Screening wild cherry (Prunus avium) for resistance to bacterial canker by laboratory and field tests

Currently, bacterial canker caused by Pseudomonas syringae is a major cause of dieback and tree death in wild cherry (Prunus avium) plantations. The evaluation of breeding collections is needed to produce less susceptible clones or cultivars. Resistance tests were performed using excised shoots (1 and 2 years old) from 79 clones in the laboratory. A subset of 10 clones was also tested in the field. The clones were inoculated with four to seven isolates of a set of 15 isolates of P. s. pv. morsprunorum, P. s. pv. syringae, P. s. pv. persicae, P. syringae pv. avii and P. fluorescens. In the laboratory tests, older and larger shoots were more susceptible. In the field test, size and age of the shoots were not related to girdling by the bacterial canker. Two‐year‐old shoots were best for clonal discrimination. Correlations between 1 and 2‐year‐old shoots were significant but not high. The isolates varied a lot between experiments, but as the clone × isolate interactions were always low, breeding could thus be facilitated. The ranking of clones was conserved quite well between two laboratory tests, but not between two others. Good agreement was found for the best clones in the laboratory tests and in the field test. However, the two worst clones in the latter were among the best in one laboratory test. At least two independent tests in the laboratory are needed to evaluate resistance/susceptibility of clones. Broad sense heritability for resistance varied from 0.27 to 0.51. Although moderate, such heritability clearly encourages a breeding approach to reduce the problem of bacterial canker.     

毛白杨33个无性系黑斑病和溃疡病的调查

对毛白杨33个无性系黑斑病和溃疡病进行了调查，结果表明，毛白杨不同无性系对黑斑病和溃疡病的抗性有明显差异。对黑斑病抗性最强的为11号无性系，抗性最差的为2号、8号无性系，对溃疡病抗性最强的为14号、33号无性系（无溃疡病发生），抗性最差的为6号无性系。     

Variation in virulence of Cryphonectria hypovirus 1 in Macedonia

We investigated variation in virulence of Cryphonectria hypovirus 1 (CHV‐1) to the chestnut blight fungus, Cryphonectria parasitica, in Macedonia by inoculating chestnut stems in the field. We inoculated trees with two isolates of C. parasitica, each infected with one of five isolates of CHV‐1, four of which were the same for both fungal isolates. Two virus isolates, [Sk28] and [Sk47], were significantly more virulent than the others when compared in the same fungal host isolates, as measured by reduced canker growth and increased callus formation. Mycelial growth rate in vitro was weakly correlated to canker growth or callus formation and is therefore not a reliable predictor for virulence. We found significant fungus × virus interactions for canker growth and callus formation, which seems due mainly to one virus isolate. Significant interactions were not expected because the two fungal host isolates are members of the same clone that is dominant in Macedonia and most of southeastern Europe. Phenotypic variation for response to viruses, therefore, is greater than variation revealed by the genetic markers used to define clones. More than half of the trees inoculated with virus‐free controls were dead within 2 years, and the 30% still alive after 5 years had cankers with extensive callus formation, indicating that natural virus transmission had occurred after inoculation. In contrast, only 2% of the trees inoculated with virus‐infected isolates were dead after 5 years. Hypoviruses naturally occurring in Macedonia reduce canker development and tree mortality similarly to those in other parts of southern Europe, and therefore, may have good potential for biological control of chestnut blight.     

Changes through time in traits of poplar clones in selection trials

Growth, survival, stem characteristics, resistance to wind, and canker disease of 51 poplar clones were evaluated at age 9 and 10 years, and compared to measurements at age 3 in two trials on the Lower Valley of the Colorado River, Argentina. About 30% of the clones in both trials had large changes in growth rankings at age 9 and 10 compared to rankings at age 3. Canker incidence increased about 4-fold between age 3, and measurements at age 9 and 10. Stem form was in general satisfactory, and wind incidence was almost nil. In trial 1, clones 588–1, Conti 12, 582–41, and 582–5 occupied the upper positions in the growth rankings at age 3 and 10, and the clone 588–1 ranked first both in growth and canker incidence in 1998. Stem growth trajectories of clones with similar growth rates did not differ among clones with, and without canker disease. In trial 2, the range in growth among clones was narrower than in trial 1, and canker disease, although of minor incidence, was present in most clones at age 9. Some of the P. deltoides clones in the trials had similar growth, and less canker disease than the Euroamerican clones commonly grown in the region, but progressive canker incidence should be addressed with additional selection trials.     

