COMBINING MUTATIONS FOR THE 2 HOMOEOLOGOUS PAIRING SUPPRESSOR GENES PH1 AND PH2 IN COMMON WHEAT AND IN HYBRIDS WITH ALIEN TRITICEAE

Two lines of common wheat cv. Chinese Spring, carrying simultaneous mu tations for the two major homoeologous pairing wheat suppressor genes Ph1 and Ph2 have been developed and their pairing behaviour compared w ith that of the ph1b mutant of the same cultivar. Besides carrying the ph1b mutation, the first double mutant line lacked the chromosome arm pair 3DS, containing Ph2, whereas the second had a euploid constituti on and carried the ph2b allele on 3DS. Hybrids of Aegilops variabilis and Secale cereale with mono-5B (ph1b) and 3D/3DL plants have also bee n obtained, where the 3D versus 3DL presence marked the two pairing al ternatives (ph1b only and ph1b + Ph2-, respectively). In the wheat x A e. variabilis hybrids, an 8% increase in total chromosome pairing, alm ost entirely ascribable to an increment of multivalent associations, w as observed in the 2n = 34 + t plants with respect to their 2n = 35 si bs. The number of bivalents showed no significant difference, but a te ndency towards a decrease, which was significant for the rod types, wa s exhibited by the Ph2- plants. A weaker but similar effect was observ ed in wheat itself. The different mutants, in fact, showed a similar p ercentage of paired chromosomes but varied in their pairing pattern. A significant reduction in the number of bivalents, owing to a decrease of the rings, only partly compensated for by an increase of the rods, was observed in the double mutants. They also exhibited an increase i n the multivalent fraction, which was significant for the most complex associations. In both common wheat and its hybrids with Ae. variabili s the addition of a ph2 mutation thus seems to reinforce the ph1b effe ct in promoting homoeologous pairing. On the other hand, such an effec t was not noticed in the wheat x S. cereale hybrids. However, possible quantitative differences could have been masked by the considerable p lant-to-plant variation and potential differences in relative incidenc e of wheat-wheat versus wheat-rye associations were undetectable in th e Feulgen-stained materials analyzed.