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IV. Cytoplasmic–Genetic Male Sterility Systems in Rice and Wheat

IV. Cytoplasmic–Genetic Male Sterility Systems in Rice and Wheat

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was attributed to nondehiscence of anthers, because both male and female

gametes were nomal.

Shinjyo and Omura (1966a)developed the first cytoplasmic male-sterile line

in cultivated rice by substituting nuclear genes of a japonica variety, Taichung

65, into the cytoplasm of indica variety Chinsurah Boro 11 (Shinjyo, 1970).

Watanabe et’uf. (1968) observed male sterility in the progeny of the indica-japonica cross (Lead/Fujisaka 5), but those of the reciprocal cross were

fertile. However, no male-sterile line was developed. Eiickson (1969)and Carnahan er uf. (1972)developed cytoplasmic male-sterile lines from crosses of an

indica variety, Birco (PI279120),with Californian japonica rice varieties Calrose, Caloro, and Colusa; the F, plants were almost completely sterile whereas

the reciprocal crosses produced about 50% seed set. The three Californian varieties, when used as recurrent paternal parents, always gave higher sterility in the

Birco cytoplasm than in their own. The sterility increased with succeeding backcrossing of Californian japonica varieties into Birco cytoplasm, and the third

backcross generation plants became completely male sterile (Camahan et ul.,

1972). Watanabe (1971) also reported development of cytoplasmic-genetic

male-sterile lines by means of indica-japonica crosses. A cytosterile line possessing. 0. gluberrima cytoplasma in the genetic background of variety Colusa

was also developed in California (Camahan et u f . , 1972).

Athwal and Virmani (1972)developed a cytoplasmic male-sterile line at the

IRRI by substituting nuclear genes of indica rice variety Pankhari 203 into the

cytoplasm of a semidwarf indica variety, Taichung Native 1. The first

cytoplasmic male-sterile line used to develop commercial F, rice hybrids was

developed in China in 1973 from a sterile plant (wild-aborted) occurring naturally in a wild rice population (Oryzu sutivu f. spontunea or 0. perennis) on

Hainan Island in 1970 (Hunan Provincial Rice Research Institute, 1977;Yuan,

1977). Subsequently, cytoplasmic male-sterile lines have been developed from

various accessions of 0. sutivu f. spontunea, indica variety Gambiaca (from

Africa), and the Chinese variety 0-Shan-Tao-Bai (Lin and Yuan, 1980). Rutger

and Shinjyo (1980)studied the distribution of male-sterile cytoplasms in various

geographical forms of 0. perennis. In Asian and American strains, the frequencies of male-sterile cytoplasm were about 64 and 48,respectively. No malesterile cytoplasm was found in the African and Oceanean strains.

2 . Wheat

The first report of cytoplasmically induced male sterility (CMS) in wheat was

that of Kihara (1951),who obtained cytosterile plants by substitution backcrossing of the common wheat genome into Aegilops cuudutu cytoplasm. Plants with

A. cuudufu cytoplasm also showed partial female sterility and pistilloidy.

Fukasawa (1953)obtained CMS plants from successive backcrosses of Aegifo-



tricum X Triticum durum". The Aegilotricum species had been synthesized from

a cross of Aegilops ovutu with T. durum. Male-sterile T. durum plants with A.

o v m cytoplasm had reduced plant height and delayed maturity compared with

normal durum plants, and these effects were consistent through subsequent generations of backcrossing. In the reciprocal cross, A. ovutu plants with T. durum

cytoplasm showed male and female fertility comparable to that of normal A.

ovutu plants, but the T . durum cytoplasm delayed maturity and reduced plant

height. Other studies by Japanese researchers established the presence of CMS

plants in the intergeneric crosses, and the sterility persisted through backcross

generations (Fukasawa, 1957, 1958, 1959; Kihara, 1958; Kihara and

Tsunewaki, 1961).




I . Rice

From the foregoing review of the literature, 19 sources of cytoplasmic male

sterility in rice can be identified (Table III). Five of these [i.e., wild rice (designated as wild aborted or WA type), 0. sutivu f. spontuneu, Chinsurah Boro II

(BT type), Gambiaca (Gam type), and 0-Shan-Tao-Bail are being used. More

than 100 cytoplasmic male-sterile lines in indica and japonica backgrounds derived from these sources are currently available in China. The male-sterile lines

from China are classified into three basic groups according to genetic properties

and relation between restorer and maintainer lines (Lin and Yuan, 1980).

