Phenotypic Characterization of Recent Clonal Lineages of Phytophthora infestans in the United States

Abstract

Phytophthora infestans, the causal agent of late blight disease, has been reported in the United States and Canada since the mid-nineteenth century. Due to the lack of or very limited sexual reproduction, the populations of P. infestans in the United States are primarily reproducing asexually and, thus, show a simple genetic structure. The emergence of new clonal lineages of P. infestans (US-22, US-23, and US-24) responsible for the late blight epidemics in the northeastern region of the United States in the summers of 2009 and 2010 stimulated an investigation into phenotypic traits associated with these genotypes. Mating type, differences in sensitivity to mefenoxam, differences in pathogenicity on potato and tomato, and differences in rate of germination were studied for clonal lineages US-8, US-22, US-23, and US-24. Both A1 and A2 mating types were detected. Lineages US-22, US-23, and US-24 were generally sensitive to mefenoxam while US-8 was resistant. US-8 and US-24 were primarily pathogenic on potato while US-22 and US-23 were pathogenic on both potato and tomato. Indirect germination was favored at lower temperatures (5 and 10°C) whereas direct germination, though uncommon, was favored at higher temperatures (20 and 25°C). Sporangia of US-24 released zoospores more rapidly than did sporangia of US-22 and US-23. The association of characteristic phenotypic traits with genotype enables the prediction of phenotypic traits from rapid genotypic analyses for improved disease management.

<b>Organic cherry tomato yield and quality as affect by intercropping green manure

“…The late blight occurs mainly in environments with high relative humidity and low temperatures. However, there is a study that indicates that tomato plants can also be infected by this disease at higher temperatures (27°C) (Danies et al, 2013;Maziero, Maffia, & Mizubuti, 2009).…”

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

“…Because widely used site-specific fungicides, such as mefenoxam (the active isomer in metalaxyl), inhibit sporulation and mycelial growth inside host tissues by specifically inhibiting RNA polymearase-1, a mutation that changes the affinity of target sites could easily lead to fungicide resistance (Davidse et al 1983). Significant variations for mefenoxam sensitivity were identified among P. infestans isolates from the different genotypes (Hu et al 2012;Danies et al 2013;Fry et al 2013;Kalischuk et al 2012). Isolates of the US-8 and US-11 genotypes were resistant to mefenoxam, while isolates of the genotypes US-22, US-23 and US-24 were initially highly sensitive to sensitive to this fungicide.…”

“…Genetic analysis of P. infestans populations has facilitated a proactive approach in the application of sustainable disease management practices that involve the elimination of specific pathogen genotypes and the selection of effective fungicides. Phenotypic markers available for characterizing P. infestans isolates include mating type (A1 or A2) (Gallegly and Galindo 1958), virulence (Malcolmson and Black 1966;Malcolmson 1969;Cooke et al 2003), host preference (Kalischuk et al 2012;Danies et al 2013), and resistance or sensitivity to the fungicide metalaxyl (Dowley and O'Sullivan 1981;Fry et al 1993).…”

“…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). However, the SSR sequences are inherently hypervariable and a single P. infestans genotype often produces more than one allelic pattern .…”

“…Migration has introduced P. infestans A2 mating types from northwestern Mexico into the United States and Canada and has probably contributed to the occurrence of several new genotypes Danies et al 2013;Peters et al 2014; Table 1). 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.…”