Graduate Thesis Or Dissertation
 

Factors influencing the development of onion pink root disease incited by Pyrenochaeta terrestris (Hansen) Gorenz, Walker, Larson

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  • A study was conducted of the influence of various climatic and soil factors on the development of onion pink root disease and of the influences of temperature, light, pH, carbon and nitrogen sources, and vitamins on the growth in vitro of an Oregon isolate of the pink root fungus, Pyrenochaeta terrestris (Hansen) Gorenz, Walker, Larson. Eleven onion lines were planted in eastern and western Oregon to determine whether the relative resistance to pink root among them would vary during the growing season and with different climatic conditions. Varietal resistance remained generally stable among the different lines. Ten onion lines were grown in mucky peat and silty clay loam soils in the greenhouse to determine the influence of soil moisture and soil type on severity of pink root. Onions grown in soil held at field capacity had less pink root than those in dryer soils. Pink root ratings were similar among onions grown in both soils. Lanstan, Vorlex, Telone, Pictel, Morton Soil Drench, SD 345, chloropicrin, Mumfume, Phaltan, E.P. 230, and E.P. 201 were tested in the field for their effect on pink root. In some fields Vorlex, chloropicrin, Mumfume, E.P. 230, and E.P. 201 increased onion yields from 30 to 75 percent. None of these fumigants noticeably reduced pink root, however. Telone controlled stubby root nematode infection but did not reduce pink root. On malt extract-yeast extract agar P. terrestris grew fastest at a temperature of 30 C, with the greatest increase in growth rate between 15 and 20 C. There was no growth at 5 C. Continuous light, alternating darkness and light, and brief exposures to germicidal ultraviolet light (2,500 A[superscript °]) did not noticeably affect the growth rate of the fungus. Growth of P. terrestris increased the pH of glucose-asparagine and sucrose-potassium nitrate liquid media. On both media the fungus grew well over a pH range from 6 to above 8 but poorly at a pH of 4 or less. Sorbose inhibited growth of P. terrestris. Maltose, galactose, glucose, fructose, sucrose, lactose, and starch in asparagine liquid and agar media each supported good growth of the fungus, as did glycine, potassium nitrate, and urea in glucose agar. The addition of thiamine, biotin, inositol and pyridoxine to sucrose -asparagine agar did not noticeably affect P. terrestris growth. Higher temperatures coincided with greater pink root infection in the field.
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Déclaration de droits
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