Downy mildew of buckwheat, Fagopyrum esculentum, in the USA caused by Peronospora

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1 Page of Downy mildew of buckwheat, Fagopyrum esculentum, in the USA caused by Peronospora cf. ducometii. Bethany Econopouly, Michael L. Derie, Stephen S. Jones, and Lindsey J. du Toit, Washington State University, Mount Vernon, WA Buckwheat (Fagopyrum esculentum, Polygonaceae) seed is milled into a flour to make soba noodles, and is used whole or milled in breads, pastries, soups, and porridges. Buckwheat was grown on ~,000 ha in Washington State in 0, and central Washington is an important region for buckwheat seed production. Symptoms of downy mildew were observed in buckwheat trials at the Washington State University (WSU) Mount Vernon Northwestern Washington Research and Extension Center (NWREC) in Skagit Co., WA in 0, 0, and 0; and in growers buckwheat crops in Jefferson Co. and Skagit Co., WA in 0 at incidences of to 00%. Pale green, - to 0-mm-diameter lesions on the adaxial leaf surface became chlorotic and, sometimes, necrotic. Under moist conditions, sparse, hyaline to light gray sporulation developed on the abaxial leaf surface. Conidiophores typical of Peronsopora developed from stomata individually or, infrequently, in groups of two or three; were 0 to um (mean ± standard deviation of ± um, n = 0) x to um (. ±. um), and branched submonopodially to (mostly ) times with the ultimate branches right angled and each bearing a sporangium. At least one of each ultimate branch per pair (n = 0) was curved slightly, with the longer branch. to.0 um (. ±. um) and the shorter branch.0 to. um (.0 ±. um). Hyaline to light brown, lemon-shaped conidia (n = 0) became oval at maturity, and were. to. um (. ±.0 um) x.0 to 0.0 um (. ±. um) with a.0 to. length:width ratio. A sample was submitted to the U.S. National Fungus Collections of the United States Department of

2 Page of 0 0 Agriculture (USDA) Systematic Mycology and Microbiology Laboratory (BPI0). The internal transcribed spacer (ITS) -.s ribosomal RNA-ITS DNA sequence (GenBank Accession KX) was 00% homologous to that of Peronospora cf. fagopyri (KP) (Pertrželová et al. 0), which should have been named P. ducometii as the disease was first reported in France by Ducomet (0). The cytochrome oxidase (cox) sequence (KX) was % homologous to that of P. polygoni KJ (Choi et al. 0), with no cox sequences of P. ducometii or P. fagopyri in GenBank. A conidial suspension (. x 0 conidia/ml, prepared by washing infected leaves in 0.0M phosphate buffer) was atomized onto twelve -day-old seedlings of buckwheat cvs. Koto and Springfield, and a breeding population of Nash Huber, after incubating seedlings overnight in plastic bags. Twelve control plants/cultivar were misted with buffer. Plants were then enclosed in plastic bags at o C for h in the dark, bags removed, and the plants held at / o C by day/night with h daylength. Downy mildew sporulation was observed on Koto after days, and on the other two entries after days. Sporulation was not observed on control plants. Severity of downy mildew was rated in August 0 for 0 Plant Introduction (PI) lines planted from a global buckwheat collection of the USDA National Plant Germplasm System. The 0 F. esculentum PIs averaged. ±.0 downy mildew severity (0-to- scale), with asymptomatic (extra). The 0 F. tataricum PI lines averaged 0. ± 0. downy mildew severity, with asymptomatic. Buckwheat downy mildew has been reported in many countries (Farr and Rossman 0; Pertrželová et al. 0) but this is the first record of outbreaks of the disease in Washington State and the USA, with evidence of resistance in some F. tataricum and F. esculentum PIs that could be used in breeding programs.

3 Page of References: Choi, Y. J., et al. 0. Mol. Ecol. Resour. :. Ducomet, V. 0. Annales de l Ecole Nationale D agriculture de Rennes :. Farr, D. F., and Rossman, A. Y. Fungal Databases. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved September 0 from grin.gov/fungaldatabases/. Pertrželová, I., et al. 0. Plant Dis. :. Siemaszko, W.. Zentralblatt fűr Bakteriologie, Parasitenkunde und Infektionskrankheiten :. 0

4 Page of extra Table. Severity of downy mildew observed on 0 cultivars or entries of buckwheat (Fagopyrum esculentum and F. tataricum) obtained from the United States Department of Agriculture (USDA) National Plant Germplasm System (NPGS) and planted at the Washington State University (WSU) Mount Vernon Northwestern Washington Research and Extension Center in 0. a Plant Introduction Cultivar or other Severity of (PI) No. name Fagopyrum species b Geographic origin downy mildew c PI PA F. esculentum Serbia PI 0 PA F. esculentum Serbia PI 0 No. F. esculentum Soviet Union PI 0 PA F. esculentum Russian Federation PI 0 F. esculentum Bhutan PI F. esculentum Bhutan PI TGR F. esculentum Zimbabwe PI TGR F. esculentum Zimbabwe PI TGR F. esculentum Zimbabwe PI PA 00 F. esculentum United States PI Tokyo/PA 0 F. esculentum Canada NA Breeding line, WSU F. esculentum United States PI Takan/PA F. esculentum Taiwan PI 00 Iwatezairai/PA 0 F. esculentum Japan PI 0 PA F. esculentum United States PI Pennline F. esculentum United States PI Aomori F. esculentum Japan PI Gunma Prefectura F. esculentum Japan PI Japanese B 0--0 F. esculentum Canada PI Kasho- F. esculentum Japan PI Southern Chinese F. esculentum Canada PI Tohno Zairai F. esculentum Canada PI Kasho F. esculentum United States PI G 0 F. esculentum Nepal PI Solianskaja F. esculentum Russian Federation PI Mancan F. esculentum Canada PI Manor F. esculentum Canada PI Giant American F. esculentum United States PI Martin's Alaska F. esculentum United States PI PA 00 F. esculentum United States

