THE INFLUENCE OF PLANT WATER-STRESS ON INFECTION AND COLONIZATION OF WHEAT SEEDLINGS BY FUSARIUM-GRAMINEARUM GROUP-1

The influence of seedling water potential on infection and colonization of wheat seedlings (Triticum aestivum) by Fusarium graminearum Group 1 was studied using wax partitioning of the soil so that the water potential of the seminal root zone was manipulated independently from the water potential of the infection zone in the subcrown internode region. Eleven days after seeds were sown, water was withheld from the root zone to induce water stress in seedlings, while nonstressed seedlings were watered every 48 h to a soil water content of 0.31 g g-1, favorable for plant growth. In the 1990 experiment, a decrease in seedling water potential of -0.32 to -2.63 MPa in the crown rot-tolerant cv. Suneca and -0.43 to -2.85 MPa in the less tolerant cv. Sunkota as a consequence of stress corresponded with an increase in colonization of wheat seedlings by F. graminearum Group 1. The incidence of infection was not related to the tolerance of the host and was similar under both stress and nonstress conditions. F graminearum Group 1 suppressed growth in nonstressed seedlings of both cultivars but not in seedlings subjected to water stress. A trend for F. graminearum Group 1 to suppress growth in the stressed seedlings was suggested, but presumably the water stress was so severe that the fungus caused much less suppression by comparison. Suneca seedling water potentials were lower than the water potentials of Sunkota seedlings under stress conditions. These results suggest that low seedling water potential predisposes wheat seedlings to colonization and further damage by the fungus.