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needed to develop hybrids. Such a hybrid is called two-line hybrid rice.
2 Advantages of Two-line Method
Compared with three-line method,two-line method has the following advantages:
2.1 The maintainer line is not needed.
Because PTGMS lines can either be used to conduct hybrid seed production under higher temperature and longer
day length conditions as well as to multiply themselves by selfing under lower temperature and shorter day length
conditions, it is not necessary to have a maintainer line to retain the male sterility. Therefore, it can simplify the hybrid
seed production process and decrease the cost of hybrid seeds.
2.2 Choice of parents in developing heterotic hybrids is greatly broadened
Since the male sterility in PTGMS lines is only controlled by recessive nuclear genes, almost all
common rice cultivars within the same subspecies can easily restore the fertility of such MS lines, which
consequently widens the choice of parents in developing superior hybrids to a great extent.As a result,the
probability of obtaining better hybrid combinations is increased.
2.3 PTGMS genes can be easily transferred from line to line.
It has been found out that the inheritance of fertility alteration is controlled by one or two pairs of nuclear
genes.
With the simple inheritance, the genes can be easily transferred into almost any rice lines with
desirable characteristics to develop new PTGMS lines for various purposes.
2.4 Unitary cytoplasm status could be easily avoided
Because the male sterility in PTGMS lines has no relation to cytoplasm, there is no negative effects
caused by sterile cytoplasms and the dominant cytoplasm status of WA types existing in CMS system could
be easily overcome.
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隆平高科国际培训学院
Longping High-tech Inermational Training conter
3 Classification of PTGMS Lines
After the discovery of japonica Nongken 58S,a nationwide research was conducted on the mechanism of
PTGMS and its application,soon afterwards a group of japonica and indica PTGMS limes were transfered from the
original Nongken 58S.Furthermore,some other germplasms with fertility aheration were found. These germplasms
are Annong S-1 from natural mutants, 5460S, R59TS and H89-1 from induced mutations and Hengnong S-1 and
IVA from hybridizing variants, etc.Based on the degree of the effects of day length and temperature on fertility
alteration
and expression,PTGMS lines can be generally classified into two categories: photoperiod-sensitive
genic male sterile or PGMS lines and thermo-sensitive genic male sterile or TGMS lines.PGMS lines,such as
Nongken 585,N5088S,7001S and Hunong 5S,refer to the lines whose fertility alteration and expression is primarily
influenced by photoperiod while TGMS lines,including Annong S-1, Hengnong S-1 and 5460S,etc.,are those lines
whose fertility alteration and expression is dominantly affected by temperature.Acoording to distribution of the
existing PTGMS lines,PGMS lines are mostly found in japonica types,whereas TGMS lines are easily acquired in
indica types.
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4 Characteristics of PTGMS Lines
4.1 PGMS lines
(1)Fertility alteration of PGMS lines is
induced mainly by day length,but temperature has also a certain
influence on alteration of fertility.Beyond a certain range of temperature the day length will have no effect on its
fertility alteration,as shown in the following pattern.
(2) The photoperiod-sensitive stage for fertility alteration is the period from development of the secondery
branch primordia to the formation of the pollen mother cell.
(3)The critical day length for inducing fertility alteration is 13.75 to 14.00 hours.
(4)The critical light intensity for inducing sterility is above 50 Lux.
This pettem is very important and useful for directing the development of usable PGMS lines. The high critical
temperature affects multiplication of the TGMS line under short day length conditions.
Fertility Alteration Pattern of
PGMS Lines
induces
male stunlity and
short day length induoas
male fartality
wy day lm.g
Biological upper limit
teperature(abou135)
Male stanlity-inducing
temsperature(bigh cntical tamperatur)
Male stenility-indacing
tamperature(low cnitical tamperatur)
Biole gical lower limil
tampersture(about20℃)
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中国杂交水稻技术援外培训基地
China-Aid Hybrid Rice Technology Training Center
Whereas the low critical temperature affects sterility fluctuation of the PGMS line when occasionally exposed to low
temperature under long day length conditions.Two points are essential in breeding PGMS lines according to the pattern. First,
the low critical male sterility-inducing temperature must be considerably low.Second,the photoperiod-sensitive temperature
range (PSTR) must be very wide. For example, the PSTR of 7001S is 24-30℃ and is viable.In
the case of Nongken
58S,however,the PSTR is 26.5-30'C.Because of its narrow PSTR and higher male sterility-inducing temperature,it is almost
useless in practice.
4.2 TGMS lines
(1) Fertility alteration of TGMS lines is induced dominantly by temperature and day length has
very little influence on alteration of fertility.
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(2) The thermo-sensitive stage for fertility alteration is the period from pollen mother cell
formation stage to the beginning of meiotic division stage.
(3)The male sterility-inducing critical temperature is 23-29C,varying from line to line.
(4)Under the critical temperature conditions for three consecutive days,the TGMS line resumes
male fertility.
The most important point in the practical utilization of TGMS lines
is that the male sterility-
inducing critical temperature must be relatively low,especially for temperate zones.
In tropical and subtropical areas, TGMS lines are more useful than PGMS lines since the day length there is relatively
short but the temperature is rather high, whereas the PGMS lines are more preferable in higher latitudes.
5 Inheritance of PTGMS Genes
Many studies have been done on the inheritance of the PTGMS genes.Although the results of different researchers are
not highly consistent,yet it is mostly accepted that the alteration of male sterility in Nongken 58S is controlled by two pairs of
genes, that of Annong S-1 and Hengnong S-1 by one pair of genes and that of 5460S by one or two pairs of genes. No matter
how many major genes are considered,there exist some minor genes that affect the expression of fertility. It has also been
found that the fertility expression may be quite different when the same PTGMS gene is introduced into different genetic
backgrounds.
In addition,the studies on the allelism of genes in different PTGMS lines have shown that the genes from different
origins are not allelic. For example, the PTGMS genes in Nongken 58S,Annong S-1,Hengnong S-1 and 5460S are all
independently inherited.
47
隆平高科国际培训学院
Longping High-tech Intemational Training center
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