5 Page of PI PA 0 F. esculentum United States PI PA 0 F. esculentum Italy PI CIfa F. esculentum Italy PI 0 No. 0 F. esculentum Soviet Union PI F. esculentum Bhutan PI F. esculentum Bhutan PI 0 F. esculentum Bhutan PI F. esculentum Bhutan 0 PI F. esculentum Bhutan PI F. esculentum Bhutan PI F. esculentum Bhutan PI F. esculentum Bhutan PI F. esculentum Bhutan PI 0 0 F. esculentum Bhutan PI F. esculentum Bhutan PI 0 Chaselimadao F. esculentum China PI Pennline F. esculentum United States PI MC 0 F. esculentum Soviet Union PI 0 MC 0 F. esculentum India PI PA 00 F. esculentum United States PI 0 PA 0 F. esculentum United States PI PA 0 F. esculentum United States PI PA 0 F. esculentum United States PI PA 0 F. esculentum United States PI CIfa F. esculentum United States PI Pulawska/PA 0 F. esculentum Poland PI PA 0 F. esculentum + several F. Switzerland tataricum PI Tempest F. esculentum Canada PI MC 0 F. esculentum Poland PI 0 MC 0 F. esculentum Poland PI MC 0 F. esculentum Canada PI MC 0 F. esculentum Poland 0 PI MC 0 F. esculentum Poland PI MC 0 F. esculentum Canada 0 PI MC 0 F. esculentum Poland 0 PI 000 Winsor Royal F. esculentum United States PI MC 0 F. esculentum Poland 0 PI MC 0 F. esculentum Poland 0 PI MC 0 F. esculentum Poland 0 PI MC 0 F. esculentum Poland 0

6 Page of PI 0 MC 0 F. esculentum Poland PI MC 0 F. esculentum Poland PI MC 0 F. esculentum Poland 0 PI MC 0 F. esculentum Poland 0 PI MC F. esculentum United States PI MC F. esculentum Poland PI MC 0 F. esculentum Soviet Union 0 PI MC 0 F. esculentum Soviet Union PI MC 00 F. esculentum Soviet Union PI CD F. esculentum Canada PI CD F. esculentum Soviet Union 0 PI Kanada F. esculentum Japan PI Japanese B 0 IR- F. esculentum Japan PI Japanese B 0 IR- F. esculentum Canada PI MC F. esculentum Poland PI Chinese F. esculentum Canada PI 0 K-0 F. esculentum Soviet Union PI K- F. esculentum Soviet Union PI Sweden- F. esculentum Sweden 0 PI Sweden- F. esculentum Sweden PI 0 CM F. esculentum Canada PI G 0 F. esculentum China PI G F. esculentum China PI G F. esculentum Nepal PI Pulawska II F. esculentum Poland PI Hruzgowska F. esculentum Poland PI 0 Enka F. esculentum Denmark PI PA 0 F. esculentum United States PI PA 00 F. esculentum United States PI PA 0 F. esculentum United States PI No known F. esculentum + F. Nepal identification tataricum PI No known F. esculentum Nepal identification PI Trigo Saraceno F. tataricum Mexico O'Alforfon PI F. esculentum + F. Bhutan tataricum PI F. esculentum + F. Bhutan tataricum plants PI 0 Yuqiao No. F. esculentum China PI 0 Nostrano F. esculentum Italy PI CIfa F. tataricum United States 0

7 Page of PI 0 CD F. esculentum Czechoslovakia 0 PI 0 CIfa 0 F. tataricum United States 0 PI G F. esculentum China PI G F. tataricum Nepal 0 PI G F. tataricum Nepal 0 PI 0 G F. tataricum Nepal 0 PI G F. tataricum Nepal 0 PI G F. tataricum Nepal 0 PI G F. tataricum Nepal 0 PI G F. tataricum Nepal 0 PI Sperli F. esculentum Switzerland PI Laharpe/PA 0 F. esculentum France Mean ± standard deviation (minimum maximum) of all 0 entries. ±. (0-) Mean ± standard deviation (minimum maximum) of 0 F. esculentum entries (including. ±.0 (0-) those with mostly F. esculentum plant type) b Mean ± standard deviation (minimum maximum) of 0 entries with F. tataricum plant type b 0. ± 0. (0-) a A single replicate plot of seeds of each buckwheat entry was planted on June 0. Entries were not planted in replicate plots because of limited seed available from the USDA NPGS. b All PIs planted in this trial were listed by the USDA NPGS as F. esculentum but the morphology of a subset or all plants in some plots was typical of F. tataricum (USDA Natural Resources Conservation Service, abit=all&duration=all&origin=all&wetland=all&imagetype=all&artist=all&copyright=all&location=all&statesele ct=all&cite=all&viewsort=&sort=sciname). c Severity of downy mildew was rated on August 0 on a 0-to- scale, where: 0 = no downy mildew symptoms 0 observed, = <0% of the leaves in a plot had downy mildew, = 0 to % of the leaves had downy mildew, and = >% of the leaves had downy mildew symptoms.