Finnish Cronartium ribicola does not infect alternate hosts of Cronartium flaccidum

Susceptibility of the main alternate hosts of Cronartium flaccidum, Vincetoxicum spp. and Melampyrum spp., to C. ribicola was investigated by artificial inoculations on detached leaves in the laboratory and on whole plants in the greenhouse. Neither uredinia nor telia developed on the leaves of either Vincetoxicum hirundinaria, Vincetoxicum nigrum, Melampyrum sylvaticum, Melampyrum pratense, Melampyrum nemorosum, Melampyrum arvense, Melampyrum cristatum or Melampyrum polonicum following inoculation by the 26 aeciospore sources collected from Pinus strobus, Pinus monticola, Pinus flexilis and Pinus peuce in 2000–2003. The results suggest that Finnish C. ribicola does not infect the main alternate hosts of C. flaccidum. Cronartium ribicola and C. flaccidum can thus be identified reliably by inoculations on their main alternate hosts.     

Aeciospores of Cronartium flaccidum,C. ribicola and Endocronartium pini show no differences in morphology

The morphology of the aeciospores of the pine stem rust fungi Cronartium flaccidum, Cronartium ribicola and Endocronartium pini, collected from nine locations in Finland, Sweden and Italy, was compared. Surface structures of 900 aeciospores were visually classified using a scanning electron microscope, and dimensions of 1100 aeciospores were measured from micrographs. The data grouping was tested with discriminant analysis. The spores had well-defined smooth areas and annulate warts on their surface. E. pini, C. flaccidum and C. ribicola could not be distinguished by the surface structures of the spores. The grouping of spores by dimensions into sample locations was statistically significant by one discriminant function, while the grouping into species was not. The observed similarities corroborated the current views on the close relationship of C. flaccidum and E. pini.     

Distribution and frequency of Cronartium flaccidum on Melampyrum spp. in permanent sample plots in Finland

Abstract

In 2006, the distribution and frequency of pine stem rust Cronartium flaccidum was studied on Melampyrum spp. in permanent sample plots of an EU forest health monitoring program and of a BioSoil program in Finland. The frequency of Melampyrum spp. infected with C. flaccidum was low, but the rust was recorded in new locations of eastern Finland. No uredinia of C. flaccidum were observed in samples collected from over 700 plots. Telia were common on Melampyrum sylvaticum but were occasionally also found on Melampyrum pratense and Melampyrum nemorosum. Melampyrum pratense was the most common species growing in plots on mainly dry sites. Melampyrum sylvaticum was seldom detected, suggesting that alternate hosts are absent from northern Finland or that the current sample plot network is too sparse for effective disease monitoring in the north. No relationship between C. flaccidum, Melampyrum spp. and rust incidence in host trees was observed, which implies that the autoecious Peridermium pini is a more likely pathogen than C. flaccidum locally. Because plots containing M. sylvaticum occur almost solely in southern Finland, the plots with M. sylvaticum reflect the best changes in rust epidemics in that area. In the future, nutrient-rich sites containing M. sylvaticum may serve as a source of rust epidemics. It is unlikely that C. flaccidum will spread to dry sites via M. pratense.     

Relative Susceptibility of Four Melampyrum Species to Cronartium flaccidum

The relative susceptibility of Melampyrum arvense, M. pratense, M. sylvaticum and M. nemorosum to Cronartium flaccidum was investigated by artificial inoculations. Uredinia and telia were artificially produced on plants from sown seed or transplanted from the wild in the greenhouse. This is the first report in which C. flaccidum telia were artificially produced on leaves of whole plants of M. arvense and M. pratense, the first report of successful artificial disease establishment on M. arvense and the first report of telia production on the upper surface of Melampyrum leaves. As an earlier unreported observation, telia were occasionally formed on both upper and lower leaf surfaces of M. arvense, M. sylvaticum and M. pratense. Host species, spore source and their interaction each affected some aspects of disease development. Melampyrum arvense and M. sylvaticum were the most susceptible hosts, while M. nemorosum was least susceptible. Melampyrum arvense should be considered a potentially important alternate host of C. flaccidum with its limited area of distribution.     

Cronartium flaccidum fruitbody production on Melampyrum spp. and some important alternate hosts to pine

Four Vincetoxicum species, Paeonia anomala and Melampyrum sylvaticum known to act as alternate hosts for Cronartium flaccidum, and a potential host Melampyrum pratense were inoculated either in vitro or in vivo with various aeciospore sources of C. flaccidum. All fresh C. flaccidum aeciospore sources variably produced uredia or telia on Vincetoxicum hirundinaria, Vincetoxicum mongolicum, Vincetoxicum fuscatum, Vincetoxicum nigrum, P. anomala, nine geographic provenances of M. sylvaticum, and two provenances of M. pratense. This is the first time that C. flaccidum telia were artificially produced on M. sylvaticum and the first time that M. pratense was shown to act as alternate host for C. flaccidum. The results suggest that M. sylvaticum is relatively susceptible to C. flaccidum, whereas M. pratense is almost resistant to this rust. The low host-specificity of the Finnish population of C. flaccidum was demonstrated, as V. hirundinaria from Italy was susceptible to the rust.     

