Ascospore discharge and germination in Xanthoria polycarpa Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/5h73q073g

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  • Xanthoria polycarpa is a foliose lichen, commonly found as an epiphyte in the Willamette Valley of western Oregon. This study was undertaken to determine some of the effects of environmental factors on ascospore discharge and germination in X. polycarpa. Ascospores were collected on glass slides suspended above lichen thalli. Abundant discharge occurred in the fall, winter, and spring. Discharge in the summer was rare, and occurred only when thalli were wet. Discharge was correlated with rainfall. No striking time pattern of discharge was exhibited by apothecia incubated on moist filter paper. Horizontally discharged ascospores travelled from 1 to 24 mm away from the apothecia. Spores commonly occurred in groups of eight, indicating that all of the spores in one ascus can function as one projectile. Ascospore discharge occurred when apothecia were incubated in the light or in the dark. Discharge occurred at 5, 10, 15, and 20 C. No discharge occurred at 25 or 30 C. Saturated salt solutions were used to produce atmospheres of various relative humidities. Discharge occurred at 100% RH and when apothecia were placed on moist filter paper. No discharge occurred at relative humidities less than 100%. Ascospores inoculated on water agar germinated within 3 to 4 days when incubated at 15 C. The highest percentage of ascospores germinated at 10, 15, and 20 C. Germination values at 5 and 25 C were lower. No germination occurred at 30 C. Little or no germination occurred when spores were subjected to alternating 15 and 30 C. Ascospore germination occurred equally well in the light as in the dark. A citrate-phosphate buffer was used to adjust the pH of water agar. The highest percentage of spores germinated at pH 5 and pH 6. Germination also occurred at pH 4, pH 7, and pH 8. Germination at pH 3 was poor. Ascospores dried on coverslips and incubated at various relative humidities did not germinate. Germination did occur when spores were incubated in water or on an agar medium. The percentage of spore germination was higher on water agar than in water. No difference in germination was found between spores inoculated on washed and unwashed Noble agar. The percentages of spores germinating on water agar and lichen extract were higher than the percentages of spores germinating on bark extract agar and malt-yeast extract agar.
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