STUDIES ON THE GENOME CONSTITUTION OFTRITICUM TIMOPHEEVIZHUK. I. EVIDENCE FOR GENETIC CONTROL OF MEIOTIC IRREGULARITIES IN TETRAPLOID HYBRIDS

Abstract

One line of T. timopheevi was erossed to 79 varieties belonging to several different tetraploid wheat species. Two of these hybrids had regular meiosis, but the remainder had irregular metaphase 1 stages. It was noted that the average numbers of univalents in these hybrids varied from hybrid to hybrid. The extremes were found in hybrids of 2 T. polonicum varieties with T. timopheevi: one had an average of 2.79 univalents, while the other showed an average of 12.06 univalents. The first hybrid regularly formed cells without univalents (14II, 1IV, 12II, or 2III 11II). The Emmer species which induced few univalents and those which induced many univalents in their hybrids with T. timopheevi were intercrossed and their F1''s had regular meioses and good fertility. From these facts and the observation of very regular secondary pairing of almost all univalents in one T. pyramidale X T. timopheevi hybrid, the conclusion was drawn that T. timopheevi possesses, in fact, the AB genomes and that the irregular meiosis in its hybrids was induced by a set of genes specific to T. timopheevi, that partially prevented chiasma formation (desynapsis). A slight asynaptic effect could also have been present. However, the action of these genes was modified by the genotypes of the hybrids, which induced a great range of uni-valent formation. A theory of genetic differentiation as a process of speciation, probably having taken place in the tetraploid progenitor of T. timopheevi, is suggested.