Forest Pathology

Menkis, Audrius; Bakys, Remigijus; Stein Åslund, Matilda; Davydenko, Kateryna; Elfstrand, Malin; Stenlid, Jan; Vasaitis, Rimvydas; Hietala, Ari Mikko

doi: 10.1111/efp.12572pmid: N/A

Ash dieback (ADB) caused by the pathogen Hymenoscyphus fraxineus is the cause of massive mortality of Fraxinus spp. in Europe. The aim of this work was to check for the presence of the molecular marker for ADB tolerance in mapped healthy‐looking F. excelsior trees, and to compare its occurrence in trees exhibiting severe ADB symptoms. Monitoring of 135 healthy‐looking F. excelsior on the island of Gotland, Sweden, showed that after 3–4 years 99.3% of these trees had 0%–10% crown damage, thus remaining in a similar health condition as when first mapped. After 5–6 years, 94.7% of these trees had 0%–10% crown damage. Molecular analysis of leaf tissues from 40 of those showed the presence of the molecular marker in 34 (85.0%) trees, while it was absent in 6 (15.0%) trees. Analysis of leaf tissues from 40 severely ADB‐diseased trees showed the presence of the molecular marker in 17 (42.5%) trees, but its absence in 23 (57.5%) trees (p < .0001). The results demonstrated that monitoring of healthy‐looking F. excelsior is a simple and straightforward approach for the selection of presumably ADB‐tolerant ash for future breeding. The cDNA‐based molecular marker revealed moderate capacity on its own to discriminate between presumably ADB‐tolerant and susceptible F. excelsior genotypes.

Silva, Ana Cristina; Henriques, Joana; Diogo, Eugénio; Ramos, Ana Paula; Bragança, Helena; Doğmuş‐Lehtijärvi, H. Tuğba

doi: 10.1111/efp.12570pmid: N/A

The fungus Sydowia polyspora is frequently isolated from conifers worldwide and is considered a pathogen on several hosts. Stone pine (Pinus pinea) is one of the most important forestry species throughout the Mediterranean basin due to the value of the edible pine nut. Stone pines showing tip dieback, needles with tan‐ to yellow‐coloured lesions and shoot death, observed in stands in Portugal, were sampled for analysis. Fungal colonies covered with cream‐coloured spore masses, were consistently obtained. Morphological and phylogenetic analyses of the ITS rDNA region enabled identification of these isolates as S. polyspora. Inoculation tests showed that the fungus caused lesions on excised P. pinea shoots. The symptoms observed might have a negative effect on pine nut production, and thus, evaluation of the impact of this disease is of relevance to future research. This paper is the first to report S. polyspora causing disease on P. pinea.

doi: 10.1111/efp.12521pmid: N/A

Silva, Ana Cristina; Henriques, Joana; Diogo, Eugénio; Ramos, Ana Paula; Bragança, Helena; Doğmuş‐Lehtijärvi, H. Tuğba

doi: 10.1111/efp.12586pmid: N/A

Aguayo, Jaime; Fourrier‐Jeandel, Céline; Capdevielle, Xavier; Vétillard, Fabrice; Piou, Dominique; Iturritxa, Eugenia; Robin, Cécile; Scanu, Bruno

doi: 10.1111/efp.12574pmid: N/A

Fusarium circinatum is the causal agent of pitch canker, a destructive disease that threatens natural and planted pine forests around the world. Although pitch canker has caused problems in Spain and Portugal, concerning Europe as a whole, the fungus is not established across the pine distribution area. Its dispersion by wind and/or insect vectors could nevertheless play a role in the colonization of currently uninfected stands. It is therefore crucial to develop monitoring tools for its detection. To this end, we assessed the molecular detection of the pathogen in environmental samples of bark beetles and passive spore traps, collected in two infected Pinus radiata plantations in Basque country, Spain. The spread pattern of F. circinatum was assessed by an experimental design that included insect and spore traps installed at the centre, at the edge and outside the plots. Our results showed that F. circinatum was detected in both types of samples, at almost all collection dates. In both type of samples, positive detections were mainly found at the centre of the plots, a lower proportion at the edge, and very few outside. This suggests that long‐distance dispersion of Fusarium circinatum does not rely on wind spore dispersal neither on insect flight. Our study also shows that molecular methods are a powerful tool to monitor the pathogen in environmental samples.

Zhang, Yaowen; Shen, Rong; Mo, Yixue; Li, Qiqin; Lin, Wei; Yuan, Gaoqing; Sieber, Thomas

doi: 10.1111/efp.12575pmid: N/A

Sterculia nobilis is an important tropical woody plant with high ornamental and economic value. At present, there are few reports of diseases on this plant. In August 2018, an unknown leaf spot disease was observed on S. nobilis in Nanning, China, affecting the inner leaves of the canopy and causing considerable defoliation. The pathogen was isolated, and pathogenicity tests carried out on detached leaves to verify Koch's postulates. Based on morphological observations and polygenic analyses, the pathogen causing leaf spots on S. nobilis was identified as Colletotrichum siamense.

