1-8-3, Miwadai, Higashi-Ku, Fukuoka, Japan
Tateoka (1963, 1964) classified species of the genus Oryza into four sections, Oryzae, Ridleyanae, Granulatae and Schlechterianae. Based on this taxonomy, O. minuta PRESL. and O. grandiglumis PROD. belong to section Oryzae, while O. meyeriana BAIL. to section Granulatae and O. ridleyi HOOK. to section Ridleyanae, respectively.
O. minuta X O. meyeriana: From 210 spikelets of O. minuta (Y22, BBCC) crossed with O. meyeriana (WO615), 4 F1 hybrids were obtained (F\1\ 3). The F1 hybrids resembled the female parent more closely than to the male parent in most morphological characters such as growth habit, leaf shape, awn length and color of awns and stigmas, etc. The somatic chromosome numbers of the F1 hybrids are expected 2n = 36. At MI of meiosis in the F1 hybrids, most chromosomes failed to pair. The mean numbers of univalents and bivalents per cell were 34.8 and 0.27, respectively (Table 1). Meiotic abnormalities included the presence of univalents during MI, anaphase laggards, anaphase bridges and unequal separation, etc. Pollen and seed in the F1 hybrids showed complete sterility caused by the chromosomal abnormalities.
O. grandiglumis X O. ridleyi: From 107 spikelets of O. grandiglumis (WO613, CCDD) which were pollinated with O. ridleyi (WOOO1), 1 hybrid was obtained. The F1 hybrid strongly resembled O. grandiglumis morphologically except for length
Fig. 1. Morphology and meiosis in two F1 hybrids.
1: An adult plant of F1 3. 2: An adult plant of F1 82-73. 3: MI in
F1 3. 4: AI in F1 82-73, showing laggards.
and color of awns. As expected, the hybrid had 2n=48 chromosomes. At MI of
meiosis, the mean numbers of bivalent and univalent per cell were 0.19 and
47.0 respectively (Table 1). A large number of irregularities such as
bridges, laggards and irregular separation, etc. were commonly observed.
Pollen and seed of the F1 hybrid showed complete sterility.
From these observations, the author concluded that the genomic constitutions of O. meyeriana and/or O. ridleyi were not homologous to either one of the 2 chromosome sets composing the chromosome complex of O. minuta (BBCC) and/or O. grandiglumis (CCDD), respectively.
The author expresses his thanks to Drs. H. I. Oka and Y. Sano, National Institute of Genetics, Mishima, for providing the seeds of wild rice species.
Table 1. Chromosome configulations in the F1 hybrids of O. minuta x O.
meyeriana and O. grandiglumis x O. ridleyi
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Chromosome configuration
No. of ======================================== Fertility (%)
F1 hybrid cells II I =================
observed ================ ================== Pollen Seed
Range Mean Range Mean
===============================================================================
F1 3 30 0-3 0.27 30-36 34.86 0 0
F1 82-73 26 0-2 0.19 45-48 47.01 0 0
===============================================================================
References
Tateoka, T., 1963. Taxononic Studies of Oryza III. Key to the species and their enumeration. Bot. Mag. Tokyo 76: 165-173.
Tateoka, T., 1964. Notes on some grasses. XVI. Embryo structure of the genus Oryza in relation to the systematics. Amer. J. Bot. 51: 539-543.