Pathogenicity of some isolates of Seiridium (Coryneum) cardinale,agent of cypress canker disease

Ramets of 200 clones of Cupressus sempervirens were inoculated with 6 isolates of Seiridium cardinale. No significant differences were found among isolates, while there were highly significant differences among clones when length and width of canker were assumed as discriminating traits.     

Pitch canker ratings of longleaf pine clones correlate with Fusarium circinatum infestation of seeds and seedling mortality in containers

The incidence and severity of pitch canker was rated among 16 clones of mature longleaf pine (Pinus palustris) in a seed orchard and cones were collected from five of those clones across the range of pitch canker disease ratings. Seed were extracted and commercially processed by clone and the percentages contaminated with Fusarium circinatum determined. Seed from each clone were sown either without treatment or with one of three fungicide treatments in a soil‐less mix at a commercial container nursery to evaluate the effects of F. circinatum (syn. F. subglutinans) on seed and seedling survival. The percent of seed with F. circinatum correlated with the pitch canker ratings in the orchard for the year of collection (r = 0.88, p = 0.05) and, when sown without fungicide treatment, with the number of seedlings produced (r = ?0.94, p = 0.01) and with seedling mortality after germination (r = 0.92, p = 0.02). The same orchard clones were more symptomatic of pitch canker through three annual surveys. Fusarium circinatum was isolated from a higher percent of seed from more symptomatic clones and a lower percent of their seed produced plantable seedlings. We propose that removing such clones from seed collections should reduce seedling mortality at the nursery.     

Infection of susceptible/tolerant barley genotypes with Barley yellow dwarf virus alters the host plant preference of Rhopalosiphum padi clones depending upon their ability to transmit BYDV

Discovering mechanisms of plant–virus–vector interactions is fundamental to understand their ecology and evolution and to apply this knowledge in plant protection. To study the influence of varying Barley yellow dwarf virus (BYDV) transmission efficiencies on host plant preference of Rhopalosiphum padi (L.) clones, we performed host choice experiments with two barley cultivars (BYDV susceptible cv. ‘Rubina’ and BYDV tolerant cv. ‘Vixen’) including healthy and virus-infected plants. For the susceptible barley cultivar ‘Rubina’, aphid clone R07 (high transmission efficiency) preferred BYDV-infected over healthy host plants after 24 h, while clones D10 (medium transmission efficiency) and R09 (low transmission efficiency) preferred neither host. In contrast, BYDV infection of ‘Vixen’ did not affect the plant’s appeal for aphid clone R07. Host plant access, indicated by ingestion and observed by electrical penetration graph technique for a period of 2 h, was facilitated on BYDV-infected cv. ‘Rubina’ for the clones R07 and D10, whereas an opposite effect was observed for the clone R09. For R07 and R09, the difference was not visible after a period of 5 h. As observed earlier for BYDV-infected wheat, enhanced emission of volatile organic compounds associated with virus-induced attraction was detected for BYDV-infected cv. ‘Rubina.’ It is concluded that host plant preference is possibly linked with a high BYDV transmission efficiency as observed for the clone R07, leading to a fitness advantage of this clone as indicated by early increased ingestion. This advantage is not present on BYDV-tolerant genotypes most likely due to the absence of infection symptoms.

     

杨树新无性系的引进及选择研究

在杨树新无性系引进的基础上 ,先后通过苗期试验和无性系品比试验林的观测 ,以湖北省中潜 2号和中潜 3号作为对照 ,从生长指标与形质指标两方面对新无性系进行了选择研究。结果表明 :不同来源的无性系在苗期的生根繁殖、扦插保存率、1a生苗木高生长上存在较大差异 ;品比试验林观测指标数据通过层次聚类和灰色关联分析 ,选择出了优于或接近于对照中潜 2号和中潜 3号的 6个黑杨新无性系 ,即DD1 0 2 - 4、DD95 - 3、DD86- 1 4、DD95 - 1 1、DD89- 2 3和DD66- 0 ,可为我省乃至长江流域短周期工业原料林的建设和选育杨树优良品种提供丰富的造林和育种材料。     

Genetic variability of the ‘bark canker resistance’ character in several natural provenances of Cupressus sempervirens

Several Aegean (Greece) and Anatolian (Turkey) cypress provenances were studied for resistance variability to bark canker, a disease caused by the fungal pathogen Seiridium cardinale. The investigation also examined whether the low disease rate within the natural area of cypress was due to genetic or geographic‐climatic reasons. Results demonstrated strong variability for the ‘bark canker resistance’ character, in particular for trees within families. As trees from the provenances studied were not found to have genetic superiority for bark canker resistance, the above‐mentioned low disease rate could be due to geographic‐climatic barriers that inhibit the development of the fungus or its ability to infect the host. Several half‐sib progenies exhibited high resistance, suggesting that this character is totally inherited through the maternal line. Should this finding be confirmed by further research, it would facilitate the task of genetic improvement for resistance, allowing progenies of resistant trees to be obtained.     

