Biological control of pigweeds (Amaranthus retroflexus, L. A. Powellii, S. Watson and A. bouchonii Thell.) with phytophagous insects, fungal pathogens and crop management

Pigweeds (Amaranthus spp.) are of economic importance worldwide. In Europe, Amaranthus retroflexus is one of the ten weed species of greatest economic importance. It is a serious problem weed in several field crops (e.g. maize), as well as in vegetables, orchards and grape vines. It is an annual spreading by seeds which have a long viabilityand are dispersed principally by wind and water, but also by machinery. There is great variability in seed germination which renders control with post-emergence herbicides difficult. In addition, triazine herbicide-resistant populations occur in ten European countries. The aim of this subproject of COST action 816 is to investigate the possibilities of classical and inundative biological control of Amaranthus spp., to characterize potentialbiological control agents and to develop methods for their integration with current phytosanitary measures in the target crops. The project was initiated with an extended literaturesurvey followed by field surveys for insects and pathogens associated with Amaranthus spp. in several European countries. Promising isolates of fungal pathogens have been tested ondetached leaves and whole plants, and initial studies on the application of pathogens causing damping off in seedlings have been made. Further, the variability of different provenances ofAmaranthus spp. in response to fungal attack has been investigated     

Signs, larval burdens, and serological responses of dogs experimentally infected with Trichinella spiralis Owen, 1835.

The effects of infections of Trichinella spiralis on 10 specific-pathogen-free Beagles were examined. Eight puppies received either 100, 500, 1,000, or 5,000 larvae, and 2 adult dogs received 1,000 larvae. Blood was drawn every 4 days, beginning 5 days before infection, for the determination of relative eosinophil numbers. Creatine kinase levels were monitored before infection, two weeks after infection, and one month after infection. The dogs were euthanized 1 month postinfection, and larvae were counted in muscle digests of 10 gram samples of diaphragm, pectoralis superficialis, masseter, biceps brachii, and vastus lateralis. The dogs displayed minor signs of gastrointestinal upset during the first week after infection. The dogs also developed a slight eosinophilia with a magnitude that was dependent on the number of larvae the dog received. All infected dogs, but one that had received 500 larvae, had a positive reaction with larval excretory-secretory products of T. spiralis; adult dogs had the greatest immunologic response. The creatine kinase levels were found not to be related to either the time postinfection or the magnitude of the larval dose. The number of larvae recovered from the muscles (maximum of 70 per gram) was dependent on the dosage of larvae received, but there was no significant predilection of the larvae for any of the five examined muscle groups.     

Cytokine response to infection with the microsporidian, Encephalitozoon cuniculi.

The production of three cytokines, interferon gamma (IFN-gamma), interleukin 10 (IL-10) and interleukin 12 (IL-12), was measured after intraperitoneal infection of immunocompetent Balb/c mice and immunodeficient SCID mice with the microsporidian, Encephalitozoon cuniculi Levaditi, Nicolau et Schoen, 1923. High levels of IFN-gamma were detected in ex vivo cultures of peritoneal exudate cells (PEC) of Balb/c mice, a lower, but earlier IFN-gamma response was observed in PEC from SCID mice. The early IL-10 response was detected in ex vivo cultures of splenocytes from Balb/c but not from SCID mice, explaining a delay in the IFN-gamma response in Balb/c mice. IL-12 was detected in PEC cultures from SCID mice, indicating an alternative pathway of IFN-gamma production by NK cells stimulated by IL-12 derived from macrophages.     

Association of the pitch canker fungus, Fusarium subglutinans f.sp. pini, with Monterey pine seeds and seedlings in California

The causal agent of pitch canker disease of pines, Fusarium subglutinans f.sp. pini , is a recent introduction to California. The work presented here demonstrates that this pathogen is seed-borne in Monterey pine ( Pinus radiata ). The pathogen was isolated from up to 83% of seeds collected from cones on recently infected branches. Seedling emergence from infested Monterey pine seeds was 9%, compared with 67% for uninfested seeds. The fungus was isolated more frequently from seedlings originating from diseased branches than from symptomless branches. However, more than 50% of seeds from symptomless Monterey pine branches produced symptomless seedlings from which the pathogen was isolated. It is hypothesized that F. s . pini is carried within the seeds, where it may remain dormant until germination. The implications of these findings for the regeneration of native and landscape-planted Monterey pines, and for the transport of this non-native pathogen in pine seeds and seedlings to previously uninfested areas, are discussed.     

Fusarium oxysporum,F. proliferatum and F. redolens associated with basal rot of onion in Finland

In recent years in Finland, Fusarium infections in onions have increased, both in the field and in storage, and Fusarium species have taken the place of Botrytis as the worst pathogens causing post‐harvest rot of onion. To study Fusarium occurrence, samples were taken from onion sets, harvested onions and also from other plants grown in the onion fields. Isolates of five Fusarium species found in the survey were tested for pathogenicity on onion. Fusarium oxysporum was frequently found in onions and other plants, and, of the isolates tested, 31% caused disease symptoms and 15% caused growth stunting in onion seedlings. Fusarium proliferatum, a species previously not reported in Finland, was also identified. Over 50% of the diseased onion crop samples were infected with F. proliferatum, and all the F. proliferatum isolates tested were pathogenic to onion. Thus, compared to F. oxysporum, F. proliferatum seems to be more aggressive on onion. Also some of the F. redolens isolates were highly virulent, killing onion seedlings. Comparison of the translation elongation factor 1α gene sequences revealed that the majority of the aggressive isolates of F. oxysporum f. sp. cepae group together and are distinct from the other isolates. Incidence and relative proportions of the different Fusarium species differed between the sets and the mature bulbs. More research is required to determine to what extent Fusarium infections spoiling onions originate from infected onion sets rather than the field soil.     

