北京地区桃树腐烂病的发生与诱因

1960—62年初步調查发現:桃树腐烂病疤主要分布在主干与主枝上,其中主枝基部(五(木义)骨)占60％;病疤多为西南向;流胶为发病后的共同表現;病害可深入皮层与木质部。各主要栽培品种均能感病,以大久保等最重,士蒼与耐寒品种病輕。病菌可自剪口、冻伤、虫伤等处侵入。3—10月田間接种均能发病,潛育期4—10天,以春季較短。病害每年自3月开始发生,3—5月最为严重,以后随树势生长旺盛,病害发展卽受限制。冻害为主要誘因,凡栽培不当如肥、水过多和过晚,以及与秋菜間作等促使徒长或延期休眠而誘发冻害者,均能誘致腐烂病,改进以上栽培管理,提高抗冻、抗病力是防治腐烂病的根本途径。     

苹果树腐烂病的发病过程和药剂防治研究

本文分两部分。第一部分概述了陕西风县秦岭高地苹果树腐烂病的发生发展过程,指出腐烂病菌主要是先在树皮的落皮层内潜伏侵染,进而侵害健组织。第二部分为防治试验。根据腐烂病的发生发展过程,于6月下旬和11月中旬对主干和大枝下部涂40%福美砷可湿性粉剂50倍悬浮液二次,获得了施药部位新病减少90%,“病疤重犯”减少80%的防治效果。与在辽宁兴城的试验,防效近似。     

First report of the canker pathogen Endothia gyrosa on Eucalyptus in South Africa

During country-wide surveys of Eucalyptus plantations for Cryphonectria canker, cankers distinctly different from those usually associated with Cryphonectria cubensis were observed. These cankers were less severe and were exemplified by cracked and slightly swollen areas on the bark. Endothia gyrosa , a well-known pathogen of woody plants including Eucalyptus spp., was consistently associated with these cankers. The pathogen is easily distinguished from C. cubensis by the presence of orange-brown stromata and non-septate ascospores. Inoculations on Eucalyptus grandis resulted in lesions similar to those observed on naturally infected trees. The disease associated with E. gyrosa is widespread in South Africa, and research is required to establish control strategies.     

Relative significance of nursery infections and orchard inoculum in the development and spread of apple canker (Nectria galligena) in young orchards

Three nurseries produced apple rootstocks (M9) and budwood (cv. Royal Gala), which they exchanged at the end of the first year. Each nursery then budded its own budwood onto the rootstocks it had produced and that from the other two nurseries. Budded trees were grown on for a further year before being planted at HRI, East Malling in southern England; NIHPBS, Loughgall in Northern Ireland; and ADAS, Rosemaund in the West Midlands of England. Canker development was monitored twice a year. The position of the infected trees within the orchard was recorded, as was the position of the canker on each tree (main-stem or peripheral). Nectria galligena was isolated from representative cankers and analysed using molecular techniques. At the sites in Northern Ireland and HRI there was a strong positional effect, especially of peripheral cankers, indicating that most of the inoculum was external and had been spread from neighbouring orchards. There was little or no positional effect on main-stem cankers at any of the three sites. The proportions of different isolates taken from peripheral cankers was different in Northern Ireland from that in England, suggesting different populations associated with the geographic areas. In contrast, the populations of N. galligena obtained from main-stem cankers were very similar in England and Northern Ireland. It was concluded that a small proportion of trees developing canker were infected during propagation, with no symptom development until after planting. In a second trial it was demonstrated that trees infected during the propagation phase, and particularly at budding and heading back, could develop canker up to 3 years later. While it is clear that some canker developing in the orchard can be associated with the nursery of production, in climatic conditions conducive to the formation and dissemination of conidia, inoculum from surrounding infected orchards is the primary source of the pathogen. Aerial spread is therefore an essential element of the epidemiology of N. galligena, and its control is a crucial part of any canker-control programme.     

