Survival of European Ash Seedlings Treated with Phosphite after Infection with the Hymenoscyphus fraxineus and Phytophthora Species

Abstract

The European Fraxinus species are threatened by the alien invasive pathogen Hymenoscyphus fraxineus, which was introduced into Poland in the 1990s and has spread throughout the European continent, causing a large-scale decline of ash. There are no effective treatments to protect ash trees against ash dieback, which is caused by this pathogen, showing high variations in susceptibility at the individual level. Earlier studies have shown that the application of phosphites could improve the health of treated seedlings after artificial inoculation with H. fraxineus. Three-year-old F. excelsior seedlings were inoculated with the following pathogens: a H. fraxineus, Phytophthora species mixture (P. plurivora, P. megasperma, and P. taxon hungarica), in combination with two pathogens and mock-inoculated as the control, and then either watered or treated with ammonium phosphite (Actifos). Results showed significant differences in the survival of seedlings and symptoms of disease development among the treatments. Chlorophyll-a fluorescence parameters indicated a decrease in photosynthetic efficiency in infected plants, suggesting that they were under strong biotic stress, but none of the parameters could be used as a reliable bioindicator for ash decline disease. The application of Actifos enhanced the production of triterpenes (ursolic and oleanolic acid), and decreased the production of phenols (tyrosol) and sterols (β-sitosterol) in seedlings infected with H. fraxineus. Treatment with Actifos caused seedlings to enhance their response to pathogen(s) attack and increase their survival probability.

Interactions between Phytophthora cactorum, Armillaria gallica and Betula pendula Roth. Seedlings Subjected to Defoliation

“…For the moment we are not able to demonstrate by statistical analysis that P. cactorum significantly alters the physiology or the behavior of birch seedlings, nevertheless we confirmed its activity (by baiting) and presence (by isolations and qPCR) in the rhizosphere and root tissues of B. pendula. This is in line with other experiments performed on ash seedlings [51]. Inoculation of potted ash seedlings, Fraxinus excelsior, by P. plurivora via soil two months before shoot inoculation via wounds by Hymenoscyphus fraxineus, demonstrated induction of plant resistance and less mortality (by 40%) than expected, and achieved in H. fraxineus treatment alone (100%).…”

“…Phytophthora could also mask its presence in plants, because the birch seedlings did not react like in the case of root infection by Armillaria, as the level of phenolic compounds in the roots rose only by about 5-6 times (not 15 times like in the case of the fungus). Keča et al [51] showed that P. plurivora, introduced into the soil two months before stem inoculation of ash seedlings with Hymenoscyphus fraxineus (T. Kowalski, Baral, Queloz, Hesoya, comb. nov.), increased plant tolerance to fungal disease.…”

Effect of Phosphinothricin on Transgenic Downy Birch (Betula pubescens Ehrh.) Containing bar or GS1 Genes

“…Chlorophylls and carotenoids are the main components of the photosynthetic apparatus, and change in their content could provide information on the physiological state of leaves [47]. Chlorophyll content [7] and fluorescence [48] are among well-known signs in assessing plants' damage after stress treatment. In our work, birch saplings with the bar gene did not reveal alterations in the chlorophylls and carotenoids content when treated with a standard field dose, but the effect of a double dose depended on the line.…”

Transcriptional responses in developing lesions of European common ash (Fraxinus excelsior) reveal genes responding to infection by Hymenoscyphus fraxineus

“…We found 1009 genes that were differentially expressed between the proximal, symptomatic and the distal, non-symptomatic samples showing that the developing necrosis in the bark and the phloem is associated with substantial transcriptional changes leading up to e.g. the metabolic changes that are associated with necroses in ash [8,28].…”

“…The cytosolic MVA pathway produces isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) precursors for isoprenoids such as terpene-, sterol-and steroid biosynthesis in plants, HMGR1 is considered the rate-limiting enzyme that control the flux through the pathway [31][32][33][34]. It is established that infection with H. fraxineus lead to accumulation of phenolic and isoprenoid compounds in ash [8,28]. The susceptibility of ash trees to H. fraxineus have been associated to iridoid glycoside levels in leaf tissues; highly susceptible genotypes displayed higher levels of several different iridoid glycosides than resistant genotypes [7,9].…”