K.L. Bayliss

The role of global trade and transport network topology in the human-mediated dispersal of alien species

More people and goods are moving further and more frequently via many different trade and transport networks under current trends of globalisation. These networks can play a major role in the unintended introduction of exotic species to new locations. With the continuing rise in global trade, more research attention is being focused on the role of networks in the spread of invasive species. This represents an emerging field of research in invasion science and the substantial knowledge being generated within other disciplines can provide ecologists with new tools with which to study invasions. For the first time, we synthesise studies from several perspectives, approaches and disciplines to derive the fundamental characteristics of network topology determining the likelihood of spread of organisms via trade and transport networks. These characteristics can be used to identify critical points of vulnerability within these networks and enable the development of more effective strategies to prevent invasions.

Toward doubled haploid production in the Fabaceae: progress, constraints, and opportunities

The Fabaceae species have a major role to play in sustainable farming systems, but they have lagged behind other families in respect to the development of doubled haploid protocols for plant improvement. Currently, no plant improvement program uses doubled haploids on a routine basis for any member of the Fabaceae. There has recently been renewed interest in haploid research as the usefulness of doubled haploid material in molecular mapping has become clear. This review provides a comprehensive account of the current information regarding the development of haploid protocols in the Fabaceae. In the Fabaceae crop species there have been isolated reports of haploid plant induction in the phaseoloid clade; soybean, cowpea and pigeonpea, as well as promising progress towards haploidy in peanut and winged bean. As yet there have been no reports of haploid plant production in the galegoid clade, but early stage haploid embryogenesis has been achieved in chickpea, field pea, and lupin. Success in the production of haploid plants has also been reported within the pasture genera Lotus, Medicago, and Trifolium and the arboreal genera Cassia, Peltophorum, and Albizzia. A review of the literature has enabled us to identify some general similarities between the protocols developed for haploid plant induction across the various legumes. These are the culture of intact anthers; use of a cold pretreatment to induce sporophytic development; targeting of microspores at the uninucleate stage of development; and use of MS (Murashige and Skoog, 1962) based nutrient medium with plant growth regulators to encourage continued division following induction. These protocol commonalities will assist researchers to identify approaches suited to their target Fabaceae species. The paucity of research funding for haploid research in most Fabaceae species has highlighted the need for strong collaborative linkages between institutions and researchers. Referees: Professor Laima Kott, Crop Science Department, University of Guelph, Guelph ON N1G 2W1.

First record of ‘Candidatus Phytoplasma australiense’ inPaulownia trees

Paulownia trees exhibiting symptoms similar to Paulownia Witches’-Broom disease were identified in three commercial plantations in Western Australia. PCR confirmed the presence of a phytoplasma and RFLP analysis produced patterns similar to ‘Candidatus Phytoplasma australiense’. This is the first report of this phytoplasma in Paulownia.

Pro-embryos of Lupinus spp. produced from isolated microspore culture

Several species of lupin (Lupinus spp.) are grown in Australia as crop and pasture plants. Lupin breeding, and legume breeding in general, is constrained by the inability to produce doubled haploid (DH) plants, which would accelerate the selection and release of new varieties. This technology is still in the developmental phase for legumes, although other major grain crops such as wheat, barley, and canola successfully use DHs on a commercial scale. A new, reproducible method of microspore culture that leads to cell division and pro-embryos in lupin is reported here. Microspores at the late uninucleate stage of development are mechanically isolated from lupin buds and embryogenesis induced by a combined heat shock and sucrose starvation stress treatment. Addition of further components to the growth medium promotes division of up to 50% of microspores to ≥16 cells within 24 h. Further development of these multicellular structures or pro-embryos appears to be limited by the rigid outer exine layer, which needs to rupture for continued cell division to the globular embryo stage. Further research is required to break this barrier to development of haploid lupin embryos.

First record of a phytoplasma-associated disease of chickpea (Cicer arietinum) in Australia

Chickpeas growing in the agricultural region of Kununurra, Western Australia, were found with symptoms of leaf stunting, little leaf and proliferating branches. Deoxyribonucleic acid was extracted from symptomatic and asymptomatic plants and tested for phytoplasma by PCR. The PCR product from symptomatic leaves was sequenced and confirmed the presence of a phytoplasma with high similarity to the 16SrII group ‘Candidatus Phytoplasma aurantifolia’. This is the first molecular evidence for a phytoplasma-associated disease in chickpea.

Identification of sweet potato little leaf phytoplasma associated with Vigna unguiculata var. sesquipedalis and Lycopersicon esculentum

Vigna unguiculata var. sesquipedalis (snakebean) and Lycopersicon esculentum (tomato) plants with phytoplasma-like symptoms were found in the horticultural region in Broome, Western Australia. The symptoms on snakebean included ‘witches’ broom’ and proliferation of small leaves, and on tomato they varied from phyllody and ‘big bud’ to ‘witches’ broom’ and proliferation of small leaves. Using universal primers for phytoplasmas, the complete 16S rRNA gene and intergenic spacer region, and part of the 23S rRNA gene were amplified by PCR. Sequence analysis identified that the agent associated with the symptoms was a strain of sweet potato little leaf strain V4 (SPLL-V4) phytoplasma (16SrII group, strain of ‘Candidatus Phytoplasma australiense’). SPLL phytoplasma has not been reported before in snakebean or tomato in this isolated agricultural region.

