Louise Morin

Have biopesticides come of age

Biopesticides based on living microbes and their bioactive compounds have been researched and promoted as replacements for synthetic pesticides for many years. However, lack of efficacy, inconsistent field performance and high cost have generally relegated them to niche products. Recently, technological advances and major changes in the external environment have positively altered the outlook for biopesticides. Significant increases in market penetration have been made, but biopesticides still only make up a small percentage of pest control products. Progress in the areas of activity spectra, delivery options, persistence of effect and implementation have contributed to the increasing use of biopesticides, but technologies that are truly transformational and result in significant uptake are still lacking.

Investigating the host-range of the rust fungus Puccinia psidii sensu lato across tribes of the family Myrtaceae present in Australia.

The exotic rust fungus Puccinia psidii sensu lato was first detected in Australia in April 2010. This study aimed to determine the host-range potential of this accession of the rust by testing its pathogenicity on plants of 122 taxa, representative of the 15 tribes of the subfamily Myrtoideae in the family Myrtaceae. Each taxon was tested in two separate trials (unless indicated otherwise) that comprised up to five replicates per taxon and six replicates of a positive control (Syzygium jambos). No visible symptoms were observed on the following four taxa in either trial: Eucalyptus grandis×camaldulensis, E. moluccana, Lophostemon confertus and Sannantha angusta. Only small chlorotic or necrotic flecks without any uredinia (rust fruiting bodies) were observed on inoculated leaves of seven other taxa (Acca sellowiana, Corymbia calophylla ‘Rosea’, Lophostemon suaveolens, Psidium cattleyanum, P. guajava ‘Hawaiian’ and ‘Indian’, Syzygium unipunctatum). Fully-developed uredinia were observed on all replicates across both trials of 28 taxa from 8 tribes belonging to the following 17 genera: Agonis, Austromyrtus, Beaufortia, Callistemon, Calothamnus, Chamelaucium, Darwinia, Eucalyptus, Gossia, Kunzea, Leptospermum, Melaleuca, Metrosideros, Syzygium, Thryptomene, Tristania, Verticordia. In contrast, the remaining 83 taxa inoculated, including the majority of Corymbia and Eucalyptus species, developed a broad range of symptoms, often across the full spectrum, from fully-developed uredinia to no visible symptoms. These results were encouraging as they indicate that some levels of genetic resistance to the rust possibly exist in these taxa. Overall, our results indicated no apparent association between the presence or absence of disease symptoms and the phylogenetic relatedness of taxa. It is most likely that the majority of the thousands of Myrtaceae species found in Australia have the potential to become infected to some degree by the rust, although this wide host range may not be fully realized in the field.

Are the microcyclic rust species Puccinia melampodii and Puccinia xanthii conspecific

The taxonomic relationship between two microcyclic rust species, Puccinia melampodii and Puccinia xanthii, recorded from a number of Asteraceae hosts, was explored by comparing teliospore morphology, host specificity and sequence data. Teliospore morphology varied between and within individual rust accessions but, in general, teliospores of P. xanthii were larger than those of P. melampodii. Field observations and cross-inoculation greenhouse studies showed that P. melampodii accessions were highly specific to their original host species and unable to establish compatible interactions with related Asteraceae species. Though small amounts of genetic variation were detected between P. melampodii and P. xanthii accessions, the ITS and TEF phylogenetic analyses comprising several other rust species grouped these accessions within a well supported clade. Our data indicate that despite differences between P. xanthii and P. melampodii accessions these rusts cannot readily be separated at the species level, supporting earlier taxonomic conclusions and the recent proposal to group them into a morphospecies. Based on host-specificity data, the name Puccinia xanthii var. parthenii-hysterophorae is proposed to accommodate all Mesoamerican records of P. melampodii associated with the host Parthenium hysterophorus.

