| Chromosome pairing at diakinesis in hexaploid Triticale1)
T. TSUCHIYA2) Department of Plant Science, University of Manitoba, Canada Previous studies of chromosome association were made almost exclusively at metaphase I of microsporocytes in hexaploid Triticale (NAKAJIMA 1952, 1956, 1963, NAKAJIMA and ZENNYOZI 1966, SANCHEZ-MONGE 1959). The present author, during the study of meiosis in some hexaploid Triticale, was able to make excellent preparations of diakinesis cells. These preparations of chromosome configurations at diakinesis were found to be the source of valuable information on the nature of chromosome pairing in the hexaploid Triticale. The materials were plants of the primary Triticale (6A 190) from the following cross: T. durum var. Stewart x S. cereale var. Prolific. Experimental materials were grown in the growth cabinet with the temperature of about 20C and 16 hr. daylight time. Table 1 shows chromosome configurations at diakinesis and metaphase I. From this table it was shown that 87% of the sporocytes had 21 bivalents at diakinesis while it was 59% at MI. The number of bivalents per sporocyte was 20.83 at diakinesis and 20.42 at MI. The number of univalents per sporocyte was 0.34 at diakinesis and 1.16 at MI. At diakinesis more closed bivalents were observed than at MI as shown in Table 2. As is clearly seen in the Figure on the cover, most of the bivalents were closed ones associated by two chiasmata. Some bivalents, however, were not tightly associated; the homologous chromosomes seemed to be laid side by side without connection by true chiasma. Usually one nucleolus was observed which was tightly attached by two bivalents. Occasionally two nucleoli were observed at this stage. At metaphase I the frequency of sporocytes with 21 bivalents, the number of bivalents per sporocyte, and the number of closed bivalents were reduced to 59%, 20.4, and 15.6. respectively. The number of univalents per sporocyte and open bivalents per sporocyte was increased (Table 2). Mean number of chromosomes consisting of open bivalents and univalents was about 12.0 at metaphase I, while the corresponding figure was only 3.0 at diakinesis. These results show that most of the open bivalents and univalents at metaphase I of hexaploid Triticale resulted from desynapsis or terminalization of chiasmata occuring in most rye chromosome bivalents after diakinesis. Since most univalents at metaphase I of octoploid Triticale were also originated from rye chromosomes (MUNTZING 1957. SANCHEZ-MONGE 1959), it would be reasonable to assume that the chromosome associations at diakinesis would be better than at metaphase I in octoploid Triticale. Literature Cited MUNTZING, A. 1957. Proc. Intern. Genet. Symp. Tokyo and Kyoto (Cytologia. Suppl. Vol.) : 51-56. NAKAJIMA, G. 1952. Bot. Mag. (Tokyo) 65: 288-294. NAKAJIMA, G. 1956. La Kromosomo 27-28: 973-986. NAKAJIMA, G. 1963. La Kromosomo 55-56: 1829-1850. NAKAJIMA, G. and A. ZENNYOZI 1966. Seiken Zihd 18 : 39-48. SANCHEZ- MONGE, E. 1959. Proc. 1st Intern. Wheat Genet. Symp.: 181-194. (Received April 21, 1970) |
| 1) This work was supported by research grants from the Rockefeller Foundation
(RF 65019) and the National Research Council of Canada. 2) Presently, Associate Professor of Department of Agronomy, Colorado State University, Fort Collins, Colorado, 80521, U.S.A. |