Natural occurrence and distribution of stem cankers caused by <Emphasis Type="Italic">Phytophthora megakarya</Emphasis> and <Emphasis Type="Italic">Phytophthora palmivora</Emphasis>on cocoa

Epidemiological studies were conducted in five cocoa growing districts in the Eastern Region of Ghana solely infected by Phytophthora palmivora and five districts in the Ashanti and Brong Ahafo Regions prevalently infected by Phytophthora megakarya to determine the natural incidence, the vertical distribution on trees and the probable sources of stem canker infections, and to isolate and identify the causal pathogens. The incidence of canker in the solely P. palmivora infected area was higher (between 0% and 16.0%) than in the area mainly infected with P. megakarya (0.5–8.0%). Differences were found in the natural height distribution of cankers in the two areas, whilst the areas solely infected with P. palmivora showed a near normal curve, those prevalently infected with P. megakarya were positively skewed. Most of the cankers caused by P. megakarya were found at the base or near the base of the tree trunks (1–40cm above ground level), while those of P. palmivora were concentrated between 41 and 100cm from the ground level. The majority (71.8%) of cankers in the solely P. palmivora infected area were cushion-borne, followed by 24.3% from unknown sources and only 3.9% from the soil. In contrast, a significantly large proportion (32.6%) of the cankers in the prevalently P. megakarya infected area were soil-borne, although cushion-borne cankers formed the majority (48.4%) due to the presence of P. palmivora infection whilst those of unknown sources constituted 19.0%. Phytophthora megakarya was frequently isolated from all the three sources of canker infections, indicating P. megakarya readily causes stem canker on cocoa. These results emphasise the importance of different reservoirs as sources of primary inoculum for diseases caused by the two Phytophthora species particularly pod rot infection on cocoa.     

Phytophthora species in oak ecosystems in Turkey and their association with declining oak trees

From 1999 to 2001, a survey on the occurrence of Phytophthora spp. in the rhizosphere soil of healthy and declining oak trees was conducted in 51 oak stands in Turkey. Seven Phytophthora spp. were recovered from six out of the nine oak species sampled: P .  cinnamomi , P .  citricola , P .  cryptogea , P .  gonapodyides , P .  quercina , Phytophthora sp. 1 and Phytophthora sp. 2. The most frequently isolated species, P .  quercina , was very common on slopes susceptible to drought. It occurred in four different climatic zones and on six Quercus spp., suggesting that it is native to oaks. The second most common species, P .  citricola , was separated into three subgroups: type C was recovered only in Anatolia, whereas A and B occurred only in the European part of Turkey. Phytophthora cinnamomi was recovered at one site only, and may not be involved in oak decline in Turkey. The other four species were recovered sporadically. On affected sites there was a significant association between deteriorating crown status and the presence of Phytophthora spp., particularly P .  quercina . The occurrence of Phytophthora species was significantly influenced by soil pH. Stem inoculation tests on oak seedlings revealed that Q .  petraea was the most susceptible species.     

Testing variability in pathogenicity of Phytophthora cinnamomi

Forty eight isolates of Phytophthora cinnamomi from various host plants in France (35 isolates) and in other countries were tested for pathogenicity. Seedlings of chestnut, northern red oak, pine and eucalyptus were infected by soil contamination. Taproots, stems and bark strips of plants of chestnut and different oak species were inoculated with mycelium agar disks. Results of the different experiments were in good agreement. All isolates appeared pathogenic to all the different test species but with variable levels of virulence. Isolates with consistent low or high level of virulence, which could be used as standards in further studies, were identified. Interaction between P. cinnamomi isolates and host plant species was significant in terms of lesion lengths. These interactions could not be related to host from which P. cinnamomi was isolated. Consistent with this, in Quercus rubra, the isolate-provenance interaction was not significant. This feature is encouraging for provenance screening for resistance to P. cinnamomi in this species. The variation in virulence was not related to other isolate characteristics (mating type, electrophoretic type, age).     

