Asymptomatic systemic disease of Canada thistle (Cirsium arvense) caused by Puccinia punctiformis and changes in shoot density following inoculation

Canada thistle (Cirsium arvense) is one of the worst weeds in temperate areas of the world. A rust fungus, Puccinia punctiformis, was first proposed as a biological control agent for C. arvense in 1893. The rust causes systemic disease which ultimately kills C. arvense plants. In 2013 it was demonstrated in four countries, that inoculation of C. arvense rosettes in the fall with ground telia-bearing leaves can initiate epidemics of systemic rust disease with an average of 28% of inoculated rosettes producing a systemically diseased shoot the following spring. Other rosettes that emerged near inoculation points in spring were stunted and appeared diseased. To determine whether other rosettes were diseased, a chemiluminescence western slot blot test, applying polyclonal antibodies raised against P. punctiformis antigens, was developed to detect the fungus in roots. Rosettes were inoculated with telia-bearing leaves in the fall in Maryland, USA and Veroia, Greece. Roots of asymptomatic rosettes that emerged adjacent to inoculation points the following spring were tested for the presence of the fungus with the slot blot test. Rosettes that had diseased shoots were recorded. Based on the slot blot tests, 50–60% of the asymptomatic rosettes adjacent to inoculation points were positive for presence of the rust and likely to be systemically diseased. To demonstrate that systemic disease leads to C. arvense decline, C. arvense shoot densities were measured annually at 10 sites, in three countries, that had been inoculated with telia-bearing leaves in the fall between 2008 and 2012. Changes in C. arvense shoot densities over time were calculated. Average reductions in C. arvense density across the 10 sites were 43.1 ± 10.0% at 18 months after inoculation, 63.8 ± 8.0% at 30 months after inoculation, and 80.9 ± 16.5% at 42 months after inoculation, and 72.9 ± 27.2% at 54 months after inoculation; the 54 month reduction was, however, based on only two sites.     

Quantitative resistance of Cirsium arvense to root bud infection by Puccinia punctiformis

A method is presented to test clones of Cirsium arvense for resistance to root bud infection by the rust fungus Puccinia punctiformis. Root buds were stained and cleared to detect mycelium of the rust. The fraction of root buds infected was determined and used as a measure of resistance. Clones of C. arvense, collected from three sites, were tested for resistance to infection. Variation in resistance was determined between and within sites. The results are discussed with a view to using P. punctiformis to control C. arvense.     

Mowing during rainfall enhances the control of Cirsium arvense

Pastoral farmers in New Zealand have described dramatic demises in populations of the weed Cirsium arvense (L.) Scop., a perennial herb indigenous to Eurasia, following its mowing during rainfall. To test the hypotheses (1) that the mowing of C. arvense during rainfall increases the control of this weed and (2) that the causal organism in this ‘mowing-in-the-rain’ effect is the vascular wilt fungus Verticillium dahliae, two series of field experiments were carried out in C. arvense-infested pastures in New Zealand, one in autumn 2008 (Experiment series 1, 9 farms), and another in spring/summer 2008–2009 (Experiment series 2, 12 farms). The effect of mowing in the rain as compared to mowing in the dry was to reduce the % ground cover of the thistle in the spring following treatment by 21 and 32% in Experiment series 1 and 2, respectively. Correlations of this ‘rain versus dry’ effect with the incidence of V. dahliae in the subterranean parts of C. arvense shoots sampled in each of the two field experiment series provided no statistical evidence that the effect increased with V. dahliae incidence. Thus these experiments provide no support for the hypothesis that V. dahliae is the biological mechanism for the ‘mowing-in-the-rain’ effect. Nevertheless, they do support mowing during rainfall as a simple and effective management tactic for C. arvense.     

Does transmission of the rust pathogen,Puccinia punctiformis,require stem mining vectors?

Recent research in Europe has suggested that stem mining insects may be important for vectoring the pathogen Puccinia punctiformis, and largely responsible for its systemic infection in the weed, Cirsium arvense. However, here we present comparative survey data showing that the level of systemic disease is the same in Europe and New Zealand, with and without stem miners, respectively, casting doubt on the idea that these insects are necessary for transmission of the fungus.     

