Christopher Steel

Grapevine bunch rots: impacts on wine composition, quality, and potential procedures for the removal of wine faults.

Bunch rot of grape berries causes economic loss to grape and wine production worldwide. The organisms responsible are largely filamentous fungi, the most common of these being Botrytis cinerea (gray mold); however, there are a range of other fungi responsible for the rotting of grapes such as Aspergillus spp., Penicillium spp., and fungi found in subtropical climates (e.g., Colletotrichum spp. (ripe rot) and Greeneria uvicola (bitter rot)). A further group more commonly associated with diseases of the vegetative tissues of the vine can also infect grape berries (e.g., Botryosphaeriaceae, Phomopsis viticola ). The impact these fungi have on wine quality is poorly understood as are remedial practices in the winery to minimize wine faults. Compounds found in bunch rot affected grapes and wine are typically described as having mushroom, earthy odors and include geosmin, 2-methylisoborneol, 1-octen-3-ol, 2-octen-1-ol, fenchol, and fenchone. This review examines the current state of knowledge about bunch rot of grapes and how this plant disease complex affects wine chemistry. Current wine industry practices to minimize wine faults and gaps in our understanding of how grape bunch rot diseases affect wine production and quality are also identified.

Evaluation of Fungicides for the Management of Botryosphaeria Canker of Grapevines

The family Botryosphaeriaceae comprises a number of species that are associated with the dieback disease of grapevine (Vitis vinifera), referred to as Botryosphaeria canker. To date, there are few effective agents available for the management of this disease. In this study, fungicides were evaluated for controlling the disease using a combination of in vitro tests and field trials. Twenty fungicides registered for use on other diseases in Australian viticulture were tested in vitro for their effect on mycelial growth of four species within the Botryosphaeriaceae. The concentrations of fungicide at which 50% of mycelial growth is inhibited (EC50 values) were significantly affected both by fungicide and isolate (P < 0.001). Differences in sensitivities of the four species to the fungicides were negligible (0.41 to 0.59 mg/liter). The most effective fungicides were fludioxonil, carbendazim, fluazinam, tebuconazole, flusilazole, penconazole, procymidone, iprodione, myclobutanil, and pyraclostrobin, for which EC50 values were <1.0 mg/liter. These fungicides were evaluated under field conditions, in addition to the pruning wound protectants Bacseal Super, Garrison, and ATCS tree wound dressing, as well as the biological control agent Vinevax. In field trials, carbendazim (Bavistin), fluazinam (Shirlan), tebuconazole (Folicur), Garrison, and ATCS tree wound dressing applied to freshly cut pruning wounds were the most effective and reduced infection by Diplodia seriata and D. mutila by 41 to 65%. These results suggest that the occurrence of Botryosphaeria canker on grapevines may be reduced via treatment of pruning wounds with selected fungicides as soon as possible after pruning.

Survey of Botryosphaeriaceae associated with grapevine decline in the Hunter Valley and Mudgee grape growing regions of New South Wales

Species belonging to the fungal family Botryosphaeriaceae are important pathogens of grapevines in Australia. A survey of declining grapevines in the Hunter Valley and Mudgee grape growing regions of New South Wales revealed 36% were infected with species belonging to the Botryosphaeriaceae. The incidence of Diplodia seriata was greatest, followed by Neofusicoccum parvum, Botryosphaeria dothidea and Lasiodiplodia theobromae. These identifications were made using a combination of molecular and morphological characters. Although D. seriata was the most common species found, its role as a primary pathogen of grapevines in Australia is yet to be ascertained. The accuracy of estimating the incidence of species was increased by surveying up to 25 grapevines per vineyard and by sampling both the trunks and cordons. Other pathogens capable of causing trunk diseases were also isolated in this survey, demonstrating that diagnosis based on symptoms alone is not sufficient and isolations on artificial media and sometimes DNA sequencing are required for a definitive diagnosis of the causal organism of decline.

Invasion, development, growth and egg laying by Meloidogyne javanica in Brassicaceae crops

Invasion, development and egg laying by Meloidogyne javanica in 11 Brassicaceae and four non-Brassicaceae crop species/subspecies was investigated. At 10 to15 and 15 to 20°C, fodder rape cv. Rangi was invaded less than the good hosts tomato cv. Grosse Lisse and field pea cv. Dun but more than the poor host oat cv. Cooba. With an inoculum of 50 second stage juveniles (J2), invasion of Rangi, and the intermediate host subterranean clover cv. Trikkala, were similarly invaded when inoculated with 50 and 100 J2, cv. Rangi was invaded less than tomato. The intermediate host subterranean clover cv. Trikkala and Rangi were similarly invaded when inoculated with 50 and 100 J2 but cv. Trikkala was less invaded with 200 J2. Oat cv. Cooba was always less invaded than the other hosts. Invasion of 3-week-old seedlings of cv. Rangi and 12 cultivars of seven other Brassicaceae crop species/subspecies were similar. Three weeks after inoculation, more M. javanica had developed to the mature female stage in tomato than in the eight Brassicaceae species/subspecies. Females growing in tomato and field pea were always larger than those in rape cv. Rangi. Females in Rangi were larger but those in oilseed radish cv. Adagio were smaller than in 11 other cultivars of seven Brassicaceae, except in plants grown in winter. Egg masses from four Brassicaceae species contained fewer eggs than egg masses from tomato at 6 weeks after inoculation, but at 7 and 8 weeks only those from fodder rape cv. Korina had consistently fewer than tomato. Results are discussed in relation to host status, glucosinolates and potential use of Brassicaceae for control of Meloidogyne.