Brenneria quercina and Serratia spp. isolated from Spanish oak trees: molecular characterization and development of PCR primers

Brenneria quercina has been reported as one of the causal agents of oak decline in Spain. To investigate the bacterial variability of this pathogen from different Spanish oak forests, a collection of 38 bacterial isolates from seven geographic locations and from different oak species was analysed by sequencing 16S rDNA and rep-PCR fingerprinting. All Spanish isolates of B. quercina were grouped by rep-PCR into a homogenous cluster that differed significantly from B. quercina reference strains from California. 16S rDNA analysis revealed that 34 out of 38 isolates were Brenneria . However, four isolates belonged to the genus Serratia , suggesting that this bacterium could cause cankers in oak trees. The information obtained by rep-PCR fingerprint analysis was used to develop PCR primers for the sensitive and specific detection of B. quercina from infected plant tissues. Pathogenicity tests performed with Brenneria and Serratia isolates showed that both were able to grow and cause cankers in oak trees.     

Analysis of the genetic diversity and phylogenetic relationships of <Emphasis Type="Italic">Biscogniauxia mediterranea</Emphasis> isolates associated with cork oak

Biscogniauxia mediterranea is one of the most frequent fungal pathogens involved in cork oak decline in the Mediterranean Basin, causing charcoal canker. In Portugal, this disease is widespread on adult declining trees but nowadays it increasingly affects young trees and exhibits atypical symptoms, leading to the hypothesis that some change in the fungus may have occurred. In order to evaluate the genetic diversity and phylogenetic relationship of B. mediterranea associated with cork oak, 102 isolates were obtained from young and adult trees of Quercus suber and other hosts species with different disease expression, from several Mediterranean countries. The collection of isolates was analyzed by individual and multigene phylogenies using Maximum-Likelihood approach based on nucleotide sequences of the internal transcribed spacers of ribosomal DNA, translation elongation factor 1-α and β-tubulin genes, and by microsatellite-primed PCR profiles. Sequence analyses separated the Mediterranean isolates from those from other regions, while MSP-PCR analysis revealed relevant but unstructured diversity among the Mediterranean isolates under study, making this a monophyletic but diverse population. Considering the adaptive capacity of the fungus in the Mediterranean-climate ecosystems and the present climatic change scenario, all conditions are gathered to favor aggravation of the disease in cork oak stands.     

Cloning and Characterization of a Putative Antifungal Peptide Gene (Pm-AMP1) in Pinus monticola

ABSTRACT We have been working on proteins that are involved in the defense response of western white pine (WWP) (Pinus monitcola) to the blister rust fungus Cronartium ribicola. Our objective was to identify candidate genes that could be used for improving resistance of WWP to this rust pathogen. During proteomic analysis of bark proteins extracted from WWP trees exhibiting slow-canker-growth (SCG) resistance, a 10.6-kDa peptide, termed Pm-AMP1, was found to be enriched at the receding canker margin. The cDNA encoding this peptide was cloned and characterized. A BLASTX search revealed that the Pm-AMP1 encoded by its cDNA has a 50% homology with MiAMP1, a broad-spectrum antifungal protein isolated from Macadamia integrifolia. Based on the deduced amino acid sequence, an antibody was produced against the Pm-AMP1. Immunochemical quantification of the Pm-AMP1 in bark samples of susceptible WWP trees revealed this protein to be barely detectable in the cankered tissues, but occurring in higher concentrations in healthy tissues away from canker margins. Foliage of SCG-resistant trees contained higher concentrations of the Pm-AMP1 than foliage from susceptible cankered trees. Both wounding and methyl jasmonate treatment of WWP needles induced the expression of this protein, further supporting its putative role as a defense response protein.     

