Somatic Nuclear Division inTilletiaSpecies Pathogenic on Wheat

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Abstract
Somatic nuclear division was studied in secondary sporidia and hyphae of T. caries, T. foetida and T. controversa [from wheat, Triticum aestivum] by means of HCl-Giemsa and H3PO4-acetic orcein staining techniques. The morphology of division figures was determined by observing individual nuclei from different perspectives in cells suspended to glycerine. The chromatin in resting nuclei was granular to filamentous; 1 or more dark-staining bodies were observed near the periphery of the nucleus. During sporidia formation, most of the parent cell protoplast migrated into the developing sporidium concomitant with basipetal septation of the parent cell. In the bud cell, the nucleus contracted into an intensely staining spherical mass. The contracted nucleus was transversed by a linear, unstained area (the spindle) that usually was positioned eccentrically and oriented parallel to the long axis of the bud cell. Chromatin separating from the contracted nucleus was in the shape of a cylinder surrounding the unstained spindle. In side view, the chromatin appeared as 2 elongating parallel lines stretching out from the contracted configuration. During chromatin migration, most of the chromatin aggregated on opposing sides of the spindle forming 2 parallel lines which separated transversely as the chromatin aggregated at the poles. The spindle transversed the daughter nuclei giving them a bisected appearance in side view. In polar view, chromatin at the ends of division figures and the daughter nuclei were doughnut-shaped, with the unstained spindle occupying the hole in the doughnut. After division, 1 daughter nucleus returned to the parent cell and usually remained contracted; the other migrated to the distal end of the bud cell and entered an interphase-like condition. Septation occurred between the parent and daughter sporidium and then the parent sporidium usually senesced. The same division process was observed in monokaryotic and dikaryotic sporidia and hyphae of the 3 spp. studied. Chromosomes could not be counted, but these observations cast doubt on previous reports that n = 2 in these Tilletia spp.

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