Phenotypic and genotypic structure of Phytophthora infestans populations on potato and tomato in France and Switzerland

Abstract

A total of 134 isolates of Phytophthora infestans were collected from potato and 42 from tomato fields in Switzerland and France in 1996 and, and compared with isolates from other countries. The structure of the populations was analysed phenotypically and genotypically, and associated to geographical, seasonal and host origin. Phenotype characteristics of the isolates included mating type; sensitivity to phenylamide fungicides; virulence on potato differentials; and pathogenic fitness. Genotypes were assessed for mitochondrial DNA haplotype with restriction fragment length polymorphism-polymerase chain reaction (RFLP-PCR) as well as amplified fragment length polymorphism (AFLP) and simple sequence repeats or microsatellites (SSR). The majority (96%) of isolates originating from potato were the A1 mating type, whereas half the isolates collected from tomato were A2 mating type. Isolates with sensitive, intermediate and resistant responses to the phenylamide fungicide metalaxyl-M were detected in the populations. Isolates from potato represented races with highly complex virulence spectra, whereas those from tomato belonged to simple races. The pathogenic fitness of isolates was highest on the host of origin, and was significantly reduced for isolates from potato on tomato. One of the four haplotypes, Ia, dominated the population (93% of isolates). Among isolates collected from potato, 15 different SSR genotypes were detected of which two, A-03 and A-06, dominated the population. From tomato, 11 SSR genotypes were found of which four, A-03, B-03, D-03 and F-01, formed the major proportion of the population. Every ninth and fourth isolate from potato and tomato, respectively, represented a different SSR genotype. Four genotypes were isolated from both hosts, whereas 11 and seven genotypes, respectively, originated exclusively from either potato or tomato. The SSR genotype D-02, represented by the 'old' Ib haplotype, was still detected in a few isolates in the current population, and in older reference isolates from different countries. The SSR genotype was not associated with mating type or sensitivity to phenylamide fungicides. A total of 40 AFLP genotypes were distinguished among the isolates, every second isolate representing another genotype. The diverse phenotypic and genotypic structure of the current field populations in Europe suggests that they may have evolved from local processes including sexual recombination, host preference and selection rather than through long-distance migration.

Virulence and aggressiveness of Phytophthora infestans isolates collected in Poland from potato and tomato plants identified no strong specificity

“…This finding is in agreement with prior studies by Lebreton and Andrivon (1998), Oyarzun et al (1998), Knapova andGisi (2002), andBlandón-Diaz et al (2012), and indicates lower host specificity of T isolates than P isolates to a potato host. Cohen (2002) found that P and T isolates collected in Israel between 1998 and 2000, when heavy epidemics of late blight occurred in tomato, had similar complex virulence spectra with unexpectedly high frequencies of the factor against the R9 gene and low frequency of the factor corresponding with R2.…”

“…The virulence spectra of isolates recently collected from potato in Poland (Śliwka et al 2006;Chmielarz et al 2014) were similar to our results. The frequencies of P isolates that were virulent against respective R-genes in our study were higher than those reported by Andrivon et al (1994), Świeżyński et al (2000), Knapova andGisi (2002), andBlandón-Diaz et al (2012). On the whole, the P isolates tested in this study showed 100 % of virulent forms against R1, R3, R4, R7, R10, and R11 and frequent presence of virulence against R5, R6, and R8 differentials.…”

“…Although P. infestans isolates are obtained from both potato and tomato, aggressiveness and virulence tests of the isolates have been evaluated primarily on potato differentials (Lebreton and Andrivon 1998;Dorrance et al 1999;Vega-Sánchez et al 2000;Derie and Inglis 2001;Klarfeld et al 2009;Blandón-Diaz et al 2012;Harbaoui et al 2013). Aggressiveness and virulence of isolates from potato and tomato have also been compared on leaflets of the two host plants (Wilson and Gallegly 1955;Oyarzun et al 1998;Lebreton et al 1999;Jaime-Garcia et al 2000;Cohen 2002; Knapova and Gisi 2002;Blandón-Diaz 2011). Sporulation of isolates has also been observed in a few experiments (Legard et al 1995;Lebreton et al 1999;Knapova and Gisi 2002;Klarfeld et al 2009), indicating that the pathogen undergoes adaptation to the host.…”

“…Aggressiveness and virulence of isolates from potato and tomato have also been compared on leaflets of the two host plants (Wilson and Gallegly 1955;Oyarzun et al 1998;Lebreton et al 1999;Jaime-Garcia et al 2000;Cohen 2002; Knapova and Gisi 2002;Blandón-Diaz 2011). Sporulation of isolates has also been observed in a few experiments (Legard et al 1995;Lebreton et al 1999;Knapova and Gisi 2002;Klarfeld et al 2009), indicating that the pathogen undergoes adaptation to the host. However, our understanding of the pathogenic specialization of the late blight pathogen is incomplete.…”

Evolution and Management of the Irish Potato Famine Pathogen Phytophthora Infestans in Canada and the United States

“…Analysis by RFLP provides greater resolution of P. infestans genotypes with well-characterized markers that are conserved and stringent but it also requires the isolation and propagation of the pathogen, a process that often takes weeks or months to complete (Goodwin et al 1992;Hausner et al 2000). Most recently, analysis of simple sequence repeats (SSRs) has been used to distinguish the P. infestans genotypes (Knapova and Gisi 2002;Lees et al 2006). This PCR-based method may be used on small samples and sporangia from a lesion, and thereby facilitate the rapid identification of a P. infestans genotype (Cooke and Lee 2004;Lees et al 2006;Danies et al 2013).…”