In this section:
Eutypa dieback symptoms and identification
Adrian Loschiavo, Mark Sosnowski & Trevor Wicks
Contents
Symptoms
Disease cycle
Field sample collection
Laboratory isolation
Identification from dead wood
Eutypa dieback, caused by the fungus Eutypa lata, is a major trunk disease of grapevines. Infected grapevines gradually decline in productivity and eventually die. Surveys have shown that eutypa dieback is widespread in premium winegrowing regions of Australia. Eutypa dieback can also be found worldwide in cool climate wine regions.
Symptoms
Eutypa dieback foliar symptoms are are most obvious in spring when shoots are 30-70 cm long (Fig 2&3). Foliar symptoms include stunted shoots with chlorotic leaves, often cupped and with tattered margins (Fig 4). Attempts to isolate the fungus from affected foliage have been unsuccessful. Expression of foliar symptoms may occur 3-8 years after infection. Bunch size is also often affected with decreased berry number and size (Fig 5) resulting in significant yield reduction. After many years, dieback symptoms the fungus produces a trunk canker (Fig 6) and internal wedge shaped staining (Fig 7).
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Figure 2. Grapevine with Eutypa dieback symptoms |
Figure 3. Grapevine with Eutypa dieback symptoms |
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Figure 4. Stunted grapevine shoot, cupped and chlorotic leaves with necrotic margins |
Figure 5. A normal bunch (left) and a bunch from a vine affected by eutypa dieback |
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Figure 6. Canker on a grapevine trunk |
Figure 7. Cross section of a grapevine trunk with wedge shaped staining of dead wood |
Disease cycle
E. lata ascospores are released from diseased wood after it becomes wet (min. 2 mm rain). E. lata infects when spores land on open pruning or grafting wounds. The fungus then grows slowly within the vascular tissue of the cordons and trunk toward the base of the trunk. Foliar symptoms are thought to be caused by toxic metabolites produced by the fungus in the wood and transported to the foliage. The disease cycle is illustrated in Fig 1.
Figure 1. Eutypa dieback disease cycle in grapevines
(taken from 'Grape Pest Management' Flaherty et al., 1992)
Field sample collection
- Select grapevines expressing foliar symptoms in spring, with dieback of cordons or obvious cankers on the trunk (Fig 2&6).
- Confirm wood symptoms by cutting the vine trunk or cordon to reveal wedge shaped staining (Fig 7). Remove a slice of cankered cordon or trunk (1-2 cm thick).
- Preferred samples for isolation include the interface of dead and live woody tissue.
- Note thet E. lata cannot be isolated from symptomatic green shoots.
Laboratory isolation
- Remove all bark from exterior of sample.
- Completely immerse sample in 2.5 % NaOCl (Sodium Hypoclorite) for 12 min.
- Remove sample and wash in sterile distilled water twice.
- In a laminar flow, cut the sample longitudinally, then into small pieces approx 5 mm x 5 mm x 5 mm focusing on the interface of necrotic and live tissue.
- Place 4 or 5 pieces on full-strength potato dextrose agar (PDA) amended with antibiotic (eg. streptomycin) and incubate at 24oC for 1-4 weeks.
- From 1 week E. lata cultures develop as white and cottony, usually very uniform in growth (Fig 8) and white to cream coloured from underneath.
- Cultures do not always sporulate but those that do, may take up to a month of incubation (Fig 9).
- Cultures that sporulate produce sickle-shaped conidia (20-35 μm long) when prepared on a slide and viewed under the microscope (Fig 10).
- Cultures can also be confirmed as E. lata using DNA primers by PCR or directly from wood using using DNA probes by slot-blot analysis (Lardner et al. 2005)
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Figure 8. E. lata culture on PDA |
Figure 9. E. lata culture on PDA |
Figure 10. E. lata conidia |
Identification from dead wood
Ascospores can be liberated from stroma on infected dead wood.
- Stroma (containing perithecia) appear as darkened, almost charcoaled, sections on infected pieces of wood (Fig 11).
- Under a dissecting microscope, slice the top layer of the stroma with a scalpel to reveal active perithecia, which appear as hollow, dark, cup shaped vessels about 0.5 mm in diameter. Inactive perithecia will be filled with white substance (Fig 12).
- Place one or two drops of water onto the exposed perithecia. If these are active, they will immediately generate asci, appearing as a milky gel.
- Carefully gather the asci with a scalpel tip and place them in a drop of water on a glass slide. Place a cover slip over the slide.
- Under a compound microscope, asci appear as long thin sacks (40 – 60 μm) containing eight ascospores (sausage shaped, 6 – 11 μm long; Fig 13).
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Figure 11. Dead grapevine wood with stroma |
Figure 12. Section through stroma showing active perithecia
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Figure 13. E. lata asci |
For further detail, contact Mark Sosnowski
or refer to: Carter (1991) Phytopathological Paper No. 32. International Mycological Institute, Surrey, U.K.
