Comparison of management strategies for controlling Nassella trichotoma in modified tussock grasslands in New Zealand: a spatial and economic analysis

The weedy grass Nassella trichotoma (nassella tussock), historically an economically damaging invader of modified tussock grasslands in New Zealand, currently causes little if any reduction in farm production. This is a result of successful historical regional management programmes in which plants have been removed manually (by grubbing) each year before they seed. To inform a debate about the need for ongoing regional management, we developed a stage‐structured spatially explicit integrodifference equation population model and linked this to a cost analysis. We used the model to compare the weed's future population trajectories and related regional control costs over 50 years under three alternative management scenarios. The total discounted (3% p.a.) costs of no management, three‐yearly grubbing and continued annual grubbing were NZ $417 million, $736 million and $131 million respectively. These analyses indicate that annual grubbing of N. trichotoma returns a net benefit of $286 million ($417 – $131 million) compared with doing nothing and a net benefit of $605 million ($736 – $131 million) compared with a 3‐yearly grubbing programme. These results support the continuation of annual grubbing as the long‐term economically optimal management strategy for N. trichotoma on pastoral farms infested by the weed in New Zealand.     

Assessing regional scale weed distributions, with an Australian example using Nassella trichotoma

Knowledge of the spatial distribution of weed infestations over regional scales is essential for effective management of source populations and to assess future threats. To this end, the distributions of Nassella trichotoma across a study area in south‐east New South Wales, Australia, were analysed using the geographically local Getis–Ord G_i* spatial hotspot clustering statistic. The clustering of N. trichotoma observations was analysed at three infestation levels: presence (at any density), patch level and the occasional plant level. The results indicate that there are c. 578 km² of cells containing N. trichotoma in strongly clustered infestations, 11.2 km² within weakly clustered infestations distinct from the main clusters, and 55 km² that are not clustered. There are 117 km² of strongly clustered patch level cells, 3 km² in distinct but weak clusters, and none outside of a cluster area. Of the occasional plant level cells, 329 km² are strongly clustered, 6.2 km² are in distinct but weak clusters, and 19 km² are not clustered. These results provide a mechanism by which control efforts can be prioritized. The analysis approach described in this paper provides a consistent, quantitative and repeatable approach to assess weed infestations across regional scales and can be applied to any weed species for which spatial distribution data are available.     

The insect vector Cacopsylla picta vertically transmits the bacterium ‘Candidatus Phytoplasma mali’ to its progeny

The phloem‐sucking psyllid Cacopsylla picta plays an important role in transmitting the bacterium ‘Candidatus Phytoplasma mali’, the agent associated with apple proliferation disease. The psyllid can ingest ‘Ca. Phytoplasma mali’ from infected apple trees and spread the bacterium by subsequently feeding on uninfected trees. Until now, this has been the most important method of ‘Ca. Phytoplasma mali’ transmission. The aim of this study was to investigate whether infected C. picta are able to transmit ‘Ca. Phytoplasma mali’ directly to their progeny. This method of transmission would allow the bacteria to bypass a time‐consuming reproductive cycle in the host plant. Furthermore, this would cause a high number of infected F₁ individuals in the vector population. To address this question, eggs, nymphs and adults derived from infected overwintering adults of C. picta were reared on non‐infected apple saplings and subsequently tested for the presence of ‘Ca. Phytoplasma mali’. In this study it was shown for the first time that infected C. picta individuals transmit ‘Ca. Phytoplasma mali’ to their eggs, nymphs and F₁ adults, thus providing the basis for a more detailed understanding of ‘Ca. Phytoplasma mali’ transmission by C. picta.     