桉树纸浆用材林树冠枝生长规律初步研究

以雷州林业局纪家林场1~5年生的华桉1号、DH32-29无性系为研究对象,从一级枝数量长度直径、二级枝数量长度直径等方面研究其枝生长规律,结果表明：华桉1号一级枝、二级枝各特征指标值及树冠小于 DH32-29,华桉1号枝条的柔韧性强于 DH32-29,表明树冠结构与林木的抗风性有关,华桉1号比 DH32-29抗风性强,在林业实践中已得到验证;两个无性系一级枝、二级枝结构因子之间的相关性呈现规律均基本一致,华桉1号一级枝、二级枝各结构因子之间的相关度低于 DH32-29。本研究可为桉树合理栽植密度的确定、空间结构优化及可持续经营提供参考和依据。     

Selection of poplar clones for the Lower Valley of the Colorado River, Argentina

Ten tree attributes were used to evaluate the performance of25 Populus deltoides clones in a selection trial in southernBuenos Aires, Argentina. A hierarchical cluster procedure wasused to group clones on a multivariate basis. Three Argentinianselections (clones INTA 347-69, 186-68 and 71-67) and one Italianselection (clone Fierolo) were recommended for larger trialsacross the region. Cluster analysis was an appropriate toolfor selecting genotypes with acceptable growth rate, desirableform and resistance to canker disease, rust and wind damage.     

‘Le Crete 1’ and ‘Le Crete 2’: two newly patented Seiridium cardinale canker‐resistant cultivars of Cupressus sempervirens

In the Mediterranean area, common cypress (Cupressus sempervirens) has traditionally been used as a multipurpose tree, for its symbolic and ornamental role, for its valuable timber, as well as for windbreaks and soil protection. The epidemic spread of the Seiridium cardinale canker has limited the use of this tree since the 1970s, inducing researchers to develop a breeding programme of cypress aimed at selecting canker‐resistant lines for different uses and to support a flourishing trade of cypress plants. ‘Le Crete 1’ and ‘Le Crete 2’ described here are two new canker‐resistant C. sempervirens varieties patented in 2010, selected through a 13‐year assessment of their response to artificial inoculations and growth traits. Both are characterized by a rapid growth and by a columnar and fastigiated habit that confers them a notable ornamental effect. Preliminary observations showed also that both tend to produce yearly few microsporophylls and little pollen. ‘Le Crete 2’ was also selected for the high growth rate it maintained on heavy, clayey soils.     

Potential of different poplar clones for sugar production

In a poplar clonal plantation with different species and hybrids, established at 13,333 cuttings ha^?1, biomass production was assessed at the end of the first rotation (3 years) and the potential of the different clones for sugar production was evaluated. The highest biomass production was observed for clones ‘AF2’ and ‘Viriato’ (46.5 and 42 t dm ha^?1, respectively). After a mild acid pretreatment and an enzymatic saccharification, the highest sugar digestibility was found for ‘Viriato’ and ‘Unal’. A clear relation between sugar digestibility and xylan removal during pretreatment was observed, while no relation with lignin content was found. Taking into account the results, the highest production of sugars per hectare was estimated for the poplar clone ‘Viriato’, being 18–48% higher than that achieved with the other clones. Therefore, this clone is a promising candidate to be used as feedstock for sugar production in a forest biorefinery.     

First hybrid plane trees to show resistance against canker stain (Ceratocystis fimbriata f. sp. platani)

Canker stain, caused by the ascomycete Ceratocystis fimbriata f. sp. platani, is a major threat to plane trees in Europe. The American plane tree (Platanus occidentalis) carries some genetic resistance, but this species is not adapted to the climatic conditions in Europe. Therefore, hybrids between susceptible oriental plane trees (Platanus orientalis) and resistant P. occidendalis were screened for disease resistance in France. Among 960 hybrids, we found 18 individuals which survived two successive inoculations. These putatively resistant trees were cut back and, after 18 months, on each tree 12 of the newly produced shoots as well as two roots, were inoculated again. From these trees, only one showed complete and another one partial resistance. This selection process resulting in the resistant clone ‘Vallis clausa’ is described in detail.     