Evaluation of Puccinia carduorum for biological control of Carduus pycnocephalus in Tunisia

Puccinia carduorum, a rust fungus from Italian thistle in Tunisia, was most aggressive on young growth stages of the weed in greenhouse tests. Repeated inoculations with the fungus significantly reduced weed biomass. Host-range tests suggest the fungus may be a safe biological control agent of Italian thistle in Tunisia.     

Classical biological control of Cirsium arvense: Lessons from the past

Cirsium arvense (L.) Scop. is a perennial herb indigenous to Eurasia that is now present throughout temperate regions of the world where it is considered one of the worst weeds of pastoral and agricultural systems. Classical biological control has been attempted in both North America (NA) and New Zealand (NZ). However, nearly 50 years after the first agent releases there are no indications of successful control. We review the status of the five agents deliberately released for control of C. arvense in NA and NZ, plus the species unintentionally introduced, and the occurrence of insects native to NA on C. arvense. We retrospectively evaluate C. arvense as a target weed, critique the agents selected for release, and contrast the different situations in NA and NZ. In retrospect, we see justification for the agents released in NA, but it is evident that these agents would not meet the more stringent host specificity requirements necessary to be released today. The failure of the program in NA is attributed to compromised safety, and lack of impact. Non-target impacts by one of the released agents, Rhinocyllus conicus, have raised safety concerns for native thistle plants. The other released agents either failed to establish, or if established, had no impact on the weed. In contrast, the situation in NZ is quite different because there are no related native thistles (Cardueae), and thus little chance of non-target impacts. Thus far, failure in NZ is attributed to lack of effectiveness due to non-establishment, or no impact, of released agents. In the past, the same agents that were released in NA were subsequently released in NZ, without considering whether or not these were the best choices. Thus, the past failure in NZ might be due to the previous lack of a NZ-specific approach to biocontrol of thistles in general and C. arvense in particular. A new approach taking into consideration the absence of native Cardueae has resulted in the release of agents more likely to be effective, and has potentially set NZ on track towards successful biological control of C. arvense, and other thistles.     

Anatomical Injury Induced by the Eriophyid Mite Aceria anthocoptes on the Leaves of Cirsium arvense

Anatomical injury of the leaves of the invasive species, Cirsium arvense (L.) Scop., caused by the eriophyid mite Aceria anthocoptes (Nal.), which is the only eriophyid mite that has been recorded on C. arvense worldwide, is described. The injury induced by the mite feeding on the leaves of C. arvense results in visible russeting and bronzing of the leaves. Other conspicuous deformations are folding and distortion of the leaf blade and curling of leaf edge, as well as gradual drying of leaves. The anatomical injury of the mature leaves of field-collected plants was limited to the epidermis of the lower leaf surface. However, on young leaves of experimentally infested plants, rust mite injuries extend to epidermal cells on both leaf surfaces and to those of deeper mesophyll layers. On these leaves, lesions on the lower leaf surface even affected the phloem of the vascular bundles. Leaf damage induced by A. anthocoptes is discussed with regard to the mite’s potential as a biological control agent of C. arvense.     

Field assessment,in Greece and Russia,of the facultative saprophytic fungus,Colletotrichum salsolae,for biological control of Russian thistle (Salsola tragus)