Ecology,distribution and control of the invasive weed Nassella trichotoma (Nees) Hack. ex Arechav.: A global review of current and future challenges

Nassella trichotoma (serrated tussock) is a highly invasive perennial C₃ weed from South America. It grows in most soil conditions, can resist fire and frost, and is unpalatable to grazing animals. Each plant can produce up to 140,000 seeds annually, and together, these characteristics make it a damaging landscape weed. It has diminished the agricultural carrying capacity of pastures in south-eastern Australia, New Zealand and South Africa, and emerging populations have now been identified in Europe and the United States, and bioclimatic models suggest its distribution could significantly expand within these regions in the near future. Research into control methods for this weed has been explored, and these include herbicides applied alone and in combination, the establishment of plant competition, the introduction of seed mitigation fencing, grazing management and exclusion zones, specific biological management and alteration of soil composition. Currently, the most effective and widely used control method is the residual herbicide flupropanate (2,2,3,3-tetrafluoropropanoic acid). This review will investigate the ecology, distribution, current control techniques and past research on this species, and make recommendations for future research and management.     

Histopathology of infection and colonization of Quercus ilex fine roots by Phytophthora cinnamomi

Quercus ilex is one of the European forest species most susceptible to root rot caused by the oomycete Phytophthora cinnamomi. This disease contributes to holm oak decline, a particularly serious problem in the ‘dehesas’ ecosystem of the southwestern Iberian Peninsula. This work describes the host–pathogen interaction of Q. ilex and P. cinnamomi, using new infection indices at the tissue level. Fine roots of 6‐month‐old saplings inoculated with P. cinnamomi were examined by light microscopy and a random pool of images was analysed in order to calculate different indices based on the measured area of pathogen structures. In the early stages of invasion, P. cinnamomi colonizes the apoplast and penetrates cortical cells with somatic structures. On reaching the parenchymatous tissues of the central cylinder, the pathogen develops different reproductive and survival structures inside the cells and then expands through the vascular system of the root. Some host responses were identified, such as cell wall thickening, accumulation of phenolic compounds in the middle lamella of sclerenchyma tissues, and mucilage secretion blocking vascular cells. New insights into the behaviour of P. cinnamomi inside fine roots are described. Host responses fail due to rapid expansion of the pathogen and a change in its behaviour from biotrophic to necrotrophic.     

Virulence of ‘Dickeya solani’ and Dickeya dianthicola biovar‐1 and ‐7 strains on potato (Solanum tuberosum)

Studies were conducted to explain the relative success of ‘Dickeya solani’, a genetic clade of Dickeya biovar 3 and a blackleg‐causing organism that, after recent introduction, has spread rapidly in seed potato production in Europe to the extent that it is now more frequently detected than D. dianthicola. In vitro experiments showed that both species were motile, had comparable siderophore production and pectinolytic activity, and that there was no antagonism between them when growing. Both ‘D. solani’ and biovar 1 and biovar 7 of D. dianthicola rotted tuber tissue when inoculated at a low density of 10³ CFU mL^?1. In an agar overlay assay, D. dianthicola was susceptible to 80% of saprophytic bacteria isolated from tuber extracts, whereas ‘D. solani’ was susceptible to only 31%, suggesting that ‘D. solani’ could be a stronger competitor in the potato ecosystem. In greenhouse experiments at high temperatures (28°C), roots were more rapidly colonized by ‘D. solani’ than by biovar 1 or 7 of D. dianthicola and at 30 days after inoculation higher densities of ‘D. solani’ were found in stolons and progeny tubers. In co‐inoculated plants, fluorescent protein (GFP or DsRed)‐tagged ‘D. solani’ outcompeted D. dianthicola in plants grown from vacuum‐infiltrated tubers. In 3 years of field studies in the Netherlands with D. dianthicola and ‘D. solani’, disease incidence varied greatly annually and with strain. In summary, ‘D. solani’ possesses features which allow more efficient plant colonization than D. dianthicola at high temperatures. In temperate climates, however, tuber infections with ‘D. solani’ will not necessarily result in a higher disease incidence than infections with D. dianthicola, but latent seed infection could be more prevalent.     