Cronartium flaccidum on Pinus spp.: relation of inoculum concentration to symptom development

An experiment on the effect of eight inoculum concentrations of basidiospores of Cronartium flaccidum, on development of symptoms on P. nigra spp. nigricans var. austriaca, P. nigra ssp. italica, P. nigra ssp. laricio var. calabrica (from Calabria and Corsica) showed that 60000 basidiospores/ml was the optimum concentration and P. nigra ssp. laricio was the most sensitive.     

Cronartium flaccidum sporulates on new Euphrasia species in natural habitats in Finland

Natural sporulation of a pine stem rust, Cronartium flaccidum, was investigated in forested habitats in northern Finland. First, a diffuse sample (100) of seven species of hemiparasitic plants was collected in their natural habitats close to one another. C. flaccidum was found to sporulate on six species. The rust was most common on Melampyrum sylvaticum with 21% of the plants and 2% of the leaves carrying telia. Telia occurred occasionally also on Euphrasia frigida, E. nemorosa, E. stricta, Pedicularis palustris ssp. palustris and Melampyrum pratense (less than 5% of the plants and 0.3% of the leaves). The rust was absent on Rhinanthus minor. Second, a diffuse sample of each of M. sylvaticum, M. pratense, Euphrasia sp. and Rhinanthus sp. was collected from 10 sample plots surrounding the city area. C. flaccidum occurred on 0.29% of the leaves of M. sylvaticum, and 0.02%–0.03% of M. pratense and Euphrasia, but it was lacking from Rhinanthus. The results indicated that C. flaccidum was most common and widespread on M. sylvaticum, but sporulated sporadically also on Euphrasia sp., P. palustris and M. pratense. This is the first report of sporulation of C. flaccidum on Euphrasia frigida and E. nemorosa in their natural habitats. In contrast, a second rust observed in this survey, Coleosporium sp. needle rust, was much more common than C. flaccidum on the investigated plants. In the first site, 43%–54% of plants and 8%–17% of leaves of Melampyrum spp. and 0%–13% of plants and 0%–2% of leaves of Euphrasia spp., Rhinanthus minor and Pedicularis palustris carried uredinia or telia. In the second site, 9%–15% of leaves of Melampyrum spp. and 1%–2% of Euphrasia sp. and Rhinanthus sp. carried rust uredinia and/or telia. The results indicate frequent spore dispersal of both Cronartium and Coleosporium in the area, and versatile rust sporulation on hemiparasitic plant species.     

Pedicularis and Castilleja are natural hosts of Cronartium ribicola in North America: a first report

White pine blister rust disease, caused by the introduced pathogen Cronartium ribicola, has severely disrupted five‐needled pine ecosystems in North America. A 100‐year effort to manage this disease was predicated in part on the premise that the pathogen utilizes only species of Ribes (Grossulariaceae) as alternate hosts on this continent. The current study presents the first conclusive demonstration that some species in the family Orobanchaceae (Pedicularis racemosa and Castilleja miniata) are functioning as alternate hosts in a natural ecosystem of North America. This finding has implications for improving our understanding of epidemiology, pathogen adaptation and host–pathogen interactions within white pine blister rust.     

Resistance of Paeonia cultivars to Cronartium flaccidum in Norway

Cultivars of Paeonia differed widely in their resistance to Cronartium flaccidum in Norway; ‘Globe of Light’ and ‘Noémie Demay’ were found to be immune. The practical importance for silviculture and horticulture is discussed.     

Incidence of Cronartium ribicola in Finnish botanical gardens and five-needle pine plantations in northern Finland

Abstract

Stump removal procedure increases the extent of exposed mineral soil in the clear felled areas. In this study, our aim was to find out whether the early growth and mycorrhization of Norway spruce (Picea abies (L.) Karst.) seedlings differ between stump removal and mounding sites. Stumps were harvested from five one-hectare study sites and other five sites were mounded after clear felling. Twenty seedlings were planted on mounds at each study site. Although the height of spruce seedlings did not differ between the treatments after three growing periods, their mean growth was ca. 10% higher at the stump removal sites. The community of ectomycorrhizal (ECM) in the seedling roots did not differ between the treatments. The high mycorrhization rate in the nursery still remained after two and three growing seasons in the field and diversity of ECM community slightly increased during the first years. Our results indicate some positive although rather small and transient effects of stump removal on the performance of planted spruce seedlings. Longer-term studies are needed to fully understand the effects of stump removal on the later seedling development and their symbiotic interactions with mycorrhizal fungi.     