Russian thistle (Salsola tragus, tumbleweed, RT) is a problematic invasive weed in the United States (U.S.) and is a target of biological control efforts. The facultative saprophytic fungus Colletotrichum salsolae (CS) kills RT plants in greenhouse tests and is specific to Salsola spp., which are not native in the U.S. However, the effectiveness of CS in controlling RT has not been previously demonstrated. The objectives of this study were to determine in field tests: (1) disease progress of CS in time; (2) the relationship of disease progress to rainfall and temperature; (3) the effect of CS on RT plant density. Field tests were established in Serres and Kozani, Greece and Taman and Tuzla, Russia with isolates of the pathogen collected in the respective countries. Solid inoculum was prepared by asceptically inoculating sterile mixtures of grain and grain hulls with axenic cultures of CS. Spore suspensions used in Russia were prepared by blending pure sporulating cultures of CS with distilled water and diluting the suspension to 10⁶ conidia per ml. Six field plots, each subdivided into 36 subplots, of an RT infested field in Serres, Greece were inoculated on October 23, 2006 by placing about 300 g of solid inoculum in the center of each plot. Four field plots, similarly subdivided, in each of two fields at Kozani, Greece were inoculated in the same way on October 1, 2010. RT density was counted and recorded in each sub-plot prior to inoculation and in September in each of 2 years following inoculation. Disease incidence and/or severity in each sub-plot were recorded at about 7-days intervals after inoculation. Rainfall and temperature data, from inoculation until 40–55 days after inoculation, were collected and recorded at Serres and at the Kozani airport meteorological station. Disease progressed rapidly at both sites and was correlated with cumulative rainfall. By 2 years after inoculation, RT had been eliminated from the Serres site and one field in Kozani. In the other Kozani field, RT density declined to 0–25% from original densities of about 80% in large areas of the field. RT plants in Taman and Tuzla, Russia were inoculated either with 250 g of grain inoculum or with a suspension of 10⁶ conidia sprayed onto each plant until runoff. The proportion of diseased tissue reached 1.0 by 55 days after inoculation in both sites. Non-inoculated plants that were near inoculated plants became diseased quickly and reached the same disease severity as inoculated plants. Disease severity was correlated with cumulative rainfall but not temperature. This pathogen and inoculation procedure offers a low-cost solution to RT infestations. Since CS is specific to Salsola spp., this effective biological control is also environmentally friendly.     

A review of white rust (Puccinia horiana Henn.) disease on chrysanthemum and the potential for its biological control with Verticillium lecanii (Zimm.) Viégas

The biology, aetiology and epidemiology of Puccinia horiana, the cause of white rust disease of chrysanthemum (Chrysanthemum spp.) is reviewed in relation to current environmental, cultural and chemical methods for its control. Importantly, basidiospore release, germination and infection can take as little as 5 h at optimum r.h. (96%) and temperature (between 17–24°C). Recent developments using the fungus Verticillium lecanii for the control of insects on glasshouse-grown all-year-round chrysanthemums rely upon the maintenance of r.h. during night periods in excess of 95%, thus predisposing plants to white rust attack. However, V. lecanii is unusual in that it can also parasitise spores and fruiting structures of a range of rust fungi including P. horiana. This mycoparasitic ability is also reviewed, and against this background, the potential for an integrated insect and white rust control programme on all-year-round chrysanthemums is assessed.     

Identification and quantification of carotenoid pigments in aeciospores of the daisy rust fungus,Puccinia distincta

Macrocyclic trichothecene toxins produced by Myrothecium verrucaria (a phytopathogen of interest in biological weed control) and the non-trichothecene toxin atranone B from Stachybotiys atra were tested for phytotoxicity in duckweed (Lemna pausicostata L.) plantlet cultures and kudzu (Pueraria lobata L.) leaf disc assays, and for mammalian cytotoxicity in four cultured cell lines. Roridin E and H, epi-isororidin E, and verrucarin A and J were phytotoxic (half-maximal effect in the concentration range 0.1-9.7 microM on duckweed and 1.5->80 microM on kudzu) and cytotoxic to mammalian cell lines (half-maximal inhibition of proliferation in the concentration range 1-35 nM). Trichoverrins A and B and atranone B were moderately phytotoxic (half-maximal effect in the concentration range 1 9-69 microM on duckweed and 13->80 microM on kudzu) and weakly cytotoxic with mammalian cell lines (half-maximal inhibition of proliferation in the concentration range 0.3->2 microM).     

