Port-Orford-cedar (Chamaecyparis lawsoniana) is a forest tree native to
a small area of Oregon and California. A root disease caused by
Phytophthora lateralis causes widespread mortality of Port-Orford-cedar.
This dissertation examines three important elements of the Port-Orford-cedar
P. lateralis pathosystem related to breeding for disease resistance:
use of resistant rootstocks to maintain genotypes of Port-Orford-cedar for
breeding; the heritability and genetic basis of disease resistance; and
variability in virulence and DNA fingerprint among a sample of P. lateralis
isolates.
Port-Orford-cedar was reciprocally grafted to western redcedar (Thuja
plicata), incense cedar (Calocedrus decurrens), and Alaska yellow-cedar
(Chamaecyparis nootkatensis). Port-Orford-cedar scion graft success was
moderate with western redcedar and incense cedar, but extreme
overgrowth of the rootstock by the scion indicated incompatibility. Xylem
union was good, but phloem union was incomplete or lacking. Nearly all
Port-Orford-cedar rootstocks and seedlings exposed to P. lateralis died of
root disease. Four percent of the Alaska yellow-cedar exposed also died,
confirming this tree as a host for P. lateralis.
Resistance of Port-Orford-cedar to P. lateralis is rare. A small number
of trees have been identified exhibiting resistance. A number of families
were tested to determine the genetic basis for resistance. Estimates of
narrow-sense and family mean heritability of resistance, as exhibited by
restriction of lesion length after inoculation, were determined. Both narrow-sense
and family mean heritabilities were between 0.61 and 0.98 in most
tests. Between 21% and 32% of the variance was due to differences
among families.
Thirteen isolates of P. lateralis were collected from three hosts
throughout the geographic range of the fungus. Variation in growth rate on
artificial media at three temperatures, virulence when used to inoculate
Port-Orford-cedar, and DNA fingerprint were compared. There were
significant differences in growth rate among isolates at 24C, but fewer
differences at lower temperatures and on a rich medium. One isolate
produced significantly shorter lesions in three different inoculation tests.
Isolates differed at only two of 189 bands produced by Inter Simple
Sequence Repeat (ISSR) DNA primers, indicating very little genetic
variation among isolates. / Graduation date: 2001
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/32598 |
| Date | 06 June 2000 |
| Creators | McWilliams, Michael G. |
| Contributors | Hansen, Everett M. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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