Date of Award:

1979

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Advisor/Chair:

F. J. Post

Co-Advisor/Chair:

D. K. Salunkhe

Abstract

A chemically defined synthetic medium was developed in which Phytophthora infestans (Mont.) de Bary race 1.2.4 grew extensively. This medium consisted of: 90.0 grams maltose, 20.0 grams DL-alanine, 20.0 grams L-proline, 1.0 gram KNO3, 0.5 gram KH2PO4, 0.25 gram MgSO4. 7H2O, 1.0 milligram thiamin per liter of distilled water. The average level of growth in this medium was 0.5864 gram dry weight mycelium per 50 milliliters medium.

The glycoalkaloids, solanidine and solanine, were synthesized by Phytophthora infestans in the above medium with 62.5 percent of the samples positive and an overall average of 0.85 milligram total glycoalkaloids per 25 milliliters medium. The level of alkaloids detected in the medium ranged from 0.0 to 5.9 milligrams per 25 milliliters medium. No glycoalkaloid production was detected when the level of growth of the fungus was below 0.35 gram dry weight mycelium per 50 milliliters medium.

Phytophthora infestans was also cultured on the following semisynthetic media: chick pea medium, rye seed medium, and lima bean medium. The fungus grew extensively in each medium, but produced alkaloids in only the chick pea medium. Fifty percent of the samples of this medium were positive for alkaloids with an overall average of 0.67 milligram total glycoalkaloids per 25 grams chick peas.

Sodium salts of the macronutrients were individually substituted for the potassium and magnesium salts of the basal medium and sodium chloride and sodium acetate were singly added to the medium. Maximum growth levels were demonstrated when 0.04 percent phosphate or 0.04 percent chloride was employed in the medium. Sodium acetate was inhibitory to Phytophthora infestans.

Glycoalkaloid production was significantly reduced in media containing sodium salts of the macronutrients. Regression analysis showed that the concentration of phosphate in the medium had the most influence on the level of glycoalkaloids synthesized by the fungus. Raising the concentration of phosphate in the medium resulted in increasing amounts of alkaloids being produced by Phytophthora infestans.

Upon addition of micronutrients to the enriched basal medium, growth of Phytophthora infestans was stimulated by levels of ferrous iron in the concentration range of 1.0-5.0 milligram 1-1. Phytophthora infestans was inhibited by all concentrations of cobalt, copper, manganese, nickel, and by concentrations of calcium greater than 0.001 milligram 1-1.

No glycoalkaloid production by Phytophthora infestanswas detected in media containing cobalt, copper, calcium, nickel, or manganese. Glycoalkaloids were produced in media containing iron at all concentrations except 5.0 milligrams 1-1 with the highest amount of alkaloids occurring in media containing 0.001 milligram 1-1. Ferrous iron seems to inhibit glycoalkaloid synthesis by Phytophthora infestans. As the level of iron in the media was increased the quantity of glycoalkaloids produced in the media declined.

Studies were carried out to determine the effect of mineral nutrition on the resistance of potato foliage to infection by Phytophthora infestans. Results indicated that the level of phosphate had little or no effect on the susceptibility of potato leaflets to late potato blight. Levels of nitrate (1.0-10.0 percent) had little effect on the blight resistance of foliage, whereas higher levels of nitrate (20.0- 25.0 percent) significantly increased the susceptibility of leaflets to infection by Phytophthora infestans.

Growth of common saprophytic and enteric bacteria was not inhibited by glycoalkaloids in the concentration range of 1 to 200 milligrams total glycoalkaloids per 100 milliliters.

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