| Monosomic analysis of a fertility-restoring gene in
Triticum spelta var. dahamelianum1) CH. M. TAHIR and K. TSUNEWAKI Laboratory of Genetics, Faculty of Agriculture, Kyoto University, Kyoto, Japan KIHARA and TSUNEWAKI (1967) reported T. spelta var. duhamelianum as an effective fertility-restorer, which restored in F1 the fertility of a male-sterile wheat with timopheevi cytoplasm completely. This particular variety of T. spelta was studied in the present investigation by monosomic analysis to clarify the fertility-restoration mechanism. For this analysis, a modified method of monosomic analysis was employed as follows: T. spelta var. duhamelianum was crossed as male parent to the 21 monosomic lines of Chinese Spring. At least two monosomic F1 plants were cytologically selected in each line. At the same time some disomic F1 plants were also isolated as the control material. Those monosomic and disomic F1 plants were crossed as the pollen parent to male-sterile line of T. aestivum cultivar Bison with timopheevi cytoplasm (hereafter expressed by (timopheevi) Bison); at least eight spikes were pollinated in each line. The seeds of all the 21 monosomic as well as disomic families of the crosses were sown in flats, and seedlings produced were transplanted to field. At the time of head emergence three spikes in each plant were covered with paraffin paper bags before anthesis to prevent cross-pollination. All the bagged spikes were harvested separately at the time of maturity, and their selfed seed fertility was estimated from the number of fully developed first and second florets and that of seeds set in them. Although about 5% of all plants from the test-cross were semi-sterile (seed setting rate was 1 -20%), a great majority of plants could be classified into two classes, completely sterile (seed set 0%) and fertile (21-100%). Including the semi-steriles in the fertile class, segregation of the sterile and fertile plants in each di- and monosomic family was tested to fit 1:1 ratio, the result being given in Table 1. Since the disomic family gave the 1:1 ratio, and both Bison and Chinese Spring with the timopheevi cytoplasm were completely sterile under our experimental condition, it is concluded that a single dominant gene of T. spelta var. duhamelianum is responsible for the fertility-restoration. Of the 21 monosomic families tested, 19 satisfied the 1:1 ratio; this fact indicates that neither of the 19 chromosomes monosomic in these families carries the fertility-restoring gene. A significant deviation from the 1:1 ratio, with much less sterile and excessive fertile plants, was observed in mono-1B. Their ratio was close to 96 fertile vs. 4 sterile, that is expected in a critical monosomic family, whose monosomic chromosome carries the fertility-restoring gene. This indicates that chromosome 1B of T. spelta var. duhamelianum carries the single dominant fertility-restoring gene. Distortion of the segregation ratio in mono-7D was reverse to that of mono-1B; in this family sterile plants were in excess as compared to fertile ones. |
| 1) This work has been supported by a Grant-in-Aid from the Ministry of Agriculture and Forestry. |
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