Host suitability of Solanum torvum cultivars to Meloidogyne incognita and M. javanica and population dynamics

Several experiments were carried out to assess the performance of commercial Solanum torvum cultivars against the root knot nematodes Meloidogyne incognita and M. javanica in Spain. The response of S. torvum rootstock cultivars Brutus, Espina, Salutamu and Torpedo against M. incognita and Mi-1.2 (a)virulent M. javanica isolates was determined in pot experiments, and of ‘Brutus’ to an N-virulent isolate of M. incognita, compared with that of the eggplant S. melongena ‘Cristal’. The relationship between the initial and final population densities of M. javanica on ungrafted and grafted ‘Cristal’ onto the S. torvum ‘Brutus’ was assessed, together with the effect on dry shoot biomass. Finally, the population growth rate and the resistance level of the four S. torvum cultivars against M. incognita was assessed under plastic greenhouse conditions in two cropping seasons. All S. torvum rootstocks responded as resistant to the M. incognita isolates and from highly resistant to susceptible against M. javanica isolates. The maximum multiplication rates of M. javanica on the ungrafted or grafted eggplant were 270 and 49, respectively, and the equilibrium densities were 1318 and 2056 eggs and J2 per 100 cm³ soil, respectively. The tolerance of the ungrafted eggplant was 10.9 J2 per 100 cm³ soil, and the minimum relative dry shoot biomass was 0.76. The population growth rate of M. incognita on eggplant cv. Cristal differed from that of the S. torvum cultivars in both cropping seasons. These results suggest that S. torvum is a valuable rootstock for managing the two Meloidogyne species irrespective of the (a)virulence status.     

Transmission of ‘Candidatus Phytoplasma pyri’ by naturally infected Cacopsylla pyri to peach,an approach to the epidemiology of peach yellow leaf roll (PYLR) in Spain

Peach orchards in the northeast of Spain were severely affected in 2012 by a previously unreported disease in this area. The symptoms included early reddening, leaf curling, decline, abnormal fruits, and in some cases death of the peach trees. All the infected peach samples were positive for ‘Candidatus Phytoplasma pyri’, but none were infected by the ‘Ca. Phytoplasma prunorum’. In this work, potential vectors able to transmit ‘Ca. Phytoplasma pyri’ from pear to peach and between peach trees were studied and their infective potential was analysed at different times of the year. Transmission trials of the phytoplasma with potential vectors to an artificial feeding medium for insects and to healthy peach trees were conducted. Additionally, isolated phytoplasmas were genetically characterized to determine which isolates were able to infect peach trees. Results showed that the only insect species captured inside peach plots that was a carrier of the ‘Ca. Phytoplasma pyri’ phytoplasma was Cacopsylla pyri. Other insect species captured and known to be phytoplasma transmitters were present in very low numbers, and were not infected with ‘Ca. Phytoplasma pyri’ phytoplasma. A total of 1928 individuals of C. pyri were captured in the peach orchards, of which around 49% were phytoplasma carriers. All the peach trees exposed to C. pyri in 2014, and 65% in 2015, were infected by ‘Ca. Phytoplasma pyri’ 1 year after exposure, showing that this species is able to transmit the phytoplasma to peach. Molecular characterization showed that some genotypes are preferentially determined in peach.     

Influence of temperature on infection and establishment of ‘Candidatus Liberibacter americanus’ and ‘Candidatus Liberibacter asiaticus’ in citrus plants

