Stepped‐up surveillance for early detection of Anoplophora chinensis in a nursery district

The Plant Protection Service of Lombardy Region (Italy) has been working to control Anoplophora chinensis for many years. A specific plan was developed by the Plant Protection Service in 2011 to implement stepped‐up surveillance for early detection of this pest in the most important nursery area in the region. The Canneto sull'Oglio district area hosts the highest concentration of commercial nurseries in Lombardy. The nurseries specialize in the cultivation of full‐size deciduous ornamental trees. The reinforced surveillance plan includes the following steps: planning, inspection of the urban green spaces, surveillance in rural areas and surveillance of identified sources of risk. A new procedure was defined for the enhanced territorial surveillance, as there were no established guidelines to follow. Two buffer zones were delineated, with a 2 km radius and a 500 m radius around all the areas dedicated to nursery cultivation, and a grid of 500 × 500 m was superimposed on it. Between one and four inspection points were defined for each cell, depending on the risk to plant health, and more than 3450 inspection points were identified, corresponding to 11 233 potential host plants that were to be inspected. In addition, the fields of 16 nurseries classified as high risk sources were inspected as well as the potential hosts in the buffer zone of 100 m radius around them. The annual cost of the surveillance is 30 000 EUR, which corresponds to about 0.025% of the annual production value of the nurseries in this district.     

Frost promotes the pathogenicity of Pseudomonas syringae pv. actinidiae in Actinidia chinensis and A. deliciosa plants

Frost occurs in all major areas of cultivation, presenting a threat for the production of kiwifruit crops worldwide. A series of experiments were performed on 1‐year‐old, potted plants or excised twigs of Actinidia chinensis and A. deliciosa to verify whether strict relationships exist between bacterial canker outbreaks from Pseudomonas syringae pv. actinidiae (Psa) attacks and the occurrence of autumn and winter frost events. The association between the occurrence of autumn frost and the sudden outbreak of bacterial canker in A. chinensis in central Italy has been confirmed. Both autumn and winter frosts promote Psa multiplication in the inoculated twigs of both species. The day after the frost, reddish exudates oozing from the inoculation sites were consistently observed in both species, and Psa was re‐isolated in some cases. During the thawing of both A. deliciosa and A. chinensis twigs, the 2‐cm upward and downward migration of Psa from the inoculation site was observed within 3 min, and the leaves were consistently colonized with the pathogen. A consistent brown discoloration, accompanied with a sour‐sap odour, was observed throughout the length of the excised twigs of both Actinidia species after Psa inoculation and winter frost. Psa inoculation induced a remarkably higher necrosis in excised twigs that were not frozen compared with P. s. pv. syringae inoculation. Antifreeze protection using irrigation sprinklers did not influence the short‐term period of Psa and P. s. pv. syringae multiplication in both A. deliciosa and A. chinensis twigs. Thus, the damage from frost, freeze thawing and the accumulation of Psa in Actinidia twigs promotes the migration of the pathogen within and between the orchards. Taken together, the results obtained in this study confirmed that A. deliciosa is more frost tolerant than A. chinensis, autumn frosts are more dangerous to these crops than winter frosts, and in the absence of Psa, young kiwifruit plants remain sensitive to frost.     

First record of Xylotrechus chinensis (Coleoptera,Cerambycidae) in Greece and in the EPPO region

Xylotrechus chinensis belongs to the entomofauna of China, Japan, the Korean Peninsula and Taiwan. Prior to this paper it has been intercepted twice outside its native range, once in Philadelphia (USA) and once in Germany (Europe). In spring 2017, it was detected for the first time in Greece, in Heraklion city (Island of Crete) infesting the trunk of trees of Morus species planted near the harbour of the city. It can thus be hypothesized that X. chinensis was transported from its native range with commodities that are handled in the harbour. Eradication efforts are being taken in order to prevent its further spread, which could threaten several other tree species because X. chinensis attacks a wide range of hosts. This is the first record of this pest from the EPPO region.     

