Lisääntyvätkö patogeenisienten aiheuttamat metsätuhot tulevaisuuden ilmastossa?

Osa Metsäekosysteemien toiminta ja metsien käyttö muuttuvassa ilmastossa (MIL) -tutkimusohjelman loppuraporttia: http://urn.fi/URN:NBN:fi:metla-201210036195</a

Temperature range for germination of Thekopsora areolata aeciospores from Finnish Norway spruce seed orchards

Cherry-spruce rust caused by Thekopsora areolata (Fr.) Magnus is a serious cone pathogen of Norway spruce [Picea abies (L.) Karst.]. The rust causes great economical losses in seed orchards specialized in the production of high quality seeds. Germination range of T. areolata aeciospores from rust populations (spore sources) in seven Finnish Norway spruce seed orchards was tested on water agar and malt agar at nine temperatures varying between 6–30 °C. The temperature range of spore germination was high varying between 6 °C and 27 °C, while germination was retarded at 30 °C. The peak in germination rate of all spore sources occurred between 15–24 °C. In a model with fixed effects of agar media, temperature and spore source, temperature had the most significant effect on germination. Spore source had a less significant effect, while agar media had a non-significant effect on germination. The rust was able to germinate at low temperatures corresponding to temperatures when the thermal growing season starts at 5 °C in the spring. As spores from cones from both the spruce canopy and the ground showed very similar germination ranges, it indicated the great capacity of all spores of the rust to germinate early in the spring. Hot temperatures with over 30 °C drastically reduced germination of the rust

Temporal and spatial dispersal of Thekopsora areolata basidiospores, aeciospores, and urediniospores

Cherry spruce rust causes huge yield losses in Norway spruce seed production in Fennoscandia. The causal agent, Thekopsora areolata, has three types of spores that disperse during spring: basidiospores are produced on basidia that grow out from teliospores in overwintered bird cherry leaf litter to infect new pistillate spruce cones, aeciospores are released from old diseased spruce cones to infect bird cherry leaves, and urediniospores are produced from new bird cherry leaves for reinfection. No study has examined the dispersal of T. areolata spores, including the basidiospores that cause primary infection in spruce cones. In this study, teliospores of T. areolata were germinated in the laboratory and the morphology of basidiospores was described. T. areolata spores were sampled in Ultuna, Sweden and Joutsa, Finland with 21 spore traps at each site. Peaks in aeciospores were observed from 11 to 25 May and from 2 to 8 June at the Finnish site, and from 4 to 18 May at the Swedish site. Urediniospores were first observed 2-3 weeks after the peaks in aeciospores and they were mainly distributed within 10 m from the bird cherry trees. Peaks of 1-2 weeks in basidiospore detection coincided with multiple rain events. The basidiospore peak overlapped with the spruce pollen peak in Finland but not in Sweden. The quantities of basidiospores from different spore traps within 100 m from the spore source had no gradient. Information on spatial and temporal spore release is important for making decisions on disease management strategies

Low disease incidence and cone bagging in Picea abies are associated with low genotypic diversity in Thekopsora areolata

Thekopsora areolata infects pistillate cones of Picea spp. with monokaryotic basidiospores in the spring. Receptive monokaryotic hyphae in the cones are fertilized by monokaryotic spermatia in the summer, and dikaryotic aecia are produced in cones in late summer. Infected cones produce no fertile seeds, meaning the disease causes large reductions in seed production. To understand the seasonal variation of T. areolata genotypic diversity, 548 aecia from 55 infected cones were sampled from multiple seed orchards in 2015, 2019 and 2020. Cone bagging experiments were performed during two seasons to investigate the sexual reproduction of T. areolata. In addition to the published simple-sequence repeat (SSR) markers, we developed 10 new polymorphic SSR markers to improve the resolution of population genetic analysis. Aecia were genotyped with 18 SSR markers in total. In 2015, when disease incidence was high in the seed orchards, the T. areolata populations had high genotypic diversity (H = 4.69). In 2019 and 2020, when disease incidence was low, the T. areolata populations had lower genotypic diversity (H = 3.88 and 3.85) and several cones were dominated by a single multilocus genotype. The genotypic diversity of T. areolata in a recently established seed orchard was exceptionally low (H = 2.01). Seven bagged cones that were infected produced either aecial primordia or aecia with lower diversity than exposed cones. The results indicate that cross-fertilization is important for sexual reproduction and aecia formation of T. areolata, and genotypic diversity of T. areolata increased with higher disease prevalence

