304 Cytologia 35

Cytogenetic Studies of officinalis Complex III. The genomic constitution of O. punctata and O. eichingeri

Chao-Hwa Hu

Taiwan Provincial Chung-Hsing University, Taichung, Taiwan, Republic of China

Received March 3, 1969

Oryza punctata Kostchy ex Steud. and O. eichingeri Peter are both indigenous to Africa. According to Tateoka (1965a, b), O. punctata com prises diploid (2n=24) and tetraploid (2n=48) forms having similar character istics, while O. eichingeri is diploid. The present writer asserted the genome of tetraploid forms of O. punctata to be BBCC (the same as for O. minuta), though it is differentiated from that of minuta by translocation (Hu and Chang 1965a). The eichingeri strains (W0015, W0043) formerly used by Morinaga and Kuriyama (1960), Nezu et al. (1960) and Li et al. (1962) for genomic studies were re-identified by Tateoka (1965a) to be tetraploid forms of O. punctata. Thus, the genomes of O. eichingeri and diploid O. punctata have not yet been determined. Recently, Sampath (1966; also presented an exhibit at XII International Congress of Genetics, Tokyo, 1968), basing on morphology, assumed that the B genome is present in diploid eichingeri forms. However, Katayama (1967) successfully crossed a diploid punctata strain (W1514) with O. minuta, but it failed to produce hybrids in crosses with O. officinalis. In the punctata-minuta hybrids, he observed 12 bivalents and 12 univalents. In another cross between a diploid and a tetraploid strain of O. punctata, Katayama also found 12 bivalents and 12 univalents. He then considered that the diploid punctata has the B genome. To determine the genomes of the above species, the writer obtained genetic stocks belonging to punctata and eichingeri from the International Rice Research Institute (IRRI), , and also from the National Institute of Genetics (NIG), Japan. Most of these strain had been studied taxonomi cally by Tateoka (1962, 1965a, b). Observations of these living and their hybrids showed that one of the eichingeri strains was tetraploid and that the genomes of diploid and tetraploid eichingeri forms might be CC and BBCC, respectively. But the genome of diploid O. punctata could not be clearly distinguished to be B or C.

Materials and methods Living plants of 14 strains belonging to O. punctata and O. eichingeri obtained from the above two institutions were grown in an isolated green-house 1970 Cytogenetic Studies of Oryza officinalis Complex III 305

of Chung-Hsing University, Taichung. The plants used for the present study

are described in Table 1. In addition to the above, the Oryza species used for the crossings were

an officinalis strain (W002, from Bangkok, Tailand), a minuta strain (W0045,

from Philippines), a latifolia strain (CR-2, from Costa Rica), and two sativa

strains (KT and T.65 from Taiwan). Emasculation was made by hot water treatment (43•Ž for 7 minutes)

before natural flowering (about 5 AM). When the F, seeds did not develop

well, the embryos were cultured on White's medium. For cytological observations, young panicles were fixed in Farmer's

solution, to which a trace of ferric chloride was added. The pollen mother

cells were studied by the aceto-carmine smearing method.

Observations 1. Chromosome number and characters of punctata and eichingeri strains Chromosome counts of the strains studied are given in Table 1. As already mentioned, Tateoka (1965b) considered that O. eichingeri is diploid. But a strain, W1524, which showed typical characteristics of eichingeri, was

Table 1. Strains of O. punctata and O. eichingeri observed and their chromosome number

* Used by Hu and Chang (1965a). ** Identified by Tateoka (1965a) . *** Species identification and chromosome number were first studied by the present writer. tetraploid. All the plants observed showed no particular disturbance in chromosome pairing, though in some of the pollen mother cells a few uni 306 Chao-Hwa Hu Cytologia 35

valents or a few bivalents showing early anaphasic separation appeared. Two strains (W1525 and W1527) which are intermediates between punctata and eichingeri showed no meiotic irregularity. All these strains had high pollen and ovule fertilities. Since O. punctata and O. eichingeri have similar morphological features, diploid and tetraploid were thought taxonomically undistinguishable (Tateoka 1965a). However, several characters of living plants were useful in dis tinguishing one from the other. As shown in Table 2, punctata had longer

