The control of weeds through fungi; principles and prospects

MALDI-TOF MS-based analysis of dried seed proteins immobilized on filter paper

Matrix-assisted laser-desorption and ionization time-of-flight mass spectroscopy (MALDI-TOF MS) is commonly used for the characterization of protein-containing biological samples. For this, we have previously developed sample-preparation methods that can be used for discrimination between Impatiens species and also between regional biotypes of Himalayan balsam (Impatiens glandulifera), initially using leaf samples and, more recently, using seed material. In the current article, we have developed a further MALDI-TOF MS-based method that can be used with seeds that uses only simple equipment and minimally hazardous reagents prior to storing and/or shipping dried seed proteins immobilized on filter paper for MALDI-TOF MS analysis. We have investigated I. glandulifera regional-biotype seeds originating from four different sites within the UK for which the parent plants differ in their susceptibility to the biological control agent Puccinia komarovii var. glanduliferae. Using a combination of time-course comparisons and principal-component analysis, we have demonstrated good MALDI-TOF MS spectral conservation, even after storage for 1 month at 35°C, of dried seed-protein samples immobilized on filter paper. This method may provide a further useful tool for the matching of biological control agents optimally to susceptible (regional) target-plant biotypes, and for seed characterization and/or identification in general.

Differentiation between closely-related Impatiens spp. and regional biotypes of Impatiens glandulifera using a highly-simplified and inexpensive method for MALDI-TOF MS

BACKGROUND

Matrix-assisted laser-desorption and ionisation time-of-flight mass spectroscopy (MALDI-TOF MS) is a powerful tool for the characterisation and/or identification of protein-containing samples. Several MALDI-TOF MS sample-preparation methods are currently available but few of these are well suited to the analysis of plant material. We have recently developed a simple, rapid, and relatively-cheap method for MALDI-TOF MS that is applicable to plant material (in addition to microbial and insect material), and our aim in this study was to distinguish between closely-related plant species and/or between regional biotypes within an invasive weed species using this method with a view to optimising the selection of biological control agents that can be used for weed management.

RESULTS

We have employed a combination of principal-component analysis and closest-relatedness diagrams derived from MALDI-TOF MS spectral-comparison data to discriminate between the closely-related Impatiens spp. Impatiens noli-tangere, Impatiens parviflora, Impatiens scabrida, Impatiens balsamina, and two regional biotypes of the invasive weed Impatiens glandulifera. We have also developed a method for sample discrimination based upon comparison between blind-test MALDI-TOF MS spectra and reference-sample spectra. Using this latter method, we have been able to discriminate on the basis of the acid-soluble-protein mass spectra generated between four regional biotypes of I. glandulifera that differ in their susceptibility to the biological control agent Himalayan balsam rust (Puccinia komarovii var. glanduliferae) using mature leaf material. Using younger leaves, discrimination was not possible between these four regional biotypes.

CONCLUSIONS

MALDI-TOF MS analysis is able to discriminate between closely-related plant species within the genus Impatiens and between regional biotypes of I. glandulifera. Because of this, MALDI-TOF MS holds great promise for improving weed biological control, a management technique which uses highly-specific co-evolved natural enemies for the control of an invasive non-native plant species, through the optimal matching of biological control agents with susceptible target species/regional biotypes.

Biological control of invasive plant species: a reassessment for the Anthropocene

The science of finding, testing and releasing herbivores and pathogens to control invasive plant species has achieved a level of maturity and success that argues for continued and expanded use of this program. The practice, however, remains unpopular with some conservationists, invasion biologists, and stakeholders. The ecological and economic benefits of controlling densities of problematic plant species using biological control agents can be quantified, but the risks and net benefits of biological control programs are often derived from social or cultural rather than scientific criteria. Management of invasive plants is a 'wicked problem', and local outcomes to wicked problems have both positive and negative consequences differentially affecting various groups of stakeholders. The program has inherent uncertainties; inserting species into communities that are experiencing directional or even transformational changes can produce multiple outcomes due to context-specific factors that are further confounded by environmental change drivers. Despite these uncertainties, biological control could play a larger role in mitigation and adaptation strategies used to maintain biological diversity as well as contribute to human well-being by protecting food and fiber resources.

A novel method to prepare concentrated conidial biomass formulation of Trichoderma harzianum for seed application

AIMS

To prepare concentrated formulation of Trichoderma harzianum MTCC-3841 (NBRI-1055) with high colony forming units (CFU), long shelf life and efficient in root colonization by a simple scrapping method.