Identification and pathogenicity of Cryphonectriaceae species associated with chestnut canker in China

Cryphonectriaceae species cause serious canker diseases on chestnut, oak and eucalypt trees. Recently, canker symptoms with typical orange fruiting bodies were observed on Chinese chestnut and oak trees in Hebei, Hubei, Shaanxi and Shandong Provinces in China. In the present study, isolates of these fungi were identified based on phylogenetic and morphological evidence, and their pathogenicities were tested on detached chestnut (Castanea mollissima) branches. DNA sequence comparisons of the internal transcribed spacer (ITS) regions and two regions of β-tubulin (TUB1/TUB2) indicate that these isolates represent five species in the Cryphonectriaceae, viz. Cryphonectria japonica, Cryphonectria parasitica, Aurantiosacculus castaneae sp. nov., Cryphonectria neoparasitica sp. nov. and Endothia chinensis sp. nov. The sexual morph of Aurantiosacculus is discovered for the first time and can be distinguished from the other genera in Cryphonectriaceae by dark brown ascospores and tubiform appendages at both ends. Cryphonectria neoparasitica sp. nov. is different from the other Cryphonectria species by its aseptate ascospores. Endothia chinensis sp. nov. is the sole species in Endothia infecting the host genus Castanea. Additionally, it is much smaller than E. gyrosa and narrower than E. singularis in ascospores. The inoculation results showed that these five Cryphonectriaceae fungi isolated from chestnut or oak are all pathogenic to tested chestnut branches. Cryphonectria parasitica appears to be the most aggressive fungus, followed by C. neoparasitica sp. nov., C. japonica, E. chinensis sp. nov. and A. castaneae sp. nov.     

Anoplophora species in Europe: infestations and management processes1

By the end of summer 2005, four sites of infestation by Anoplophora glabripennis (Coleoptera, Cerambycidae) had been detected in three European countries: Austria in 2001, at Braunau am Inn; France in 2003, at Gien, and in 2004, at Sainte‐Anne‐sur‐Brivet; and Germany in 2004, at Neukirchen am Inn. Two sites of infestation by Anoplophora chinensis have been detected in two European countries: Italy in 2000, at Parabiago, and France in 2003, at Soyons. The history of the A. glabripennis and A. chinensis discoveries is presented, as well as the respective management responses (monitoring and destruction of the infested trees). By the end of summer 2005, the eradication was not yet fully achieved in any of the four A. glabripennis‐infested sites. In contrast, no new A. chinensis‐infested trees had been found at Soyons, France, since 2003. At Parabiago, Italy, monitoring is taking place: the A. chinensis infestation affects 16 municipalities over more than 60 km². By summer 2005, destruction on a large scale of the infested trees had not yet taken place, but tree‐cutting of more than 1000 trees had been planned for winter 2005‐06. Given the current substantial extent of the A. chinensis infestation near Milan, and the density of the established A. chinensis populations, there is a high probability that the status of the pest in Italy will soon be raised from ‘introduced’ to ‘invasive’.     

Impact of kiwifruit bacterial canker on productivity of cv. Hayward kiwifruit using observational data and multivariable analysis

A virulent strain of Pseudomonas syringae pv. actinidiae biovar 3 (Psa), which causes bacterial canker in kiwifruit, was first recorded in New Zealand in November 2010. This strain has severely affected Actinidia chinensis var. chinensis ‘Hort16A’ kiwifruit productivity but its effect on green Actinidia chinensis var. deliciosa ‘Hayward’ kiwifruit productivity has been variable. An observational study design was used to develop explanatory models to quantify the impacts of Psa infection on productivity (tray equivalents per hectare) of Hayward kiwifruit harvested in 2012, using data captured by industry from 2599 orchards. A total of 934 orchards were Psa positive at the end of the study period. Multivariable linear regression was used to model 2012 productivity in the presence of Psa, while controlling for regional differences, elevation, 2011 productivity, harvest dates and application of agrichemicals. The model showed productivity was initially higher in the presence of Psa, and was not reduced until after 1 year of infection. The relationship between protective spray use and productivity was also quantified. It is likely that improved disease management has offset the impact of the disease and future research should consider a reassessment of the effects of disease after longer term exposure to Psa in New Zealand. The use of an observational cohort study to assess disease impacts using multivariable analysis could have wider application in the field of plant epidemiology.     

