Genetic diversity of the cytoplasm in Triticum and Aegilops : IV. Distribution of the cytoplasm inducing variegation in common wheat.

Twelve kinds of common wheat nuclei were placed into the cytoplasms of 23 species of Aegilops and Triticum by repeated backcrosses in the Laboratory of Genetics, Kyoto University. Using these nucleus-cytoplasm hybrids, the distribution of the variegation-inducing cytoplasms was investigated. The variegation was maternally inherited, and was found to be temperature-dependent; it was expressed only at low temperatures, accompanied by a remarkable reduction in the content of chlorophyll a and b, and recovered to almost normal level in a greenhouse kept at 25 °C. The variegation was expressed only by special combinations of the wheat nuclei and alien cytoplasms; nine common wheat nuclei, Tve, P168, CS, N26, Slm, Sk, S615, Sphr, and Splt, and six cytoplasms, T. boeoticum, Ae. umbellulata, Ae. triuncialis, Ae. biuncialis, Ae. columaris, and Ae. triaristata 6x, expressed weak to strong variegation in almost all combinations. Combinations of three common wheat nuclei (JF , Comp and Macha) and 17 other cytoplasms showed no variegation: JF , Comp and Macha appeared to have a sort of restoring gene(s) against variegation. Since distribution of the variegation-inducing cytoplasms was confined to the A and C(u) type plasmas, it was assumed that the plasmagene(s) responsible for the variegation originated in the diploid level and was transmitted from Ae. umbellulata to three tetraploid and one hexaploid species of Polyeides section through the process of amphidiploidization.