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United States Department of Agriculture

Agricultural Research Service

Title: Powdery Mildew Resistant Hop Germplasm Release: 'Kazak 2000'

Authors
item Hummer, Kim
item Gent, David
item Henning, John
item Mahaffee, Walter
item Ocamb, Cynthia - OREGON STATE UNIVERSITY

Submitted to: Acta Horticulturae
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2008
Publication Date: September 1, 2008
Citation: Hummer, K.E., Gent, D.H., Henning, J.A., Mahaffee, W.F., Ocamb, C. 2008. Powdery Mildew Resistant Hop Germplasm Release: 'Kazak 2000' [abstract]. Acta Horticulturae. p.59

Interpretive Summary: A USDA-sponsored plant collecting expedition in collaboration with the Vavilov Institute of Plant Industry (VIR), St. Petersburg, Russian Federation, and the Aral Sea Experiment Station for Plant Genetic Resources, Chelkar Town, Kazakhstan, was conducted in the fall of 2000. Hop cones were collected from wild plants growing on trees in a moist area about 50 km NE of Emba. A portion of the seeds were brought to the US and donated to the USDA ARS National Clonal Germplasm Repository in Corvallis, Oregon. Of 74 seedlings that were germinated from Kazakhstani seedlots, four seedlings from PI 635262 demonstrated powdery mildew resistance. One of these resistant seedlings, ‘Kazak 2000,’ exhibited a special response after inoculation with powdery mildew, especially when incubated at hot temperatures. In greenhouse tests with an Oregon field populations of powdery mildew, no signs of mildew were observed following repeated inoculations. In laboratory tests 'Kazak 2000’ did not develop powdery mildew when when three specific races were used. Only about 55% of leaves were infected with 11 different races of mildew. In field plots in Oregon from 2003 to 2007, only one powdery mildew colony was observed on a leaf despite multiple local-source inoculations each year and exposure to natural inoculum sources. Infection of cones was not observed. Limited quantities of cuttings of ‘Kazak 2000’ are available for research or breeding. Requests should be made to the Hop Curator, USDA-ARS, National Clonal Germplasm Repository, Corvallis, OR 97333.

Technical Abstract: A USDA-sponsored plant collecting expedition in collaboration with the Vavilov Institute of Plant Industry (VIR), St. Petersburg, Russian Federation, and the Aral Sea Experiment Station for Plant Genetic Resources, Chelkar Town, Kazakhstan, was conducted in the fall of 2000. Hop cones were collected from wild plants growing on trees in a moist area about 50 km NE of Emba. A portion of the seeds were brought to the US and donated to the USDA ARS National Clonal Germplasm Repository in Corvallis, Oregon. Of 74 seedlings that were germinated from Kazakhstani seedlots, four seedlings from PI 635262 demonstrated powdery mildew (caused by Podosphaera macularis (Braun and Takamatus) resistance. One of these resistant seedlings, ‘Kazak 2000,’ exhibited a hypersensitive response after challenge by powdery mildew, especially when incubated at temperatures greater than 29oC post-infection. In greenhouse assays with an Oregon field population of P. macularis, macroscopic signs of powdery mildew were not observed following repeated inoculations. In laboratory assays at 18oC, ‘Kazak 2000’ did not develop powdery mildew when challenged with a P. macularis isolate capable of overcoming resistance genes Rb, R3, and R5. Infection of 28 or 55% of detached leaves was observed when challenged with isolates capable of overcoming Rb, R3, R4, R5, R6 or Rb, R1, R2, R3, R5, and R6, respectively. In experimental field plots in Oregon from 2003 to 2007, only one powdery mildew colony was observed on a leaf despite multiple local-source inoculations each year and exposure to natural inoculum sources. Infection of cones was not observed. Limited quantities of cuttings of ‘Kazak 2000’ are available for research or breeding. Requests should be made to the Hop Curator, USDA-ARS, National Clonal Germplasm Repository, Corvallis, OR 97333.

Last Modified: 4/16/2014
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