Bacterial Canker and Dieback Disease of Apricots (Pseudomonas syringae van Hall)

Bacterial canker and dieback (Pseudomonas syringae van Hall) of apricot is a widespread disease in Europe, except for the Mediterranean areas. Cankers usually develop at pruning wounds or other points of injury. Phloem and cambium become susceptible from just after leaf drop until budding. If the phloem necrosis does not girdle the branch or trunk, cankers develop by the middle or the end of summer. In early summer, the bacterium actually dies out in the infected tissue, and the tree remains resistant during the summer. During this period, the pathogen lives epiphytically on the surface of the leaves, without causing any symptoms. The extent of bacterial necrosis of the phloem depends on the severity of winter frost. Without winter frost, bacterial induced tissue necrosis does not occur. Necrosis is found only if P. syringae has enough time to proliferate before the onset of frost. The most effective method of control is to carry out spring rather than winter pruning.     

Effects of cultivar resistance and fungicide application on stem canker of oilseed rape (Brassica napus) and potential interseasonal transmission of Leptosphaeria spp. inoculum

Phoma stem canker is a damaging disease of oilseed rape (Brassica napus) that causes annual yield losses to UK oilseed rape growers worth approximately £100 million, despite the use of fungicides. In the UK, oilseed rape is sown in August/September and harvested in the following July. The disease epidemics are initiated by ascospores released from Leptosphaeria spp. pseudothecia (ascocarps) on stem stubble in the autumn/winter. Control of this disease is reliant on the use of cultivars with “field resistance” and azole fungicides. This study investigated the effects of cultivar resistance and application of the fungicide prothioconazole on the severity of stem canker before harvest and the subsequent production of pseudothecia on the infected stubble under natural conditions in the 2017/2018, 2018/2019, and 2019/2020 cropping seasons. The application of prothioconazole and cultivar resistance decreased the severity of phoma stem canker before harvest, and the subsequent production of Leptosphaeria spp. pseudothecia on stubble in terms of pseudothecial density. Results showed that stems with less severe stem cankers produced fewer mature pseudothecia of Leptosphaeria spp. on the infected stubble. This investigation suggests that the most sustainable and effective integrated control strategy for phoma stem canker in seasons with low quantities of inoculum is to use cultivars with medium or good field resistance and apply only one spray of prothioconazole when required.     

Effect of soil solarization on the control of Phytophthora root rot in avocado

Phytophthora root rot is of paramount importance in avocado orchards of southern Spain. Soil solarization has been demonstrated to control the pathogen in infested areas from which infected trees had been removed. We aimed to determine whether soil solarization in established avocado orchards controls the disease. Soil solarization increased average maximum hourly soil temperatures by 6.5–6.9°C in unshaded areas of avocado orchards in coastal areas of southern Spain, depending on depth and year. The corresponding temperatures in shaded areas were c. 2–3°C lower. P. cinnamomi in soil, on infected avocado rootlets, and in a nutrient substrate buried at 30–60 cm depth was reduced to negligible amounts after 6–8 weeks of solarization in both unshaded and shaded locations of avocado orchards. P. cinnamomi could not be detected in avocado rootlets up to 14 months later, suggesting a long-term effect. Soil solarization did not affect growth of the trees, and fruit yields were increased as compared with control plots. Following soil solarization for 3 weeks from mid-July 1994, when maximum hourly temperatures reached 33–36°C, P. cinnamomi could not be recovered from a depth of up to 45 cm in unshaded areas or from a depth of up to 30 cm in shaded areas after the initial 10-day period. The viability of inoculum of the pathogen buried at depths between 15 and 60 cm in bare soil was determined by sequential sampling in two solarization experiments starting 12 June and 4 July 1995, respectively. In the first experiment, P. cinnamomi could not be detected at any depth after 4–8 weeks of solarization in unshaded areas but could be recovered at all depths except 15 cm in shaded areas. In the second experiment, where temperatures were higher and the soil surface not shaded, P. cinnamomi could not be recovered after 2 weeks at 15 and 30 cm.     

