Author: S.H. Wu, C. K. Tsai, C.C. Wang and H.M. Wang
J Integr Plant Biol 1961, 9 (3): -.
1.The present work comprises a study of 22 hybrid lines in different generations of 15 varieties of cultivated rice crossed with kaoliang and cytological studies of certain progenies of the so-called hybrids. The seed of the hybrids were obtained from several sources and the hybrid plants were grown with their parents under the same environmental conditions. 2. All the so-called hybrid plants, in general, bear a close resemblance to the female parent. However, the F1 plants of some cross combinations show distinct variations in certain characters, such as height, color, fructification, and especially the form of spike and grains. Variations may occur in F2 generation instead of F1, or even still later generations of other cross combinations. 3. As compared to the female parent, the so-called hybrids are usually taller, give smaller number of tillers, show higher vigor of growth and earlier earing, but in other cases, some of the hybrids may have a tendency of late maturity. 4. The hybrids of rice and kaoliang often possess many desirable characters for the rice breeder, for instance, healthy tillers, large leaves, strict culms, good fructification and high resistance to disease. However, the sterility of the hybrids from different cross combinations varies greatly. 5. The segregation of F2 plants raised from different cross combinations is not the same. In some cases, there may be only a single plant of the F2 generation differing from the others, in other cases, the segregation may be so sharp that the F2 plants can be easily classified into 4 distinct types, namely: the tall purple (color of leaf sheath and leaf ring), tall white, dwarf purple and dwarf white, and in the third cases, the plants of the F2 generation may show even more complicate combinations of variable characters and it is difficult to classify them into distinct types. 6. Cytological studies of 12 hybrid lines of the cross combinations mentioned above were carried out. In all the hybrid plants observed, the chromosome number is essentially the same as that of the rice plant, that is n=12, while chromosome number other than n=12 is only found in rare cases. As a result of the recent progress in cytological studies of the rice-kaoliang hybrids, a number of minute variations of chromosome morphology were found in addition to the size dif- ferences as reported in our previous paper. For instance, there are “v”- and “-” aped chromosomes in diakinesis, and also one of the diakinetic chromosomes bears satellite-like structures which were not described before. Moreover, there are one or rarely two chromosomes that retain their diskinetic forms while the others are transformed into the form of metaphase chromosomes. 7. Various abnormalities in meiosis generally applied to diagnose hybrid were observed also in these hybrids, such as, laggards or premature of separation of chromosomes, formation of chromosome bridges, binucleate microsporocytes, microsporocytes with two spindles or multipolar spindles, formation of cyncytes and other irregularities. However, the frequency of these abnormalities is lower than it has been reported in the hybrids of other plants. It should be pointed out that all the abnormalities in meiosis described here were observed in fertile plants. The cytological features of the sterile hybrids of rice and kaoliang will be studied later. 8. The most conspicuous characters in the microsporocytes of the socalled hybrids are as follows: 2n microsporocytes were common, a multinucleolar stage, or in other cases, a number of small chromatin granules were always met with in diakinesis, in the cytoplasm of the primary and secondary microsporocytes many dark-stained granules in different sizes were observed. The staining reaction of these granules is the same as that of the nucleolus. It is assumed that these features might bear an important biological significance in the hybridization of rice and kaoliang. 9. It is pointed out that histochemical and cytochemical studies of the hybrids compared with their parents are in urgent need for solving the problems dealing with hybridization of rice and kaoliang.