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Production of monosomics in durum wheat
Akira MOCHIZUKI Faculty of Agriculture, Kobe University, Kobe, Japan Since 1959, the author has maintained three different monosomic lines originated from the backcross progeny of alien addition lines of durum wheat. These lines with 27 chromosomes showing 13II+1I at meiosis, are fairly fertile and transmit monosomic condition to selfed progeny. The deficient chromomes of these lines have not been identified yet, but the facts suggest that there are possibilities to have monosomics in tetraploid wheat without compensations of any homoeologous chromosomes. In order to obtain the monosomics in durum wheat, mono- or nullisomics of Triticum aestivum var. Chinese Spring deficient for the A or B genome chromosomes were crossed with T. durum var. Stewart in 1963. After recurrent backcrosses of 34 chromosome F1 plant (13II+8I) with durum in order to eliminate the seven chromosomes of the D genome, monosomic plants (13II+1I) were found in BF2 families of four chromosome lines; 1A, 3A, 4A and 3B (Table. 1). The chromosome numbers of BF1 may vary from 27 to 35 theoretically. No plants with 27 chromosomes were observed in this generation and about five percent of BF1 plants with 28 chromosomes were used for female plants of next backcrossing. These 28 chromosome plants are not distinguished clearly in their appearances but classified into two groups according to their meiotic associations. About 30 to 50 percent of them show 13II+2I, and the rest 14II. The former should be used for the female plant in every backcrossing. One of the two univalent chromosomes of the female came from durum and the other must belong to the D genome. Bivalent or heteromorphic bivalents which are occasionally formed between the two univalent chromosomes suggest that the univalents concerned must be homoeologous and the association may prevent to form nullisomic gametes (13 chromosome gamete). Frequencies of the monosomics in the backcross progeny varied from one to ten percent with the chromosome lines as given in Table 2. Although it increased in the progeny obtained from the backcross durum monosomics by durum, it is still low. However, the frequency will be high in plants obtained from shrivelled seeds. It is reasonable to consider that deficiency of only one chromosome in the tetraploid wheat caused poor development in endosperm formation and this fact is practically useful in examining monosomics. In case of 6A, it is not possible to classify them clearly into two groups: namely shrivelled and plumped seeds. In 1966, new monosomics have been obtained in six other 2A, 5A, 6A, 7A, IB and 6B lines, Consequently the monosomics have been established in all seven lines of the A genome and three lines of the B genome in durum wheat. The monosomic plants show 13II+1I at meiosis and a little weak in seedling stage but set seeds and transmit the monosomic condition to their selfed or backcrossed progeny. There are some variations of the characteristics in each individual of monosomic lines because the substitution of of Chinese Spring chromosomes involved in these monosomics with that of durum are still only partially complete. (Received Feb. 3, 1968) |