Group I . The WA cytosteriles are typical of this group, but Gam type and

some male-sterile lines derived from 0.sutivu f. spontuneu also belong here.

The function of the male sterility gene is sporophytic; pollen grains abort at the

uninucleate stage. Maintainer lines are found in both indica and japonica rices.

Group ZZ. This group consists of BT-type male-sterile lines developed by

Shinjyo and Omura (1966a). The function of the male sterility gene is gametophytic; pollen grains abort between the binucleate and the trinucleate stages. The

restoration spectrum of Group I1 is wider than that of Group I; it is easier to

sterilize japonica varieties than indica varieties to this type of male sterility.

Group ZZZ. The cytoplasmic-genetic male sterility mechanism of this group is

derived from some 0. sativa f. spontuneu lines. The Hong-Lien is typical of this

group. Pollen grains abort at the binucleate stage and the relation between restorers and maintainers in this group is in contrast to that of Group I. For

example, the maintainers of Group I, such as Zhen Shan 97 and Er-Jiu-Ai 4,

become restorers of this group, and the restorers of Group I, such as Tai-Yin 1,

are good maintainers of this group.

Among the various sources of cytosterility, cytoplasmic male-sterile lines



Table IU

Cytoplnsmie sourceS Identifkd to Induce Male Sterility in Rice

Cytoplasm source


Nuclear source







Oryza sativa f. spontanea

Fujisaka 5



Fujisaka 5


Fujisaka 5

Several indica and

japonica rim

Norin 8

Taichung 65


B h (PI279120)

w u 10

Several japonica

rice varieties in


Fujisaka 5

calrose, calm

Orya glaberrima



Taichung (Native) 1

Pankhari 203


Wild rice with aborted

pollen (0.sativa f.

spontanea or 0.perennis) or WA


0.@pogon (KR 7)






2 or 3





Weeraratne (1954);Sampath and Mohanty


Katsuo and Mizushima


Katsuo and Mizushima


Heu and Chae (1 970)

Lin and Yuan (1980)

Kitamura (1962a)

Shinjyo and Omura


Lin and Yuan (1980)

L. P. Yuan (personal


Watanabe et al. (1%8)

Erickson (1%9); Carnahan

er al. (1972)

Carnahan er al. (1972)

s. s. Virmalli


Athwal and V



Yabuno (1977)

Yuan (1972);Lin and

Yuan (1980)

Er-Jiu-Nan 1,


Zhen Shan 97,

V20, V41, and

several other indica and j a p

onica rices

Taichung 65

Gang-Yi-Ya Ai

Zhao, Yat-AiZhao

Toride 1 and several other indica

and japonica



Cheng and Huang (1979)

Lin and Yuan (1980)


Lm and Yuan (1980)



Table III Continued

Cytoplasm source

IARI 10061

IARI 10560

Jeerege Samba

0. perennis (Wl080)

0 . perennis (W1092)

Nuclear source





IARI 11445

IARI 11445



Parmar et al. (1981)


Shinjyo et al. (1981)

Shinjyo and Motomura


Taichung 65

Taichung 65


derived from the WA cytosterility system have been found to be the most stable

in China and at the IRRI for their complete or nearly complete pollen sterility

(Lin and Yuan, 1980; Virmani et al., 1981). According to L. P. Yuan (personal

communication), the probability of developing stable male-sterile lines is higher

from relatively wider crosses where the female parent is a primitive line and the

male parent is an advanced line. The closer the relation between the two parents,

the harder it is to obtain a stable male-sterile line, and vice versa.

In the IRFU hybrid rice breeding program, 11 cytosterile lines representing 5

cytoplasmic sources (i.e., Gambiaca, Birco, 0 . sativa f. spontanea of Group I,

Taichung Native 1, and BT) are available. Only 7 of these lines [Zhen Shan 97A,

V20A, Er-Jiu Nan lA, and V41A (all WA type), Yar Ai Zhao A (Gam type),

Pankhari 203A (TN type), and Wu 10A (BT type)] are relatively stable for pollen

sterility. The lines MS519A and MS577A possess stainable pollen as do fertile

plants, but these pollen grains do not germinate or affect fertilization. All these

lines are highly susceptible to major diseases and insects in the tropics, and they

cannot be used to develop commercial F, hybrids. Pankhari 203A is tall and

photoperiod sensitive, and Wu 10A is a japonica type. At the IRRI, the cytosterility system(s) of some of these lines is being transferred into the genetic

background of improved breeding lines and varieties that possess disease and

insect resistance.