METHODS AND RESULTS

NBRI-1055 spores scrapped from potato dextrose agar plates were used to prepare a concentrated formulation after optimizing carrier material, moisture content and spore harvest time. The process provides an advantage of maintaining optimum moisture level by the addition of water rather than dehydration. The formulation had an initial 11-12 log(10) CFU g(-1). Its concentrated form reduces its application amount by 100 times (10 g 100 kg(-1) seed) and provides 3-4 log(10) CFU seed(-1). Shelf life of the product was experimentally determined at 30 and 40 °C and predicted at other temperatures following Arrhenius equation. The concentrated formulation as compared to similar products provides an extra advantage of smaller packaging for storage and transportation, cutting down product cost. Seed application of the formulation recorded significant increase in plant growth promotion.

CONCLUSIONS

Stable and effective formulation of Trichoderma harzianum NBRI-1055 was obtained by a simple scrapping method.

SIGNIFICANCE AND IMPACT OF THE STUDY

A new method for the production of concentrated, stable, effective and cost efficient formulation of T. harzianum has been validated for seed application.

An epidemiological study of Puccinia punctiformis (Str.) Röhl as a stepping-stone to the biological control of Cirsium arvense (L.) Scop

The infection cycle of the autoecious rust fungus Puccinia punctiformis on the clonal plant Cirsium arvense was described in terms of intensity (amount of pathogen per unit area and used for systemic infection) and extent (area occupied by the pathogen and used for local lesion infection) at four grassland sites in The Netherlands. The incidence of systemic infection was relatively low and systemically infected shoots were typically concentrated at a few locations within a site. Incidence of local lesion infection was relatively high and widespread in ail sites. Spatial and temporal distribution of teliospores, the inoculum for systemic infection, were quantified in order to explain the relatively low and spatially unequal incidence of systemic infection. Because of the large impact of systemic infection on C. arvense shoots, it is concluded that a spatially homogeneous distribution of teliospores may be a prerequisite for the biological control of C. arvense by P. punctiformis.

Tansley Review No. 28 Fungal diseases in multispecies plant communities

The potential of diseases to cause diversity in mixed-species plant communities and to influence the development of those communities is reviewed. Fungal diseases in natural populations are as severe and damaging as on crops. Epidemics occur on endemic host plants and in mixed-species communities with the same characteristics as in crops. Natural communities differ in the proportion of species that are hosts of fungal pathogens, and only a small proportion of diseases re-occur every year in the same community. Disease proneness in communities differs between sites and between years. Also the parasitic mycoflora differs between sites in the same vegetation type, variation being partly due to the fluctuating composition of host species. The presence of a host species at a particular site does not ensure the occurrence of a particular disease. Climate and weather greatly influence the distribution and density of plants. These, in turn, and together with direct effects, determine the prevalence and intensity of diseases which vary markedly. As fungi are naturally amongst the pioneer decomposers of plant material, most hosts are affected after flowering and/or fruit set. There is no compelling evidence that high disease intensities are correlated with high plant densities in natural communities. Diversity in a community is not an automatic safeguard against high disease incidence or severity. Also, disturbance of balanced communities by man is not a prerequisite for damaging epidemics. The impact of disease on the proportions of host species comprising a community depends on the consistent occurrence of sufficiently high disease intensities, particularly during those plant growth stages most prone to negative effects from disease. The impact of exotic diseases can be very serious during the first few years after their introduction, but populations can recover once the exotic pathogen has become endemic. In endemic plant populations the effect of diseases, despite occasional severe outbreaks, is limited or erratic. Disease reduces the reproduction and survival of plants, but practically nothing is known about the competitiveness of a diseased plant species in the next season. In conclusion, the effect of plant diseases on adult plants and, thereby, on the history of a community should not be overrated. More important for the diversity of communities, particularly during immigration and re-colonization by plant species, could be attacks of fungi on juvenile plants since the few available in situ studies suggest that fungal pathogens may cause high mortality. Very little evidence is, however, yet available. Benefits for comparative epidemiology of studies in natural plant communities are briefly discussed. CONTENTS Summary 383 I. Introduction 384 II. Disease intensities and their effects on wild plants 384 III. Differences in disease proneness amongst wild plant communities 387 IV. Factors affecting the prevalence and intensity of diseases in multispecies communities of wild plants 389 V. Possible impacts of diseases on multispecies communities 397 VI. Diseases in multispecies plant communities as subjects for epidemiological research 400 References 401.