II. 52. Cytology and breeding behavior of novel compensating diploid plants in barley.
T. Tsuchiya and An Hang. Department of Agronomy, Colorado State University, Fort Collins, Colorado 80523, U.S.A.
The senior author reported the occurrence of a plant with 2n=13+2 telocentric chromosomes (Tsuchiya, 1971), its breeding behavior and the plants with 2n=12+4 telocentrics (2 pairs) derived from the plant with 13 + 2 telos (Tsuchiya, 1973). These plants are tentatively called novel compensating diploids. In this note, the cytology of these novel compensating diploids and their breeding behavior is reported.
The meiotic chromosome configurations were studied in both lines. All 80 microsporocytes analyzed at diakinesis showed 1III + 6II in the plants with 2n=13+2 telos. The trivalents were always associated in the order of telo-complete-telo fashion; the complete chromosome was always in the middle with two telocentric chromosomes associated with both ends. Although all 80 cells analyzed showed 1III + 6II, there were a few cells with 7II + 1I and apparently 6II + 2I among several hundred microsporocytes observed.
The meiotic chromosome configurations were exclusively 8II at diakinesis in the plants with 2n=12+4 telos. Two of 8 bivalents were definitely formed by four telocentric chromosomes and often showed interstitial chiasma. The separation of chromosomes at anaphase I was normal giving rise to gametes with n=6+2 telos in most of the sporocytes.
The breeding behavior was studied in selfing of and reciprocal crosses with normal diploid (2n=14).
In the selfed progeny of the plants with 2n=13+2 telos, the plants with 2n=14, 13+2 telos and 12+4 telos were obtained in approximately a 1:2:1 ratio (38:76:32). In addition to those three chromosomal types, telotrisomic plants (Triplo 1L and Triplo 1S) and plants with 13+3 telos (1 telo 1L+2 telo 1S) were found. In the crosses between these two chromosomal types and 14-chromosome plants, the progenies were mostly 2n=14 or 13+2 telos with 1:1 ratio (Table 1). In the progeny of 13+2 telos x 14, telotrisomic plants were also found (Table 1).
Table 1. Transmission of telocentric chromosomes in two novel compensating diploid lines in barley.
In the progeny of the selfed 12+4 telos, only 12+4 telos were found. The cross 14x12+4 telos produced only 13+2 telos. However, the cross 12+4 telos x 14 segregated two plants with 12+4 telos, although the majority of the plants had 13+2 telos. The origin of two plants with 12+4 telos are not known at present; however, the possibility of selfing from failure of emasculation cannot be ruled out.
The gross morphology of these novel compensating plants was exactly the same as 14-chromosome siblings and normal. This indicates that these two types of novel compensating diploid plants are genetically well balanced.
These compensating diploid plants will be useful in the study of chromosomal evolution and various cytogenetic analyses.
References:
Tsuchiya, T. 1971. Occurrence of a plant with 2n=13+2 telocentric chromosomes in barley. BGN 1:63.
Tsuchiya, T. 1973. A barley strain with 2n+12+4 telocentric chromosomes (2 pairs). Cereal Res. Comm. 1(3):23-24.
