The Effect of the Common Bunt on the Growth of Wheat Seedlings and Calluses

The growth of wheat (Triticum aestivum L., cv. Zhnitsa) seedlings and calluses infected with spores of common bunt causal agent Tilletia caries (DC) Tul. was studied. Inoculation with the pathogenic fungus enhanced both in vivo and in vitro growth due to cell division activation and cell expansion. These growth characteristics were also retained in wheat calluses infected with T. caries and grown on the hormone-free Murashige and Skoog nutrient medium. This implies the production of hormone-like substances by the fungus itself or by the infected plant. At the phase of fungal penetration into the plants, infection resulted in IAA accumulation in seedlings. Later, the IAA content reduced to a control level and the phytohormone balance was shifted toward cytokinins. Similar changes in the IAA and cytokinin levels were observed during early fungus development on wheat callus tissues. Such a sequence of events is supposed to be required for successful fungal penetration and localization in plant tissues and for the establishment of compatible interactions between the pathogen and the host plant.