The objectives of this work were (i) to determine the influence of temperature on infection of citrus by ‘Candidatus Liberibacter asiaticus’ and ‘Candidatus Liberibacter americanus’, the two bacterial species associated with citrus huanglongbing (HLB) in Brazil, and (ii) to determine the influence of temperature on citrus colonization by ‘Ca. L. asiaticus’, which has taken over from ‘Ca. L. americanus’ as the predominant species in Brazil since 2008. Two experiments were carried out with graft‐inoculated Valencia oranges on Rangpur lime rootstocks. Immediately after inoculation the plants were maintained for 423 days in growth chambers under the following night/day temperature conditions: 17/22, 22/27 or 27/32°C, with a dark/light photoperiod of 8/16 h. Infection and colonization of plants were determined using quantitative PCR (qPCR). ‘Candidatus Liberibacter americanus’ did not infect the plants maintained at 27/32°C; however, infection by ‘Ca. L. asiaticus’ occurred at all studied temperatures. Two months after inoculation, ‘Ca. L. asiaticus’ was distributed throughout the inoculated plants, with mean C_t values in the range of 30–31 for leaves and 25–28 for roots. Over time, ‘Ca. L. asiaticus’ reached the highest titres in mature leaves (mean C_t value = 26·7) of citrus plants maintained at 22/27°C. ‘Candidatus Liberibacter asiaticus’ colonization of citrus plants was negatively affected by the daily temperature regime of 27/32°C (mean C_t value in mature leaves = 33·6).     

Liberibacters associated with orange jasmine in Brazil: incidence in urban areas and relatedness to citrus liberibacters

Two surveys (2005/2006 and 2009) were conducted in the state of São Paulo, Brazil, to investigate the incidence of ‘Candidatus Liberibacter asiaticus’ and ‘Ca. L. americanus’, two liberibacters associated with citrus huanglongbing (HLB) disease and both transmitted by Diaphorina citri, in orange jasmine (Murraya exotica), a widespread ornamental tree in cities and villages. The graft‐transmissibility of the two species, and their DNA relatedness to citrus‐associated liberibacters, were also investigated. Quantitative PCR was applied to PCR‐positive orange jasmine and HLB‐positive citrus growing in backyards and orchards to assess their inoculum source potentials. Liberibacters were detected in 91 of 786 sampled orange jasmine plants in 10 of 76 sampled locations. PCR‐positive trees exhibited yellow shoots and/or dieback symptoms indistinguishable from those on PCR‐negative trees. ‘Candidatus Liberibacter americanus’ was more common in 2005/2006 (96·6%) and ‘Ca. L. asiaticus’ in 2009 (84·8%). rplJ nucleotide sequences were identical within all populations of either species. Graft transmission succeeded only in homologous host combinations, including ‘Ca. L. americanus’ (2/10) from/to orange jasmine and ‘Ca. L. americanus’ (5/18) and ‘Ca. L. asiaticus’ (5/9) from/to citrus. Symptoms were mild and developed less rapidly in orange jasmine than in citrus, probably as a result of lower liberibacter multiplication rates. Respective titres of ‘Ca. L. americanus’ and ‘Ca. L. asiaticus’ in orange jasmine averaged 4·3 and 3·0 log cells g^?1 tissue, compared with 5·5 and 7·3 in citrus. The results indicate that orange jasmine does not favour liberibacter multiplication as much as citrus. However, its importance in HLB epidemics should not be underestimated as it is a preferred host of D. citri and is not under any strict tree‐eradication programme or measures for insect control.     

High genetic and virulence diversity detected in Neofusicoccum luteum and N. australe populations in New Zealand vineyards

Genotypic and virulence diversity of Neofusicoccum luteum and N. australe isolates recovered from grapevines displaying symptoms of dieback and decline in New Zealand were investigated. The universally primed PCR (UP‐PCR) method was used to investigate the genetic diversity of 40 isolates of N. luteum and 33 isolates of N. australe. Five UP‐PCR primers produced a total of 51 loci from N. luteum and 57 from N. australe with a greater number of polymorphic loci produced in N. australe (86%) compared with N. luteum (69%). Analysis of UP‐PCR data showed both species found in New Zealand vineyards were genetically diverse at both the inter‐ and intra‐vineyard levels with only a single pair of clonal isolates in N. luteum. Cluster analysis of UP‐PCR data produced four genetic groups in N. luteum and 10 in N. australe (P < 0.05). For both species, there was no relationship between the genetic groups and the origin of isolates. The mean genetic diversity (H) of N. luteum was less than for N. australe, being 0.1791 and 0.2417, respectively. Pathogenicity assays of both species using isolates from either the same or different genetic groups inoculated onto either green shoots or grapevine trunks, showed virulence diversity within the population; however, no correlation was identified between genetic groups and virulence.     

