Genetic Structure of the Population of Phytophthora infestans Attacking Solanum ochranthum in the Highlands of Ecuador

Abstract

Thirty-nine isolates of Phytophthora infestans were collected from the wild host Solanum ochranthum in the highland tropics of Ecuador and characterized with a set of phenotypic and molecular markers (mating type, metalaxyl sensitivity, the allozyme loci Gpi, and Pep, mitochondrial DNA haplotype, RFLP, and SSR), as well as for pathogenicity on various hosts. Three groups of isolates (A, B, and C) were identified based on their multilocus genotypes and variable abilities to cause disease on different hosts. Group A had a combination of alleles for the Gpi (86/100), Pep (96/100) and mtDNA (Ia) loci, as well as an RFLP fingerprint, that have not been reported for P. infestans in Ecuador, or elsewhere. Group B shares many marker characteristics with the US-1 lineage described in Ecuador on tomato, pear melon (S. muricatum), and S. caripense, but has SSR alleles not present in typical US-1 isolates. Group C for all markers tested is identical to the EC-1 lineage described on cultivated and wild potatoes in Ecuador. All isolates from S. ochranthum were able to re-infect their host of origin in the detached leaf assay; however, we did not draw clear conclusions as to the relative aggressiveness of the three groups on this host. Isolates of group A were the most specialized and were generally non-pathogenic or weakly pathogenic on all hosts other than S. ochranthum. Groups B and C infected tuber-bearing hosts, including the cultivated potato but were generally non-pathogenic on other non-tuber bearing hosts. Solanum ochranthum was infected by isolates coming from tuber-bearing Solanum hosts (i.e., the EC-1 lineage of P. infestans) and some US-1 isolates from non-tuber bearing hosts. Thus, in nature this species might be a potential reservoir of inoculum of different pathogen populations able to infect the cultivated hosts potato, tomato and pear melon (S. muricatum). Unlike potato and tomato in Ecuador, each of which is primarily attacked by a highly specialized pathogen population, S. ochranthum appears to harbour at least three pathogen groups of different genetic make-up. The unresolved issue of potential host specificity in isolates found on S. ochranthum could complicate efforts to use this species in tomato improvement.

Phytophthora betacei, a new species within Phytophthora clade 1c causing late blight on Solanum betaceum in Colombia

“…To date, host range and distribution of P. andina is restricted to the Andean region of Ecuador and Peru where it has been reported in tree tomato crops (these isolates belong to the EC-3 clonal lineage) and wild solanaceous species (isolates belonging to the EC-2 clonal lineage) (Oliva et al 2010). These observations, along with previous reports based on phylogenetic analyses using both nuclear and mitochondrial markers, reveal this species as polyphyletic, suggesting it might be a species complex comprising at least two genetically distinct lineages (Adler et al 2002, Kroon et al 2004, Chacón et al 2006, Oliva et al 2010, Cárdenas et al 2012, Forbes et al 2013, Goss et al 2014, Lassiter et al 2015, Forbes et al 2016).…”

The Irish potato famine pathogen Phytophthora infestans originated in central Mexico rather than the Andes

“…unknown to science (16). Surprisingly, populations of P. infestans and P. andina are clonal in South America and are not in Hardy-Weinberg equilibrium (6,(17)(18)(19). Thus, the question of whether P. infestans originated in the Andes or central Mexico remained unresolved.…”

“…Posterior distributions for parameters were wide, indicating limited confidence in the parameter estimates. (6,9,10,(17)(18)(19). Both mating types of P. infestans are known to have been present since at least the 1960s in central Mexico (37,38).…”

Genetic diversity of Phytophthora infestans in the Northern Andean region

“…Each P. infestans clonal lineage is associated with a different host group: US-1 lineage with tomato, EC-1 with potato, EC-2 with wild solanaceous species, particularly with the Anarrhichomenum section, and EC-3 with S. betaceum [ 15 - 17 ]. Additionally, genetic differentiation is found among isolates of P. infestans associated with S. ochranthum [ 18 ]. Geographically, no clear subdivision was found in Ecuador when using allozymes and RFLP markers [ 15 ].…”