Cleistothecia of Uncinula necator: an additional source of inoculum in Italian vineyards

Density and viability of populations of cleistothecia of Uncinula necator from bark, leaves, and soil were determined in three vineyards in the Florence and Siena provinces of Tuscany for 3 years. A higher density of cleistothecia was found on fallen leaves than on bark. However, the percentage of viable cleistothecia was higher on bark. No viable cleistothecia were recovered from soil. U. necator overwintered as mycelium in dormant infected buds, which gave rise to flag shoots, only in Santa Cristina, where 20 and 92 flag shoots per hectare were detected before bloom in 1994 and 1995, respectively. Disease incidence and severity increased similarly at Corti, Fornace, and at Santa Cristina, although powdery mildew epidemics started from ascospores only in Corti and Fornace, whereas flag shoots were present at Santa Cristina. Cleistothecia were formed in autumn in both 1994 and 1995, and their dispersal started in late September to mid-October, with the maximum number of cleistothecia trapped in funnels during the second half of October. Cleistothecia appear to function as the sole source of primary inoculum for grape powdery mildew in some Italian vineyards and serve as additional sources of inoculum where the pathogen also overwinters in infected buds. In Australia but not in New York, the pathogen also overwinters as cleistothecia on fallen leaves

Maturation of cleistothecia of Uncinula necator (powdery mildew) and release of ascospores in southern Australia

We paired genetically characterised isolates of U. necator under controlled conditions and raised the resultant cleistothecia to maturity. Progeny were recovered from cleistothecia formed in the glasshouse and growth room 97-110 days after cleistothecial initials were observed. Cleistothecia collected from naturally infected leaves from vineyards in the Adelaide Plains and Langhorne Creek, South Australia, in March and April (autumn) 1998 and stored in the same vineyards, were induced to release ascospores in the laboratory between March 1998 and February 1999. This paper is the first report of cleistothecia of U. necator releasing ascospores during summer, autumn and winter in southern Australia. Cleistothecia did not require a period of over-wintering in order to release ascospores that infected detached grapevine leaves in vitro. Furthermore, cleistothecia that over-wintered in the field were triggered to release ascospores in the laboratory in spring. Release of ascospores in spring was coincident with observations of ascospore-derived infections in the Waite Campus vineyard, confirming that cleistothecia provide an additional source of primary inoculum for powdery mildew in South Australia. Autumn release of ascospores suggests the possibility that U. necator may complete two sexual generations per year in Mediterranean climates, with consequent increased risks of development of fungicide resistance and changes in pathogenicity.Gee, L. M. ; Stummer, B. E. ; Gadoury, D. M. ; Biggins, L. T. ; Scott, E. S

The effect of Uncinula necator (powdery mildew) and Botrytis cinerea infection of grapes on the levels of haze-forming pathogenisis-related protiens in grape juice and wine

Copyright © 2008 Australian Society of Viticulture and Oenology Inc.Powdery mildew on Chardonnay grapes resulted in increased levels of a grape thaumatin-like protein, VvTL2, in the free run juice compared to that from uninfected grapes. These increased levels persisted through winemaking and at the highest level of infection (> 30% of bunches infected) had a significant impact on the haziness in the wine following a heat test. Infection of Cabernet Sauvignon grapes (1-20% of bunches infected) did not affect the protein concentration of free run juice, and only traces of pathogenesis-related (PR) proteins remained detectable in the Cabernet Sauvignon wines from either infected or healthy grapes. In contrast, infection of Chardonnay or Semillon grapes by Botrytis cinerea in the vineyard resulted in decreased levels of all PR proteins in the free run juice and in a total protein extract from infected berries compared to that from uninfected grapes. Similar trends were observed when B. cinerea was grown in the laboratory on surface-sterilised berries or in filter-sterilised juice.Teresa Girbau, Belinda E. Stummer, Kenneth F. Pocock, Gayle A. Baldock, Eileen S. Scott and Elizabeth J. Water