Identification and characterization of bacterial strains associated with diseased oak trees in Northern Iran

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.     

Bacillus pumilus and Stenotrophomonas maltophilia as two potentially causative agents involved in Persian oak decline in Zagros forests (Iran)

The oak decline is known as one of the most destructive complex diseases causing high economic losses around the world, especially in Iran. The main objective of the present study was to investigate the possible role of bacteria as causative agents of oak decline in the Zagros forests of Iran. To do this, stem, root and leaf samples were taken from symptomatic Persian oak trees (Quercus brantii) in different zones of Zagros forests (Ilam Province, Iran). From 150 bacterial isolates, 20 showed pathogenicity against Geranium seedlings. Among 20 hypersensitivity test positive strains, four strains showed pathogenicity against oak saplings. Based on morphological and 16S rRNA gene sequence analysis, three strains were identified as Bacillus pumilus and one strain as non‐sporulating Gram‐negative Stenotrophomonas maltophilia. Pathogenicity studies of different B. pumilus and S. maltophilia strains revealed that they have potential to cause the disease in oak saplings and symptoms of disorder in Persian oak trees. To our knowledge, there are no previous records of B. pumilus and S. maltophilia causing decline on Fagaceous trees like Q. brantii. More detailed field and molecular studies are required to confirm the absolute role of such bacteria in occurrence of oak decline in Zagros forests.     

“Candidatus Phytoplasma solani” associated with Eucalyptus witches’ broom in Iran

During summer of 2015, Eucalyptus camaldulensis plants showing witches’ broom, little leaf and general yellowing of the foliage were observed in west of Fars and Khozestan province of Iran. DNA from samples of 22 symptomatic and two asymptomatic trees was extracted and subjected to molecular analyses. Nested‐PCR test using R16F2n/R16R2 primers confirmed phytoplasma presence in 63% of symptomatic Eucalyptus plants. Sequence analysis along with virtual RFLP of the 16S ribosomal DNA allowed to classify three Eucalyptus witches’ broom strains into the “stolbur” (“Candidatus phytoplasma solani”) 16SrXII‐A subgroup. Comparison of the secA and secY gene sequences with sequences deposited in GenBank confirmed the phytoplasma identity. Real and virtual RFLPs of the amplified secY gene using HaeIII, MseI and RsaI restriction enzymes showed profiles indistinguishable from each other. This is the first study reporting E. camaldulensis as a new host species for “Ca. P. solani.”     

The true nature of Ganoderma in Iran: Taxonomy based on ITS and mtSSU rDNA

The genus Ganoderma Karst. has broad‐spectrum usage in biotechnology, medicine and the food industry. The complexity of the morphology within species has led to uncertain identification in the past, but recent advancements in molecular identification methods have provided scientists with the opportunity to better understand the taxonomy of the species. The present study attempts for the first time to elucidate the distinctiveness of the Ganoderma species growing in Iran concerning those elsewhere in the world based on mitochondrial small subunit ribosomal DNA (mtSSU rDNA) and internal transcribed spacer (ITS) sequence data. The results disclosed that the G. lucidum Karst. samples collected in Iran are more similar to the European Ganoderma species than to the Asian (Chinese) one used in this study.     

栎树秋季叶色多样性及相关生理特性的变化

目的 研究栎树叶片变色期相关生理物质含量的变化,探索其叶色多样性与生理特征变化间的内在联系。 方法 以红栎组的纳塔栎、舒玛栎、柳叶栎、月桂叶栎、樱皮栎,白栎组的琴叶栎、牛栎以及白栎等8种栎属植物4 年生苗为试材,对其色差参数（L*、a*、b*）、色素、可溶性糖和营养元素含量进行测定分析。 结果 秋季栎树叶片叶色参数L*值变化幅度小,较为稳定。色差参数a* 值、b*值、叶绿素含量和类胡萝卜素含量呈下降趋势,花青素含量则逐渐上升;N、P含量在叶片变色期逐渐降低,而可溶性糖含量增加。同时a*值与花青素、可溶性糖含量、C∶N和C∶P呈极显著正相关,与叶绿素、类胡萝卜素、N和P含量呈极显著负相关。通常红栎组栎树叶色较白栎组红。由于各树种各指标变化幅度不同,导致不同树种叶色差异显著,且叶色保持期不同。叶片变色后期各栎树叶色从绿色变为黄红色、深红色、鲜红色或棕色。其中纳塔栎秋季叶色最红,同时呈现红色的时间最长。 结论 红栎组栎树较早进入变色期;变色前期各指标变化幅度小,此后叶绿素和类胡萝卜素被快速分解,花青素大量合成,是影响栎树秋季叶色的关键因素;变色期叶片N和P含量逐渐下降且利用率显著提高。     