Castilleja and Pedicularis confirmed as telial hosts for Cronartium ribicola in whitebark pine ecosystems of Oregon and Washington

The primary objective of this research was to determine whether native species of Castilleja and Pedicularis are naturally infected by Cronartium ribicola in whitebark pine ecosystems of the Oregon and Washington Cascade Range, USA. Secondary objectives were to monitor the phenology of aecial and telial hosts to determine whether there is sufficient time for C. ribicola to complete its life cycle within high‐elevation stands and to evaluate the variety of susceptible native host species within these genera through field and growth chamber inoculation. These objectives were approached through fieldwork in 2008 and 2009 in whitebark pine ecosystems at Mt. Rainier, Mt. Adams, Mt. Hood, Mt. Bachelor, Tumalo Mtn. and Crater Lake. Forty‐nine observational study plots were established and monitored. Natural C. ribicola infection was detected on 84 Pedicularis racemosa plants and five Castilleja plants (C. applegatei, C. miniata and C. parviflora). Field observation provided evidence that there is sufficient time for C. ribicola to complete its life cycle on hosts within high‐elevation whitebark pine stands. In 2009, 18 field inoculation plots were established at Mt. Rainier and Crater Lake. Field inoculation confirmed the susceptibility of two additional species within these genera, C. arachnoidea and P. bracteosa. All four Castilleja species inoculated in the growth chamber developed infection, with an overall infection incidence of 62% (167 out of 270 plants). The identity of the rust species on field specimens as C. ribicola was verified through PCR and sequencing of the ITS1‐5.8S‐ITS2 region of DNA. Improved understanding of the role of these newly recognized hosts in white pine blister rust epidemiology should be used to prioritize sites for the restoration of ecologically valuable whitebark pine.     

茶藨生柱锈菌锈孢子生物学特性研究

用6个不同地点的五针松疱锈病病原菌锈孢子作温度、相对湿度、酸碱度、营养条件及光照条件5个因素下的孢子萌发实验,结果表明:锈孢子的萌发率普遍低,一般不超过10%;在0~35℃均可以萌发,最适的温度是20~30℃,但不同来源地的孢子最适温度有一定的差别;相对湿度10%以上锈孢子都可以萌发,以50%~75%的萌发率最高;锈孢子萌发适应的pH值范围较广,以pH值6~9较适宜,但以中性的酸碱度最佳;光暗交替对孢子萌发有利,营养条件对萌发的影响不明显,各种浸汁对萌发率影响不大。经方差分析,在最适的温湿度和酸碱度条件下,各地的锈孢子萌发率差异显著;在不同的营养条件和光照条件下,锈孢子萌发率差异不明显。     

Penetration of Cronartium flaccidum into pine needles

The penetration of Cronartium flaccidum into the cotyledons, primary needles and secondary needles of Pinus pinaster and P. nigra var, laricio was investigated. SEM examination showed that the fungus did not form appressoria and that the germ tube penetrated directly into the stomata.     

Susceptibility of Ribes spp. to pine stem rusts in Finland

Susceptibility of Ribes spp. to three pine stem rusts, Cronartium ribicola, Cronartium flaccidum and Peridermium pini, was investigated by inoculations both in laboratory and in greenhouse conditions, and by observing sporulation on Ribes spp. leaves under natural and artificial inoculum in 16 experiments. Twenty‐seven Ribes spp. cultivars were inoculated in 2000–2004 using 41 sources of C. ribicola aeciospores from a wide geographic range, and six Pinus spp.; 51 sources of C. flaccidum and 11 sources of P. pini from Pinus sylvestris. The results were very similar both after artificial inoculations and observations under natural inoculum in repeated experiments over the years. Cronartium ribicola uredinia and telia developed frequently or moderately on nine Ribes nigrum cultivars but were not present on two cultivars. Sporulation developed on five Ribes rubrum cultivars but was absent on two cultivars. Three Ribes uva‐crispa cultivars were only weakly susceptible to C. ribicola, while all R. alpinum cultivars were resistant to the rust. The other Ribes spp. tested, Ribes niveum, Ribes aureum, Ribes odoratum, Ribes sp. × nigrolaria, Ribes glandulosum and Ribes × culverwellii Jostaberry, were all susceptible to C. ribicola. Cultivars of R. nigrum were more susceptible than those of any other species. No significant variation in virulence of the aeciospores was observed between and among Ribes hosts over the years. Cronartium flaccidum and Peridermium pini did not form any uredinia or telia on Ribes spp. in any of the experiments.     

