The activity of nucleolar organizing chromosomes in multigeneric F-1 hybrids involving wheat, triticale, and tritordeum

The nucleolar activity in interspecific hybrids between tritordeum, wheat, and triticale was studied using the silver salt - nylon technique. rRNA gen es from the major NORs from wheat (chromosome pairs 1B and 6B) and Hordeum chilense (chromosome pairs 5H(ch) and 6H(ch)) were active in genomic consti tutions AABBH(ch)H(ch), AABBH(ch), and AABBDH(ch). The rye chromosome 1R NO R suppression found in triticale and in wheat x rye F-1 hybrids is also obs erved in trigeneric hybrids, genome constitution AABBRH(ch), derived from c rosses between triticale and tritordeum. As expected, the maximum number of NORs per metaphase cell is coincident with the maximum number of nucleoli per interphase cell. Occasional extra nucleolar activity was observed, prob ably owing to minor sites of wheat NORs, since no other sites of active or inactive rRNA genes were detected in H. chilense. However, it is notable th at the two H. chilense loci and two major rDNA loci of wheat origin are exp ressed together.