Root infection by Phytophthora cinnamomi in seedlings of three oak species

The combination of soil infestation with Phytophthora cinnamomi and repetitive flooding was studied on 1-year-old plants of Quercus ilex (holm oak) and Q. suber (cork oak). In a second experiment, using 2-year-old plants of the same species and of red oak ( Q. rubra ), the soil infestation was followed by two drought-rewatering cycles. Oak predawn leaf water potential (PLWP) and stomatal conductance (gs) were monitored during both experiments. Root infection, root loss, wilting and mortality were assessed at the end of the experiments. Q. ilex exhibited the highest susceptibility to P. cinnamomi , and Q. rubra the lowest. Root infections caused by P. cinnamomi were more severe in the flooding than in the drought experiment. The most noticeable effect of the infection on plant water relations was a decrease in stomatal conductance. This occurred at different times after inoculation, varying with species susceptibility and experiment. Inoculation with P. cinnamomi induced a decrease of PLWP in Q. ilex plants, and in some Q. suber plants exhibiting a severe root loss. The results further showed that the relationship between PLWP and gs was modified by infection with P. cinnamomi . The combination of flooding and infection with P. cinnamomi acted synergistically on the water relations of Q. ilex . By contrast, there was no significant increase in disease severity due to the postinoculation water stress imposed on the oaks.     

Phytophthora crown rot of almonds in Australia 1

Phytophthora crown rot, caused primarily by Phytophthora cambivora, has caused considerable losses in almond orchards in the Willunga and northern plains areas approximately 50 km north and south of Adelaide (AU), respectively. Other Phytophthora species including P. citrophthora, P. cryptogea, P. megasperma and P. syringae have also been associated with diseased trees. Tree losses have been associated with P. cactorum isolated from trunk cankers on scaffold limbs on trees in the Riverland almond-growing area approximately 350 km north-east of Adelaide. The Al mating type of P. cambivora was the most pathogenic to almond seedlings. Cvs Mission and Chellaston, which are commonly used as rootstocks, were highly susceptible to crown rot whereas peach cv. Nemaguard was resistant. An excised twig assay has been developed to screen micropropagated shoots for resistance to P. cambivora. Metalaxyl applied at 5 g active substance per tree in spring, winter and autumn in a shallow trench close to the trunk prevented the development of trunk cankers. Foliar sprays of phosphonate (H₃PO₃) at 2 g active substance per litre in autumn and spring also inhibited canker development.     

Susceptibility of pines in South Africa to the pitch canker fungus subglutinans f.sp. pini

Fusarium subglutinans f.sp. pini (F.s. pini)is the causal agent of pitch canker of pines. The fungus has recently been found in South Africa on the diseased roots of seedlings, but has as yet not been detected on mature trees in commercial forests. Inoculation of 1 -year-old and seedlings with isolates of resulted in canker development and shoot mortality. No significant differences in virulence were found among eight isolates of the pathogen on and but isolate MRC 6214 was significantly more virulent on seedlings than MRC 6209. Disease development was significantly more severe on and than on Pathogenicity tests on 4-year-old and trees yielded comparable results. Resinous cankers, similar to those described for pitch canker, developed on trees in the vicinity of inoculation points but development ceased before stems were girdled.     

Fine-level genetic structure of white pine blister rust populations

ABSTRACT The fine-level genetic structure of the white pine blister rust agent, Cronartium ribicola, was investigated by sampling multiple monokaryotic spermogonia directly on cankers in four eastern Canadian white pine (Pinus strobus) plantations and assessing genetic variability, using random amplified polymorphic DNA (RAPD) markers. Ninety-eight percent of the cankers surveyed contained a single DNA haplotype, suggesting spermogonia within cankers are the result of clonal reproduction. A single canker contained two haplotypes that were divided between the upper and lower parts of the canker, suggesting it represented two confluent cankers. In contrast, genotypic diversity was high among cankers. Thirty-seven haplotypes were found among forty-three cankers sampled, and an analysis of molecular variance indicated that 93% (P < 0.001) of the total genetic diversity was attributable to sampling of different cankers, strongly suggesting that multiple infections do not take place in the white pine blister rust pathosystem, i.e., a canker is the result of infection by a single genotype. This result is in contrast with the high level of genetic diversity previously reported among dikaryotic aecidia within cankers and is consistent with the hypothesis that variability in the aecidial stage is the result of outcrossing between resident spermogonia and alien spermatia. The genetic structure of the spermogonial stage, which is the vegetative extension of infection by basidiospores and, therefore, the indirect result of meiosis, was consistent with random mating; the observed genotypic diversity was not significantly different (P > 0.05) from the genotypic diversity expected under the assumption of panmixis. The results indicate that monokaryotic cankers can be genotyped by sampling a single unopened spermogonia per canker.     

