Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph.D.)--Murdoch University, 2006. / Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 183-201.

Breeding Port-Orford-cedar for resistance to Phytophthora lateralis, a causal agent of root disease, begins by screening, through artificial inoculation, phenotypically resistant trees selected from natural stands. The successful program selected tolerant or resistant POC parent trees for the purpose of disease management. Candidate resistant POCs were used in my dissertation to: 1. validate screening methods such as stem- and root-dip inoculation; 2. test for increased virulence of P. lateralis; and 3. evaluate detection techniques. The results showed that the established screening methods were appropriate, and no evidence of changed virulence was found. A PCR technique was more reliable than other techniques for detection of P. lateralis in seedlings. An additional test for foliar infection showed that initial penetration through wounds and natural openings was possible. POC seedlings and rooted cuttings from resistant and susceptible families were used to demonstrate resistance mechanisms. In order to explain the mechanisms at the cellular level, the susceptible response of POC seedlings to P. lateralis was first observed with light microscopy. Zoospores encysted on lateral roots, germinated, and penetrated by means of appressoria. Direct penetration between epidermal cells was common but penetration through epidermal cell walls was also observed. The hyphae colonized the root cortex inter- and intracellularly. Wound inoculation on stems resulted in inter- and intra cellular hyphal growth in cambial, sieve, and parenchyma cells in the secondary phloem. Several resistance mechanisms were observed: 1) there was a difference in zoospore attraction between susceptible and certain resistant POCs revealed by microscopic observation, direct count of encysted zoospores, and quantitative real-time PCR; 2) the frequency of encystment, penetration, and colonization of resistant seedlings was much lower than susceptible seedlings, but no differences in infection pathway were observed by means of light or electron microscopy; 3) collapsed cell walls were present in resistant POCs showing increased cell wall thickness, wall appositions, and electron dense materials. / Graduation date: 2005

Thesis (Ph.D.)--Murdoch University, 2005. / Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 160-177.

In 1991 Pacific yew (Taxus brevifolia Nutt.) was reported as a new host for Phytophthora lateralis Tucker and Milbrath which is an aggressive root rot pathogen thought previously to be specific to Port-Orford-cedar. This study was designed to compare the pathogenicity of P. lateralis on the two hosts, and to characterize sites where Pacific yew mortality occurs. The specific objectives were: 1) compare root colonization and mortality of Pacific yew and Port-Orford-cedar seedlings and rooted cuttings; 2) compare lesion length on inoculated Pacific yew and Port-Orford-cedar branches and stems; 3) compare zoospore attraction to freshly cut Pacific yew and Port-Orford-cedar rootlets; 4) compare amount of mortality of Pacific yew and Port-Orford-cedar in infested drainages and determine extent of yew mortality; and 5) characterize sites where P. lateralis causes Pacific yew mortality. Root colonization of P. lateralis was significantly greater in cedar than in yew. Seedling mortality averaged 58% for cedar and 4% for yew. Lesion length on the cedar seedling stems was twice the lesion length on yew stems, and cedar branches had lesions four times longer than yew branches. Abundant zoospore aggregation occurred on cedar rootlets along the zone of elongation and the region of maturation. In comparison, far fewer zoospores encysted along the yew rootlets, and were concentrated on the root hairs. The stream survey of three infested drainages in southwest Oregon and northwest California revealed a total of 1199 dead Port-Orford-cedar (46% mortality), and 86 dead Pacific yew (10% mortality). At sites where P. lateralis-induced mortality occurred, the interaction of slope and distance from the stream was negatively correlated with tree death. Based on results of this study, we conclude that Pacific yew is less susceptible to P. lateralis than Port-Orford-cedar, but that mortality of Pacific yew in the field is greater than previously reported. In addition, Pacific yew mortality was observed most often on level to nearly-level sites close to the stream's edge where root exposure to P. lateralis-infested water was frequent in scope and duration. / Graduation date: 1995

Thesis (M.E.S.)--The Evergreen State College, 2008. / Title from title screen viewed (4/7/2009). Includes bibliographical references (leaves 114-126).

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

Maize grey leaf spot (GLS), caused by Cercospora zeae-maydis, and potato late blight (LB), caused by Phytophthora infestans, are foliar diseases of maize and potato, two of the most widely grown crops in KwaZulu-Natal (KZN), after sugarcane and timber. Commercial maize in KZN accounts for just on 4.3% of the national maize crop. This is worth R563 million using an average of the yellow and white maize price for the 2001/02 season (at R1 332.87 ton(-1)). In 2003 KZN produced about 5% of the national potato crop (summer crop: 7531 300 10kg pockets from 2243 hectares). This equates to a gross value of R89.4 million based on an average price of R1 188 ton(-1) in 2001. Successful commercial production of maize and potatoes depends upon control of these diseases by translaminar fungicides with highly specific modes of action. This study extends an existing model available for timing of fungicide sprays for GLS and tests and compares two LB models for two calendar-based spray programmes. The study also evaluated the use of an early blight model which is caused by Alternaria solani, and over the single season of evaluation showed potential for use in KZN. For the GLS model it was found that a number of refinements are needed, e.g., the amount of infected maize stubble at planting and not the total amount of maize residue at planting. Based on two years' data, it was found that for the LB models there are no significant differences in levels of control between using a predicted fungicide programme and a calendar-based programme. The importance of knowing initial infection sites, and hence initial inoculum, was demonstrated. This led to the creation of a KZN LB incidence map, now being used to more accurately time the start of a preventative spray programme and to time the inclusion of systemic fungicides in the preventative spray programme. This study has contributed to the further development and expansion of the Automatic Weather Station Network (AWSN) at Cedara, which now comprises 15 automatic weather stations in KZN. The AWSN is currently used to aid farmers and advisers in decision-making regarding fungicide spray timing for GLS and LB. / Thesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 2003.