Tuber Blight Development in Potato Cultivars in Response to Different Genotypes of Phytophthora infestans

Abstract

Migrations or introduction of new genotypes of Phytophthora infestans to a specific region imposes a different perspective for potato production. During 2009-2010, a late blight epidemic affected the Northeastern United States, which quickly spread through several states. The epidemic was characterized by the appearance of a new genotype of P. infestans designated US-22, which was isolated from tomato and potato. Potato tubers are an essential component of late blight epidemics where the pathogen cannot overwinter on Solanaceous plants. Six potato cultivars were inoculated with 12 isolates of P. infestans (five different genotypes), including isolates of the genotype US-22. Tuber blight development was characterized in terms of tissue darkening expressed as area under the disease progress curve values and lenticel infection. The responses indicated that US-8 was more aggressive than US-22, but US-22 isolates obtained from potato were more aggressive on potato than those acquired from tomato. Tuber periderm responses to infection were limited, yet US-8 isolates infected the periderm more often than US-22 isolates. There were significant differences among the cultivars tested but cv. Jacqueline Lee was the most resistant overall. Although isolates of P. infestans genotype US-22 were less aggressive in comparison with US-8 isolates, US-22 isolates still infected potato tubers and were as aggressive us US-8 isolates on some cultivars. Management of late blight caused by isolates of US-22 through host resistance may be feasible but imposes a different set of criteria for consideration from those that US-8 imposed.

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

“…The pathogenicity of Michigan P. infestans isolates on tuber tissue was variable, although isolates within the US‐22 genotype tended to be less aggressive on tubers than the US‐8 isolate, which was reported to be the most tuber‐aggressive genotype (Rojas et al ., ). Infected seed tubers, volunteer tubers and cull tubers can lead to outbreaks of potato late blight; therefore, management and cultural practices, such as seed certification and reduction of sources of inoculum, will play a pivotal role to contain the expansion and survival of the clonal lineage US‐22, reducing the transmission season‐to‐season.…”

“…In addition, a set of 12 reference isolates were included: US-1, US-10, US-11, US-14, US-8 MI, 2400 (US-1), 1810 (US-1), SCRI 07-39 (Blue-13), SCRI 3298A (Blue-13), US-8 (Fry), US-22 (Fry) and IMK 165 (US-22). The experiment was conducted once per season, each tuber was considered a replication unit, and all tubers were incubated in a controlled environment, under conditions previously described (Rojas et al, 2014). After incubation, digital image analysis was used to assess tuber tissue infection as an average on the apical, middle and basal section of each tuber.…”

“…The severity of tuber tissue infection was expressed as relative average reflective intensity (RARI). RARI (%) has a minimum value of 0 (no symptoms) and maximum value of 100 (black tuber surface), as previously described Rojas et al, 2014). Data were analysed by ANOVA using JMP v. 10.0.…”

“…The combination of these phenotypic and genotypic markers has been used to establish the existence of new clonal lineages, such as US-8, which replaced the clonal lineage US-1 in North America (Fry & Goodwin, 1997). The clonal lineage US-8 was characterized as metalaxyl-M resistant and one of the most aggressive clonal lineages on potato foliage and tubers, with devastating effects (Gavino et al, 2000;Kirk et al, 2001b;Rojas et al, 2014). Since the occurrence of the genotype US-8, several other clonal lineages or genotypes have been reported in the US and Canada (Kawchuk et al, 2011;Hu et al, 2012;Seidl Johnson & Gevens, 2014).…”

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

“…For example, isolates of the P. infestans US-23 genotype have been shown to produce considerably more sporangia on tomatoes as compared to potatoes ). Genotypes US-22 and US-23 are pathogenic to both potatoes and tomatoes, although they show a preference for tomatoes, while genotype US-24 is particularly pathogenic on potatoes and less aggressive towards tomatoes Rojas et al 2014). Moreover, recent results indicate a transcontinental distribution of the US-23 P. infestans genotype on infected tomato transplants being sold commercially (Kalischuk et al 2012).…”