Dieback symptoms on olive trees caused by the fungus Eutypa lata1

The fungus Eutypa lata was isolated from olive trees for the first time in 1988 from two young 3-year-old trees. It was evident that the infection was initiated from the graft union. The trees were also infected by Armillaria mellea. In a second case in 1991, extensive cankers were observed along the branches which often were girdled and died. The infected area extended from the bark into the sapwood and even into the heartwood. Cultures made on potatodextrose agar from the margin of necrotic and healthy tissues resulted in typical colonies of the fungus E. lata, as well as of Verticillium dahliae. The colonies of E. lata produced the characteristic pycnidia of the anamorph Libertella blepharis 3–4 weeks later. Pathogenicity tests made on olive, apricot, almond and walnut trees resulted in the death of the inoculated twigs or in canker formation and extensive brown discoloration of the wood.     

The early development of disease caused by Phytophthora cinnamomi in Eucalyptus marginata and Eucalyptus calophylla grooving in rehabilitated bauxite mined areas

The soil-borne plant pathogen Phytophthora cinnamomi is widely distributed in the jarrah ( Eucalyptus marginata ) forest of Western Australia. Infested areas of the forest are mined for bauxite and the presence of the pathogen could after the survival of trees re-established after mining. Monitoring of 21 revegetated bauxite mined areas found that survival of jarrah and marri ( Eucalyptus calophylla ) trees was high (85–92% and 93–99%, respectively) after 5–7 years but P. cinnamomi was recovered from dead trees. To identify trees for more detailed study, plant symptoms of stress such as suppressed growth, wilting, yellowing of crown, coppice and epicormic growth and visible stem lesions were used. Over a period of 15 months, 30 E. marginata and 28 E. calophylla were carefully excavated and examined for lesions and the presence of P. cinnamomi. P. cinnamomi was consistently isolated from the lignotuber and collar regions of both hosts but never from the roots alone, except in one instance from E. calophylla where it was isolated from a non-lesioned root. In E. calophylla , the lignotuber appears to be very susceptible to invasion by P. cinnamomi in contrast to the roots which appear resistant. The invasion of the pathogen into the lignotuber and collar regions of both species was consistently associated with ponding of water around the plants. This ponding persists for many hours to days after rain and appears to provide an infection court for P. cinnamomi. Development of rehabilitation procedures to reduce this ponding will minimize the risk of tree deaths caused by this pathogen.     

The Influence of Fungicide Sprays on Infection Of Apple cv. Bramley's Seedling By Nectria galligena

In 1990, a long-term trial was initiated by planting young apple trees, cv. Bramley's Seedling, inoculated, at single sites in the leader shoots, with Nectria galligena. The effect of spring–summer and autumn fungicide spray programmes, applied during 1991–1993, on the development of new cankers was assessed up to May 1994. Spring–summer fungicide programmes, applied as for the control of apple scab, reduced numbers of new cankers by between 65% and 76% compared with the untreated control. Sterol demethylation inhibiting fungicides (hexaconazole, myclobutanil, penconazole) had a similar effect on canker to dithianon. Autumn application of copper oxychloride at 5% and 50% leaf-fall further reduced numbers of new cankers. The combination of a spring–summer benzimidazole (carbendazim or thiophanate-methyl) with a scab fungicide (dithianon) and autumn copper oxychloride did not improve canker control compared with applying copper oxychloride after spring–summer myclobutanil+mancozeb. The percentage of fruit which developed rots in long-term storage was decreased by spring–summer benzimidazole application, but not by other fungicide programmes even those which achieved similar levels of canker control.