| Homology of chromosomes of Aegilops caudata
with common wheat M. MURAMATSU Curtis Hall, University of Missouri, Columbia, Missouri, U.S.A. In a study of some of Kihara's derivatives of crosses between Aegilops caudata and Triticum aestivum, it was desired to learn to what extent the chromosomes of Ae. caudata are homologous with those of T. aestivum. Since Okamoto (1957), Riley and Chapman (1958), and Riley, Chapman and Kimber (1959) have shown that pairing of homoeologous chromosomes is greater in the absence of chromosome V of T. aestivum, hybrids of Ae. caudata were made to monosomic V (variety Chinese Spring) as well as to monotelo XVII Chinese. An F1 plant deficient for chromosome V (27 chromosomes) was compared with another carrying telo XVII (28 chromosomes). The plant lacking chromosome V showed much more chromosome conjugation (Table 1). Since Ae. caudata has three acrocentric (i-type) chromosomes, it is possible to identify the bivalent which include them. It is also possible, with somewhat greater difficulty, to identify the bivalents which include the J-type chromosomes of Ae. caudata. These five chromosomes apparently pair with fairly high frequency. Chromosome XVII has been identified as corresponding to the satellited caudata chromosome which was introduced into common wheat by Kihara. In the F1 hybrid between a strain of monotelo XVII and Ae. caudata, it is frequently possible to identify the telo XVII. 63 cells were checked, and 19 of them were considered to have a heteromorphic bivalent involving telo XVII. These results show that at least six of the caudata chromosome have considerable homology with wheat chromosomes. The amount of pairing is comparable to that which has been observed in diploid hybrids involving the genomes concerned. In T. aegilopoides x Ae. caudata up to seven bivalents have been found, and in Ae. caudata x Ae. squarrosa up to 13 of the 14 chromosomes can be included in pairing (Sears 1941). Thus the reduced pairing in the normal aestivum-caudata hybrid must be due wholly or in large part to the effect of chromosome V. Riley and Chapman found up to 19 chromosomes conjugated in a nullihaploid of Holdfast. Indications are that the chromosomes of Ae. caudata have virtually as much homology with these genomes A, B, and D as the T. aestivum chromosomes have among themselves. |