Bakhshi ganje, Meysam; Shams‐Bakhsh, Masoud; Mackay, John; Rahimian, Heshmatollah; Fossdal, C. G.

doi: 10.1111/efp.12571pmid: N/A

Oak decline syndrome is characterized by periodic occurrences of decline and death of oaks over widespread areas. An outbreak of a new emerging disease on oak trees was reported in the Hyrcanian forest of Iran (Mazandaran and Golestan provinces) that showed stem bleeding and canker symptoms. Bacterial isolates were characterized through biochemical and physiological tests, protein electrophoresis, DNA fingerprinting (rep‐PCR, ERIC and BOX primers) and sequencing of 16S rRNA and MLSA (multilocus sequencing analysis) for housekeeping genes (gyrB, infB and atpD). A complex community of the genus Brenneria spp. (Brenneria goodwinii, Brenneria roseae subsp. roseae, Brenneria sp. and Brenneria nigrifluens) and a few isolates in the genus Gibbsiella were identified as major groups involved. Isolate differentiation was more accurate using concatenated partial gene sequences within the main groups. All bacterial isolates showed hypersensitivity reactions (HR) on Pelargonium leaves (Pelargonium × hortorum). Pathogenicity studies of different Brenneria and Gibbsiella strains revealed that they have potential to cause the disease in oak seedlings and devastating oak canker and stem bleeding symptoms in northern Iran. Due to the presence of several potentially pathogenic agent(s) associated with the oak decline, identification of the principal agent(s) is of major interest. To our knowledge, this is the first report of potentially pathogenic bacteria associated with oak bleeding and canker in Iran.

Dadam, Daria; Siasou, Eleni; Woodward, Stephen; Clark, Jacquie A.; Cleary, M.

doi: 10.1111/efp.12569pmid: N/A

In this study, we investigated whether birds could be vectors facilitating long‐distance spread of Phytophthora ramorum in Britain. Migratory bird species associated with the main sporangium‐producing host plants and most likely to pick up P. ramorum spores were considered. Swabs were taken from the flank and “feet” of 1,014 birds over a 12‐month period (April 2011–March 2012) in the west of Britain and subsequently analyzed for the presence of P. ramorum using nested PCR. Ten positive samples from 10 birds were identified: three in Cornwall, one in Devon, three in Gloucestershire, two in north Wales and one in Merseyside. Phytophthora ramorum was detected on samples from four species of thrushes (Redwing Turdus iliacus, Fieldfare T. pilaris, Blackbird T. merula and Song Thrush T. philomelos) and one species of warbler (Chiffchaff Phylloscopus collybita). All birds that tested positive were sampled in late autumn and winter (October–February), when long‐distance movements (over 100 km) would have stopped. The low incidence of P. ramorum found using PCR suggests that the incidence of inoculum, whether viable or not, on birds was low. The apparently low incidence of inoculum on birds suggests migratory passerine birds can carry P. ramorum inoculum on their feathers and “feet,” albeit at low frequency. The dates of positive samples indicate that birds would not have been moving long distances at the time but further work is needed to estimate the extent of their contribution to the spread of P. ramorum in Britain.

Zhou, Jianghong; Xia, Fei; Che, Shaochen; Wang, Jianhong; Zhang, Guofeng; Woodward, Stephen

doi: 10.1111/efp.12576pmid: N/A

Brown slime flux seeps slowly out of wounds and flows down the bark of roadside Populus tomentosa in Beijing, China. Two bacterial isolates, SL2‐2 and SL3‐3, obtained from the brown slime flux were identified as Providencia rettgeri based on 16S rRNA gene sequencing. After inoculation into the bark of roadside P. tomentosa with sterile deionized water as a control, both SL2‐2 and SL3‐3 triggered the seepage of brown slime flux from the wounds; no slime flux arose from the control. In conclusion, P. rettgeri was the pathogenic bacterium causing brown slime flux on P. tomentosa probably by inhibiting wound healing. To our knowledge, this is the first report of P. rettgeri as a pathogen of plants.

Rao, Govind Pratap; Bahadur, Amar; Das, Sukhen Chandra; Ranebennur, Hemavati; Mitra, Surabhi; Kumar, Manish; Kumar, Shailender; Hantula, Jarkko

doi: 10.1111/efp.12573pmid: N/A

Leaf yellowing symptoms were observed on Acacia mangium in the Sipahijala district of Tripura, India, during June 2017. Symptomatic and asymptomatic leaf samples (three of each) were collected from roadside trees of A. mangium for DNA extraction using the CTAB method. Amplicons of ~1.25 kb and ~480 bp were detected in all the symptomatic samples using the phytoplasma‐specific universal 16S rRNA and secA gene primers. Pair wise sequence analysis of 16S rRNA gene sequences, virtual RFLP and phylogenetic analysis revealed that the phytoplasma strain associated with A. mangium belonged to phytoplasma subgroup 16SrII‐C. This is the first report of an association between the 16SrII‐C subgroup and A. mangium leaf yellowing.