Table 2. Identification of O. punctata and O. eichingeri

spikelets than eichingeri, and in both species, the tetraploid strains had smaller spikelets than the diploid strains. The acute and narrow triangular sterile glumes were a good criterion to distinguish eichingeri from punctata. Further, the fertile glumes (lemma and palea) of eichingeri strains were smooth, thin 1970 Cytogenetic Studies of Oryza officinalis Complex III 307 and crumbly when pressed by the fingers, but those of punctata were not. They may also be distinguished by plant morphology. As shown in Figure 1, a diploid punctata strain (W1514) had erect tillers and was tall, while an eichingeir diploid strain (101424) had spreading tillers, elongated lower internodes showing as umbelliferous form at heading. The diploid plants of both species could be distinguished from officinalis strains. The officinalis strains (e.g. W002) had many unelon gated internodes excepted on the flowering culms. But differences between tetraploid punctata and tetra ploid eichingeri were minor. Figure 2 shows a punctata tetraploid plant (W0015) having spreading tillers and an eichingeri tetra ploid (W1524) showing an um belliferous form. The latter was similar to the small size plant of O. minuta (W0045). The culm of punc tata was spongy and wrapped by the leaf-sheath, and that of eichin geri was slender, stiff and exposed. Figs. 1-2. 1, plant types of diploid of O. officinalis (W002), O. The writer eichingeri (101424) and O. punctata (W1514). 2, plant types of has observed ten tetraploid of O. minuta (W0045), O. eichingeri (W1524) and O. punctata (W0015). punctata strains, two eichingeri strains and two intermediates of punctata-eichingeri. Variations among punctata strains were found as follows: Strain W1515 was of short stature, while 101434 had a median height and semi-spreading tillers, though they were collected from the same natural population. Strain W1514 was tall, erect and had relatively long ligules. The tetraploid strains W0015 and 308 Chao-Hwa Hu Cytologia 35

W0043 both were yellowish green and tillers spreaded at 45•‹, while strains

W1023 and W1024 had dark-green and semi-spreading tillers. Differences in anthocyanin coloration were also found among diploid strains of O. punctata.

2. Hybrids between O. punctata and O. eichingeri

A total of 11 species crosses (including one reciprocal) were made, except two due to formation of restitution nuclei in meiosis, as shown in Tables 3 to 6. In each cross combination where several F,s were grown, the plant morphology and pattern of chromosome pairing among plants were found to be similar. The behavior of chromosomes observed at metaphase I of pollen mother cells is given in Tables 3, 5 and 6.

Table 3. Pairing of chromosomes at metaphase I in diploids of officinalis•~eichingeri,

punctata•~eichingeri, and intermediates of punctata-eichingeri

1. 2X•~2X hybrids

Three cross combinations were observed, in comparison with the two intermediate punctata-eichingeri strains (Table 3). In the F, plants of O. officinalis (W002)•~O. eichingeri (101424) and its reciprocal, 12 bivalents were found in most of the pollen mother cells. This suggests that diploid eichingeri and diploid officinalis forms might have similar genomes. But, the hybrids produced sterile pollen grains and no seed. A punctata strain (101434) and an eichingeri strain (101424) showed in their hybrid, a maximum of seven bivalents with a mean of 2.23, and the plant was completely sterile. The F, plants between O. punctata and O. eichingeri showed combined two species characters or intermediate features 1970 Cytogenetic Studies of Oryza officinalis Complex III 309 distinguishing the two species. Their characters were then compared with those of the intermediate punctata-eichingeri strains (W1525 and W1527). The F1 and the intermediate plants showed no significant differences in the size of spikelets, but differences were found in awn length and shape, sterile lemmas, branches of panicle, plant stature, etc. as given in Table 4. The intermediate strain W1525 has punctata glumes while W1527 shows eichingeri crumbly glumes. Both strains showing a high fertility, do not seem to be natural F1 hybrids between two species.

