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Applied and Environmental Microbiology, December 2005, p. 7788-7791, Vol. 71, No. 12
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.12.7788-7791.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Genetic Similarity of Flag Shoot and Ascospore Subpopulations of Erysiphe necator in Italy

Paolo Cortesi,^1* Anna Mazzoleni,¹ Cristina Pizzatti,¹ and Michael G. Milgroom²

Istituto di Patologia Vegetale, Università degli Studi di Milano, I-20133 Milan, Italy,¹ Department of Plant Pathology, Cornell University, Ithaca, New York 14853²

Received 21 February 2005/ Accepted 5 August 2005

The overwintering mode of the grape powdery mildew fungus, Erysiphe necator (syn. Uncinula necator), as mycelium in dormant buds (resulting in symptoms known as flag shoots) or as ascospores in cleistothecia, affects the temporal dynamics of epidemics early in the growing season. We tested whether distinct genetic groups (I and III) identified previously in E. necator correlate to overwintering modes in two vineyards in Tuscany, Italy, to determine whether diagnostic genetic markers could be used to predict overwintering. Samples from one vineyard were collected from flag shoots; the other vineyard, 60 km away, had no flag shoots, and mildew colonies were assumed to be derived from ascospores. Genetic markers putatively diagnostic for groups I and III showed that both types were common in the flag shoot subpopulation. Both genetic types were found in the ascospore population, although group III was dominant. We did not find strong genetic differentiation between the two subpopulations based on inter-simple sequence repeat markers. Although there was significant (P < 0.001) genetic differentiation between these subpopulations in 1997 and when 1997 and 1998 subpopulations were pooled ( = 0.214 and 0.150, respectively), no differentiation was evident between vineyards in 1998 ( = 0.138, P = 0.872). Moreover, we did not observe distinct lineages corresponding to overwintering modes, as observed in previous studies. We could not determine if differentiation resulted from biological differences or restricted gene flow between the two vineyards. Our samples were taken from both subpopulations early in the epidemic, while previous studies confounded overwintering mode and sampling time. These results do not support a strong correlation between overwintering and genetic groups, highlighting the need to base population biology studies on sound biological and epidemiological knowledge.

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* Corresponding author. Mailing address: Istituto di Patologia Vegetale, Università degli Studi di Milano, Via Celoria 2, I-20133 Milano, Italy. Phone: 39-02-50316771. Fax: 39-02-50316781. E-mail: paolo.cortesi{at}unimi.it.

Supplemental material for this article may be found at http://aem.asm.org.

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Applied and Environmental Microbiology, December 2005, p. 7788-7791, Vol. 71, No. 12
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.12.7788-7791.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Montarry, J., Cartolaro, P., Delmotte, F., Jolivet, J., Willocquet, L. (2008). Genetic Structure and Aggressiveness of Erysiphe necator Populations during Grapevine Powdery Mildew Epidemics. Appl. Environ. Microbiol. 74: 6327-6332 [Abstract] [Full Text]