| Simultaneous development of sets of monosomics, telocentrics
and isosomics for use in intervarietal chromosome substitution in common
wheat1) S. S. MAAN. K. A. LUCKEN, and N.D. WILLIAMS2) The use of telocentric and isosomic stocks minimizes the risk of univalent shift during the backcrossing phase of intervarietal chromosome substitution (SEARS, 1953; PERSON, 1956). It also saves time and effort by eliminating the need for selfing after every backcross (UNRAU et al., 1956). However, these stocks are available only in "Chinese Spring" wheat, and alternate selfing and backcrossing must be done when chromosome substitution is made into other varieties in which only monosomic sets are available. In this paper we outline a procedure for the simultaneous development of monosomic, telosomic and isosomic sets in a recipient variety. The procedure minimizes the risk of univalent shift in developing monosomics, and at the same time transfers telocentrics and isochromosomes to the recipient variety for subsequent use in the intervarietal chromosome substitution. The variety A can be crossed either as male or female with Chinese Spring telosomics or isosomics (MAAN and LUCKEN, 1966). The F1 plants with an isochromosome or a telocentric (2n =42; 20II+heteromorphic pair=20II+HetII) can be crossed as female with pollen from variety A. After each backcross, plants with 2n=20II+HetII can be selected by microscopic examination of the PMC at the first meiotic metaphase and crossed with pollen from variety A. When the desired number of backcrosses have been made, the plants with 2n=20II+HetII are selfed, and individual plants of the progenies are examined for the number and pairing of chromosomes during meiosis. The plants with 2n=41 (20II+1I or 20II+a telocentric or an isochromosome) are selected. If the monosomic is obtained first, the monotelosomic or mono-isosomic can be obtained from the cross of monosomic x a sister plant with 20II+HetII. If the monotelosomic or mono-isosomic is obtained first, the monosomic can be obtained from the cross of monotelosomic or mono-isosomic x variety A. |
| 1) Contribution from the Department of Agronomy, North Dakota State University,
Fargo, North Dakota, in cooperation with the Crops Research Division, Agricultural
Research Service, U. S. Department of Agriculture. Published with the approval
of the Director, North Dakota Agricultural Experiment Station, as Journal
Article No. 88. 2) Assistant Professors of Agronomy, North Dakota State University, and Research Geneticist, Crops Research Division, Agricultural Research Service, U. S. Department of Agriculture, Fargo, North Dakota, USA. |
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