Chromosomal variation in the Lindström strain of wheat carrying accessory chromosomes of rye

Abstract

In the Lindstrom strain of wheat B chromosomes from the variety Transbaikal of rye coexist without difficulty with the wheat chromosomes. In progenies of plants with 4 B chromosomes of the standard type a marked variation was obtained, the number of B chromosomes ranging from 0 to 10. In the offsrping from plants with 2 B chromosomes the range of variation was from 0 to 6. There are two causes of this variation – occurrence of univalent B chromosomes in meiosis and non-disjunction of the B chromosomes at the first pollen mitosis and at the corresponding stage in the ovules. Definite evidence of nondisjunction was obtained from reciprocal hybrids between individuals with 0 and 2 B chromosomes. This non-disjunction, which is characteristic of the B chromosomes in rye and is thus retained in the Lindstrom strain leads to an average increase in B chromosome number in the offspring and to a preponderance of even over odd numbers of B chromosomes. However, the rate of numerical increase is much lower in the Lindstrom strain than in Transbaikal rye. This difference is exclusively or primarily due to a lower rate of meiotic pairing of the B chromosomes in the Lindstrom strain than in the Transbaikal rye. The poor pairing of the B chromosomes in the Lindstrom strain must be caused by a disturbing effect of the wheat chromosomes or the wheat cytoplasm.