2 . Wheat

Early Japanese research on cytoplasms, coupled with the discovery by Wilson

and Ross (1962) that T. timopheevi cytoplasm induces male sterility, led to the




establishment of major research programs in Japan, the United States, and Bulgaria to determine the cytoplasmic variation in species of the genera Triticum and

Aegilops. Cytoplasmic male sterility in wheat was reviewed by Maan (1973a)

and by Sage (1976). Over 15 different cytoplasms have been recognized, several

of which induce male sterility in common wheat and could form a basis for

alternative systems of hybrid production (Maan,1975; Mukai and Tsunewaki,


Nearly all hybrid wheat breeding research continues to be based on the T.

timopheevi system, and its widespread use has been largely the result of its

apparently neutral effect on agronomic and quality characters. Most other

cytoplasms from Triticum and Aegilops have deleterious effects on various traits

(Maan, 1973a; Sage, 1976). Of the altemative cytoplasms available, most show

no advantage over that of T. timopheevi, and time and resources limit change.

However, the potential for genetic vulnerability to a major disease is always

present when a single cytoplasm is used; the southern corn leaf blight epidemic in

the United States in 1970 (caused by Helminthosporium maydis, race T) is a

good example. Ghiasi and Lucken (1982a) compared the reactions of A.

speltoides and T. timopheevi cytoplasms to various restorer gene combinations

and examined a number of agronomic and quality traits. They concluded that A.

speltoides cytoplasm can be used interchangeably with that of T. timopheevi in

hybrid wheat breeding, providing an alternative that can broaden genetic variability. On the basis of nucleocytoplasmicinteractions (Maanand Lucken, 1971,

1972) and cytogenetic evidence (Kimber and Athwal, 1972; Kimber, 1973;

Shands and Kimber, 1973), it has been suggested that A. speltoides may have

contributed the G genome and cytoplasm to T. timopheevi. However, the restorer

line R5 (T. zhukovskyi/3* ‘Justin’) is an effective restorer for T. timpheevi

cytoplasm but not for A. speltoides cytoplasm, and this interaction provides the

genetic basis for differentiation of the two cytoplasms. Gomaa and Lucken

(1973) compared the breeding behavior of the restorers R5 and BR4704 in T.

timopheevi and T . boeoticum cytoplasms. Fertility restoration (RB genes effective in T. boeoticum cytoplasm were also effective in T. timopheevi cytoplasm,

but not necessarily vice versa. The reduction in vigor noted when the genomes of

common wheat are substituted into T. boeoticum cytoplasm (Hori and Tsunewaki, 1967; Maan and Lucken, 1967, 1972; Gomaa, 1973) has curtailed the use

of T. boeoticum as an alternative cytoplasmic source for hybrid breeding. It

should be recognized from the previous statements that nucleocytoplasmic interactions are often significant; in T. timopheevi cytoplasm, small differences

between male-sterile lines and their maintainers have also been noted for a

number of traits (Jost et al., 1976b). Several researchers have also observed

reductions in germination and seedling vigor with progressive backcrossing in

certain wheat genomes into T. timopheevi cytoplasm.







1 . Rice

Although a number of sources for cytoplasmic male sterility in rice have been

identified, more than 90% of the area planted to hybrid rice in China is occupied

by hybrids derived from WA cytosterile lines. This situation makes hybrid rice in

China potentially vulnerable to disease or insect epidemics. Work is in progress

in China (Lin and Yuan, 1980)and at the IRRI (Virmani etal., 1981)to diversify

usable sources of cytoplasmic male sterility for hybrid rice development. Rice

species (i.e., Oryza gluberrimu, 0. fatuu, Asian forms of 0. perennis, and 0 .

rufipogon) and varieties (i.e., PTB16, Tadukan, Lead 35, Akeboro, IARI

10061, IARI 10560,and Jeerege Samba) that are known to induce cytoplasmic

male sterility may result in cytosterile lines that possess different cytosterility

systems. The use of protoplast fusion techniques should expedite the development of new cytosterile lines (E. C. Cocking, personal communication).

2 . Wheat

Additional cytosterility systems that supply male-sterile plants with good vigor

and female fertility have been produced with the cytoplasms of Zhukovskyi (2n

= 42; AAA’A’GG), Triticum araraticum (2n = 28; AAGG), and T. dicoccoides

var. nudiglumis (2n = 28;AAGG) (Maan, 1975;Maan and Lucken, 1971). The

fertility restoration systems of the previously mentioned cytosterility systems are

also under complex genetic control and cause difficulties in breeding agronomically suitable restorer lines.

