Smith - 2003 - Rice origin, history, technology, and production

Genetics, Cytogenetics, Mutation, and Beyond 161
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nomenclature and gene symbols were reviewed and accepted during the Rice Genetics
and Cytogenetics (Anonymous, 1964) symposium held at the International Rice
Research Institute (IRRI) in the Philippines. Unfortunately, no mechanism was established
for monitoring the gene symbols, so the Japanese scientists organized a com ­
mittee in 1979 to promote cooperation and adoption o f uniform gene symbols for rice
in Japan. Eventually, the Rice Genetics Newsletter (RGN) was published in 1984, and
it contained proposed rules for gene symbolization. The following year, at the First
International Rice Genetics Symposium, the Rice Genetics Cooperative (RGC) was
organized to promote international cooperation in rice genetics and publish the RGN.
The RGC now coordinates and m onitors gene symbols with new symbols and revised
linkage maps being published in the annual RGN (Khush and Kinoshita, 1991).
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CYTOGENETICS
Trisomie Series
For use in mapping the individual genes to chromosom e, various researchers identified
trisom ie rice plants, plants having 25 chromosomes {2n + 1 = 2x — 25). These
plants have an additional complete chromosome or primary trisóme. This means
that a plant trisomie for chromosome 1 has three copies o f chromosome 1 and two
copies o f chromosomes 2 through 12. Triploid plants crossed as female with diploid
plants were often the source o f trisomie plants. The first report o f primary trisomies
was Yunoki and Masuyama (1945), who obtained at least six morphologically distinguishable
trisomie plants. Later, there were additional reports o f primary trisomies
being obtained from triploid plants (Khush and Singh, 1991). Complete series o f all
12 primary trisom ie chromosom es have been reported in the background o f seven
different rice cultivars, including CS-M 3, a California breeding line (Khan, 1974),
Guangluai 4 (Zhang and Zhu, 1986), IR36 (Khush et al., 1984), Kehtza (C. Hu, 1968),
Nipponbare (Iwata and Omura 1984), Sona (M isra et al., 1986), and Zhongxian 3037
(Cheng et al., 2001).
Three o f these rice cultivars: (1) IR36, an indica cidtivar developed by IR R I in
the Philippines (Khush et al., 1984,1996; K. Singh et al., 1996, R. Singh and Khush,
2000); (2) Nipponbare, a temperate japónica cultivar developed in Japan (Iwata and
Omura, 1984; Wang and Iwata, 1995); and (3) Zhongxian 3037, a Chinese indica
cultivar (Cheng et al., 2001), have various secondary trisomie, telotrisom ic, and/or
alien addition lines available. Plants identified as secondary trisomies have the additional
chrom osom e as an isochrom osome, a chrom osom e with two identical arms.
In telotrisomic plants, the additional chromosom e has only one arm, and in the alien
addition lines, the additional chrom osom e is from an Oryza species other than O.
sativa.
The IR36 trisomie series was used to develop a classical linkage map (Figure
2.3.1), which located 43 marker genes to the chromosom e arm (K. Singh et al., 1996;
Khush et a l, 1996). Further efforts were carried out on these lines to develop a
molecular linkage map using restriction fragment length polymorphism (RFLP)
markers which corresponded to the physical map and classical map. M ost o f the
markers are from the Cornell University map (Causse et a l, 1994), but a few markers
are from the Rice Genome Research Program (RGP) map (Kurata et a l, 1994). Since