Variation of diverse sources of Cronartium flaccidum

Three pine species, each with different climatic requirements, were found to be susceptible to three collections of Cronartium flaccidum from sea level, hills, and mountains of central Italy. There was, however, a highly significant interaction between the three host species and rust collections from the different geographic areas.     

茶藨生柱锈菌致病性分化的初步研究

采用交互接种的方法对华山松疱锈病、红松疱锈病的病原菌茶藨生柱锈菌的致病性分化进行了研究。结果表明:(1)红松疱锈病的病原菌锈孢子只能侵染其本地的转主寄主植物东北茶藨子;(2)华山松疱锈病的病原菌锈孢子能转主侵染多种不同地区的茶藨子植物;(3)所有华山松疱锈病病原菌的锈孢子均不能转主侵染东北茶藨子;(4)初步认定马先蒿属植物不是华山松疱锈病病原菌的转主寄主。     

Anatomical and cellular responses of Pinus monticola stem tissues to invasion by Cronartium ribicola

White pine blister rust (Cronartium ribicola) causes extensive damage to white pines and their associated ecosystems across North America. The anatomical and cellular characteristics of C. ribicola colonization in Pinus monticola branch and stem tissues were studied as a basis for understanding host tree reactions that may be related to resistance. Samples examined showed typical fusiform swelling and some had produced aecia. The reaction of phloem and xylem tissues was compared with non-infected tissue using light and electron microscopy. Cortical parenchyma and phloem polyphenolic parenchyma cells underwent mitotic division, cell swelling, and ca sixfold greater accumulation of phenolic compounds in colonized vs. control stems. In the cortex and secondary phloem, haustoria were common in parenchymatous cells, and hyphae were abundant in the intercellular spaces, but cell death was rare, unless aecia had ruptured the stem cortex. Hyphae were also common in xylem rays, tracheids and between tracheids. Disease-induced changes in the cambial zone included development of cambium-derived xylem traumatic resin ducts. Results demonstrate that diverse host defence responses were activated in the bark of apparently susceptible trees, but lack of mechanical damage by C. ribicola to the phenol-containing host cells and the resin duct system allowed extensive colonization and development of aecia despite elicitation of these stem defences. Interactions between P. monticola and C. ribicola are discussed and compared with other conifer–fungus pathosystems.     

茶藨生柱锈菌锈孢子形态分化研究

本研究从我国辽宁、云南、四川、山西等4省6地的五针松疱锈病发病林分中采集茶藨生柱锈菌锈孢子,对其形态分化进行了系统的研究。结果表明:我国茶藨生柱锈菌在形态上存在分化现象。锈孢子大小为21.10~40.10×14.97~29.40μm之间,变幅较大,其中辽宁清原红松上的锈孢子最小(18.72~30.73×16.04~24.07μm)。锈孢子的超微形态结构也存在差异,红松上的锈孢子的疣突基部和顶部基本一样宽,而华山松上锈孢子疣突的基部比顶部稍宽;不同病区华山松疱锈菌环纹数、疣突的排列和间距不一。寄主在病原菌的变异中发挥着积极的促进作用。     

茶藨生柱锈菌寄主遗传多样性研究

运用随机扩增多态DNA (RAPD)标记对分布于我国4省6病区63份茶藨生柱锈菌寄主红松和华山松进行遗传多样性分析.用6个随机引物对寄主松针进行PCR扩增,共得到138个DNA位点,其中多态位点117个,多态位点比率为84.78%,RAPD的Shannon指数遗传多样性为0.315 5,RAPD的Nei指数基因分化系数为0.525 5.不同来源寄主的遗传多态性规律顺序:辽宁清原红松＞云南洱源华山松＞山西沁水华山松＞云南巧家华山松＞四川广元华山松＞云南东川华山松.从RAPD聚类分析树状图可以看出,先将63个松针样品分成2个不同的RAPD组群(红松组群和华山松组群),然后又将不同地理来源的华山松组群按地理区域分成5个亚群,同一采集的华山松亚群中又分成感病组和抗病组.研究表明,种间的遗传多样性是由种的遗传属性所决定的,而地理因素只是影响种内遗传多样性的一个因子.     

樟子松疱锈病重寄生菌的分离鉴定

樟子松疱锈病是樟子松枝干上的主要病害,为利用重寄生菌对樟子松疱锈病进行生物防治,对其病原菌松芍柱锈菌Cronartium flaccidum(Alb.et Schw.)Wint.的重寄生菌进行了分离和鉴定,得到重寄生菌拟枝孢镰刀菌Fusarium sporotrichioides Sherb.、深绿木霉Trichoderma atroviride,并测定ITS序列,获得基因登录号。经显微观察发现接种重寄生菌后锈孢子受到不同程度的破坏,且存在两种不同的作用机理。