Virulence of the invasive ash pathogen Hymenoscyphus fraxineus in old and recently established populations

Following its introduction from Asia in the 1990s, the ascomycete Hymenoscyphus fraxineus has caused a severe dieback of Fraxinus excelsior in Europe. In this study, the virulence of 200 H. fraxineus isolates were assessed and compared. These isolates equally represented (i) two geographically distant populations with a different disease history (Switzerland, recently established populations at the epidemic front versus Lithuania, old established populations), and (ii) isolates from two different types of host tissue (necrotic bark lesions as dead‐end tissue versus fallen leaf petioles as primary host tissue). Inoculations conducted on 3‐year‐old F. excelsior seedlings showed that the vast majority of the isolates (98%) were able to induce necrotic bark lesions after 10 months. Although a high variation in virulence was observed among isolates, no significant differences were detected between the older and the epidemic‐front populations. Decline in virulence of populations of invasive organisms is generally assumed with increasing age of epidemics. However, this does not appear to hold true for H. fraxineus. Either the Lithuanian population is still too young (15 to 20 years old) to show a decline in virulence, or the size of the host population may still not be critical for pathogen survival. Given that bark lesions represent an epidemiological dead end and do not benefit the survival of H. fraxineus, a trend towards reduced ‘bark virulence’ of isolates originating from leaf petioles compared to isolates from the bark lesions was expected. However, such a trend was observed neither in old, nor in recently established populations.     

Pre‐infection processes of Botryosphaeriaceae spp.: adhesion of conidia to different substrata

Species of Botryosphaeriaceae are important wound pathogens of grapevines as causal agents of botryosphaeria dieback, but the behaviour of their conidia pre‐infection is unknown and may be important for disease development. Adhesion properties of conidia were investigated for Botryosphaeria dothidea, Neofusicoccum luteum and N. parvum on substrata with different affinities for water. Greatest adhesion on any surface was reached after 5 min for isolates N. luteum MM558, B. dothidea 007 and N. parvum G652 (53·1, 54·0 and 50·6%, respectively) and for N. luteum isolate CC445 after 20 min (61·4%). As conidia adhered well to all artificial substrata, it appeared as if the attachment process was nonspecific. Overall, surface wettability did not play a major role in the adhesion of conidia. Spore surface proteins appeared to play a role in the adhesion process because treatment of conidia of N. luteum MM558 with a protease completely prevented adhesion. Histochemical labelling of conidia and germlings with Coomassie brilliant blue (specific for proteins) was positive for all isolates, with a blue ‘halo’ often seen surrounding conidia or near the germ tube emergence point after incubation times conducive to germination. Alcian blue also stained material surrounding conidia after longer incubation times, which indicated that mucopolysaccharide and protein production may be involved in a second phase of adhesion.     

Phoma leaf spot of wasabi (Wasabia japonica) caused by Leptosphaeria biglobosa

A leaf spot disease on wasabi plants grown in commercial greenhouses in the Fraser Valley of British Columbia was characterized. Mycelial growth and pycnidial formation were observed within lesions when leaves were incubated under conditions of high humidity. Isolation from diseased tissues consistently yielded colonies of a Phoma species. Sequence analysis of the rDNA internal transcribed spacer (ITS1‐5.8S‐ITS2) region of eight isolates showed 100% nucleotide sequence identity with Phoma wasabiae and Leptosphaeria biglobosa subspecies ‘occiaustralensis’ and 99.2% identity with L. biglobosa ‘canadensis’. Pathogenicity studies on wasabi leaves showed that wounding greatly facilitated infection and enhanced lesion development for most isolates but was not required for all isolates. Chlorotic areas appeared around the inoculation sites within 4 days, followed by necrosis. Isolates displayed a range of virulence, from weakly to highly virulent, on wasabi leaves. Similar results were observed on leaves of canola cultivar Westar, i.e. wounding significantly increased lesion size and isolates displayed a range of virulence. An isolate of Leptosphaeria maculans ‘brassicae’ from canola was highly virulent on wasabi and canola leaves, causing lesions similar to those of L. biglobosa ‘occiaustralensis’ while an isolate of L. biglobosa ‘canadensis’ from canola was weakly virulent on both hosts and required wounds to infect. These results demonstrate that isolates of L. biglobosa ‘occiaustralensis’ from wasabi are as virulent as L. biglobosa ‘canadensis’ on wasabi and canola leaves but in some cases were comparable in virulence to L. maculans ‘brassicae’.     

