WATER POTENTIAL AND THE SAPROPHYTIC GROWTH OF FUSARIUM-ROSEUM GRAMINEARUM

The saprophytic growth of Fusarium roseum (Lk.) emend. Snyd. & Hans. Graminearum" Group 1 and Group 2 on agar was stimulated by osmotic water potentials of - 1 to - 2MPa. Growth was negligible at - 14 to - 15MPa after 3 days incubation at 25°C. There was no significant difference between the response of cultures of Group 1 and Group 2 to decreasing water potential. A slight shift in the optimum water potential at which maximum growth of cultures of both groups occurred was apparent at 30°C. This shift was most obvious with a Group 2 culture. Growth ceased at a higher water potential in nutrient-deficient media. This fungus responded differently to decreasing matric as opposed to osmotic water potential. Growth decreased linearly with decreases in matric water potential from 0 Pa down to - 7.7MPa (the lowest potential tested). The growth response of the fungus to decreasing osmotic water potential in liquid culture was similar to that on the solid medium. There is no evidence to suggest that F. roseum "Graminearum" Group 1 and Group 2 have evolved different water potential requirements for saprophytic growth. © 1979."