Division of Genetics, Indian Agricultural Research Institute, Delhi-12
1. T. timopheevi system involves two major genes and some modifiers for full fertility restoration of male sterile common wheat.
2. Hexaploid wheat varieties show differential pollen sterility and fertility under two environments, e.g., pots and field, when T. timopheevi cytoplasm and genes for fertility restoration are incorporated into them.
3. Some varieties appear to carry modifiers for fertility restoration which may be of weak or strong action. Development of fertility restoration lines in these varieties is easy since the modifiers appear to be complementary to fertility-restorer genes.
4. The expression of modifiers was manifested in field only and not in pots as in P.V. 18 and Kalyansona. The expression of modifiers is clear both in field and in pots as in N.P. 830, N.P. 875 and Sonalika. The varieties Sharbati Sonora, C. 306, Lerma Rojo, S. 310 and C. 303 either do not carry modifiers or the modifiers are of very weak action.
5. In general, for all varieties the expression of sterility was complete in pots whereas in field complete sterility to full fertility was found when donor parent in the cross involved was highly sterile.
6. If a line is sterile in pot it may or may not be sterile in field depending on the stability of sterility which in turn is dependent on the genetic background of a variety. If a line is fertile in pot, it will invariably be fertile in field also.
Therefore, for quick results, selections for sterility should be done in field and that for fertility in pots.
7. Male sterile and fertility restorer lines can be developed easily in some varieties and with difficulty in others by simultaneous careful manipulation of modifiers, genetic background of a variety, genetic male sterility (genetic male sterility is found in intervarietal crosses particularly which involve dwarf varieties) and right environment and through rigorous selection for sterility or fertility in F1 and subsequent backcross generations.
8. N.P. 830 restorer, N.P. 875 restorer and Sonalika restorer appear to be promising. N.P. 830 is most promising followed by N.P. 875 and Sonalika. Test crosses of these restorers with sterile lines needs to be made to confirm their fertility restoring ability.
9. A large number of wheat varieties may be expected to fall in one of the three classes indicated in the scheme (Table 4 and Table 5). For hybrid wheat, selection of varieties for development of A, B and R lines will be very important. For instance, the varieties, Sharbati Sonora, C. 306 and others in Class I are most suitable for conversion to sterile lines, whereas N.P. 830, N.P. 875 and Sonalika for conversion to fertility restorer lines.
10. Modifiers or partial fertility restoring genes mayhave arisen as a result of simultaneous cytoplasmic and genetic differentiation in the progenitors of T. timopheevi with the selection pressure favouring fertility restoring genes which later introgressed into cultivated wheats over a long period of time.
11. If a source carrying single gene for full fertility restoration can be identified either in common wheat varieties or in some other species or genera, it will be more useful for the development of hybrid wheat. Recently, Oehler and Ingold (1966) reported a commercial variety Primepi carrying a dominant gene for fertility restoration.
