Graduate Thesis Or Dissertation
 

Factors influencing the production and survival of inoculum of Elytroderma deformans

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  • This study concerns factors affecting production and survival of ascospores of Elytroderma deformans (Weir) Darker, a needle cast of ponderosa pine (Pinus ponderosa Laws.). The results show that summer cooling and a reduction in host vigor delays and diminishes the number of fertile hysterothecia produced. Evidence is offered for classification of Elytroderma as an obligate parasite. It was demonstrated that completion of the perfect stage requires a living host and that the rate and amount of fungal activity is directly related to host vigor. Results of additional experiments revealed that secondary fungi entering infected needles via pycnidial scars play a definite role in reducing the number of hysteothecia attaining maturity, and that the casting of needles is independent of the stage of development of the hysterothecia on the needle. In controlled humidity and temperature experiments, testing the ability of ascospores to survive in the hysterothecium after attaining maturity, it was found that survival occurred only under very low humidities at cool temperatures. Ascospore germination studies in the presence of natural pine needle microflora revealed that best germination takes place between 5° and 20°C and that germ tube elongation was maximum at 5°C. From the results of these experiments the prerequisites of an Elytroderma induced epiphytotic are hypothesized.
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