Molecular and morphological characterization of Ektaphelenchoides maafiae n. sp. (Nematoda: Ektaphelenchinae) from northern forests of Iran

Ektaphelenchoides maafiae n. sp. was isolated during a survey of nematodes associated with bark samples of an oak tree (Quercus castaneifolia) in Gorgan, Golestan Province, northern Iran. The new species has a body length of 480–546 μm (in females) and 431–480 μm (in males). The cuticle is weakly annulated, with three lateral lines. Lip region offset. The stylet is 13–15 μm long without basal swellings. The excretory pore is located at the level of the metacorpus base to slightly posterior, and hemizonid is at 15–17 μm posterior to the excretory pore. The post‐uterine sac is short, 6–8 μm long. Spicules having rounded condylus, rostrum short, conical with bluntly pointed tip, a cucullus (apophysis) presented on the dorsal distal end. Male tail bearing four (2 + 2) caudal papillae, conical, with sharply pointed terminus. The new species is close to four known species of the genus, including E. hunti, E. ruehmi, E. caspiensis and E. poinari, but differs from them by body size, shape of tail terminus, stylet length, shape and size of spicules, length of post‐vulval uterine sac and number of caudal papillae. Phylogenetic analysis based on small subunit (SSU) and partial large subunit (LSU) sequences of rDNA confirmed its status as a new species.     

Phytophthora species associated with dieback of sweet chestnut in Western Turkey

Sweet chestnut (Castanea sativa) is an important tree species in the Marmara and Aegean regions of Turkey as these two regions produce the great majority of edible nuts, especially those used for marron glacé production. Chestnut forests and orchards in these regions showing severe dieback symptoms not associated with chestnut blight were investigated to determine the role of Phytophthora spp. in the decline syndrome. Soil samples were collected from around 108 symptomatic chestnut trees at 29 sites and Phytophthora spp. isolated using soil baiting technique and selective medium. Species isolated were identified by cultural characteristics and ITS sequencing. Phytophthora x cambivora was the dominant species detected in 13 sites, followed by P. cinnamomi (5 sites), P. plurivora (3 sites) and P. cryptogea (1 site). Phytophthora x cambivora was present in both regions, while P. cinnamomi was found only in the Marmara region in coastal areas around Istanbul. When inoculated at the stem bases of 3‐year‐old chestnut saplings, P. cinnamomi produced significantly longer necrotic lesions (7.8–12.0 cm) than P. x cambivora (2.6–6.3 cm) by 12 days after inoculation. Phytophthora plurivora was the least aggressive species causing only small lesions. Phytophthora cryptogea, which represents the first record on chestnut in Turkey, produced intermediate sized lesions in between P. x cambivora and P. plurivora. These results indicate that P. x cambivora and in some areas P. cinnamomi play major roles in the observed dieback of sweet chestnut in western Turkey.     

永安桉树造林与生态问题调查研究

通过时南方集体林区县——永安市桉树造林状况以及群众反映桉树造林导致土壤板结、林地土壤肥力下降、抑制林内其他植物生长和造成居民生产生活用水困难等问题进行调查分析的基础上,提出正视桉树生态问题、生物多样性保护措施、推广桉树混交造林与平衡施肥技术,引导种植户采用科学的桉树造林、经营管理方式,促进桉树健康稳定发展。