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Genetic variability and pathogenicity on Rhododendron of Phytophthora cactorum x P. hedraiandra hybrids
Boekbijdrage - Boekhoofdstuk Conferentiebijdrage
During the past decade, interspecific hybrids of several Phytophthora species have been described. P. cactorum x P. hedraiandra hybrids even seem to have displaced the parental species on Rhododendron in some countries.
A real-time PCR method using polymorphic sites in the rDNA ITS1 region was developed to discriminate between P. cactorum x P. hedraiandra hybrids and the parental species. This technique was applied to 184 isolates from 10 European countries that were previously designated as P. cactorum or P. hedraiandra based on morphological characteristics. Using the developed real-time PCR method, we found that several isolates were in fact hybrids of both species. Sequencing or PCR-RFLP of the coxI gene revealed that, in most cases, the hybrids carried coxI of P. hedraiandra. In a few cases, however, coxI of P. cactorum was present, suggesting different hybridization events. Hybrid isolates also contained different P. cactorum/P. hedraiandra ITS copy number ratios. At least four groups of hybrids could be distinguished based on these data.
The genetic variability between isolates of P. cactorum, P. hedraiandra and a selection of hybrid isolates of the four designated groups was assessed using AFLP analyses. In most cases, the fragments were shared with one or with both of the parental species. Some fragments were unique for P. cactorum, P. hedraiandra or the hybrids. The presence of differential fragments between certain hybrid isolates also suggests that they are the result of distinct hybridization events.
Pathogenicity of P. cactorum, P. hedraiandra and their hybrids was tested using Rhododendron leaf inoculation assays. Inoculations were carried out by placing a mycelium plug on wounded leaves or by dipping leaves in a zoospore suspension. Some of the hybrids were more pathogenic than either of the parental species.
These data indicate that Phytophthora cactorum x P. hedraiandra hybrids are more common than previously recognized and that hybridization between these species may have taken place several times, followed by genome reorganization. The higher pathogenicity of some isolates as compared to the parental species may explain the increased prevalence of hybrids on Rhododendron.
A real-time PCR method using polymorphic sites in the rDNA ITS1 region was developed to discriminate between P. cactorum x P. hedraiandra hybrids and the parental species. This technique was applied to 184 isolates from 10 European countries that were previously designated as P. cactorum or P. hedraiandra based on morphological characteristics. Using the developed real-time PCR method, we found that several isolates were in fact hybrids of both species. Sequencing or PCR-RFLP of the coxI gene revealed that, in most cases, the hybrids carried coxI of P. hedraiandra. In a few cases, however, coxI of P. cactorum was present, suggesting different hybridization events. Hybrid isolates also contained different P. cactorum/P. hedraiandra ITS copy number ratios. At least four groups of hybrids could be distinguished based on these data.
The genetic variability between isolates of P. cactorum, P. hedraiandra and a selection of hybrid isolates of the four designated groups was assessed using AFLP analyses. In most cases, the fragments were shared with one or with both of the parental species. Some fragments were unique for P. cactorum, P. hedraiandra or the hybrids. The presence of differential fragments between certain hybrid isolates also suggests that they are the result of distinct hybridization events.
Pathogenicity of P. cactorum, P. hedraiandra and their hybrids was tested using Rhododendron leaf inoculation assays. Inoculations were carried out by placing a mycelium plug on wounded leaves or by dipping leaves in a zoospore suspension. Some of the hybrids were more pathogenic than either of the parental species.
These data indicate that Phytophthora cactorum x P. hedraiandra hybrids are more common than previously recognized and that hybridization between these species may have taken place several times, followed by genome reorganization. The higher pathogenicity of some isolates as compared to the parental species may explain the increased prevalence of hybrids on Rhododendron.
Boek: abstractbook 2nd ISHS Symposium on Woody Ornamentals of the Temperate Zone
Jaar van publicatie:2012