Franekowiak et al. (1976) presented a proposal for hybrid wheat using

Aegilops squarrosa cytoplasm that seeks to avoid the breeding of restorer lines.

The D genome of common wheat contains genetic factor(s) €or restoration of

fertility of T. aestivum with A. squarrosa cytoplasm. The nucleus of T. aestivum

was substituted into A. squurrosa cytoplasm and the seed was treated with a

mutagenic agent (ethyl methanesulfonate, EMS)to inactivate the critical gene(s)

that causes fertility. Ten male-sterility mutants from an M, population of 45,000

plants expressed sterility in F, or F, generation, which indicates control by a

single recessive gene. Crosses with four spring wheats produced completely

fertile F, progeny. However, the major weakness of the system was that no malesterile genes that function specifically in the A. squarrosa cytoplasm were found.

The development of fertile T. aestivum B lines with homozygous recessive genes

for the maintenance of the A lines was not completed.

Mukai and Tsunewaki (1979)proposed a similar system using the cytoplasms

of Aegilops kotschyi and A. variabilis. When 12 common wheat genotypes were



substituted into these cytoplasms, 3 were found to be male sterile. Crosses with

Chinese Spring produced a fertile F, hybrid, and restoration was attributed

primarily to a single dominant gene (Rfvl).Trificurnspelfa var. duhumelianum

carries a gene on chromosome 1B which interacts with A. kofschyi and A .

vuriabilis cytoplasms to give male-sterile plants. Cultivars that carry the 1B/lR

rye translocation and thereby lack the short, satellited arm of chromosome 1B

display the same male-sterile interaction. Normal wheat cultivars carry gene(@

that overcome this sterility and therefore constitute male or restorer parents for

hybrids. Comparisons with T. fimpheevi cytoplasm for 12 agronomiccharacters

showed that A. bfschyi cytoplasm influenced only dry matter (reduced to 12%).

The A. vuriabilis cytoplasm reduced plant height 496, ear number 18%, and dry

matter 26%. Several hybrid programs in the United States and elsewhere are

currently evaluating this system.



The techniques available for detecting cytoplasmic variation in a crop species


1. Substitution backcrossing

2. Use of cytoplasm-differentiating genes

3. Interaction of restorer (Rfigenes with the cytoplasm

4. Study of pollen abortion patterns

5 . Restriction endonuclease fragment analyses of organelle DNAs.

Work on these lines in rice has been limited. Chinese scientists have used

techniques 2, 3, and 4 and reported that the WA cytosterility system is different

from the BT system because the restorer gene(s) for the former have sporophytic

action and those for the latter have gametophytic action (Y. Y. Dong, unpublished). Shinjyo (1969, 1975) and Kinoshita et al. (1980) have also reported

gametophytic action of the restorer gene for BT cytosterilelines. By studying the

pollen abortion pattern of different CMS lines, Xu (1982) found that pollen of

WA cytosterile lines abort at the uninucleate stage and those in BT cytosteriles

abort at the binucleate and trinucleate stages (Q. L. Jiang, unpublished). Chaudhary ef al. (1981) also established differences between WA, TNl, and BT

male-sterile lines maintained at IRRIon the basis of their pollen abortion pattern.

Chaudhary ef al. further suggested that the pollen abortion stage in a CMS line

depended on the distance of relation of its cytoplasmic and nuclear donor parents. It appears that cytosterile lines with pollen abortion at the uninucleate stage

are more stable for complete pollen sterility than lines with pollen abortion at the

binucleate or trinucleate stage.

Cytoplasmic variation in the Triticinae was reviewed by Maan (1973b, 1975)



and Sage (1976). The literature reveals that all genomically distinct species of

Triticwn and related genera examined differ cytoplasmically. The sterility- fertility interactions between genomes from Triticum spp. and cytoplasms from

Aegilops spp. indicate that male fertility-restoring genes derived from one

cytoplasm donor species may restore fertility to male-sterile wheats that have

cytoplasms of one or more of the other related species. Maan (1973b) drew

attention to the fact that a number of factors will influence the expression and

detection of cytoplasmic effects: (1) stability of the cytoplasm, (2) stability of the

nuclear genome, (3) choice of cytoplasm and genome donor, (4) persistence of

nuclear genes from the cytoplasm donor, and ( 5 ) genotype-environment


In substitution backcrossing of the genome of one species into the alien

cytoplasm of another, sufficient backcrosses are required to eliminate all nuclear

genes derived from the cytoplasm donor species and produce a new nucleocytoplasmic combination. If this results in relatively stable male sterility, the

cytoplasms of the two species involved in the cross may be considered distinct.