Distribution and damage caused by Halyomorpha halys in Italy

Since the first occurrence of Halyomorpha halys (Heteroptera: Pentatomidae) in Italy in 2012, the pest has spread in the Po Valley causing severe damage in summer 2015, particularly in pear orchards. At present, populations of H. halys have been reported in the regions of Emilia‐Romagna (Modena, Reggio Emilia and Bologna provinces), Piedmont, Lombardy, Veneto and Friuli. The damage caused by H. halys is typical of pentatomids and is aggravated by the pest's polyphagy and by the behaviour of adults which move continuously from plant to plant, from hedges or herbaceous crops to fruit orchards. The unpredictability of H. halys’ movements, along with the effect of the aggregating pheromone that concentrates the pest in certain areas of the orchards, therefore making chemical spraying complicated.     

Current situation and characterization of Pseudomonas syringae pv. actinidiae on kiwifruit in Galicia (northwest Spain)

Bacterial canker of kiwifruit, caused by Pseudomonas syringae pv. actinidiae (Psa), is a disease that is spreading rapidly in several kiwifruit‐producing countries, causing significant economic losses. In 2011, it was detected for the first time in Spain, in the south of Galicia (northwest Spain). Kiwifruit orchards were therefore inspected and sampled in 2011 and 2012 to determine the pathogen distribution, and the isolates obtained were characterized by morphology, fatty acids profile, biochemical tests and molecular techniques. Isolates were obtained from Actinidia deliciosa ‘Hayward’ (from leaves, canes, flower buds, fruits and roots), from A. deliciosa ‘Summer’, from Actinidia chinensis ‘Jin Tao’ (from canes and leaves) and from A. chinensis pollinator ‘Belén’ (from canes). Results of the analysis of the cfl gene (phytotoxin production‐related), the tox–argK gene cluster and phylogenetic analysis of the cts gene demonstrated that all Psa isolates from northwest Spain correspond to the Psa3 population, which includes strains of haplotype 2. This is the first record of Psa3 and haplotype 2 in Spain.     

Real‐time and qualitative PCR for detecting Pseudomonas syringae pv. actinidiae isolates causing recent outbreaks of kiwifruit bacterial canker

Since 2008, Pseudomonas syringae pv. actinidiae virulent strains (Psa‐V) have quickly spread across the main areas of kiwifruit (Actinidia deliciosa and A. chinensis) cultivation causing sudden and re‐emerging outbreaks of bacterial canker to both species. The disease caused by Psa‐V strains is considered worldwide as pandemic. Recently, P. syringae strains (ex Psa‐LV, now called PsD) phylogenetically related to Psa‐V have been isolated from kiwifruit, but cause only minor damage (i.e. leaf spot) to the host. The different biological significance of these bacterial populations affecting kiwifruit highlights the importance of having a diagnostic method able to detect Psa‐V, which is currently solely responsible for the severe damage to the kiwifruit industry. In order to improve the specific molecular detection of Psa‐V, a real‐time PCR assay has been developed based on EvaGreen chemistry, together with a novel qualitative PCR (PCR‐C). Both methods are based on specific primer sets for the hrpW gene of Psa. The real‐time PCR and PCR‐C were highly specific, detecting down to 50 and 200 fg, respectively, and were applied to a range of organs/tissues of kiwifruit with and without symptoms. These methods are important tools for both sanitary and certification programmes, and will help to avoid the spread of Psa‐V and to check possible inoculum sources. In addition to being used as routine tests, they will also enable the study of the biology of Psa‐V and the disease that it causes, whilst avoiding the detection of other populations of related P. syringae present in kiwifruit.     