Isolation and pathogenicity of Phytophthora species from declining Rubus anglocandicans

Rubus anglocandicans is the most widespread and abundant blackberry species within the European blackberry (Rubus fruticosus) aggregate in Western Australia (WA). European blackberry is also one of the 32 Weeds of National Significance in Australia. A disease recorded as ‘blackberry decline’ was first observed in some blackberry sites in WA in 2006. A disease survey was conducted in the Manjimup‐Pemberton region along the Warren and Donnelly River catchments in WA between 2010 and 2012. Phytophthora amnicola, P. bilorbang, P. cryptogea, P. inundata, P. litoralis, P. multivora, P. taxon personii, P. thermophila and a P. thermophila × amnicola hybrid were recovered from declining and adjacent decline‐free sites, as well as from streams and rivers. Phytophthora cinnamomi was isolated from dying Banksia and Eucalyptus species from two non‐decline sites. Of these species, P. bilorbang and P. cryptogea were more pathogenic than the others in under‐bark inoculations using excised stems (primocanes), in planta primocane inoculations in blackberry growing wild in native forest stands, and in glasshouse pot trials. It was concluded that blackberry decline is a complex syndrome and Phytophthora species, in particular P. bilorbang and P. cryptogea, together with temporary inundation, are major biotic and abiotic factors contributing to blackberry decline.     

Molecular tracing of the transmission routes of bois noir in Mediterranean vineyards of Montenegro and experimental evidence for the epidemiological role of Vitex agnus‐castus (Lamiaceae) and associated Hyalesthes obsoletus (Cixiidae)

Epidemiological aspects and transmission routes of bois noir (BN), a grapevine yellows disease induced by ‘Candidatus Phytoplasma solani’, have been exhaustively studied in the affected vineyards of continental Europe but not in the Mediterranean coastal zone. Because ‘Ca. Phytoplasma solani’ and its principal vector Hyalesthes obsoletus presumably originate from the Mediterranean, gaining knowledge of the epidemiological peculiarities of the disease in this area is essential for understanding its global spread and diversification, as well as for designing local management strategies. In this study, molecular epidemiology was applied to trace transmission pathways of ‘Ca. Phytoplasma solani’ in the Mediterranean vineyards of Montenegro, using multilocus sequence typing of tuf, vmp1 and stamp genes of the isolates associated with various hosts. Thus, ‘Ca. Phytoplasma solani’ was tracked from a tentative reservoir plant (inoculum source) through an associated vector population to the infected grapevine. Three pathways of transmission were documented, originating from Urtica dioica, Convolvulus arvensis and Vitex agnus‐castus; however, only the route originating from U. dioica was direct, whereas the latter two were overlapping and could be intermixed. Vitex agnus‐castus is a natural source of ‘Ca. Phytoplasma solani’, representing an important link in disease epidemiology in the Mediterranean and a possible origin of several genotypes occurring in central Europe. Experimental confirmation of the role of Vitex‐associated H. obsoletus in BN transmission in Montenegrin vineyards indicates its tentative role as a vector in the wide area of the Mediterranean, where some of the major wine‐producing regions are located.     