Host finding and recognition by Altica carduorum, a defoliator of Cirsium arvense

Altica carduorum Guer. (Coleoptera: Chrysomelidae) populations aggregate on vigorously growing stands of its host, the thistle Cirsium arvense (L.) Scop. (Asteraceae). The beetle needs contact to recognize a Cirsium species and biting to distinguish its host C. arvense. Feeding or mechanical damage on C. arvense, but not other Cirsium species, aggregates the beetles. Also feces from feeding on C. arvense, but not other Cirsium species, aggregates the opposite sex. Adults also aggregate on larval feces. We suggest that initial host location in the spring depends on random encounter by beetles overwintering in a stand of C. arvense. The beetles commonly make short flights after feeding and either land on another C. arvense plant, which establishes a secondary aggregation centre, or return to the original one. In this manner beetles released on a stand of C. arvense in China spread a radius of 600 m in a year, but those released 35 m away from their host failed to find it. Altica carduorum will develop on any Cirsium species to which it is confined, but is monophagous in the field because host finding is dependent on aggregation to wound and feces substances that are specific to C. arvense.     

Studies on the rustMaravalia cryptostegiae,a potential biological control agent of rubber-vine weed (Cryptostegia grandiflora,Asclepiadaceae: Periplocoideae) in Australia,I: Life-cycle

Three spore types are described forMaravalia cryptostegiae: hemileioid urediniospores; thin-walled, hyaline, ellipsoidal, non-resting teliospores and ovoid to lacrimoid basidiospores. Field surveys in the Madagascan native range of rubber-vine failed to confirm the existence of spermogonia and morphologically distinct aecia within the life-cycle. Greenhouse inoculations with basidiospores were unsuccessful. Cytological studies revealed that rubber-vine rust has a similar nuclear cycle to that reported for coffee leaf rust,Hemileia vastatrix. The working hypothesis is proposed thatMaravalia cryptostegiae is a primitive, autoecious tropical forest rust with only a short or partially expanded life-cycle represented by two teliospore forms. The predominant, functional form is uredinioid with a novel nuclear cycle, in which there is a delayed meiotic division (the Kamat phenomenon). The non-dispersed form appears to be vestigial or non-functional since it germinates to produce a metabasidium with genetically variable and unstable basidiospores. The relationships and evolutionary significance of the generaMaravalia andHemileia are discussed.     

Studies on the rust,Maravalia cryptostegiae,a potential biological control agent of rubber-vine weed,Cryptostegia grandiflora (Asclepiadaceae: Periplocoideae), in Australia,II: Infection

The parameters which govern infection of rubber-vine weed by the rustMaravalia cryptostegiae were investigated. The infection process, from appressorial formation to sporulation, is described and illustrated. Uredinioid teliospores have an optimum temperature range for germination at 22–27 °C, both in vitro and in vivo. However, germination on the rubber-vine leaf was more than double (81–92%) that in the absence of the host, and appressoria were formed only in vivo. An optimum temperature of 20–22°C and a dew period of 12 hours or more gave the highest level of infection as measured by sporulation density. The latent period from inoculation to pustule formation decreased with increasing temperature; the shortest period (8–11 days) being recorded at 25–27°C. At the lower temperatures (18°C), this was significantly extended (19–21 days). Four successive inoculations significantly reduced plant height and dry weight, although a compensatory growth flush occurred after the third inoculation. The addition of cryoprotectants had a negative affect on spore viability and subsequent infectivity. Cooling dry spores to –196°C at the rate of 10°C min^–1 gave the best results, with high germination (93–65%) up to 8 days after thawing.     

Euscelis incisus (Cicadellidae,Deltocephalinae), a natural vector of 16SrIII‐B phytoplasma causing multiple inflorescence disease of Cirsium arvense

