Influence of competition and host plant resistance on selection in Phytophthora infestans populations in Michigan, USA and in Northern Ireland

Abstract

Competition between genotypes of Phytophthora infestans was studied by inoculating potato cultivars with differing susceptibility to late blight in field experiments over three years in Northern Ireland, UK, and Michigan, USA. Multiple isolates of six genotype groups of P. infestans were chosen from the local populations in both N. Ireland and Michigan for inoculation of separate field trials planted in 2003, 2004 and 2005. Four cultivars were used in each trial; two (susceptible cv. Atlantic and the partially resistant cv. Stirling) were common to both locations, whereas the two additional cultivars (with partial resistance to late blight) were cvs Santé and Milagro in N. Ireland and cvs Pike and Jacqueline Lee in Michigan. Single-lesion isolates of P. infestans were obtained from leaves at 1% level of infection, characterized using pre-assigned markers and re-assigned to their respective genotype groups. Extreme selection occurred within the population of genotypes of P. infestans in N. Ireland in each year, with different genotype groups dominating the infection of different cultivars. Selection was observed on all cultivars tested, but was greatest on the more resistant cultivars. Over the 3 years, all of the 114 isolates obtained from cv. Milagro belonged to a single group, whereas among the 118 isolates from cv. Atlantic all six groups were represented. By contrast, in Michigan, the US-8 genotype dominated infection in all cultivars in each year; only 12 of 374 isolates characterized belonged to other genotypes (11 US-14 and a single US-10 isolate).

Identification of Phytophthora species baited and isolated from forest soil and streams in northwestern Yunnan province, China

“…P. taxon PgChlamydo which was detected in high frequency (59.72% of all isolates), is also frequently isolated from streams, rivers, irrigation water and soils in western North America, Argentina, Europe and Australia (Brasier et al 1993;Hansen and Delatour 1999;Greslebin et al 2005;Burgess et al 2009;Reeser et al 2011a,b). Extreme selection occurred within the population of genotypes of P. infestans in North Ireland in each year with different genotype groups dominating the infection of different resistant potato cultivars (Young et al 2009). The abundance of Phytophthora species and strains might result from the high diversity of forest vegetation, stands and environment in mountainous areas.…”

Effect of Different Genotypes of Phytophthora infestans (Mont. de Bary) and Temperature on Tuber Disease Development

“…This suggests that the genes responsible for foliage resistance are not present or at least active in the tubers. Inoculation with the US-8 genotype of P. infestans, the dominant genotype in North America (Young et al 2009), resulted in significant tuber late blight development for most cultivars and ABL tested. These findings are in agreement with Lambert and Currier (1997) and Lambert et al (1998) who found that the US-8 genotype isolates were the most ) circumstantially suggest that highly aggressive genotypes of P. infestans, such as the US-8 genotype, may produce limited primary inoculum due to severe tuber rotting and deterioration of tubers before emergence.…”

“…Cultures of P. infestans isolates corresponding to clonal lineages US-1 (Pi95-3), US-1.7 [Pi88 (2002-06) (Young et al 2009). The selected isolates were from the collection of W. Kirk (Michigan State University).…”

“…These isolates were acquired from field infections from 1995 to 2006 on foliage and tubers of potatoes of commonly grown in Michigan, USA. Pathogenicity was determined on foliage and tubers in tuber and detached leaf tests (Young et al 2009). Since the genotypes US-1, US-1.7 and US-11 are rare in the US only single isolates representative of the range of genotypes were selected for this study.…”

Phenotypic and genotypic variation in Michigan populations of Phytophthora infestans from 2008 to 2010

“…Populations of P. infestans in the northeastern US have been extensively characterized, but Michigan populations have never been comprehensively studied. Nonetheless, some recent studies have published characteristics of a few P. infestans isolates collected in Michigan (Young et al, 2009;Catal et al, 2010). The clonal lineage US-1 of P. infestans was present from before 1991 until around 1995, when the population shifted to clonal lineage US-8 (Kirk et al, 2004).…”