Phytophthora pachypleura sp. nov., a new species causing root rot of Aucuba japonica and other ornamentals in the United Kingdom

Isolates of an unknown Phytophthora species from the ‘Phytophthora citricola complex’ have been found associated with mortality of Aucuba japonica in the UK. Based on morphological characteristics, growth–temperature relationships, sequences of five DNA regions and pathogenicity assays, the proposed novel species is described as Phytophthora pachypleura. Being homothallic with paragynous antheridia and semipapillate sporangia, P. pachypleura resembles other species in the ‘P. citricola complex’ but can be discriminated by its distinctively thick‐walled oospores with an oospore wall index of 0·71. In the phylogenetic analysis based on three nuclear (ITS, β‐tubulin, EF‐1α) and two mitochondrial (cox1, nadh1) DNA regions, P. pachypleura formed a distinct clade within the ‘P. citricola complex’ with P. citricola s. str., P. citricola E and P. acerina as its closest relatives. Phytophthora pachypleura is more aggressive to A. japonica than P. plurivora and P. multivora and has the potential to affect other ornamental species.     

Unique infection structures produced by Pseudocercosporella capsellae on oilseed crops Brassica carinata,B. juncea and B. napus in Western Australia

White leaf spot disease (Pseudocercosporella capsellae) is widespread across oilseed, vegetable and forage brassicas. Light (LM) and scanning electron (SEM) microscope studies were undertaken to investigate host–pathogen interactions on cotyledons of resistant and susceptible Brassica carinata, B. juncea and B. napus. Under LM, unique brown structures were present, particularly on susceptible genotypes, in two morphologically distinct forms: first, as thread‐like structures within cortical tissue by 24 h post‐inoculation (hpi) and secondly, as brown ropy strand structures either within cortical tissues (internal ropy strands), or extruded out through stomatal pores (ropy strand extrusions). Under LM, these brown structures were most prevalent in highly susceptible B. juncea ‘Vardan’ that had both a high incidence within cortical tissue (70%) and of ropy strand extrusions (73%), as did susceptible B. napus ‘Trilogy’ within cortical tissue (60%). Under SEM, both these genotypes showed thread‐like structures smaller than hyphae forming highly branched networks and ropy strand‐like structures. While there were fewer brown structures in susceptible B. carinata UWA #012 (35%), fine, thread‐like structures forming networks were again prominent (SEM). In contrast, for resistant genotypes, brown structures (LM) were of very low frequency or absent; only 5% in resistant B. juncea ‘Dune’ and none in resistant B. napus ‘Hyola 42’ or highly resistant B. carinata ATC94129P. Under SEM, fine, thread‐like structures were present in the resistant B. juncea ‘Dune’ and B. napus ‘Hyola 42’. Liquid chromatographic analyses of brown structures revealed that both internal ropy strands within cortical tissues and ropy strand extrusions contained the mycotoxin cercosporin.     

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.     

Using panicle dry weight to estimate seed production in Echinochloa crus‐galli

A better understanding of weed seed production is a key element for any long‐term management allowing some weeds to shed seeds. The challenge with measuring seed production in weeds is the large effort required in terms of time and labour. For the weed species Echinochloa crus‐galli, it was tested whether the number of seeds per panicle dry weight or per panicle length can be used to estimate seed production. Experiments were conducted in three maize fields in north‐eastern Germany. The effect of factors that could influence this relationship, such as the time of seedling emergence, the density of E. crus‐galli, the control intensity of other weeds, seed predation and field, was included. A few days before maize harvest, all panicles were removed and weighed, panicle length was measured, and for a subsample of 178 panicles, the number of seeds was counted manually. Panicle dry weight predicted the number of seeds per panicle better (R² = 0.92) than did panicle length (R² = 0.69). The other factors except for ‘field’ and ‘seed predation’ had no effect on these relationships. The relationships between seed number and panicle dry weight found in this study closely resembled those reported in an earlier study. Based on our results, we conclude that both plant traits are appropriate for the estimatation of seed production, depending on required level of precision and availablilty of resources for the evaluation of sustainable weed management strategies.