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Title: FORMATION OF PHYTOPHTHORA INFESTANS OOSPORES IN NATURE ON TUBER IN CENTRAL MEXICO

Author
item FERNANDEZ-PAVIA, S. - PICTIPAPA, METEPEC, MX
item Grunwald, Niklaus - Nik
item FRY, W. - CORNELL UNIV, ITHACA, NY

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2001
Publication Date: 1/1/2002
Citation: FERNANDEZ-PAVIA, S.P., GRUNWALD, N.J., FRY, W.E. FORMATION OF PHYTOPHTHORA INFESTANS OOSPORES IN NATURE ON TUBER IN CENTRAL MEXICO. PLANT DISEASE. 86:73. 2002.

Interpretive Summary: Oospore formation by P. infestans in nature has been reported on potato leaflets in central Mexico, but there are no reports of oospore formation on tubers. A severe late blight epidemic occurred in Calimaya, Mexico, in fields where the potato cultivar Alpha was planted during the summer of 2000. Four hundred potato tubers that were left in the field were collected din the upper 10 cm of soil and examined for late blight symptoms. Tubers with soft and dry rot symptoms were observed, but no symptoms of pink rot (Phytophthora erythroseptica) were found. Four percent of the tubers showed late blight symptoms. Aplerotic oospores with amphyginous antheridia typical of P. infestans were observed. The number of oospores observed in our tuber sample was much lower than previously reported on leaflets (>1000 oospores per leaflet) in the Toluca valley. Low numbers of oospores have been reported on tubers artificially inoculated with P. infestans under field conditions. To our knowledge, this is the first report of oospores o P. infestans found on tubers in Mexico under natural field conditions.

Technical Abstract: Oospore formation by P. infestans in nature has been reported on potato leaflets in central Mexico, but there are no reports of oospore formation on tubers. A severe late blight epidemic occurred in Calimaya, Mexico, in fields where the potato cultivar Alpha was planted during the summer of 2000. Yield reduction was observed despite numerous applications of fungicide. Four hundred potato tubers that were left in the field were collected in the upper 10 cm of soil and examined for late blight symptoms. Tubers with soft and dry rot symptoms were observed, but no symptoms of pink rot (Phytophthora erythroseptica) were found. Four percent of the tubers showed late blight symptoms. Sections of ten tubers with late blight symptoms were air dried for two weeks in the laboratory and homogenized with a mortar and pestle. Glycerol was added to the homogenized tissue and observed microscopically. Aplerotic oospores (10-15 5oospores per tuber) with amphyginous antheridia typical of P. infestans were observed. P. mirabilis morphologically similar to P. infestans is present in the area but it does not infect potato tubers. The number of oospores observed in our tuber sample was much lower than previously reported on leaflets (>1000 oospores per leaflet) in the Toluca valley. Low numbers of oospores have been reported on tubers artificially inoculated with P. infestans under field conditions. Infected tubers that are left in the field may contribute as an additional source of primary inoculum. To our knowledge, this is the first report of oospores of P. infestans found on tubers in Mexico under natural field conditions.