Fifteen groups, comprising 106 substances, were studied for their effect on the germination of conidia ofHelminthosporium sativumPamm., King and Bakke in soil. Spores usually germinated when substances from groups composed of natural products were included in the substrate. Of these substances, wheat germ, bran, certain oil meals, molasses, orange juice, and green plant tissues were very effective, whereas refined flours and commercial sugars were only slightly so. When wheat straw and roots of wheat plants were added to the soil the conidia did not germinate. In contrast to the above-mentioned groups, most of the substances in the acid, salt, vitamin, protein, amino acid, oil, saccharide, plant hormone, and miscellaneous groups were not effective. The exceptions in these groups were ascorbic acid, galactose, and raffinose.
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