Table 4. Comparison of a diploid Fi hybrid and natural intermediates of punctata and eichingeri

2. 4X•~2X hybrids

In the triploids between punctata, eichingeri, minuta and latifolia

(W0045•~101434, W0045•~W1514, W1524•~W1514, CR-2•~101424 and CR-2•~101434), the majority of observed PMC's showed 12 bivalents and

12 univalents, except for the last one (CR-2•~101434) which showed six

bivalents at maximum. The frequence of cells with different chromosome 310 Chao-Hwa Hu Cytologia 35

configurations in the above five cross combinations are given in Table 5. The formation of 12 bivalents suggests that the genome of diploid punctata is homologous with one of the two genomes (BC) of O. minuta. In the same

Figs. 3-8. Diploid hybrids. All are shown metaphase I of pollen mother cells of F1 hybrids. 3, O. officinalis (W002)•~O. eichingeri (101424) 1211. 4 and 5, O. punctata (101434)•~O. eichingeri (101424) 24I and 4II+16I. 6, O. sativa (KT)•~O. eichingeri (101424) 2II+20I. 7 and 8, O. sativa (T.65)•~O. punctata (W1514) 7II+10I and 8II+8I.

manner, the tetraploid eichingeri had the genome of diploid punctata. When the plants of O. latifolia (CR-2) with genomes CCDD were crossed eichingeri 1970 Cytogenetic Studies of Oryza officinalis Complex III 311

(101424) and punctata (101434), maximum pairing was 12 bivalents in the Fl plants of the first cross, and the latter (101434) showed six bivalents, the mean being 2.0. This suggests that the genome of diploid eichingeri was

Figs. 9-15. Triploid hybrids. 9 and 10, O. eichingeri (W1524)•~O. punctata (W1514)

9II+1III+1Iv+11I and 5II+2III+1Iv+16I. 11, O. minuta (W0045)•~O. punctata (101434) 12II+12J. 12 and 13, O. latifolia (CR-2)•~O. punctata (101434) 5II+26I and 1II+34I. 14 and 15, O. minuta (W0045)•~O. eichingeri (101424), a relatively normal cell forming 10 bivalents

and 16 univalents (Fig. 14), and formation of restitution nucleus (Fig. 15). 312 Chao-Hwa Hu Cytologia 35

Table 5. Pairing of chromosomes at metaphase I in triploid hybrids of punctata and eichingeri

Table 6. Pairing of chromosomes at metaphase I in tetraploid eichingeri (W1524) and its hybrid with O. minuta 1970 Cytogenetic Studies of Oryza officinalis Complex III 313

present in the O. latifolia, but the punctata only had a partial homology to the genomes of O. latifolia. Besides the above, multivalents and more than

12 bivalents, e. g. chromosome configuration of 12II+1IV+8I, 12II+1III+9I and 13II+10I, were also found in some cells. This suggests the present of homoelogous chromosomes in the genome and translocation difference between the genomes of the species. In addition to the above normal bivalent formation, the F1 plants of latifolia (CR-2)•~eichingeri (101424) frequently showed irregular meitoic behavior of the chromosomes, e. g. short spindles, chromosomes contracted in

the center of cell (Fig. 15), and tends to formation of a restitution nucleus.

These phenomena particularly were found in the F1s of minuta (W0045)•~

eichingeri (101424). In a few cells, the pairing was relatively regular, and

in one of them formed ten bivalents with 16 univalents (Fig. 14). This

indicates that one of the two genomes of O. minuta (W0045) may be homolo

gous with the genome in diploid eichingeri (101424).

Figs. 16-19. Tetraploid hybrids. 16 and 17, O. eichingeri (W1524)•~O. minuta (W0045) 24II. 18 and 19, O. latifolia (CR-2)•~O. eichingeri (W1524). Formation of restitution nuclei, short spindles with 6 bivalents (Fig. 18) and 36 univalents (Fig. 19).

3. 4X•~4X hybrids

The two tetraploid hybrids, eichingeri (W1524)•~minuta (W0045), and latifolia (CR-2)•~eichingeri (W1524), showed different features in meiosis.

The former cross showed 24 bivalents at both diakinesis and metaphase I 314 Chao-Hwa Hu Cytologia 35

(Figs. 16 and 17; Table 6). The formation of pollen grains and seed setting was also normal. The F1 plants appeared to be intermediate between the two parents. This indicates that the genomes of tetraploid eichingeri (W1524) are homologous with those of O. minuta (W0045). They may have the

BBCC genomes in common. In contrast, in the Fl plants of latifolia (CR-2)•~

eichingeri (W1524), irregular meiotic behavior was similar to that of minuta eichingeri hybrid to form restitution nuclei. Although these two species were considered to have genome C in common, but pairing was disturbed and few bivalents were found (Figs. 18 and 19).

