STUDIES ON THE FUSARIA WHICH CAUSE WILT IN MELONS: II. THE EFFECT OF LIGHT, NUTRITION, AND VARIOUS CHEMICALS ON THE SPORULATION OF CERTAIN FUSARIAL ISOLATES, AND PRELIMINARY INVESTIGATIONS ON THE ETIOLOGY OF WILTING OF THE MUSKMELON FUSARIUM

Abstract

Light was shown to affect the amount of macrospore production in a number of Fusarium species. Macrospore production and the ratio of macrospores to microspores increased with increasing light intensity and vice versa. Only colony areas exposed to light during active growth produced macrospores on potato dextrose or Czapek's agars. Light also greatly stimulated macrospore production on V-8 vegetable juice agar. Both carbon and nitrogen sources were also important in determining the kind and amount of sporulation in the species tested. Colony growth was appressed in light, and pigmentation of the mycelium often was produced in response to light.Various chemicals, known to be enzyme inhibitors, induced different effects on growth and sporulation, depending on the substrate used as the carbon source. For example, sodium fluoride inhibited growth and sporulation when glucose was the substrate, but was without effect when sodium acetate, which supports equally vigorous growth, was the substrate.Studies on the etiology of wilting indicated that the muskmelon Fusarium produces at least three chemical fractions which may contribute to wilting. One was thermostable, non-dialyzable, apparently a protein, and possibly an enzyme. The second was thermostable and was probably a low molecular weight carbohydrate. These two induced wilting in plant cuttings rather than in intact plants, whereas the third fraction induced wilting in plants with undamaged root systems, and was thermostable, partially dialyzable, and stable through a wide pH range. Appropriate tests, however, indicated also that translocation through the vessels was significantly interfered with in plants showing incipient or more advanced wilting symptoms.