Biological control of an Australian noxious weed “Angled Onion” (Allium triquetrum L.) using molecular and traditional approaches

Angled onion ( Allium triquetrum L.) is a noxious weed in Australia and is difficult to control, especially in natural habitats. Research on biological control of A. triquetrum began in mid-2008 at the School of Applied Sciences, RMIT University, in collaboration with the Department of Primary Industries, Frankston, Victoria. There was no report of biological control of this Australian noxious weed and no research was conducted on the genetic diversity of A. triquetrum over the Australian states. Genetic analysis of A. triquetrum provenances across Australia was performed using RAPDs, PCR-RFLP and sequencing, suggested that the degree of variation was relatively small, making it a suitable biological control target. The aim of the project was initially to evaluate Stromatinia cepivora , a fungal pathogen causing white rot disease of cultivated Allium species, as a biocontrol agent to control the weed in infestations. It was not known whether the fungi would be pathogenic on this weed or if genetic differences between fungal strains or plant provenances would affect the pathogenicity and virulence. This study was the first report of pathogenicity of S. cepivora on A. triquetrum in Australia. The results achieved in this study demonstrated that there was a difference in pathogenicity and virulence of S. cepivora isolates on test-tube-grown plants in that only the DPI fresh isolate was pathogenic to Wonthaggi provenance (VIC). These results reflected the genetic diversity of both biocontrol agent and the host plants. During this study two soft rotting bacteria Pectobacterium carotovorum subsp. carotovorum and bacterium close to Ochrobactrum sp. isolated from infected A. triquetrum bulbs were also evaluated as biocontrol agents for wetter areas where sclerotia of the fungus are reported as not germinating. Pectobacterium carotovorum subsp. carotovorum has not previously been considered as a potential biological control agent for A. triquetrum in Australia, yet. The pathogenicity testing results for both test-tube-grown and potted A. triquetrum indicated that this strain of the bacterium was highly virulent on A. triquetrum in vitro in 24 h and in vivo in 2 weeks and it was not pathogenic on cultivated Allium species. The isolated bacterium close to Ochrobactrum sp. was pathogenic and virulent in vitro but not in vivo in all A. triquetrum provenances and cultivated Allium species tested. In test-tube trials both the bacterium and the fungus were separately pathogenic and highly virulent; infected plants died. However; the bacterium inhibited the fungus from growing when tested together, though host plants still died. Therefore the novel Ochrobactrum sp. had potential for control of the fungus in cultivated Allium species. In this study S. cepivora and P. carotovorum subsp. carotovorum were evaluated as potential biocontrol agents for A. triquetrum in pot trials and this research is now proceeding to field trials

Cultivars to face climate change effects on crops and weeds: a review

International audienceAbstractClimate change is caused by the release of greenhouse gases in the atmosphere. Climate change will impact many activities, but its effects on agricultural production could be acute. Estimates of annual damages in agriculture due to temperature increase or extended periods of drought will be more costly than damages in other activities. Yield losses are caused both by direct effects of climate change on crops and by indirect effects such as increased inputs in crop production for weed control. One possible solution to counteract the effects of climate change is to seek crop cultivars that are adapted to highly variable, extreme climatic conditions and pest changes. Here we review the effects of climate change on crop cultivars and weeds. Biomass increase will augment marketable yield by 8–70 % for C3 cereals, by 20–144 % for cash and vegetable crops, and by 6–35 % for flowers. Such positive effects could however be reduced by decreasing water and nutrient availability. Rising temperature will decrease yields of temperature-sensitive crops such as maize, soybean, wheat, and cotton or specialty crops such as almonds, grapes, berries, citrus, or stone fruits. Rice, which is expected to yield better under increased CO2, will suffer serious yield losses under high temperatures. Drought stress should decrease the production of tomato, soybean, maize, and cotton. Nevertheless, reviews on C4 photosynthesis response to water stress in interaction with CO2 concentration reveal that elevated CO2 concentration lessens the deleterious effect of drought on plant productivity. C3 weeds respond more strongly than C4 types to CO2 increases through biomass and leaf area increases. The positive response of C3 crops to elevated CO2 may make C4 weeds less competitive for C3 crops, whereas C3 weeds in C4 or C3 crops could become a problem, particularly in tropical regions. Temperature increases will mainly affect the distribution of weeds, particularly C4 type, by expanding their geographical range. This will enhance further yield losses and will affect weed management systems negatively. In addition, the expansion of invasive weed species such as itchgrass, cogongrass, and witchweed facilitated by temperature increases will increase the cost for their control. Under water or nutrient shortage scenarios, an r-strategist with characteristics in the order S-C-R, such as Palmer amaranth, large crabgrass, johnsongrass, and spurges, will most probably prevail. Selection of cultivars that secure high yields under climate change but also by competing weeds is of major importance. Traits related with (a) increased root/shoot ratio, (b) vernalization periods, (c) maturity, (d) regulation of node formation and/or internode distance, (e) harvest index variations, and (f) allelopathy merit further investigation. The cumulative effects of selecting a suitable stress tolerator-competitor cultivar will be reflected in reductions of environmental pollution, lower production costs, and sustainable food production