Distribution, host range and phenology of the rust fungus Puccinia myrsiphylli in South Africa

A form of the South African plant, Asparagus asparagoides, has become a severe environmental weed in Australia, where it is known as bridal creeper. During surveys conducted in South Africa, information was gathered on the distribution, host range and phenology of the rust fungus, Puccinia myrsiphylli, to assess its suitability as a biological control agent for bridal creeper. The distribution of the rust encompasses all rainfall regions of South Africa. In the winter-rainfall region, the rust was first recorded on A. asparagoides in autumn and then increased in abundance until highest levels were reached in spring, just before the foliage senesced. A similar but less distinct phenology was recorded in the region where rainfall is not restricted to any particular season (aseasonal). The rust fungus was recorded in summer-rainfall regions, but sampling was not frequent enough there to determine its phenology. Strains of P. myrsiphylli were found on five other Asparagus species. Further research is required to determine whether these strains should be separated into different species. P. myrsiphylli was common on the widespread form of A. asparagoides (the form that occurs in Australia), but was never recorded in the field on a second form of A. asparagoides that is restricted to the south-western Cape, supporting the suggestion that the two forms may be different species. Furthermore, Aecidium schlechterianum, Aecidium myrsiphylli and Uredo myrsiphylli are newly listed as anamorphs of Puccinia myrsiphylli.

Teliospore germination, basidiospore formation and the infection process of Puccinia xanthii on Xanthium occidentale

Teliospore germination, basidiospore formation and the infection process of Puccinia xanthii on Xanthium occidentale were examined using light and scanning electron microscopy. Telisopores germinated within 30 min after hydration. The germ-tube differentiated into a four-celled metabasidium within 4 h of exposure to high relative humidity. A basidiospore was formed at the tip of a conical sterigma arising from each cell. Mature basidiospores left on the telial surface often produced secondary basidiospores. Basidiospores germinated by producing a single unbranched germ-tube of variable length on the leaf surface. The end of the germ-tube sometimes differentiated into an appressorium. Host penetration through the epidermis occurred at 3 to 6 h after inoculation and was associated with the formation of an intraepidermal vesicle. A septum was formed between the intraepidermal vesicle and the primary hypha at 15 h after inoculation. Primary hyphae ramified through the intercellular spaces of the palisade parenchyma cells or penetrated adjacent epidermal cells. The first terminal intracellular hypha (M haustorium) was observed at 24 h after inoculation. The terminal intracellular hypha arose from an unspecialized intercalary or terminal mother cell. Terminal intracellular hyphae showed considerable variation in shape and never grew out of the infected hosts mesophyll cells.

Can global weed assemblages be used to predict future weeds

Predicting which plant taxa are more likely to become weeds in a region presents significant challenges to both researchers and government agencies. Often it is done in a qualitative or semi-quantitative way. In this study, we explored the potential of using the quantitative self-organising map (SOM) approach to analyse global weed assemblages and estimate likelihoods of plant taxa becoming weeds before and after they have been moved to a new region. The SOM approach examines plant taxa associations by analysing where a taxon is recorded as a weed and what other taxa are recorded as weeds in those regions. The dataset analysed was extracted from a pre-existing, extensive worldwide database of plant taxa recorded as weeds or other related status and, following reformatting, included 187 regions and 6690 plant taxa. To assess the value of the SOM approach we selected Australia as a case study. We found that the key and most important limitation in using such analytical approach lies with the dataset used. The classification of a taxon as a weed in the literature is not often based on actual data that document the economic, environmental and/or social impact of the taxon, but mostly based on human perceptions that the taxon is troublesome or simply not wanted in a particular situation. The adoption of consistent and objective criteria that incorporate a standardized approach for impact assessment of plant taxa will be necessary to develop a new global database suitable to make predictions regarding weediness using methods like SOM. It may however, be more realistic to opt for a classification system that focuses on the invasive characteristics of plant taxa without any inference to impacts, which to be defined would require some level of research to avoid bias from human perceptions and value systems.

