Multinucleate condition of Puccinia striiformis in colonies isolated from infected wheat leaves with macerating enzymes

A fluorescence microscopy study was carried out to examine the multinuclear condition in parasitic colonies of one isolate of Puccinia striiformis in leaf tissue of a susceptible wheat. At 5 and 10 days after inoculation, colonies were isolated with macerating enzymes and sequentially stained with 4′-6-diamidino-2-phenylindole and Calcofluor for nuclear counts in the intercellular hyphal cells, haustorium mother cells, and urediniospores. In 10-day-old colonies, more than 98% of the hyphal cells located adjacent to the uredinia were binucleate. Elsewhere in the colonies, the hyphal cells were highly variable in nuclear number; approximately 20% contained two nuclei, 18% contained four, 26% contained six, and 28% contained eight. In 5-day-old colonies, the hyphal cells were also highly variable in nuclear number, regardless of where they were located in the colony. The nuclear condition of haustorium mother cells was less variable; the majority contained either two or four nuclei. All urediniospores examined were binucleate. In the parasitic state, the multinucleate condition apparently occurs only in P. striiformis and not in other cereal rust fungi. Key words: multinucleate condition, stripe rust, Puccinia striiformis, DAPI, Calcofluor.