Tomasz Oszako, Katarzyna Sikora, Małgorzata Borys, Katarzyna A. Kubiak and Miłosz Tkaczyk
In the last decades, a new wave of oak decline has been observed in Poland. The most important pathogenic organisms involved in this phenomenon are probably soil-borne pathogens Phytophthoragenus, especially P. quercina. In this work, we sought to test the influence of elevated CO2 concentration on the susceptibility of oaks (Quercus robur L.) to infection by P. quercina. In order to test the susceptibility of oak fine roots to infection, we applied phosphite-based fertiliser Actifos in 0.6% concentration. One-year-old oak seedlings were grown for one year in greenhouse with either an ambient atmosphere (400 ppm CO2) or an elevated (800 ppm) concentration of CO2. Oaks grown at the elevated CO2 concentration developed longer shoots as proved by statistically significant differences. However, there was no difference in the development of root systems. The application of Actifos had a positive significant effect on the development of shoots and the surface area of fine roots under the elevated CO2 concentration.
Miłosz Tkaczyk, Katarzyna Sikora, Justyna A. Nowakowska, Katarzyna Kubiak and Tomasz Oszako
Global climate change is associated with higher concentrations of atmospheric carbon dioxide (CO2). The ongoing changes are likely to have significant, direct or indirect effects on plant diseases caused by many biotic agents such as phytopathogenic fungi. This study results showed that increased CO2 concentration did not stimulate the growth of 1-year-old beech Fagus sylvatica L seedlings but it activated pathogenic Phytophthora species (P. plurivora and P. cactorum) which caused significant reduction in the total number of fine roots as well as their length and area. The results of the greenhouse experiment indicated that pathogens once introduced into soil survived in pot soil, became periodically active (in sufficient water conditions) and were able to damage beech fine roots. However, the trees mortality was not observed during the first year of experiment. DNA analyses performed on soil and beech tissue proved persistence of introduced Phytophthora isolates.
Tomasz Oszako, Katarzyna Sikora, Lassaâd Belbahri and Justyna A. Nowakowska
In Poland, about 20% of forest nurseries use irrigation water coming from natural superficial reservoirs, presumed to be the first source of infection caused by harmful pathogens belonging to the Oomycota class, especially Phytophthora genus and Pythium genus. The forest nursery is the only place where forest managers can react before pathogens leave it with asymptomatic plants or soil attached to their roots. The aim of this research was detection and identification phytopathogens in water samples. In order to recognise genus Phytophthora or Pythium in water collected from 33 places in five different forest districts in Poland, two DNA-based approaches of identification were applied: (i) the TaqMan probes, and (ii) sequencing of the ITS6/4 region.
The genomic DNA was obtained from 17 of 33 investigated water samples. TaqMan probes helped to identify 8 oomycetes present in 17 water samples. Based on ITS rDNA sequencing data, pathogens were identified in 17 cases, and this to the genus level (6 cases) and to the species level (11 cases). In total five Oomycetes species were identified, i.e. 3 Pythium species (Py. citrinum, Py. angustatum, Py. helicoides) and two Phytophthora species (P. lacustris sp. nov. - former taxon Salixsoil, P. gallica sp. nov.).
Tomasz Oszako, Katarzyna Sikora, Lassaâd Belbahri and Justyna A. Nowakowska
Pathogens of Phytophthora genus are common not only in forest nurseries and stands, but also in water courses. Species of Phytophthora spread with plants for plantings (and soil attached to them) and with water courses as well, attacking the plants growing in riparian ecosystems. Several specialized organisms damaging only one tree species were identified like P. alni on alders or P. quercina on oaks. Some Phytophthora species can develop on several hosts like P. plurivora and P. cactorum on oaks, beeches, alders, ashes and horse chestnuts. Other oomycetes like P. gallica species was found for the first time in Poland in water used for plant watering in forest nursery. Species P. lacustris and P. gonapodyides were found in superficial water. Phytophthora species P. polonica was identified in the declining alder stands for the first time in the world, and P. taxon hungarica and P. megasperma were found in the rhizosphere of seriously damaged ash stands for the first time in Poland. The most often isolated species were P. plurivora (clade 2) with frequency 37% and P. lacustris with frequency 33% (clade 6). The best represented clade 6 revealed the occurrence of 6 species: P. gonapodyides, P. lacustris, P. megasperma, P. sp. raspberry, P. taxon hungarica and P. taxon oak soil.
Aneta B. Lyubenova, Justyna A. Nowakowska, Katarzyna Sikora, Kaloyan Kostov, Małgorzata Borys, Slavtcho B. Slavov and Tomasz Oszako
Our aim was to examine the virulence of eight Phytophthora isolates belonging to three species (Phytophthora cryptogea, Phytophthora plurivora and Phytophthora quercina) obtained from diverse European ecosystems (in Bulgaria, Poland and Germany) towards three forest tree hosts – English oak (Quercus robur L.), Turkey oak (Quercus cerris L.) and European beech (Fagus sylvatica L.).
All plants grown from seeds in a greenhouse conditions were artificially inoculated under the stem bark with Phytophthora cultures. The tested isolates turned to be more aggressive to Turkey oaks than to English oak trees. In case of European beech, the isolates of P. cryptogea and P. plurivora exposed various virulence. The potential hazard of the introduced foreign isolates for the oak and beech forests in Poland and Bulgaria is discussed. Amongst the tested isolates, P. quercina P290 from German highly infected Bulgarian Turkey oaks; therefore, its negative potential impact on Bulgarian oak forests could be considered as high (if unintentionally introduced). Also, two Bulgarian isolates belonging to P. cryptogea and P. plurivora are risky for Polish beech forests, if exposed to the pathogen. The observed pathogenicity of the tested Phytophthora species proved their potential as important contributors to decline of valuable forest ecosystems dominated by oaks (Q. robur and Q. cerris) or beech (F. sylvatica), in both Poland and Bulgaria. We found that investigated Phytophthora pathogens could develop in the living plant stem tissues without causing any disease symptoms, which is another demonstration that phytosanitary control by simple observation of plant material is not effective.
Miłosz Tkaczyk, Katarzyna Sikora, Justyna A. Nowakowska, Ewa Aniśko, Tomasz Oszako, Lassaâd Belbahri and Ivan Milenković
To investigate susceptibility of young Scots pine seedlings to four Phytophthora species: Phytophthora cactorum, Phytophthora cambivora, Phytophthora plurivora and Phytophthora pini; seven-day-old seedlings of Scots pine (15 seedlings per experiment) were infected using agar plugs of the respective species. Control group also consisted of 15 seedlings and was inoculated with sterile agar plugs. Results unambiguously show that after 4.5 days, all seedlings show clear signs of infection and display severe symptoms of tissue damage and necrosis. Moreover, three and two seedlings in the P. cactorum and P. cambivora infected seedlings groups, respectively, collapsed. The length of largest necrosis measured 13.4±3.90 mm and was caused by P. cactorum. To rule out any putative contamination or infection by secondary pathogens, re-isolations of pathogens from infection sites were performed and were positive in 100% of plated pieces of infected seedlings. All re-isolations were, however, negative in the case of the control group. Detailed microscopic analyses of infected tissues of young seedlings confirmed the presence of numerous Phytophthora species inside and on the surface of infected seedlings. Therefore, our results suggest Phytophthora spp. and mainly P. cactorum and P. cambivora as aggressive pathogens of Scots pine seedlings and highlight a putative involvement of these species in the damping off of young Scots pine seedlings frequently observed in forest nurseries.