| Specific interaction between the D genome and the three
alien cytoplasms in wheat M. MURATA and S. TSUJI Laboratory of Genetics, Faculty of Agriculture Kyoto University, Kyoto, Japan KIHARA (1973) reported that emmer wheat (AABB) with the cytoplasm of Aegilops squarrosa (DD) is very weak and highly male sterile. Since common wheat (AABBDD) with this cytoplasm shows high fertility and normal growth, his results imply that the D genome should have the restoring genes to the squarrosa cytoplasm for both growth vigor and male fertility. Moreover, common wheat with the cytoplasms of Ae. cylindrica (CCDD) or Ae. crassa (DDD2D2McrMcr) also manifests high fertility and normal growth. It is thus concluded that the cytoplasm of both species is derived from Ae. squarrosa (TSUJI and TSUNEWAKI 1974, MURATA and TSUNEWAKI 1975). From this conclusion, we can expect the same kind of nucleo-cytoplasmic interactions between the nuclei of emmer or common wheat and the cytoplasms of Ae. cylindrica and Ae. crassa as that found between these wheats and the squarrosa cytoplasm. We, therefore, started to analyze the specific interactions between the D-genome and the cytoplasms of the above three species having D-genome in common, in the following two ways : (1) Removal of the D-genome from common wheat with each of the three alien cytoplasms, and (2) production of the aneuploid series of D-genome chromosome in common wheat with the alien cytoplasm. Although these works have not yet been completed, their outlines and the results so far obtained are reported here. Materials used are the three alien cytoplasm substitution lines of Triticum aestivum cv. Chinese Spring (CS in abbrev.). The first approach will be carried out by the successive backcrosses with emmer wheat. In the spring of 1975, F1 pentaploid hybrids (AABBD) between the three cytoplasm substitution lines of CS and T. durum var. melanopus were produced and investigated (Fig. 1). Selfed seed fertilities of the hybrids (5x) and of the corresponding cytoplasm substitution lines (6x) are given in Table 1. The pentaploids with the three alien cytoplasms manifested considerably reduced fertilities as compared with the reciprocal hybrids between normal CS and T. durum var. melanopus. All three cytoplasms clearly showed the same pattern of response. This confirms that these three cytoplasms are similar to one another. In the second approach, it is attempted to produce mono-, nullitetra- and ditelosomics of the cytoplasm substitution lines of CS, only for D-genome chromosomes. Although MAAN and LUCKEN (1967, 1968) has produced the monosomics with the T. timopheevi cytoplasm by crossing ms-Bison with monoiso- and monotelosomics as the male parent, we adopted a different method. In the spring of 1974, three cytoplasm substitution lines of CS were first crossed with the nullitetrasomic series (male) , resulting in the monotrisomics (19II+ 1I + 1III) with three alien cytoplasms. All monotrisomic plants investigated in 1975 were highly fertile and vigorous in spite of the deficiency of one D-chromosome (Table 2). When the monotrisomics are backcrossed with nullitetrasomics, we can find the nullitetrasomics among the offspring. At the same time, when they are crossed with normal CS (male), three types of the segregants, i.e., 41-, 42- and 43-chromosome individuals, will be obtained. The 41-chromosome plants of each line are expected to be the monosomics of a D-genome chromosome. If the female transmission rates of the univalent and an extrachromosome of the trivalent in the monotrisomics are assumed to be 25% and 40%, respectively (SEARS 1944, 1953), we can expect the ratio of the three segregants to be 9: 9: 2. Their frequencies were investigated in a small population (Table 3). The segregation ratio observed fitted fairly well to the expected one, and about a half of the offspring was the monosomic which we wanted to obtain. It, therefore, can be said that this method is available for production of the monosomic series with an alien cytoplasm. The data on the pentaploids indicate that the restoring genes for fertility and plant vigor to the three cytoplasms exist in the D-genome of common wheat. From the results given in Table 2, it seems probable that the fertility restoration to each alien cytoplasm is controlled by multiple factors rather than by a single dominant factor, because no single line of the monotrisomics showed clear reduction of fertility. Although the monosomic lines obtained by our method might also give the same results as the monotrisomics did for fertility, these lines will be useful in studying the specific nucleo-cytoplasmic interactions, e.g., by crossing them with other lines such as ditelosomics of CS or emmer wheat. (Received Sept. 25, 1975) |