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Title: Natural occurrence of Phytophthora infestans on woody nightshade (Solanum dulcamara) in New York

item Deahl, Kenneth
item Perez, Frances
item Jones, Richard
item Baker, Con
item MCGRATH, MEG - Cornell University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2010
Publication Date: 9/1/2010
Citation: Deahl, K.L., Perez, F.G., Jones, R.W., Baker, C.J., Mcgrath, M. 2010. Natural occurrence of Phytophthora infestans on woody nightshade (Solanum dulcamara) in New York. Plant Disease. 94:1063.

Interpretive Summary: Late blight is a devastating disease of tomatoes and potatoes and is capable of rapidly destroying entire crops under favorable conditions. This study documents how wild weed hosts from various geographic regions may secretly harbor the pathogen and act to further spread the disease. These findings may be useful to other potato pathologists, mycologists, and potato breeders who have an interest in the host range of fungal pathogens. Pathogen population structure and variability in isolate occurrence may be important in disease-management systems and serious consideration should be given to these findings when planning control strategies for this disease.

Technical Abstract: The oomycete, Phytophthora infestans, is a devastating pathogen of potato worldwide. Several strains of P.infestans are able to infect other cultivated and weed species of the family Solanaceae and cause symptoms similar to late blight on these hosts. Changes in P. infestans populations have stimulated investigations to determine if tomato/potato strains from more recent immigrant populations infect a wider host-range than those from the older population. Expansion of the host range may be one of the mechanisms involved in pathogenic changes in natural populations of P. infestans and to determine its significance, it is necessary to establish if the pathogen strains on non-potato hosts represent distinct genotypes/populations or are freely exchanging with those on tomato or potato. This paper reports characterization of P. infestans isolates from a Solanaceous host growing within and around fields of blighted potatoes and tomatoes in New York and the comparison with isolates collected from adjacent infected hosts. Isolates were characterized for mitochondrial DNA (mtDNA) haplotype, mating type, metalaxyl resistance, allozymes of glucose-6-phosphate isomerase and peptidase, and DNA fingerprint with the RG57 probe. Analysis showed close similarity of the woody nightshade isolates to potato and tomatoes isolates. Moreover, tomato and potato strains had distinctly similar fingerprints. Potato growers should be aware that both weed and cultivated Solanaceous species can be infected with P. infestans and may serve as clandestine reservoirs of inoculum. Because some of these plants do not show conspicuous symptoms, they may escape detection and fail to be either removed or treated and so may play a major role in the introduction and spread of pathogens to new locations.