Distribution and abundance of invasive Tamarix genotypes in South Africa

The exotic Tamarix chinensis and T. ramosissima, believed to have been introduced into South Africa in the early 1900s to control erosion on mine dumps, are invading riparian zones and have been proven to hybridise with T. usneoides, which is native to southern Africa. In this study, we document the abundance of invasive Tamarix genotypes in South Africa. Eleven riparian zones from the Northern, Eastern and Western Cape Provinces were surveyed. Three quadrats of 600 m² each were selected per site. Plant density, canopy cover and tree height were recorded to quantify invasiveness. Leaf samples were randomly collected from an average of eight individuals per site to record genotypes of the invaders. Tamarix density and canopy cover were significantly greater than those of co‐occurring trees and shrubs in Olifants River in De Rust (Western Cape Province). A linear correlation between percentage Tamarix spp. cover and other co‐occurring tree and shrub species showed a strong negative relationship (R² = 0.78). Genetic analysis showed that the Western and Eastern Cape Provinces have the highest proportion of the exotic Tamarix species and their hybrids. This suggests that these two provinces require urgent management intervention to contain the spread of the weed. The distinctions made between the native and the exotic Tamarix species and their hybrids should also facilitate the testing and future release of potential biological control agents.     

Termite cuticular extracts improve acceptance of bait for controlling invasive Asian needle ants,Brachyponera chinensis

BACKGROUND

The Asian needle ant, Brachyponera chinensis, is an invasive ant currently spreading in urban and natural habitats throughout the eastern United States. Recent studies have documented the negative impact of B. chinensis on native ecosystems and human health, yet effective control strategies are lacking. Control difficulties are, in part, due to the unique biology of B. chinensis, which is a predatory ant and a termite specialist. Given that subterranean termites are an important nutritional resource for B. chinensis, the current study evaluated the potential of termite cuticular extract to improve the target-specificity and efficacy of commercial bait used for B. chinensis control.

RESULTS

The efficacy of bait augmented with termite cuticular extracts was evaluated in laboratory and field trials. In laboratory assays, B. chinensis colonies were offered granular bait treated with termite cuticular extract. Results demonstrated that the acceptance of commercial bait is significantly increased by the addition of termite cuticular extract or synthetic (Z)-9-pentacosene, a major component of termite cuticular extract. Foraging activity of Asian needle ants was significantly greater on baits augmented with termite cuticular extract or (Z)-9-pentacosene relative to standard bait. Furthermore, bait augmented with termite cuticular extract worked substantially faster relative to standard bait. To evaluate population effects, field studies were conducted in forested areas invaded by B. chinensis. Bait treated with termite cuticular extract scattered on the forest floor provided rapid control of B. chinensis and ant densities throughout the treated plots declined by 98% within 14 days.

CONCLUSION

The incorporation of termite cuticular extracts and individual cuticular hydrocarbons such as (Z)-9-pentacosene into traditional baits used for B. chinensis control may offer a novel tool to manage this increasingly problematic invasive ant. © 2023 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Feeding and oviposition of <Emphasis Type="Italic">Anoplophora chinensis</Emphasis> on ornamental and forest trees

Studies were conducted on maturation feeding and oviposition of Anoplophora chinensis (Forster) (Coleoptera: Cerambycidae), a recently introduced quarantine pest in Europe on different plant species of great importance for urban and forest environments in Italy. The tested plant species were Aesculus hippocastanum, Acer negundo, A. campestris, Castanea sativa, Corylus avellana, Platanus x acerifolia, Quercus petrea, Q. pubescens, Q. rubra, Tilia platyphyllos, Ulmus minor and U. pumila. Tested adults of A. chinensis originated from a population of a recently infested site in Italy (Rome) and all experiments were conducted in a walk-in insect cage under quarantine conditions. Adults of A. chinensis showed a maturation feeding preference for twigs of Acer species (A. negundo and A. campestris) and for C. avellana. In the oviposition experiments conducted on bolts of tested plant species, A. chinensis females did not show clear preferences and some data did not reflect the preferences shown during the feeding experiments. Nevertheless, A. negundo and A. campestris were well accepted plant species for oviposition besides A. hippocastanum and T. platyphyllos.     