Kuusen siemenviljelmillä esiintyvien pintakasvillisuuden lajien alttius kuusentuomiruosteelle

Kuusentuomiruoste (Thekopsora areolata (Fr.) Magnus) on tärkeä kuusilajien (Picea spp.) käpytuholainen Euroopassa ja Aasiassa. Sieni aiheuttaa merkittäviä taloudellisia menetyksiä etenkin metsäkuusen (Picea abies (L.) H. Karst.) korkealaatuisen siemenen tuotantoon erikoistuneilla siemenviljelmillä. Tauti voi aiheuttaa kymmenkertaisen alenemisen siementen itämisessä. Sienellä on viisi eri itiömuotoa kuusella ja väli-isäntäkasveilla, joten sen torjunta on hankalaa, koska ei tiedetä, pitäisikö taudin torjunnassa keskittyä väli-isäntäkasvien poistoon, itiöinnin katkaisemiseen kuusen kävyistä kasveihin, hyönteisten vähentämiseen kävyissä vai käpyjen tartunnan vähentämiseen fungisideilla tai biotorjunta-aineilla

Variation of compounds in leaves of susceptible and resistant alternate hosts of Cronartium pini and C. ribicola

Leaf compounds may contribute to plant defense against Cronartium rusts. Secondary compounds are either natural or induced in leaves. We studied the variation of compounds in leaves of six alternate hosts of Cronartium pini and two of C. ribicola that represented either susceptible or resistant species to these rusts. Extracts from the plant leaves were analyzed using LC-MSMS (liquid chromatography tandem mass spectrometry) and compounds were compared between susceptible and resistant species of the same plant genera to identify significant differences between resistant and susceptible species. Also, LC–MS (liquid chromatography mass spectrometry) with external calibration was used to quantify 12 candidate compounds known from the literature. Among these compounds, the most abundant significant ones in C. pini -resistant Melampyrum pratense were chlorogenic acid and quercitrin, in Veronica chamaedrys ferulic acid, quercitrin and luteolin and in Impatiens glandulifera quercitrin, ferulic acid, kaempferol, rutin and hyperoside. In C. ribicola -resistant Ribes rubrum the most abundant significant compounds were caffeic acid, p-coumaric acid and quercitrin. Among all extracted leaf compounds, concentrations of three compounds were over 1000 times greater in rust-resistant M. pratense, three compounds in V. chamaedrys, eight compounds in I. glandulifera, and one compound in R. rubrum than in rust-susceptible species. Among the compounds, the most promising possibly linked to rust resistance were chlorogenic acid and quercitrin

Low disease incidence and cone bagging in Picea abies are associated with low genotypic diversity in Thekopsora areolata

Thekopsora areolata infects pistillate cones of Picea spp. with monokaryotic basidiospores in the spring. Receptive monokaryotic hyphae in the cones are fertilized by monokaryotic spermatia in the summer, and dikaryotic aecia are produced in cones in late summer. Infected cones produce no fertile seeds, meaning the disease causes large reductions in seed production. To understand the seasonal variation of T. areolata genotypic diversity, 548 aecia from 55 infected cones were sampled from multiple seed orchards in 2015, 2019 and 2020. Cone bagging experiments were performed during two seasons to investigate the sexual reproduction of T. areolata. In addition to the published simple-sequence repeat (SSR) markers, we developed 10 new polymorphic SSR markers to improve the resolution of population genetic analysis. Aecia were genotyped with 18 SSR markers in total. In 2015, when disease incidence was high in the seed orchards, the T. areolata populations had high genotypic diversity (H = 4.69). In 2019 and 2020, when disease incidence was low, the T. areolata populations had lower genotypic diversity (H = 3.88 and 3.85) and several cones were dominated by a single multilocus genotype. The genotypic diversity of T. areolata in a recently established seed orchard was exceptionally low (H = 2.01). Seven bagged cones that were infected produced either aecial primordia or aecia with lower diversity than exposed cones. The results indicate that cross-fertilization is important for sexual reproduction and aecia formation of T. areolata, and genotypic diversity of T. areolata increased with higher disease prevalence