Bacterial canker of Maackia amurensis var. buergeri caused by a putative Pseudomonas syringae

A new disease of Maackia amurensis var. buergeri was recently found on the northern island of Hokkaido, Japan. Affected trees were heavily damaged and had cankers on both trunks and branches. After natural infection, a series of swellings on the bark surface developed longitudinally. These swellings burst and coalesced to become long cankers. It is proposed that the disease be designated ‘bacterial canker of Maackia’. The causal pathogen was isolated and characterized tentatively as Pseudomonas syringae on the basis of laboratory tests. Pathogenicity of the bacterium was confirmed by inoculation into the host.     

Characterization of Lasiodiplodia theobromae (Pat.) Griffon & Maubl causing stem canker on Teak (Tectona grandis L.) in Ecuador

Teak is a very important tropical timber in Ecuador. In 2017, teak samples displaying stem canker symptoms were collected in two provinces of Ecuador. From 11 symptomatic trees, 11 isolates resembling a species of Lasiodiplodia were obtained. All isolates obtained induced stem canker on teak plants after artificial inoculation, confirming them as the cause of the observed canker symptoms. Bayesian inference with concatenated sequences of complete ITS and partial TEF-α and β-TUB gene sequences from two representative isolates clustered teak isolates with other sequences of Lasiodiplodia theobromae available in Genbank. This is the first report of L. theobromae causing stem canker on teak plants in Ecuador.     

Sphaeropsis canker,a new disease of cypress in Greece

The fungus Sphaeropsis sp. is reported for first time in Greece to cause cankers on Cupressus sempervirens. The cultural characteristics on PDA, spore shape and size and canker morphology were identical to those of the fungus described as Diplodia pinea f. sp. cupressi in Israel. The cankers of Sphaeropsis sp. are characterized by resin exudation, with fissuring of the bark over a dry sector of the wood. The pathogenicity of the Sphaeropsis sp. was proved by artificial inoculations on selected cypress clones resistant and susceptible to Seiridium cardinale. The mean canker length of the susceptible clone was significantly more than that of the resistant clones. It appears that the defence reaction in cypress against both fungi is similar. In artificial inoculations on Pinus halepensis and Pinus pinea, Sphaeropsis sp. was nonpathogenic. During a 3‐year period, in an experimental plot in western Peloponnese, the fungus spread from one, initially, to 13 cypress clones. Drought stress during the summer appears to be the main factor predisposing the cypress plants to become susceptible to the fungus.     

竹叶花椒‘云林1号’‘云林2号’无性系选育与栽培研究

为选育具有早实、丰产、品质优良、抗逆性强且刺少的适合在昆明市、昭通市及气候相似地区种植的竹叶花椒优良无性系,采用优株标准制定→群众报优→初选、复选→决选→无性繁殖与子代测定→品比试验→优良无性系的选育技术路线开展竹叶花椒优良无性系选育。选育出的‘云林1号’和‘云林2号’竹叶花椒,其主要优良性状明显,具特异性;经无性繁殖后,后代各性状具有一致性和稳定性。2个无性系嫁接繁殖后性状稳定一致,表现出生长快、早实、少刺、抗性强,果实颗粒饱满、果皮厚、密生疣状凸起的油点,色泽翠绿鲜亮,芳香浓烈,麻味纯正、持久等优良特性,品质符合国家林业行业标准规定的特级花椒要求。     

Research on poplar canker (Xanthomonas populi subsp. populi) in the Netherlands. Part III

A new inoculation method for testing the resistance of poplars to bacterial canker caused by Xanthomonas populi subsp. populi (Ridé) Ridé & Ridé is discussed. The procedure is based on a more natural infection method and involves spraying plants in spring with bacterial suspensions.     

A serious new wilt disease of Eucalyptus caused by Ceratocystis fimbriata in Central Africa

In a recent survey of Eucalyptus clones in the Republic of Congo, Central Africa, a serious wilt and die-back disease of two different hybrid clones was observed. Affected trees ranged in age from approximately 6 months to 4 years. Isolations from symptomatic plant material consistently yielded a Ceratocystis species. On the basis of morphology and sequence data this fungus was identified as Ceratocystis fimbriata, a well-known wilt and canker pathogen of many economically important plants. The Eucalyptus isolates were compared with other Ceratocystis spp. based on sequence data generated from the ITS and 5.8S region of the rRNA operon. The results confirmed the identity of the Ceratocystis isolates from Eucalyptus as C. fimbriata and showed that they group with other C. fimbriata isolates from Brazil, South Africa and Europe. Inoculations on young Eucalyptus plants were conducted in the greenhouse and all three of the Congolese isolates tested, produced typical lesions in the bark and xylem. This study represents the first report of C. fimbriata as a pathogen of Eucalyptus in Africa. This is a serious new disease that will require considerable study in order to ensure that losses, caused by C. fimbriata, do not continue.