基于植物代谢组学和昆虫肠道细菌分析光肩星天牛的寄主适应性

为探究光肩星天牛Anoplophora glabripennis对传统抗性树种白蜡的适应性机制,利用代谢组学分析不同白蜡品种木质部次生代谢产物,利用16S rRNA测序技术对取食白蜡后的光肩星天牛肠道细菌群落组成进行检测,并采用Pearson方法分析两者的相关性。结果表明,在洋白蜡Fraxinuspennsylvanica和中国白蜡F. chinensis木质部中共筛选出27类抗虫性差异代谢产物,其中黄酮苷、双黄酮及多黄酮、简单酚类、香豆素及其衍生物和木质素苷在中国白蜡中含量较丰富;而2-芳基苯并呋喃类黄酮、阿朴啡类、麦角林及其衍生物和有机氮化合物在洋白蜡中占优。光肩星天牛取食洋白蜡和中国白蜡2种寄主后肠道细菌群落组成存在明显差异,优势菌门分别为变形菌门和厚壁菌门;优势菌属分别为拉乌尔菌属Raoultella（55.79%）和乳球菌属Lactococcus（57.52%）;筛选到21个差异菌属,其中13个菌属在中国白蜡中的相对丰度显著高于洋白蜡。相关性分析结果表明,尽管类黄酮、简单酚类、香豆素及其衍生物和木质素苷等酚类化合物在中国白蜡中含量更高,但取食中国白蜡后光肩星天牛肠道内一方面存在优势菌群参与代谢上述物质,如肠球菌属Enterococcus、拉乌尔菌属对类黄酮和木质素苷的代谢;另一方面中国白蜡通过一些特异菌属和共有菌属的增殖参与代谢,如乳杆菌属Lacto-bacillus和放线菌属Actinomycetes对类黄酮、乳球菌属对简单酚类、鞘氨醇杆菌属 Sphingobacterium对香豆素及其衍生物、放线菌属和肠球菌属对木质素苷的代谢。生物碱在中国白蜡中的含量低于洋白蜡,未发现特殊菌属降解该类物质。推测相对于洋白蜡,取食中国白蜡后光肩星天牛肠道菌群更具特异性和多样化,可以帮助光肩星天牛快速代谢相关次生物质,顺利完成其在中国白蜡上的生活史。     

Partial characterisation of a novel <Emphasis Type="Italic">Tobamovirus</Emphasis> infecting <Emphasis Type="Italic">Actinidia chinensis</Emphasis> and <Emphasis Type="Italic">A. deliciosa</Emphasis> (Actinidiaceae) from China

Actinidia chinensis and A. deliciosa plants from China, showing a range of symptoms, including vein clearing, interveinal mottling, mosaics and chlorotic ring spots, were found to contain ~300 nm rod-shaped virus particles. The virus was mechanically transmitted to several herbaceous indicators causing systemic infections in Nicotiana benthamiana, N. clevelandii, and N. occidentalis, and local lesions in Chenopodium quinoa. Systemically- infected leaves reacted with a Tobacco mosaic virus polyclonal antibody in indirect ELISA. PCR using generic and specific Tobamovirus primers produced a 1,526 bp sequence spanning the coat protein (CP), movement protein (MP), and partial RNA replicase genes which showed a maximum nucleotide identity (88%) with Turnip vein clearing virus and Penstemon ringspot virus. However, when the CP sequence alone was considered the highest CP sequence identity (96% nt and 98% aa) was to Ribgrass mosaic virus strain Kons 1105. The morphological, transmission, serological and molecular properties indicate that the virus is a member of subgroup 3 of the genus Tobamovirus.     

Characterization of Pseudomonas syringae pv. actinidiae (Psa) isolated from France and assignment of Psa biovar 4 to a de novo pathovar: Pseudomonas syringae pv. actinidifoliorum pv. nov.

Since 2008, bacterial canker of kiwifruit (Actinidia deliciosa and A. chinensis) caused by Pseudomonas syringae pv. actinidiae (Psa) has resulted in severe economic losses worldwide. Four biovars of Psa can be distinguished based on their biochemical, pathogenicity and molecular characteristics. Using a range of biochemical, molecular and pathogenicity assays, strains collected in France since the beginning of the outbreak in 2010 were found to be genotypically and phenotypically diverse, and to belong to biovar 3 or biovar 4. This is the first time that strains of biovar 4 have been isolated outside New Zealand or Australia. A multilocus sequence analysis based on four housekeeping genes (gapA, gltA, gyrB and rpoD) was performed on 72 strains representative of the French outbreak. All the strains fell into two phylogenetic groups: one clonal corresponding to biovar 3, and the other corresponding to biovar 4. This second phylogenetic group was polymorphic and could be divided into four lineages. A clonal genealogy performed with a coalescent approach did not reveal any common ancestor for the 72 Psa strains. Strains of biovar 4 are substantially different from those of the other biovars: they are less aggressive and cause only leaf spots whereas Psa biovars 1, 2 and 3 also cause canker and shoot die‐back. Because of these pathogenic differences, which were supported by phenotypic, genetic and phylogenetic differences, it is proposed that Psa biovar 4 be renamed Pseudomonas syringae pv. actinidifoliorum pv. nov. Strain CFBP 8039 is designated as the pathotype strain.     