In vitro assessment of Stromatinia cepivora as a potential biological control agent for angled onion (Allium triquetrum) in Victoria, Australia

Angled on ion (AlliulIl triquetrulll L.) is a noxious weed in Australia and is difficult to control, especially in natural habitats. The genetic di versity of II provenances was assessed by RAPD-PCR and was relatively small, making it a suitable biological control target

Potential for biological control of the weed Angled Onion (Allium triquetrum) by the fungus Stromatinia cepivora in Australia

The fungus Stromatinia cepivora (Berk.) Whetzel, which causes white rot of cultivated Allium species, was assessed as a biological control agent for Angled Onion (Allium triquetrum L.), a widespread noxious invasive environmental weed in southern Australia. A. triquetrum showed relatively little genetic diversity, suggesting it was a suitable target for biological control. Genetic analysis of plants from 23 sites in the three main infested Australian states by internal transcribed spacer (ITS) and randomly amplified polymorphic DNA (RAPD) analysis suggested biotypes of A. triquetrum in Australia grouped by state, except for samples from Westernport Bay and Ararat (Victoria). Pathogenicity and virulence of two S. cepivora isolates were assessed on up to 13 A. triquetrum provenances, 6 cultivated Allium species and 9 Australian endemic monocotyledons in test-tube and pot trials. In test-tubes, sclerotia killed plants from all provenances. In pot trials with sclerotia and mycelium, the more pathogenic isolate killed plants from all but one provenance. No A. triquetrum provenance was resistant to S. cepivora, nor were common cultivated Allium species, but common Australian endemic monocotyledons from habitats infested with A. triquetrum showed no disease symptoms 90 days post-inoculation. S. cepivora thus has potential as a biological control agent for A. triquetrum in native bushland in Australia where the risk of it spreading to horticulturally important Allium species is low and can be controlled

Bulb rot in live Allium triquetrum by Pectobacterium carotovorum subsp. carotovorum Parsa Tehranchian

Allium triquetrum L. (angled onion) is an invasive weed that threatens native ground flora such as orchids, lilies and grasses in natural habitats, especially in damp situations. A soft-rotting bacterium isolated from rotting A. triquetrum bulbs after 2 months of storage at 4°C (collected from Horsnell Gully, South Australia) was assessed for its potential as a biocontrol agent. The bacterium was identified as Pectobacterium carotovorum subsp. carotovorum Waldee by 16S r- DNA sequencing and physiological tests. In test-tube trials, the bacterium produced severe soft rot symptoms of bulbs 12 h post-inoculation and rotten young seedlings collapsed after 24 h incubation at 25°C. Identical symptoms were observed at 15°C and 4°C, but with a longer development period at 4°C. Histology of infected plants revealed that the bacterium invaded both the cortical and vascular tissue. In glasshouse tests, all A. triquetrum provenances inoculated with 108 CFU of the bacterium per plant showed soft rot symptoms 20 days post-inoculation, but cultivated Allium species and Australian native monocots were not affected 3 months post-inoculation. The soft-rotting bacterium was reisolated from infected A. triquetrum bulbs and leaves in the glasshouse, fulfilling Koch postulates. Although this bacterium is normally associated only with storage rots, it is potentially an effective biological control agent for A. triquetrum in the field, as it can attack live plants too. Field trials to demonstrate efficacy are currently in progress