Austropleospora osteospermi gen. et sp. nov. and its host specificity and distribution on Chrysanthemoides monilifera ssp. rotundata in Australia

Hendersonia osteospermi was found for the first time in Australia on leaf spots of the introduced invasive plant Chrysanthemoides monilifera ssp. rotundata (bitou bush) in coastal regions of New South Wales. Pathogenicity tests on species from 11 tribes in the family Asteraceae, demonstrated that H. osteospermi caused severe necrosis on leaves and stems of C. monilifera ssp. rotundata and its congener C. monilifera ssp. monilifera (boneseed). Small necrotic spots also developed on Osteospermum fruticosum and Dimorphotheca cuneata in the Calenduleae and on Helianthus annuus (sunflower) in the Heliantheae. None of the other plant species tested developed leaf spots, although H. osteospermi was re-isolated from senescent leaves of Cynara scolymus (globe artichoke) in the Cynareae and Vernonia cinerea in the Vernonieae. Single ascospores from ascomata of a Pleospora-like fungus found on diseased stems of bitou bush produced H. osteospermi in culture, which proved the anamorph/teleomorph connection. The ITS region of both a single-ascospore isolate and a single-conidium isolate were sequenced and found to be identical. The taxonomic status of H. osteospermi is re-examined and Austropleospora osteospermi gen. et sp. nov. is described as its teleomorph based on morphology, host range tests and DNA sequence analysis. The potential of A. osteospermi for the biological control of bitou bush and boneseed in Australia is discussed.

Quest to elucidate the life cycle of Puccinia psidii sensu lato

There is controversy surrounding the described life cycle of the rust fungus Puccinia psidii sensu lato, which causes disease on several plant species in the family Myrtaceae. The objective of this study was to determine whether P. psidii s.l. is autoecious by performing basidiospore inoculations, and microscopically examining the fate of basidiospores on the leaf surface and nuclear condition at different stages of rust development. No spermogonia developed on leaves of Agonis flexuosa inoculated either with a teliospore suspension or basidiospores naturally discharged from telia. Uredinial sori that developed in all three inoculations with teliospore suspensions and in one of the five inoculations with naturally-discharged basidiospores from telia were most likely the result of urediniospore infections. Microsatellite analysis revealed that isolates made from these uredinial sori had the same multilocus genotype as that of the original isolate. No signs of penetration of plant cells by basidiospores were observed on A. flexuosa and Syzygium jambos. The nuclear condition of mycelia of uredinial sori, urediniospores, teliospores, and four-celled metabasidia was typical of that in many rust fungi. Our study could not provide unequivocal proof that P. psidii s.l. is autoecious. While it is possible that it could be heteroecious, with an unknown alternate aecial host, it is also possible that basidiospores have lost the ability to infect Myrtaceae or are infrequently operational.

Standardized Support to Measure Biomass and Fruit Production by the Invasive Climber (Asparagus asparagoides)

The difficulty of monitoring growth parameters of climbing invasive plants subjected to different control options can be overcome by using standardized support structures (trellises). The utility of such support structures on aboveground biomass accumulation and fruit production was demonstrated using the invasive climber, bridal creeper in three invaded nature reserves near Perth in Western Australia. Mean above-ground plant biomass for plots provided with trellises ranged from 204 ± 38 g/m2 to 336 ± 31 g/m2, whereas it ranged from 66 ± 10 g/m2 to 118 ± 10 g/m2 in plots with no trellises. The mean number of fruits/m2 produced on shoots in plots provided with trellises ranged from 424 ± 159 to 3,787 ± 873 and was up to almost four orders of magnitude greater than the number of fruits produced on plants in plots with no trellis (ranging from 0 to 5.25 ± 7.9). The use of standardized trellises also showed that fruit volume and fruit seed number can vary significantly between sites. Standardized trellises have been installed at sites across Australia to assess the long-term impact of biological control agents introduced to manage bridal creeper. Nomenclature: Bridal creeper, Asparagus asparagoides (L.) Druce

How 'biocontrol' fights invasive species

Credit: CSIRO/scienceimage These invasive species cost Australian agriculture more than