Host plants of Anoplophora glabripennis,a review

Anoplophora glabripennis (Asian longhorned beetle) attacks many different broadleaf tree species. Although there is no doubt that A. glabripennis can complete its life cycle on species belonging to various genera such as Acer, Populus, Salix and Ulmus, there is conflicting information about the host plant status of many other species. Plant species may have been listed because of maturation feeding or oviposition, without evidence that A. glabripennis can actually complete its life cycle on these species. In the present review, 34 plant taxa that have been listed as A. glabripennis‐hosts are placed in four different categories based on information available through literature search and by personal communication with experts. The categories are: (I) plant species on which A. glabripennis has been reported to complete its life cycle (from oviposition to emergence of new beetles) under field conditions, (II) plant species on which A. glabripennis has completed its life cycle in laboratory or semi‐field experiments (i.e. plants and beetles reared in cages), (III) plant species on which A. glabripennis has been reported to complete part of its life cycle, and (IV) others. The following genera were placed in category I: Acer, Aesculus, Betula, Cercidiphyllum, Fraxinus, Platanus, Populus, Salix and Ulmus. The species Albizia julibrissin, Corylus colurna, Elaeagnus angustifolia, Fagus sylvatica, Koelreuteria paniculata, Malus domestica, Pyrus bretschneideri and Sorbus aucuparia were also placed in category I, although records on exit holes were limited. These species may be rather poor or unattractive hosts on which A. glabripennis may only incidentally oviposit and/or complete its life cycle or the species may be rather uncommon in outbreak areas thus far and, therefore, not frequently attacked. Elaeagnus angustifolia has also been reported to be resistant. For some of the species listed the host plant status may need confirmation. The list of category I species may also become longer in the future because several of the plant species listed only recently appeared to be true hosts, i.e. supporting completion of the full life cycle of A. glabripennis.     

Development of a quantitative real‐time PCR assay for Phytophthora infestans and its applicability to leaf,tuber and soil samples

A sensitive real‐time polymerase chain reaction (PCR) assay was developed for the quantification of Phytophthora infestans, the cause of foliar and tuber late blight in potato. A primer pair (PinfTQF/PinfTQR) and a fluorogenic probe (PinfTQPR) were designed to perform a quantitative assay for the detection of P. infestans in leaves, tubers and soils. The assay was shown to be specific to P. infestans and the very closely taxonomically related non‐potato pathogen species P. mirabilis, P. phaseoli and P. ipomoea, but did not detect the potato pathogens P. erythroseptica and P. nicotianae. The assay was able to reliably detect P. infestans DNA at 100 fg per reaction and was effective in quantifying P. infestans in infected leaf tissue from 24 h after inoculation and also in infected symptomless tubers and diseased tubers. Attempts to detect oospores of P. infestans in naturally and artificially infested soil samples are described and compared with baiting tests and previous literature. It was not possible to detect oospores in soil samples due to problems with DNA extraction from the oospores themselves. However, the assay was shown to detect even very low levels of asexual inoculum (sporangia and mycelium) in soil. This work assembles all the necessary features of a quantitative P. infestans assay, which have previously been somewhat disparate: the sensitivity, specificity and quantitation are fully validated, the assay is shown to work in common applications in leaf and tuber tissue and the problems with P. infestans oospore detection are explored and tested experimentally.     