Table 7. Pairing of chromosomes at metaphase I of Fl plants of O. sativa•~O. eichingeri and O. sativa•~O. punctata

The formation of restitution nuclei in Oryza has been found in the F,

of sativa•~officinalis, and discussed by Li et al. (1964). In the present study

there was no such restitution nucleus in the diploid hybrid of eichingeri•~

punctata but found such in their tri- and tetraploid hybrids. This suggests that meiotic disturbance occurred by the inclusion a third genome.

3. F1 plants of O. sativa•~O. punctata and O. sativa•~O. eichingeri

Six cross-combinations produced viable F, plants by embryo culture on White's medium. The data on cytological observations are given in Table 7.

In the sativa•~eichingeri hybrid, chromosomes of eichingeri strain (101424) 1970 Cytogenetic Studies of Oryza officinalis Complex III 315

showed a little pairing with those of O. sativa strain KT (indica). But

varying pattern of chromosome pairing were found in the Fl plants of O. sativa•~

O. punctata. Kehtze (KT, indica) and Taichung 65 (T.65, japonica) of O . sativa were used for these crosses. Between indica and japonica strains , no major disturbance in meiotic chromosome behavior is known. Therefore,

the differences in pairing pattern between the F, plants of O. sativa•~O. punctata

may be due to differences in chromosomal structure between punctata strains. Table 7 shows that the maximum bivalent number found in the hybrid of

T.65•~W1514 was eight, while those of KT•~101434, KT•~W1515 and

T.65•~101434, were four to seven bivalents. In the cross of KT•~W1023

(punctata, 4X) the maximum pairing was five bivalents. As shown in Table 3 previously, the punctata strain (101434) showed partial pairing with an

eichingeri strain (101424), and the same punctata line was also shown to be

partly homoelogous with O. sativa. While in the triploid hybrids they showed complete pairing with one of the two genomes (BC) of minuta and tetraploid

eichingeri but gave little pairing in the hybrid with genomes CD of latifolia. This suggests that the genome of diploid punctata is homoelogous with both

C and A genomes. Unfortunately, the cross of diploid O. punctata with O.

officinalis was unsuccessful.

Discussion Morinaga (1943, 1956) proposed that the genomes of O. officinalis, O. minuta and O. latifolia are CC, BBCC and CCDD, respectively. This is mainly due to observations of chromosome pairing at metaphase I in species hybrids. The symbols have been widely adopted by other workers. The problem in Morinaga's analysis is that diploid plants with genome B and/or D have not been discovered, and tetraploid species such as O. minuta and O . latifolia showed a number of bivalents in the crosses with O. sativa (AA) (for details see Chang 1964). To solve these problems, Kihara and coworkers (Kihara et al. 1960, Nezu et al. 1961) considered that genome B was partially homologous with genome A; Sharma and Shastry (1965) speculated that the genome B might be present in a Ceylonese officinalis strain (=O. collina (Trimen) Sharma et Shastry). Katayama (1965, 1966a, b) emphasized that the genome C of officinalis is homoelogous with genome A. Li and coworkers (Li et al. 1962, Wuu et al. 1963) once considered that O. latifolia might have a modified genome of O . sativa. Later, they assumed autosyndesis can occur between C and D or B and C. The results of the present study show that the genome of diploid eichingeri is homologous with that of officinalis, and that of diploid punctata is partially homologous to those of diploid eichingeri and sativa. Therefore, diploid eichingeri and punctata may not have genome B, as Sampath (1966) and Katayama (1967) had considered. Instead of B, C and D symbols, Rechharia (1960) and Sampath (1962) Cytologia35, 1970 21 316 Chao-Hwa Hu Cytologia 35 had proposed to use O3, O1 and O2 assuming that B, C and D are variants of the genome of O. officinalis and are differentiated into several groups due to gene mutations. The writer (Hu and Chang 1965a, 1967) has shown that geographical races of O. officinalis varied morphologically and their F, hybrids showed partial to complete sterility. The F, plants of interracial hybrids showed translocations and a range of variation in chromosome pairing involving univalents formation, suggesting that structural differentiation might exist in the species. Further, in induced autotetraploid plants of officinalis, the mode of pairing showed a tendency to form bivalents (Hu 1967). But, the racial variations in characters of O. officinalis do not seem to be of species rank (Gopalakrishnan 1965, 1966). In contrast, the variation in morphological characters of the punctata eichingeri complex seems to be larger than those of O. officinalis. In the present study, at least three different types of O. echingeri (101424, W1524, and W1527) were found among a few strains observed, and all of them are indigeneous to the same place (see Table 1). According to Tateoka (1965a, b), the distribution of O. eichingeri is limited to Kenya, Uganda, Tankanyika and northeastern Congo. O. punctata is known to occur widely in Africa, from the Ivory Coast to Kenya and southwards to Rhodesia and Madagascar. The similarity of punctata and eichingeri has lead taxonomists and cyto geneticists to erroreous identifications of the species. Though they can be distinguished from each other by certain plant characters (Tateoka 1965a), variations in many characters may be continuous. So far as the writer has observed, most strains of diploid punctata have relatively long ligules, soft leaves, but little anthocyanin coloration and flowering around noon. Some of strains, e. g. W1514, are tall and elect. It is known that various forms of "O. perennis Moench" are widely distributed in tropical and subtropical zones of the world. The rhizomatous strains in. Africa called O. barthii A. Chev., have no anthocyanin in leaf. The culms stand erect and the spikelets are small. Sasaki (1935), who examined many specimens in various herbaria, concluded that O. punctata could be included in the sativa group. Sampath (1962, 1966), from morphological studies, considered that O. punctata has a genome similar to that of O. officinalis. As mentioned above, the results of the present study showed that the genomes of African diploid and tetraploid eichingeri strains were similar to those of Asiatic O. officinalis and O. minuta, CC and BBCC, respectively. However, diploid punctata strains differ in morphological characters and in the degree of chromosomal homology with other species. It may be then concluded that diploid punctata strains were differentiated into various and the eichingeri formed a group rather distinct from punctata. The genome of diploid punctata is homologous with one of the BC genomes of O. minuta, but also shows partial homology with genome A of O . sativa. Therefore, the genome of diploid punctata can not be definitely 1970 Cytogenetic Studies of Oryza officinalis Complex III 317

