VIEW ARTICLE

Physiology and Biochemistry

The Effect of Xylose on the Growth and Sporulation of an Isolate of Bipolaris maydis Race T and its Relation to pH and Ammonium Levels. T. W. Bischoff, Department of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster, and Ohio State University, Columbus 43210; M. O. Garraway, Department of Plant Pathology, Ohio Agricultural Research and Development Center, Wooster, and Ohio State University, Columbus 43210. Phytopathology 75:138-141. Accepted for publication 8 August 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-138.

Sporulation of an isolate of Bipolaris maydis race T (ATCC 36180) was significantly higher and one and a half to two times greater on media containing xylose as a sole carbohydrate source or when used in a 1:1 ratio (w/w) with glucose than on media containing only glucose after 6 days of incubation at 28 C in the dark. The effect of xylose was observed with carbohydrate concentrations of 2, 5, or 10 g/L. Moreover, the magnitude of the effect of xylose on sporulation was the same at 6, 10, or 14 days of incubation. No unique response of mycelial dry weight in the presence of xylose was observed. After 10 days of incubation on media with 5 or 10 g of carbohydrate per liter, mycelial dry weights were significantly higher than after 6 days but comparable to those after 14 days. In the absence of carbohydrate or in the presence of 2g of carbohydrate per liter there was no change in dry weight after any of the incubation times. Ammonium (as measured by using Nessler's reagent) was produced by the fungus and released in the culture medium. The levels were significantly lower with each increase in concentration of carbohydrate. In addition, ammonium was significantly lower in the presence of xylose than with glucose alone. The differences in ammonium levels due to carbohydrate concentration or xylose were observed at 6, but not at 10 or 14, days of incubation. Also, at the latter times the ammonium levels were comparable at all concentrations of glucose, glucose-xylose, or xylose. The trends in pH values paralleled those seen for ammonium. By 14 days, the final pH and ammonium levels were 8.3 and 16.5 μmoles of NH₄⁺, respectively, per milliliter. Furthermore, trends in ammonium and pH levels obtained through titration of the basal medium with ammonium hydroxide were similar to those found in fungal cultures. This suggests that pH and ammonium levels may interact in the culture medium and may affect growth and sporulation of the fungus.