Effect of soil type,organic matter content,bulk density and saturation on clubroot severity and biofungicide efficacy

Growth room experiments were conducted to assess the interaction of soil type, biofungicides, soil compaction and pathotype/host on infection and symptom development caused by Plasmodiophora brassicae, the cause of clubroot on Brassica spp. In two initial experiments, four soil types (peat soil, mineral soil, non‐calcareous sand, soil‐less mix), two biofungicides (Bacillus subtilis, Clonostachys rosea), and two pathotypes (3 and 6, Williams’ differential set) were assessed. Differences in clubroot severity associated with soil type were unexpectedly small and variable. Prestop (C. rosea) was often more effective than Serenade (B. subtilis) at reducing clubroot levels on peat and mineral soils, but less effective than Serenade on sand. Inoculation with pathotype 3 often resulted in a slightly higher mean severity than pathotype 6. The interaction of soil type × biofungicide was similar on both canola (B. napus) and Shanghai pak choy (B. rapa subsp. chinensis), whether the soil was kept saturated or allowed to drain after inoculation. The impact of soil type on biofungicide efficacy might explain, in part, why biofungicides are more effective in one location than another. The observation that clubroot severity in soil‐less mix was affected by compaction led to an investigation of soil bulk density. Severity was higher in soil‐less mix that was more compacted than in the initial experiments, and was lower in peat and mineral soils when soil bulk density was reduced by adding soil‐less mix. In this study, soil bulk density had a larger impact on clubroot than soil type, organic matter or pathotype.     

Contrasting species boundaries between sections Alternaria and Porri of the genus Alternaria

The fungal genus Alternaria comprises a large number of asexual taxa with diverse ecological, morphological and biological modes ranging from saprophytes to plant pathogens. Understanding the speciation processes affecting asexual fungi is important for estimating biological diversity, which in turn affects plant disease management and quarantine enforcement. This study included 106 isolates of Alternaria representing five phylogenetically defined clades in two sister sub‐generic groups: section Porri (A. dauci, A. solani and A. limicola) and section Alternaria (A. alternata/tenuissima and A. arborescens). Species in section Porri are host‐specific while species in section Alternaria have wider host ranges. For each isolate, DNA sequences of three genes (Alt a1, ATPase, Calmodulin) were used to estimate phylogenies at the population and species levels. Three multilocus haplotypes were distinguished among A. dauci isolates and only one haplotype among A. solani and A. limicola isolates, revealing low or no differentiation within each taxon and strong clonal structure for taxa in this section. In contrast, 37 multilocus haplotypes were found among A. alternata/tenuissima isolates and 21 multilocus haplotypes among A. arborescens isolates, revealing much higher genotypic diversity and multiple clonal lineages within taxa, which is not typical of asexual reproducing lineages. A species tree was inferred using a Yule Speciation model and a strict molecular clock assumption. Species boundaries were well defined within section Porri. However, species boundaries within section Alternaria were only partially resolved with no well‐defined species boundaries, possibly due to incomplete lineage sorting. Significant association with host specificity seems a driving force for speciation.     

Discrimination of Ambrosia artemisiifolia and Artemisia vulgaris by hyperspectral image analysis during the growing season

Ambrosia artemisiifolia (ragweed) is an invasive plant in Europe. An optical detection system for effective monitoring requires differences in the spectral reflectance properties compared with other plant species. A. artemisiifolia often occurs together with Artemisia vulgaris (mugwort). Both plant species are of the Asteraceae family and they are almost indistinguishable in appearance. With the help of hyperspectral image analysis, a method was developed to determine characteristic wavelengths for their classification. High‐resolution hyperspectral images (400–1000 nm) were generated indoors. The factors measured were two weed species, two tissue classes (leaf and stem) and three growth stages (rosette growth, inflorescence emergence and fruit development). Only the stems of A. artemisiifolia in the fruit development stage showed different reflectance behaviour compared with its leaves and with the stems and leaves of A. vulgaris. At wavelengths ranging from 550 to 650 nm, the reflectance increased, and then at wavelengths up to 680 nm, the reflectance decreased. The other tissue classes showed constantly decreasing spectral reflectance from 550 to 680 nm. In the two other early growth stages, the reflectance of all four tissue classes decreased similarly. Thus, using two wavelengths of 550 and 650 nm, classification between A. artemisiifolia and A. vulgaris at fruit development was achieved. The findings could be a first step to develop an optical outdoor detection system to identify hot spots of A. artemisiifolia.