[Structural changes in sugar cane buds during infection by the fungus Ustilago Scitaminea]

The structural changes that take place in sugar cane buds during the infection with Ustilago scitaminea were studied. Buds of the cultivars SP79-2312 and NA56-79, resistant and susceptible to this fungus, were inoculated with teliospores of U. scitaminea. They were placed in trays and maintained in darkness at 31 degrees and 80% relative humidity. Thirty buds of each cultivar left without inoculating as controls. The samplings were carried out at 16, 40 and 72 h after inoculation, taking 10 inoculated buds of each cultivar and same number of healthy buds. The tissues were fixed in glutaraldehyde and osmium tetroxide, later they were dehydrated in acetone and embedded in Spurr resin. Semi-fine and ultra-fine transverse sections were prepared, and were observed in light and electron microscopes respectively. It was proven that in spite of having broken the barrier of resistance of SP79-2312, for the inoculation method used, always the development of the fungus in this resistant cultivar was slower than in the susceptible one NA56-79. At 14 h post-inoculation, the fungus was not observed in the resistant cultivar, and it was scarce in the susceptible one. At 40 h an increament in the quantity of hyphaes was noticed and even more at 72 h. The damages in the cellular structure were more drastic from the second sampling, being increased in the last one. The detected alterations were: formation of electrodense granules inside the cells, increament of vacuoles, vesicles and endoplasmic reticulum cisternae, as well as rupture of membranes inside of the cells.