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The hundred-year history of the hazelnut industry in the Pacific Northwest
is threatened by eastern filbert blight (EFB) caused by the fungus Anisogramma
anomala (Peck) E. Müller. Marker-assisted selection (MAS) has been extensively
used for ‘Gasaway’ resistance in the hazelnut breeding program at Oregon State
University. Concern over breakdown of this resistance gene offers an incentive to
look for new sources of resistance. Three genotypes (OSU 408.040, ‘Ratoli’ and
OSU 759.010) have shown no signs or symptoms of the disease following a series
of greenhouse inoculations or exposure of potted trees under structures topped with
diseased wood. The objective of this study was to observe segregation for disease
response in the offspring of these three novel sources and identify RAPD (Random
Amplified Polymorphic DNA) markers linked to resistance. A total of 900 primers
was screened for each resistance source using three resistant seedlings, three
susceptible seedlings and the parents of a segregating population. The identified
RAPD markers were then validated in a second progeny for each resistance source.
Selection OSU 408.040, grown from seeds labeled “Weschcke hybrid”
collected at the research farm of the University of Minnesota, transmitted resistance
to half of its seedlings. Six RAPD markers (four in repulsion and two in coupling)
linked to resistance were identified for the cross OSU 245.098 × OSU 408.040. A
linkage map constructed with disease phenotypes, previously identified AFLP
markers and newly identified RAPDs spanned a distance of 18 cM. The order of
markers was similar in the progeny OSU 474.013× OSU 408.040.
Segregation in two progenies indicated that the Spanish cultivar ‘Ratoli’
transmits resistance to 50% of its progeny. Four RAPD markers (one in repulsion
and three in coupling) were identified for the progeny OSU 665.012 × 'Ratoli'. A
linkage map constructed with disease phenotypes, previously identified AFLP
markers and newly identified RAPDs spanned a distance of 28 cM. The RAPD
marker OPG17-800 is robust, segregates 1:1, and has potential for use in MAS.
Selection OSU 759.010 from the Republic of Georgia provides a new
source of resistance. Disease scores segregated 3 resistant: 1 susceptible in the
progeny OSU 759.010 × OSU 653.068, and 1 resistant : 1 susceptible in the
progeny OSU 759.010 × OSU 665.076. Thirteen RAPD markers (12 in coupling
and one in repulsion) linked to resistance were identified and a linkage map was
constructed for the first progeny. All markers except OPH12-640 were also present
in the second progeny. The markers closely linked to the resistance locus show
distorted segregation in both progenies.
Segregation ratios suggest simple inheritance for all three sources of
resistance, and several RAPDs useful for marker-assisted selection were identified. |
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