Host Specificity of Phytophthora infestans on Tomato and Potato in Ecuador

Abstract

Sixty Ecuadorian isolates of Phytophthora infestans from potato and 60 isolates from tomato were compared for dilocus allozyme genotype, mitochondrial DNA haplotype, mating type, and specific virulence on 11 potato R-gene differential plants and four tomato cultivars, two of which contained different Ph genes. Restriction fragment length polymorphism (RFLP) fingerprints of subsamples of isolates from each host were compared by using RG57 as the probe. All potato isolates had the allozyme genotype, haplotype, and mating type of the clonal lineage EC-1, which had been previously described in Ecuador. With the same markers, only one isolate from tomato was classified as EC-1; all others belonged to the globally distributed US-1 clonal lineage. RFLP fingerprints of isolate subsets corroborated this clonal lineage classification. Specific virulence on potato differentials was broadest among potato isolates, while specific virulence on tomato cultivars was broadest among tomato isolates. Some tomato isolates infected all tomato differentials but no potato differentials, indicating that specific virulence for the two hosts is probably controlled by different avirulence genes in P. infestans. In two separate experiments, the diameters of lesions caused by nine isolates from potato and 10 from tomato were compared on three tomato and three potato cultivars. All isolates produced larger lesions on the host from which they were isolated. No isolates were found that were highly aggressive on both tomato and potato. We conclude that there are two different populations of P. infestans in Ecuador and that they are separated by host.

Population studies on Phytophthora infestans on potatoes and tomatoes in southern Germany

“…The potato isolate 60 belonged to a completely different cluster than the four other isolates from tomato plants (58, 59, 61 and 62). This finding is consistent with previous reports (Legard et al 1995;Lebreton and Andrivon 1998;Oyarzún et al 1998;Lebreton et al 1999), and supports the view that some specificity to the host plant and host adaptation exists within P. infestans. However, there is also a subpopulation which is able to attack both hosts, as shown by the dendrogram in Fig.…”

“…All isolates were aggressive on potatoes, but few on tomatoes. Population surveys showed host-related differences in the nature and frequency of P. infestans clones present (Fry et al 1992;Goodwin et al 1995;Oyarzún et al 1998). Lebreton and Andrivon (1998) found that both mating types were present among the collections from both hosts, but isolates with the A2 mating type were found on potato only in one garden crop, adjacent to tomato.…”

The Effects of Host Diversity and Other Management Components on Epidemics of Potato Late Blight in the Humid Highland Tropics

“…However, if sexual reproduction of P. infestans occurs on a large scale in the future, mixtures with major genes for resistance might play a larger role. Race-nonspecific adaptation may be of use: Oyarzun et al (19) found different levels of aggressiveness of isolates from potatoes and tomatoes when infecting potato. Race-nonspecific adaptation to host genotype may be important in partitioning pathogen populations in host mixtures (3,15,16,18).…”

“…One likely difference between tropical and temperate systems is the level of inoculum that will arrive at newly planted fields. Year round potato production and the continuous presence of late blight have been described by researchers working in the highland tropics (13,19), and fungicides are used regularly throughout the year (4). This is in contrast to Europe and North America where blight epidemics must begin again each growing season.…”

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

“…A zig-zag model has been proposed to explain the recognition and evasion that occurs between the plant-pathogen recognition and interaction that limits the durability of R genes (Jones and Dangl 2006;Hein et al 2009). Both potatoes and tomatoes have major genes that confer resistance to P. infestans, namely the Rpi genes in potatoes and Ph genes in tomatoes (Black et al 1953;Oyarzun et al 1998;Vleeshouwers et al 2011). Initially, a total of 11 R genes (R1-R11) from Solanum demissum were characterized for potatoes ( Table 2).…”