Studies on Restoration and Substitution of Nucleus in Aegilotricum

I. Appearance of male-sterile durum in substitution crosses

Abstract

Exchange of nucleus by means of successive backcrosses to both parents has been carried out in an experiment with Tschermak's amphidiploid hybrid _??_ Aegilops ovata×Triticubr durum, known under the name of Aegilotricum.
In the restoration backcrosses to Ae. ovata the process of restoring the ovata genomes to the ovata plasma has been accomplished in the course of three successive crosses. The final offspring were morphologically similar to Ae. ovata, had 14 bivalents at first metaphase and normal anthers filled with functional, good pollen.
In the substitution backcrosses of Aegilotricum to T. durum, the three successive crosses resulted in durum plants with ovata plasma. They had at first metaphase 14 completely paired bivalents; the tetrad formation was normal but later all pollen was degenerating, and the small dry anthers contained empty pollen. However, the female organs were fully functional and seed setting by artificial pollination with durum or dicoccum pollen was normal. The male sterility was transmitted to the next generation by the mother.
Similar pollen degeneration was observed in normal T. durum which have matured in winter after vernalization and long-day treatments.
It is further to be noticed that durum plants with ovata plasma having extra chromosomes of Ae. ovata as univalents in addition to the 14 duram bivalents were only partially male-sterile. Especially, a 29-chromosome plant showed a very high pollen fertility of 92%.