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Angular leaf scorch (ALS), listed as a high-priority threat to the Australian wine industry, is caused by the fungus Pseudopezicula tetraspora and can cause yield losses of up to 90%. Developing contingency plans for ALS will contribute to maintaining freedom from exotic pests and diseases in Australia, providing financial benefit to the $40 billion per annum industry, and a distinct advantage in a very competitive world market.
Research was undertaken at the Cornell University New York State Agricultural Experiment Station in Geneva, NY, USA, to develop a diagnostic protocol for ALS and methodologies for undertaking research. Attempts to isolate P. tetraspora and induce development of fruiting bodies and sporulation on symptomatic leaves were largely unsuccessful, most likely due to the intensive fungicide spray program applied in commercial vineyards of NY, which may have reduced the viability of the fungus in infected leaves. Due to the inability to produce spores as an inoculum source, a method was developed for inoculation of leaves with mycelium of P. tetraspora grown in culture. This proved to be very effective, and provided a reliable inoculum source for subsequent greenhouse experiments and field trials.
Identification of P. tetraspora was achieved by microscopic analysis of symptomatic leaves, and through culture morphology and DNA sequencing of P. tetraspora (ATCC 62299). Submission of the DNA sequence data to GenBank will provide a reference for future diagnosis. A diagnostic protocol for ALS has been drafted and submitted to the Subcommittee on Plant Health Diagnostics from the Commonwealth Department of Agriculture and Water Resources, and once endorsed will be included in the Viticulture Industry Biosecurity Plan.
Grapevine cultivars vary greatly in their susceptibility to ALS but only a few V. vinifera cultivars have previously been evaluated. Greenhouse evaluations revealed that the seven cultivars most widely planted in Australia can be infected by P. tetraspora. Riesling was extremely susceptible, Sauvignon Blanc, Cabernet Sauvignon and Pinot Noir, moderately susceptible, and Chardonnay, Shiraz and Merlot, slightly susceptible. This highlights the threat that an incursion of ALS poses to Australia, and provides valuable information for effective monitoring and surveillance should an incursion occur.
Fungicides currently registered for use on grapes in Australia were evaluated in the laboratory and greenhouse for efficacy against P. tetraspora. Three fungicides; trifloxystrobin (Flint), pyraclostrobin (Cabrio) and tebuconazole (Folicur), belonging to three distinctive chemical groups that represent two different modes of action, were effective at controlling P. tetraspora and so can be used for control, containment or eradication of ALS in Australian vineyards, in the case of an incursion.
A drastic pruning strategy, previously validated for black rot disease, was evaluated in a simulated incursion of P. tetraspora in New York State. Over the three years following implementation, symptoms were recorded only on control vines, and not on treated vines, confirming the success of the eradication strategy for ALS. In the event of an incursion of P. tetraspora in Australia, the drastic pruning protocol has potential to save the wine industry many millions of dollars in lost production and vineyard re-establishment costs. The eradication protocol will be published and included in the Viticulture Industry Biosecurity Plan.
Australian researchers have gained expertise in the diagnosis, eradication and management of ALS and strengthened the existing collaborative partnership with Cornell University.
Abstract
Angular leaf scorch (ALS), caused by the fungus Pseudopezicula tetraspora, is a high-priority disease threat to the $40 billion Australian wine industry. Research undertaken at the Cornell University New York State Agricultural Experiment Station in Geneva, NY, USA, has provided contingency plans for the Australian wine industry in the event of an ALS incursion. A diagnostic protocol has been developed to enable a rapid response. Cultivars widely grown in Australia are susceptible to P. tetraspora, highlighting the threat that an incursion of ALS presents to Australia, and provides information to underpin effective monitoring and surveillance. The fungicides; trifloxystrobin (Flint), pyraclostrobin (Cabrio) and tebuconazole (Folicur) were effective at controlling ALS and could be used for containment or eradication. A drastic pruning eradication strategy has been validated for ALS and, along with the diagnostic protocol, will be included in the Viticulture Industry Biosecurity Plan. This research has increased the biosecurity capability of the Australian viticulture industry and improved industry preparedness, with potential to save the wine industry many millions of dollars in lost production and vineyard re-establishment costs, whilst maintaining the competitive advantage conferred by freedom from exotic diseases.
Objectives
To validate the efficacy of drastic pruning as an eradication strategy for angular leaf scorch (ALS). A diagnostic protocol for the disease will also be developed for national endorsement by the Subcommittee on Plant Health Diagnostic Standards (SPHDS).
Background
The Viticulture Industry Biosecurity Plan (IBP) categorises the risk of exotic pests and diseases to the Australian industry and provides generic contingency plans through PLANTPLAN, which is a national set of incursion response guidelines for the plant sector. To ensure a rapid response in case of an incursion, it is crucial that the Australian wine industry has diagnostic capability for high-priority pests and diseases.
The current strategy for eradication of an exotic plant pathogen is based on the removal of whole affected plants, followed by burning and/or burial. However this strategy may have significant economic and social impacts on the industry and communities, particularly with respect to older, high-value premium vineyards. Research led by SARDI and in collaboration with Agriculture Victoria through the CRC for National Plant Biosecurity developed and validated a drastic pruning strategy to eradicate the high-priority disease black rot from grapevines, without the need to completely remove vines. It is possible that a similar eradication strategy could be effective for other high-priority exotic diseases, such as angular leaf scorch and Rotbrenner, based on similarities in biology of the causal fungi.
Approach
The project will establish a replicated field trial at the New York Agricultural Experimentation Station, Cornell University, USA to validate the efficacy of the drastic pruning protocol for eradication of ALS. Symptoms will be recorded and samples collected in New York vineyards, to contribute to the development of a diagnostic protocol for the disease. The project will determine the susceptibility of Vitis vinifera cultivars typically grown in Australia and evaluate eradicant fungicides for angular leaf scorch using in vitro screening methods and inoculated potted or field vines.
Sector benefits
The project will provide a diagnostic capability for angular leaf scorch, a high priority pest identified in the Viticulture Industry Biosecurity Plan, by developing a protocol and a threat-specific contingency plan in case of an incursion of the disease into Australia. An important outcome of this project will be the enhancement of biosecurity research capability within the Australian wine sector.
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