Implications of Sexual Reproduction for Phytophthora infestans in the United States: Generation of an Aggressive Lineage

Abstract

Phytophthora infestans isolates (n = 26) collected in the Columbia Basin of Oregon and Washington in 1993, which had been characterized previously for mating type, metalaxyl sensitivity, and alleles at the glucose-6-phosphate isomerase locus, were analyzed for nuclear restriction fragment length polymorphism (RFLP) bands detected by probe RG57 and mitochondrial haplotype. Analyses involving the larger set of markers indicated that this group of isolates satisfied expectations of a sexual progeny: they contained much greater genetic diversity than has been reported for most other epidemic populations of P. infestans in the United States and Canada (16 unique multilocus genotypes); both mating types were present in proximity; all possible combinations of alleles occurred at many pairs of polymorphic loci; and two distinct mitochondrial haplotypes were distributed among the isolates. An in vitro laboratory cross involving the putative parents (US-6 and US-7) as parental strains produced progeny with the same general characteristics as the field isolates. Among the field progeny were two genotypes, US-11 and US-16, that had been described previously but from subsequent and largely clonal collections. Isolates obtained from tomatoes (n = 40) and potatoes (n = 7) in 24 counties in California in 1998 were analyzed as described above, and all except one US-8 isolate from potatoes were of the US-11 clonal lineage, consistent with the hypothesis that the US-11 lineage is an especially fit clonal lineage that has survived over time and can dominate pathogen populations over a large area. We conclude that the 1993 Columbia Basin collection represents a sexual progeny that generated the US-11 lineage, and that this lineage is particularly fit when tomatoes are part of the agroecosystem.

Caracterização de isolados de Phytophthora infestans do Distrito Federal e de Goiás

“…Em outros países, após a introdução de isolados do grupo A2 foi constatada a ocorrência de reprodução sexuada e formação de população recombinante (Drenth et al, 1994;Gavino et al, 2000;Goodwin et al, 1998;Sujkowski et al, 1994;Turkensteen, et al, 2000). A ocorrência de isolados do grupo A1 e do grupo A2 no Distrito Federal e em Goiás possibilita a infecção de uma mesma lavoura por isolados A1 e A2, uma vez que podem ser encontrados plantios comerciais de batateira e tomateiro próximos.…”

“…A ocorrência de isolados dos grupos A1 e A2 numa região sobre a mesma cultura aumenta as chances de reprodução sexuada e o surgimento de recombinantes, os quais podem apresentar características melhores de adaptabilidade, tais como maior agressividade e virulência, e resistência a fungicidas, o que dificulta o manejo da requeima (Goodwin, 1997). A ocorrência de reprodução sexuada em países da América do Norte e da Europa trouxe conseqüências como a geração e o estabelecimento de novos genótipos do patógeno, mais agressivos que os existentes, associados tanto a tomateiro como a batateira (Gavino et al, 2000), além da participação de outro tipo de inóculo inicial, os oósporos, que possivelmente passaram a ter papel importante na epidemiologia da doença, contribuindo para um início mais antecipado da epidemia no campo (Turkensteen et al, 2000). Assim, o conhecimento do modo de reprodução de P. infestans contribui diretamente para o manejo da requeima e a determinação da ocorrência de isolados de diferentes grupos de compatibilidade deve ser o primeiro passo para esse estudo.…”

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

“…However, evidence of possible sexual reproduction has been reported in British Columbia and the Columbia Basin of Washington and Oregon (Gavino et al 2000;Goodwin 1997;Goodwin et al 1996) and the opportunity for sexual recombination has increased considerably since 2009 in the United States and Canada with both mating types of P. infestans having been discovered in close proximity (Fig. 3).…”

“…The increased complexity of P. infestans populations has coincided with the emergence of aggressive genotypes with fungicide resistance (Goodwin et al 1995(Goodwin et al , 1996. For example, the metalaxyl resistant US-11 genotype (A1 mating type) devastated both tomato and potato crops in the United States in 1996 and 1997 (Gavino et al 2000;Derie and Inglis 2001;Wangsomboondee et al 2002). The US-11 genotype originated as an especially fit recombinant of the US-6 and US-8 genotypes and displaced both the US-1 and US-6 genotypes.…”

“…The US-11 genotype originated as an especially fit recombinant of the US-6 and US-8 genotypes and displaced both the US-1 and US-6 genotypes. By 1997, US-8 and US-11 were the predominant P. infestans genotypes affecting potato and tomato crops (Dorrance et al 1999;Gavino et al 2000). Between 1995 and 1998, the P. infestans US-18 and US-19 genotypes (both sensitive to metalaxyl) were affecting tomatoes in North Carolina, while the US-17 genotype was the predominant genotype affecting tomatoes elsewhere in the United States (Fraser et al 1999;Wangsomnoondee et al 2002).…”