postulated as A or C or B. Further, tetraploid strains of O. punctata and O. eichingeri have similar characteristics and their genomes are homologous to those of O. minuta. These species containing various homologous genomes may be considered as a group having many genes in common.

Summary

The wild African rice taxa Oryza punctata and O. eichingeri, which

are similar in many morphological characters, were often incorrectly identified

and used in genome analysis studies. A total of ten strains of O. punctata,

two strains of O. eichingeri and two intermediates of the punctata-eichingeri

complex were observed and six strains used as parents to produce species

hybrids. Seventeen cross combinations were succeeded to make F, hybrids.

It was found that both species have diploid and tetraploid forms and they

could be distinguished by certain morphological characters. The genomes of

diploid and tetraploid forms of O. eichingeri were similar to those of O.

officinalis and O. minuta, CC and BBCC. In the crosses involving diploid

punctata, however, various pairing pattern were found in different hybrids. Strain W1514 produced a maximum of eight bivalents with genome A of

O. sativa, while anothers strain 101434 showed seven bivalents with both

sativa and diploid eichingeri. These two strains gave 12 bivalents in the F,

hybrids with O. minuta and tetraploid eichingeri. Further, in the triploid

hybrids of sativa•~punctata (W1023) and latifolia•~punctata (101434) five to

six bivalents were found. The data suggest that the genome of diploid punctata

is homoelogous to both genomes A and C.

Acknowledgments This study was supported by the National Council of Sciences of the Republic of China. The writer wishes to express his sincere thanks to Dr. T. T. Chang of The International Rice Research Institute, Philippines and Dr. H. I. Oka of National Institute of Genetics, Japan for they kindly supply ing the materials and critical reading of manuscript. Thanks are also due to Mr. H. Guan for his help in field work.

Literature cited Chang, T. T. 1964. Present knowledge of rice genetics and cytogenetics. Tech. Bul. 1., Intern'l Rice Res. Ins. Gopalakrishnan, R. 1965. Subspeciation in Oryza officinalis Wall. ex Watt. J. Biol. Sci. 8 (2): 60-67.- 1966. Taxonomic status of Oryza collina (Trimen) Sharma et Shastry. Indian J. Genet. and Pl. Breeding 26: 98-100. Hu, C. H. and Chang, C. C. 1965a. A note of Fl hybrids between Oryza punctata and its related species. Jap. J. Breeding 15: 281-283.- and - 1965b. Studies on the sterility of interracial hybrids in Oryza officinalis. Genet. 21* 318 Chao-Hwa Hu Cytologia 35

52: 449.- and - 1967. Cytogenetic studies of Oryza officinalis Complex 1. F1 hybrid sterility in

geographical races of O. officinalis. Bot. Bul. Acad. Sinica 8: 8-19.- 1967. Cytogenetic studies of Oryza officinalis complex 2. Meiotic studies of induced autotetraploids of O. officinalis. Ibid. 8: 327-338.

