GROWTH OF SUGARCANE DOWNY MILDEW FUNGUS IN TISSUE-CULTURE

Dual culture of sugarcane downy mildew fungus (Sclerospora sacchari Miyake) was established by placing a diseased sugarcane explant (shoot apex or spindle leaf) on a modified Murashige and Skoog medium containing 3 ppm 2,4-D. After 3 wk incubation, dense mycelia grew both on and in the callus which had developed. The use of different varieties or illumination periods did not affect the growth of the fungus. The hyphae ceased to grow when the infected callus was subcultured. A workable procedure was devised which enabled the hyphae to proliferate on a healthy tissue when diseased tissue was placed near it. Explants excised from either resistant or susceptible varieties could nurse the growth of the fungus, indicating that resistant genes may not be expressed in tissue culture. The callus originated from mesophyll cells in leaf and parenchymatous cells of shoot apical tissue. Intercellular and intracellular hyphae were more concentrated in the peripheral layer of parenchymatous cells than in the meristemoid region. Carbohydrate callose accumulated on the hyphal walls and cell walls of the callus wherever hyphae were growing.