Differences in symptom development in subterranean clover infected with Kabatiella caulivora Race 1 and Race 2 are related to host resistance

Clover scorch (Kabatiella caulivora) is a severe fungal disease of Trifolium spp. contributing to the collapse of pasture swards across southern Australia during warm, humid spring weather. Host plant responses associated with resistance to the disease were determined in 2 cultivars of subterranean clover (T. subterraneum) separately inoculated with K. caulivora Race 1 or Race 2. Germination of conidia of both races reached a maximum 5 days post-inoculation on cv. Woogenellup (susceptible to both races) and 4 days post-inoculation on cv. Daliak (resistant to Race 1 but susceptible to Race 2). Germ tube growth of Race 1 was inhibited on cv. Daliak and the percentage of conidia penetrating leaf surfaces was lowest on this race–cultivar combination. Susceptibility was characterised by large petiole lesions, with invasive hyphae extending through the mesophyll tissue into the pith and then through the phloem tissue of vascular bundles, eventually causing the petioles to collapse. Resistance was characterised by small, black lesions with invasive hyphae extending no further than the fourth layer of mesophyll cells. A suberin-based material was observed beneath infected mesophyll cells in the incompatible interaction, beyond which no further growth of hyphae occurred. Race 2 caused a faster rate of host tissue necrosis than Race 1 and also the breakdown of starch grains in uninvaded petiole tissues. Starch grains in plants infected with Race 1 were evenly distributed in uninvaded tissue. Sporulation was rarely observed in the incompatible interaction but was common in compatible interactions within 15 days post-inoculation. These responses to K. caulivora can now be used as a breeding tool in evaluating and selecting improved resistance to clover scorch disease among breeding lines of subterranean clover.

Variability within Kabatiella caulivora Race 1 and Race 2 revealed by cultural and molecular analyses

Kabatiella caulivora is the causal agent of clover scorch, a fungal disease of clover (Trifolium) species. Variability within and between K. caulivora Race 1 and Race 2 was determined by cultural characteristics, isozymes, and amplified fragment length polymorphisms (AFLP). Cultural studies indicated isolates from both races were highly variable. No differences were identified within or between races by isozyme analysis. Similarity coefficients, determined from AFLP analysis, indicated that isolates from different races were often more similar than isolates from the same race. Comparison of single representative isolates from Race 1 and Race 2, collected at a Denmark (Western Australia) disease site, with isolates collected from another site of clover scorch outbreak at Esperance, 300 km east of Denmark, indicated most of the isolates causing the second outbreak were similar to Race 2, confirming previously conducted pathogenicity tests. It is hypothesised that Race 2 may have evolved from Race 1, and that the level of variability in the pathogen indicates the potential for development of further new races of K. caulivora. The requirement for improved selection strategies, including the screening of new cultivars and breeding lines with multiple isolates of the pathogen, is discussed in relation to these findings.

Fungal contaminants of stored wheat vary between Australian states

A survey was undertaken to determine the mycoflora associated with stored wheat in four states across Australia including Western Australia, South Australia, Victoria and New South Wales. A total of 482 fungal isolates from 15 genera were isolated. The most common genera isolated were Alternaria spp., Aspergillus sp., Aureobasidium sp., Cladosporium spp., Drechslera sp., Fusarium spp., Mucor sp., Nigrospora sp., Penicillium sp., Rhizopus sp., Stemphylium sp., Eutiarosporella spp., Ulocladium sp., Epicoccum sp., and an undescribed genus from the Hypocreales. Diversity profiling also identified fungi that were not isolated using traditional methods including Paecilomyces spp., Dendryphiella and Cryptococcus. The results indicate that the mycoflora of stored wheat varies between Australian grain growing regions, and that diversity profiling analysis identifies different fungal contaminants compared to traditional methods. This study also revealed that some pathogens of high risk to humans (e.g. Cryptococcus) may occur with a high frequency in wheat.

Temperature, humidity, wounding and leaf age influence the development of Alternaria alternata lesions on leaves of Paulownia fortunei

Alternaria blight, caused by Alternaria alternata, is a recent and serious disease of commercially grown Paulownia trees in Western Australia. This study investigated the effect of temperature, humidity, wounding and leaf age on lesion development. Temperature had a significant effect on infection, with lesion development and expansion observed to increase from 15–25°C, declining between 30 and 37°C. Relative humidity (RH) also influenced infection with limited lesion development observed at ≤92% RH whereas incubation at 98 and 100% RH resulted in large lesions. The optimum conditions determined for lesion development were incubation at 25–30°C with 98–100% RH.Wounded leaf tissue was significantly more susceptible to infection than non-wounded leaf tissue and senescent leaves were more susceptible than newly emerged leaves. Variation in pathogenicity was also observed on senescent leaves infected with different pathotypes of A. alternata. These results appear to correlate well with field observations and may be useful in the control, management and forecast strategies for Alternaria blight in Australian Paulownia plantations.