Katayama, T. 1965. Cytogenetical studies on the genus Oryza 1. Chromosome pairing of interspecific hybrid O. sativa•~O. officinalis under different temperature conditions.

Jap. J. Genet. 40: 307-313.- 1966a. Ditto 2. Chromosome pairing in the interspecific hybrid with the ABC genomes

Ibid. 41: 309-316.- 1966b. Ditto 3. Chromosome pairing in the interspecific hybrid with the ACD genomes.

Ibid. 43: 317-324.- 1967. Cytogenetical studies on Oryza F1 hybrids of the crosses BBCC•~CC, BBCC•~a

diploid strain of O. punctata and CC•~a diploid strain of O. punctata. Proc. Jap.

Acad. 43: 327-331. Kihara, H., Nezu, M., Katayama, T. C., Matsumura, S. and Mabuchi, T. 1961. Genome analysis in the genus Oryza II. Ann. Rpt. Natl. Genet. Japan 11 (1960): 40-41. Li, H. W., Weng, T. S., Chen, C. C. and Wang, W. H. 1962. Cytogenetical studies of Oryza. sativa L. and its related species. 2. A preliminary note on the interspecific hybrids within the section Sativa Roschev. Bot. Bul. Acad. Sinica 3: 209-219. - , Yang, K. K. S. and Ho, K. C. 1964. Ditto 7. Non-synchronization of mitosis and cyto kinesis in relation to the formation of diploid gametes in the hybrids of Oryza sativa L. and O. officinalis Wall. Ibid. 5: 142-153. Morinaga, T. 1943. Cytogenetical studies on Oryza sativa L. VI. The cytogenetics of F1 hybrid of O. minuta Presl. and O. latifolia Desv. Jap. J. Bot. 12: 347-357. - 1956. Chromosome pairing at meiosis in Fl hybrids and genomic constitution of Oryza. Reprinted from Internl. Genet. Symp. Sept. 6-12. Tokyo and Koyto, Science Council of Japan.- and Kuriyama, H. 1960. Interspecific hybrids and genomic constitution of various species in the genus Oryza. Agr. and Hort. (Japan) 35: 773-776, 935-938, 1091-1094, 1245 -1247. Nezu, M., Katayama, T. C. and Kihara, H. 1960. Genetic study of the genus Oryza I.

Crossability and chromosomal affinity among 17 species. Seiken Ziho 11: 1-11.

Rechharia, R. H. 1960. Origins of cultivated rices. Indian J . Genet. and P1. Breeding 20: 1-14. Sampath, S. 1962. The genus Oryza: its and species interrelationships . Oryza (India) 1: 1-29.-

1966. The genus Oryza: an evolutionary perspective . Oryza 3: 30-34. Sasaki, T. 1935. On the distribution of Oryza species . Commemmoration Papers on Crop

Science in Honor of Prof. S. Kikkawa . 631-735. (in Japanese) Shokado, Tokyo. Sharma, S. D. and Shastry, S . V. S. 1965. Taxonomic studies in genus Oryza L . IV. The Ceylonese Oryza spp. affin. O, officinalis Wall . ex Watt. Indian J. Genet. and P1. Breeding 25: 168-172. Tateoka, T. 1962. Taxonomic studies of Oryza I . O. latifolia complex. Bot. Mag. (Tokyo) 75: 418-427.- 1965a. A taxonomic study of Oryza eichingeri and O . punctata. Ibid. 78: 156-163.- 1965b. Taxonomy and chromosome numbers of African representatives of the Oryza

officinalis complex. Ibid. 78: 198-201 . Wuu, K. D., Jui, Y., Lu, K. C . L., Chou, C. and Li, H. W . 1963. Cytogenetical studies of Oryza sativa L. and its related species . 3. Two intersectional hybrids O. sativa L.•~O. brachyantha A. Chev . et Roehr. and O. minuta Presl.•~O. brachyantha A. Chev. et Roehr. Bot . Bul. Acad. Sinica 4: 51-59.