Specific Diagnosis of Two Root-Knot Nematodes, Meloidogyne chitwoodi and M. fallax, with Satellite DNA Probes

ABSTRACT Meloidogyne chitwoodi and M. fallax are serious pests of potato, and both species have been recently designated as quarantine organisms in the European Community and in Canada. The sympatric and less damaging species M. hapla is often found associated with both of them under temperate climates. Here, we describe the use of satellite DNA (satDNA) sequences previously isolated from these three root-knot nematode species for the development of specific diagnostic procedures. In dot-blot experiments, it was unambiguously possible to separate M. chitwoodi and M. fallax from M. hapla using satDNA monomers as probes. In squash-blot experiments, satDNAs allowed discrimination between single individuals of M. chitwoodi or M. fallax from M. hapla, even within root tissues, without the need for DNA purification. The same results were obtained with radioactive or digoxigenin-labeled probes with no loss of sensitivity in detection. M. fallax and M. chitwoodi could not be distinguished. From this study, it is concluded that such cloned satDNA sequences may constitute a powerful tool for the identification and management of Meloidogyne spp. populations in the field and for the implementation of quarantine regulations against these pests.     

Characterization, Genetic Structure, and Pathogenicity of Rhizoctonia spp. Associated with Rice Sheath Diseases in India

ABSTRACT Isolates of Rhizoctonia spp. were obtained from rice in India during 2000-2003. Characterization by conventional techniques and polymerase chain reaction showed that from 110 isolates, 99 were R. solani and 11 were R. oryzae-sativae. Of 99 isolates identified as R. solani, 96 were AG1-IA, 1 was AG1-IB, and 2 were AG1-IC. Amplified fragment length polymorphism (AFLP) analyzes were used to determine genetic relationships in Rhizoctonia pathogen populations collected from different geographic regions. Cluster analysis based on the AFLP data separated isolates belonging to the three different intraspecific groups of R. solani AG1 and differentiated R. solani from R. oryzae-sativae. Analysis of molecular variance (AMOVA) revealed that geographic region was the dominant factor determining population structure of R. solani AG1-1A; host cultivar had no significant effect. Pathogenicity tests on Oryza sativa cv. Zenith revealed that isolates of R. solani AG1-1A and AG1-1B were more virulent than R. solani AG1-IC and R. oryzae-sativae isolates.     

The degradation of methazole in soil. II. Studies with methazole,methazole degradation products and diuron

[¹⁴C]-Labelled methazole, 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU), 1-(3,4-dichlorophenyl)urea (DCPU), and diuron were incubated in soil at 20°C and field capacity soil moisture content. Decomposition followed first-order kinetics; half-lives for degradation of these four compounds were 2.4, 144, 30 and 108 days respectively. The amount of DCPMU and DCPU that could be extracted decreased with time and the decrease was accompanied by the generation of an equivalent amount of ¹⁴CO₂. This was not so in the studies with diuron and methazole, however, and the decrease in the concentrations of radioactivity extracted from soil treated with these compounds could not be entirely accounted for as carbon dioxide. It is concluded that the unextractable radiochemical that was present was DCPMU. Methazole appeared to be degraded through DCPMU to 3,4-dichloroaniline (DCA) with the production of only traces of DCPU.     

Fungal development and plant response in detached onion, onion bulb scales and leaves inoculated with Botrytis allii, B. cinerea, B. fabae and B. squamosa

Fungal development and plant responses were examined in detached leaves and mid-bulb scales of Allum cepa. Following inoculation with suspensions of 105 conidia/ml distilled water Botrytis squamosa consistently produced spreading lesions in leaves and bulb scales. B. allii produced spreading lesions at most sites in bulbs but was very inconsistent in its infection of leaves; lesions were often confined to inoculation sites. Limited lesions were usually produced by B. cinerea but R. fabae failed to produce symptoms at most sites. Extensive colonization by B. allii and B. tauamosa required rapid penetration and totally necrotrophic fungal growth. During development of a spreading lesion, plant cell walls became very swollen around intramural hyphae and wall swelling appeared to precede epidermal cell death. Resistance to colonization was due to poor germination, failure to produce distinct infection hyphae (associated with accumulation of deposits of granular reaction material [RM] in underlying live cells) or restriction of infection ryphae amongst small groups of dead cells (limited lesion formation). Only B. fabae germinated poorly, and germ-tubes produced often failed to attempt penetration but grew over the leaf or bulb scale surface. Reducing numbers of conidia increased the frequency of sites associated with RM accumulation; granular deposits being particularly common at sites inoculated with low numbers of B. allii conidia. Electron microscopy revealed that RM granules were osmiophilic aggregates formed between the plasma membrane and epidermal cell wall. In the absence of RM, growth of avirulent species was restricted within the swollen walls of dead epidermal cells. Results ae compared with those from studies on tulip and broad bean leaves.     

Control of Echium plantagineum L.with 2, 4-D and grazing management

This paper describes a field experiment conducted in north-east Victoria investigating the control of Echium plantagineum L. in a pasture with 2, 4–D and grazing management. Spraying with a small dose of 2, 4-D (0–14 kg a.i./ha) in late autumn/early winter, followed about 2 weeks later by heavy grazing, removed E. plantagineum from the pasture, whilst the associated pasture species, Trifoliutn subierraneum L., was retained. Continuous grazing without spraying also resulted in good control of E. plantagineum. Herbage production of the pasture in winter was, however, reduced by spraying. The reasons underlying these observations, and farm management programmes for the longterm control of E. plantagineum, are discussed.