Detection and monitoring of Greeneria uvicola and Colletotrichum acutatum development on grapevines by real-time PCR

Bitter rot (Greeneria uvicola) and ripe rot (Colletotrichum acutatum, syn. C. simmondsii) occur frequently in subtropical grape-growing regions of Australia, where they cause yield loss and bitter taints in wine. To further advance the epidemiological studies of G. uvicola and C. acutatum and contribute toward their effective management and control, a rapid and reliable species-specific real-time polymerase chain reaction (PCR) method was developed based on the polymorphic portion of the internal transcribed spacer region of the two fungi. It was found that, within 6 to 8 h postinoculation, the assay could detect as little as 20 fg of genomic DNA and 10 conidia for both species. Artificially and naturally infected grape inflorescences and mature berries were analyzed by both conventional plating methods and real-time PCR. Fungal presence was demonstrated on all plant material but development was observed only on mature berries. The results demonstrate that the real-time PCR technique is a highly specific, rapid, and sensitive method that can be used to detect and study the dynamics of G. uvicola and C. acutatum during different stages of infection and on different grape tissues.

DISEASE NOTES OR NEW RECORDS An unusual bunch rot of grapes in sub-tropical regions of Australia caused by Colletotrichum acutatum

An unusual bunch rot of wine grapes in the Hunter and Hastings Valleys of New South Wales (NSW) was identified as being caused by Colletotrichum acutatum. Symptoms included a salmon-pink discharge of conidia from infected fruit and a characteristic bitter taint to both grapes and wine. The disease was found to be widespread in sub-tropical grape growing regions of NSW. This is believed to be the first report of Colletotrichum acutatum on Vitis vinifera in Australia.

Effects of spray adjuvants on grape (Vitis vinifera) berry microflora, epicuticular wax and susceptibility to infection by Botrytis cinerea

Spray adjuvants were tested for their effects on epicuticular wax morphology, grape berry microflora and susceptibility of berries to Botrytis cinerea on Chardonnay, Shiraz and Cabernet Sauvignon cultivars. The four adjuvants used in this trial altered epicuticular wax morphology. Disintegration of the wax platelets was least for the wetter-spreader recommended for sensitive crops, and greatest for the crop oil concentrate and the activator-penetrant. Waxes did not regenerate over the season after treatment with the adjuvants. A cyprodinil/fludioxonil fungicide was effective at controlling B. cinerea infection, but when combined with an adjuvant, was less effective in the three grape cultivars. Irrespective of whether a fungicide was used, adjuvant application resulted in lower yeast and fungal populations on Chardonnay berries. There were no effects of the adjuvants on the microflora of Shiraz and Cabernet Sauvignon berries, except for the crop oil concentrate which resulted in higher bacterial populations on Cabernet Sauvignon berries. We hypothesise that spray adjuvants increased the susceptibility of grape berries to B. cinerea through epicuticular wax alteration and, in some circumstances, through the reduction of the indigenous microflora on the berry surface.

Gas Chromatography–Mass Spectrometry Method Optimized Using Response Surface Modeling for the Quantitation of Fungal Off-Flavors in Grapes and Wine

An optimized method for the quantitation of volatile compounds responsible for off-aromas, such as earthy odors, found in wine and grapes was developed. The method involved a fast and simple headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) for simultaneous determination of 2-isopropyl-3-methoxypyrazine, 2-isobutyl-3-methoxypyrazine, 3-octanone, fenchone, 1-octen-3-one, trans-2-octen-1-ol, fenchol, 1-octen-3-ol, 2-methylisoborneol, 2,4,6-trichloroanisole, geosmin, 2,4,6-tribromoanisole, and pentachloroanisole. The extraction of the temperature and time were optimized using response surface methodology in both wine base (WB) and grape base (GB). Low limits of detection (0.1-5 ng/L in WB and 0.05-1.6 in GB) and quantitation (0.3-17 in WB and 0.2-6.2 in GB) with good recoveries (83-131%) and repeatability [4.3-9.8% coefficient of variation (CV) in WB and 5.1-11.1% CV in GB] and reproducibility (3.6-10.2 in WB and 1.9-10.9 in GB) indicate that the method has excellent sensitivity and is suitable for the analysis of these off-flavor compounds in wine and grape juice samples.

Evidence that Eutypa lata and other diatrypaceous species occur in New South Wales vineyards.

Eutypa dieback, caused by the fungus Eutypa lata is a serious disease of grapevines that affects vineyard productivity and longevity. Grapevines displaying foliar symptoms typical of Eutypa dieback or evidence of dead spurs, cankers, or discoloured vascular tissue, were surveyed from 77 vineyards throughout New South Wales (NSW), Australia. Fungal cultures were tentatively identified based on cultural morphology, before further identification using sequence analysis of rDNA internal transcribed spacer regions. E. lata and several other species from the Diatrypaceae including Cryptovalsa ampelina, and species of Eutypella and Diatrypella were isolated from diseased grapevines. Eutypa dieback was found to be more widespread in NSW than first thought, with confirmation that the disease is present both in the Central Ranges and southern NSW districts, regions recognised for their cooler climates and higher annual rainfall, both of which favour the growth of E. lata.

Botryosphaeria dothidea associated with grapevine trunk disease in south-eastern Australia

Species of Botryosphaeria have been implicated in grapevine decline and dieback symptoms in Australian vineyards. In this study, we report the morphological and molecular identification of Botryosphaeria dothidea isolated from symptomatic grapevines in eastern grape growing regions of New South Wales, Australia. The pathogenicity of B. dothidea towards Vitis vinifera cv. Chardonnay is also confirmed.