We investigated multiple inflorescence disease of Cirsium arvense (CMI) and its association with phytoplasmas of the 16SrIII‐B subgroup, potential natural vector(s) and reservoir plant(s). From five locations in northern Serbia, 27 plants of C. arvense, 1 C. vulgare and 3 Carduus acanthoides with symptoms of multiple inflorescences (MIs) were collected and tested for 16SrIII group phytoplasmas. All symptomatic plants were found to be infected. Tentative reservoir plants and insect vectors were collected at a Dobanovci site where the continuous presence of CMI disease was recorded. Among the 19 most abundant plant species submitted to phytoplasma testing, all symptomless, the presence of the 16SrIII group was detected only in two legumes: Lathyrus tuberosus (2/5) and L. aphaca (1/5). Among 19 insect species from six families of Auchenorrhyncha, the deltocephalid leafhopper Euscelis incisus was the only insect carrying a 16SrIII phytoplasma (10% of analysed individuals). Transmission trials were performed with naturally infected E. incisus adults of the summer generation and with a laboratory population reared on red clover. After an acquisition period of 48 h on C. arvense symptomatic for MIs and a latent period of 28 days, 83% of the E. incisus adults (300/360) were infected with CMI phytoplasma. In two transmission tests, the leafhoppers successfully transmitted the phytoplasma to exposed plants (C. arvense and periwinkle), proving its role as a natural vector. Test plants of C. arvense infected with the 16SrIII‐B phytoplasma expressed typical symptoms similar to those observed in the field, such as MIs or the absence of flowering, shortened internodes and plant desiccation. Typical symptoms in infected periwinkles were virescence and phyllody. The molecular characterisation of the CMI phytoplasma isolates from diseased and asymptomatic field‐collected plants, vectors, and test plants was performed by sequence analyses of the 16S rRNA, rpl22‐rps3 and rpl15‐secY genes. Phylogenetic analyses of other members of the 16SrIII group of phytoplasmas indicated closest relatedness with clover yellow edge phytoplasma (CYE) of the 16SrIII‐B subgroup.     

Occurrence of Puccinia isiacae on Phragmites australis in Saudi Arabia and its possibility as a biological control agent

During the summer of 2002, symptoms of rust disease were observed for the first time on Phragmites australis in Saudi Arabia. Light brown lesions of regular shape indicating uredinia of Puccinia isiacae appeared on the leaves. The morphology and characteristics of the fungus were described in detail with both light and scanning electron microscopy. The possibility of using this fungus as a biological control agent was also discussed.     

Induced resistance activated by a culture filtrate derived from an avirulent pathogen as a mechanism of biological control of anthracnose in strawberry

In a previous report, it was described that strawberry plants pre-treated with an avirulent isolate of Colletotrichum fragariae (M23) acquired resistance to a virulent isolate of Colletotrichum acutatum (M11) causing anthracnose. In this report we present evidence that the eliciting activity can be found not only in conidial extracts but in culture supernatants of the avirulent pathogen as well. Plants of the cv. Pájaro treated with the culture filtrate (CF) derived from M23, 3 days prior to the inoculation with M11 showed significantly reduced disease severity as compared to control plants and the disease was completely suppressed when plants were pre-treated 7 days before the challenge inoculation with M11. The same effect was achieved when a single leaf was sprayed with CF, suggesting that the resistance acquired is systemic. Control treatments showed that none of the active extracts inhibited the growth of the virulent pathogen, indicating that the protection effect was due to the induction of a defense response. The latter was confirmed by the accumulation of reactive oxygen species (e.g. hydrogen peroxide, superoxide anion) and the deposition of lignin and callose, usually associated to plant defense, after the CF treatment. Experiments carried out with other strawberry cultivars treated with CF showed that also protected them against different virulent isolates, suggesting that the response observed is cultivar-nonspecific. These outcomes indicate that the protection against anthracnose in strawberry involves a phenomenon of induced resistance (IR) by action of defense-eliciting molecules produced by M23.     

杨树球二孢溃疡病的研究—生物学特性、发病规律及药剂筛选

经试验,杨树球二孢溃疡病菌(Botryodiplodia populea Z.K.Zhong)适宜生长温度为20—25℃,pH6—7,在PDA和麦芽粉培养基生长良好。该病于4月中下旬产生病斑,5月上旬呈现颗粒状的子实体,5月中旬以后逐渐成熟开裂,溢出炭黑色的分生孢子,病原菌以菌丝体在树皮内越冬。经室内药剂筛选,660B生物农药抑菌效果最佳,可达95%。