| Effect of B chromosomes on chiasma frequency of A chromosomes
in rye Yukio TSUMOTO and Mutsuo SASAKI Faculty of Agriculture, Tottori University, Tottori, Japan It has been reported that the variation in chiasma frequency of A chromosomes among PMC's increases with the increase of B chromosome frequency in rye (JONES and REES 1969). In this connection two different inbred rye lines with B chromosomes from the same origin were cytologically studied. The plants examined in this report were F2 progenies of the B4F1 with 2B chromosomes for inbred rye line 10 (IR 10) and of the B3F1 with 2B chromosomes for inbred rye line 14 (IR 14). Using IR 10 and IR 14 from MuNTZING, and the B chromosome of standard type from KISHIKAWA (1965), as the original materials, these two lines were developed following the procedures below. (1) Cross a certain inbred rye line, say A line, with a rye line having B chromosomes. (2) Backcross A line repeatedly to the hybrids to get B1F1, B2F1 and so on after selecting the plant, as a female parent, which is being apparently like the A line and checking for B chromosomes at each generation. In Table 1 are presented the chiasma frequencies converted to the frequencies of failures in chiasma formation of A chromosomes per cell at metaphase I of meiosis of PMC's in those IR 10 and IR 14 lines with various number of B chromosomes. In taking the data on the chiasma frequency a rod bivalent was treated as having 1 chiasma and a ring bivalent 2 and ca. 50 cells per plant were checked with some exceptions. As for the IR 10 series the modes of chiasma frequency of A chromosomes per cell in IR 10, recurrent parent, and B4F1 plants with 0 B, 2 B, 3 B, and 4 B chromosomes, were 13, 13, 11, 12, and 11, respectively. As for the IR 14 series, on the other hand, those in IR 14, recurrent parent, and B3F2 plants with 0 B, 1 B, 2 B, and 4 B chromosomes were 13, 13, 13, 14 and 14, respectively. Thus it is apparently clear that the more the number of B chromosomes, the less the number of chiasmata of A chromosomes per cell in the genetic background of IR 10, while the more the former the more the latter in the genetic background of IR 14. This tendency is also clearly seen on the mean chiasma frequency per cell. In addition the variance of the chiasma frequency calculated here as the variance of the number of failures in chiasma formation, providing these data follow the Poisson distribution, increased with increasing B chromosome numbers in the IR 10 series, whereas it decreased in the IR 14 series. From the above mentioned results it is quite apparent in rye that the influence of B chromosomes on the mean and the variance of the chiasma frequency of A chromosomes is dependent on what kinds of inbred lines are used as a genetic background where B chromosomes are introduced. And it seems to suggest that the genetic effect of B chromosomes is not only additive. Heading date did not differ much among the plants with various numbers of B chromosomes. However, the pollen and seed fertilities decreased proportionally with the increase of B chromosomes. The meiotic behavior of B chromosomes was as regular as it was in the report by KISHIKAWA (1965). Literature cited JONES, R. N. and H. REES 1969. An anomalous variation due to B chromosomes in rye. Heredity 24: 265-271. KISHIKAWA, H. 1965. Cytogenetic studies of B chromosomes in rye, Secale cereale L., in Japan. Agri.Bull. Saga Univ. 21: 1-81. (Received January 31, 1971) |