EFFECT OF COLONIZATION BY A STERILE RED FUNGUS ON VIABILITY OF SEED AND GROWTH AND ANATOMY OF WHEAT ROOTS

Invasion patterns of the sterile red fungus (SRF) into tissues of seminal roots of wheat were examined 4, 8 and 10 d after inoculation. At 4 d, 2·7% of the cortical cells were free of the fungus (category A), 16·2% had 1–50% (category B) and 81·1%, 50–100% (category C) of the cell lumen filled by hyphae. The percentage of cortical cells in category C increased at 8 and 20 d, with a concurrent decrease in categories B and A. Most cells within the stele were free of the fungus, especially at 4 and 8 d. Even when they were found within stelar tissues they were only at low densities. The thickness of the walls of endodermis was not affected by the presence of the SRF. The SRF colonized wheat seeds without affecting their viability. The SRF was recovered at a greater proportion from seeds incubated with the fungus for 12 h than for 8 or 10 h, although some reduction in the viability was noted with seeds incubated for 12 h. Wheat seeds exposed to the SRF for 8, 10 and 12 h germinated more rapidly than untreated seeds, the seeds incubated for 10 h showing the best effect. Forty eight hours after planting there was no difference evident in the germination percentage among seeds inoculated for 8 h, 10 h and the control treatment. The SRF or its exudate increased the shoot and root weights and root length compared to the control. The SRF also increased the diameter of wheat roots which was not affected by the exudate. The root length, however, was greater in the exudate treatment than in the treatment receiving the fungus. © 1990, British Mycological Society. All rights reserved.