou reste une préoccupation forte pour beaucoup de producteurs de pomme de terre, à l'heure où l'arsenal de matières actives disponibles tend à se réduire et dans un contexte de réduction espérée de l'emploi de pesticides. Développer des méthodes de protection intégrée valorisant mieux les différentes alternatives disponibles pour la lutte passe par une meilleure connaissance de l'évolution du parasite et son intégration au sein d'outils complets d'aide à la décision. C'est l'enjeu majeur du projet IPMBlight 2.0, qui démarre actuellement

Epidémiovigilance Mildiou 2021 : les génotypes changent !

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Mildiou en France : P. infestans sous surveillance

National audienceMildiou en France : P. infestans sous surveillance.Le réseau d’épidémiosurveillance du mildiou de la pomme de terre permet de suivre les populations de Phytophthora infestans, ses résistances aux fongicides et ses contournements de résistances variétales. C’est utile

The Effectiveness of Induced Defense Responses in a Susceptible Potato Genotype Depends on the Growth Rate of Phytophthora infestans.

International audiencePhytophthora infestans causes the devastating potato late blight disease, which is widely controlled with fungicides. However, the debate about chemical control is fueling a promotion toward alternative methods. In this context, the enhancement of natural plant immunity could be a strategy for more sustainable protection. We previously demonstrated that a concentrated culture filtrate (CCF) of P. infestans primes defense reactions in potato. They are genotype-dependent and metabolites produced decrease pathogen growth in vitro but not in vivo on tubers. Induced potato defenses are assumed to affect P. infestans life history traits depending on strains. This assumption was studied in vivo through induced leaflets on a susceptible genotype inoculated with four P. infestans strains differing for lesion growth rate. This study combines both defenses mechanistic analysis and ecological observations. Defense-gene expressions were thus assessed by quantitative reverse transcription-polymerase chain reaction; pathogen development was simultaneously evaluated by measuring necrosis, quantifying mycelial DNA, and counting sporangia. The results showed that CCF pretreatment reduced the pathogenicity differences between slow- and fast-growing strains. Moreover, after elicitation, PR-1, PR-4, PAL, POX, and THT induction was strain-dependent. These results suggest that P. infestans could develop different strategies to overcome plant defenses and should be considered in biocontrol and epidemic management of late blight

Epidémiosurveillance Mildiou : enjeux actuels & acquis récents

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An Improved PCR Method for Rapid and Accurate Identification of Mating Types in the Late Blight Pathogen Phytophthora infestans

International audienceMating type is a critical trait in heterothallic organisms. In plant pathogenic oomycetes, like the late blight pathogen Phytophthora infestans, it is usually identified through pairing between tester and candidate isolates, a method that is both laborious and applicable to live isolates only. Therefore, developing simple and fast PCR tests to reliably identify P. infestans mating types is of great interest for population genetic studies. A multiplex PCR assay combining the amplification of a locus diagnostic for P. infestans and of one diagnostic for the A1 mating type was developed and validated on a collection of 1,441 samples, covering the current and past diversity of European P. infestans populations. These samples were obtained from either freeze-dried mycelium or FTA cards on which diseased leaflets had been pressed. The multiplex assay correctly identified mating types in 97.4% of these samples. The main source of incorrect assignment was the lack of amplification of the A1 diagnostic allele, due to insufficient DNA quality and/or quantity in the reaction mix. This multiplex PCR, applicable to both live and stored material, thus constitutes a useful addition to the set of molecular tools available for population typing in P. infestans

Data from: The coexistence of generalist and specialist clonal lineages in natural populations of the Irish Famine pathogen Phytophthora infestans explains local adaptation to potato and tomato

Phytophthora infestans, causing late blight on Solanaceae, is a serious threat to potato and tomato crops worldwide. P. infestans populations sampled on either potato or tomato differ in genotypes and pathogenicity, suggesting niche exclusion in the field. We hypothesized that such niche separation can reflect differential host exploitation by different P. infestans genotypes. We thus compared genotypes and phenotypes in 21 isolates sampled on potato (n = 11) or tomato (n = 10). Typing at 12 microsatellite loci assigned potato isolates to the 13_A2, 6_A1 and 1_A1 lineages, and tomato isolates to the 23_A1, 2_A1 and unclassified multi-locus genotypes. Cross-inoculations on potato and tomato leaflets showed that all isolates were pathogenic on both hosts. However: tomato isolates performed much better on tomato than did potato isolates, which performed better on potato than did tomato isolates, thus revealing a clear pattern of local adaptation. Potato isolates were significantly fitter on potato than on tomato, and are best described as potato-specialists; tomato isolates appear to be generalists, with similar pathogenicity on both hosts. Niche separation in the field may thus result mainly from the large fitness gap on tomato between generalists and unadapted potato-specialists, while the small, but significant fitness difference on potato between both types of isolates may prevent population invasion by generalists. Extreme specialization to potato seems very costly relative to performance loss on the alternative host. This study therefore shows that local adaptation and niche separation, commonly expected to involve and generate specialists, can occur with generalists