Phenotypic variation in Nordic populations of Phytophthora infestans in 2003

Abstract

A total of 743 single-lesion isolates of Phytophthora infestans were collected in summer 2003 from Denmark, Finland, Norway and Sweden. Most of the isolates were tested for mating type, and subsets were tested for sensitivity to fungicides and virulence (host specific pathogenicity). Approximately 60% of the isolates were A1 mating type in each country. Both mating types were present in 40% of the fields where more than one isolate was tested, indicating strong potential for sexual reproduction. The proportion of metalaxyl-resistant isolates dropped to under 15% from the 60% observed in the early 1990s in Norway and Finland, possibly due to lower selection pressure because of decreased use of metalaxyl. Propamocarb-HCl sensitivity remained unchanged in the Nordic countries compared to the situation in 1997 -2000 in Finland. Four isolates collected from Finland and Sweden were able to sporulate in the presence of this fungicide at a concentration of 1000 mg L -1. In Norway and Finland the frequencies of virulence factors and pathotypes remained nearly unchanged since the 1990s, but the mean number of virulence factors per isolate increased from 5·6 to 6·3. In Denmark and Sweden virulence factors 2 and especially 6 were more common than in Norway and Finland. In addition, in the Swedish population the frequencies of pathotypes were quite even while in other countries pathotype 1,3,4,7,10,11 was most prevalent.

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

“…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. Meanwhile, virulence spectrum data for 4584 European isolates sampled for two decades as part of the Eucablight project (www.eucablight.org) and for 743 isolates sampled in 2003 in four Nordic countries (Lehtinen et al 2008) showed similar tendencies to our data.…”

“…Note that Polish P isolates had a higher value of C i than C p , indicating that the most complex races were predominant among the most common pathotypes. Similarly to other studies in the literature, rare virulence factors (e.g., against R9) in highly complex pathotypes were observed (Andrivon 1994;Andrivon et al 1994;Lehtinen et al 2008). The pronounced presence of highly complex pathotypes in a recent potato-infecting P. infestans population could be the result of sexual reproduction of the pathogen in Poland (Chmielarz et al 2014).…”

“…Both indices were higher for P isolates than for T isolates, confirming higher complexity for P isolates. Indeed, greater complexity of P isolates and more pathotypes of Polish P. infestans were observed than has been observed for populations from four Nordic countries (Lehtinen et al 2008), a Nicaraguan population (Blandón-Diaz 2011), and a Peruvian population (with the exception of 5 isolates from Huanuco; Perez et al 2001). Note that Polish P isolates had a higher value of C i than C p , indicating that the most complex races were predominant among the most common pathotypes.…”

Population studies on Phytophthora infestans on potatoes and tomatoes in southern Germany

“…Therefore, the effect of mancozeb together with a residual effect of prior applications of fungicides may counteract the higher degree of insensitivity to metalaxyl within the population. During the 1990s metalaxyl resistance was associated with the A1 mating type in many European countries (Gisi and Cohen 1996;Day et al 2004;Lehtinen et al 2008). In the present study, no association between mating type and metalaxyl sensitivity was found.…”

“…In the present study, no association between mating type and metalaxyl sensitivity was found. Lehtinen et al (2008) postulated that sexual reproduction, if present, should break any associations unless the genes for resistance and mating type are closely linked. This hypothesis was extensively tested in P. infestans population studies in central Mexico by Grünwald et al (2001).…”