Maan (1973b) reported that genomes of common wheat and durum wheat generally have similar interactions resulting in male sterility and abnormalities of plant

growth with the cytoplasms of most of the related species. When they differed,

the durum genomes were more sensitive to certain alien cytoplasms than the

common wheat genomes. Sasakuma and Maan (1978) introduced T. durum

genomes into the cytoplasms of 6 species of Triticum, 14 species of Aegilops,

and 1 species each of Secale and Haynuldia. O f the 22 alloplasmic lines, 14 were

completely male sterile, 4 were partially fertile, and the rest, which had the

cytoplasms of T. dicoccoides, A . kotschyi, A. variabilis, or H . villosa, had

normal fertility. When new nucleocytoplasmic combinations are made using T.

aestivwn or T. durum genomes, differences between cytoplasms in traits other

than male sterility often occur. These differences indicate that distinctions between cytoplasms cannot be based on male sterility alone. This subject is dealt

with jn Section IV,E.

Cytoplasm-differentiating nuclear genes include male fertility-restoring genes,

male fertility-inhibiting genes, and genes affecting plant vigor in various ways.

The relationships among these different genes are not clearly understood. However, research during the past decade has led several hybrid breeding programs to

apply the terms “hard-to-restore” and “easy-to-restore” to genotypes in which

male fertility-inhibiting genes are present or absent, respectively.

The cytoplasms of T. timopheevi and A. speltoides cannot be differentiated by

the presence of T. aestivum genomes, because male sterility is the only deleterious effect in both. However, substitution of the genome of T. timopheevi

into A . speltoides cytoplasm produces male-sterile plants with reduced vigor

(Maan and Lucken, 1972). Therefore, nuclear gene differences between the

genomes must control the behavior of T. timopheevi and A. speltoides cyto-



plasms with either T. aestivum or T. tinwpheevi genomes. Such genes were

termed cytoplasm-differentiating genes. In addition, T . tinwpheevi and A.

speltoides cytoplasms differ in their reaction with restorer R5 (Maan, 1973a).

The latter restores T. rimopkevi but not A. speltoides cytoplasm. This type of

information on the components of interacting male sterility-male fertility restoration systems is important in hybrid wheat breeding.

Restriction endonuclease fragment analysis of organelle DNAs, which is effective in demonstrating the heterogeneity of mitochondrial (MT) DNA among

normal, fertile (Levings and Pring, 1977) and male-sterile cytoplasms in corn

(Pring and Levings, 1978; Conde et al., 1979; Pring el al., 1980) and sorghum

(Pring et al., 1982). Li and Liu (1983) found the heterogeneity of chloroplast

(CT) DNA in CMS and maintaining lines in wheat, corn, and rape and suggested

that changes in CT DNA may be involved in CMS.These techniques have not

yet been used in rice and wheat for differentiating and identifying cytoplasm





The effects of sterility-inducing cytoplasm on morphological traits have been

reported for tobacco (Clayton, 1950; Chaplin and Ford, 1965), maize (Grogan

and Sarvella, 1964; Grogan et al., 1971), and sorghum (Lenz and Atkins, 1981).

Such effects in rice hybrids developed from WA cytosteriles V41A and Zhen

Shan 97A and four fertility restorer lines (IR24, IR30, Xin-ni-ai-he, and Shiu

Lian gu) have been reported in China (Lu et al., 1981). A comparison of F,

hybrids A X R and B X R indicated that ‘Sterile’ cytoplasm had negative effects

on number of spikelets per panicle, number of filled grains per panicle, 1OOOgrain weight, and yield per plant, although it had a positive effect on number of

tillers per hill. Observations at the IRRI c o n f m that such effects are present but

are cross specific; therefore it should be possible to eliminate the negative effects

of cytoplasmic male sterility through the selection of appropriate restorer lines.

Gomaa (1973) measured quantitatively and qualitatively the effects of T.

boeoticum and T . timopheevi cytoplasms on five spring wheat cultivars. The

male steriles in T. tinwpheevi cytoplasm were generally similar to their normal

counterparts for the characters measured. With T . boeoticum cytoplasm a combined analysis revealed significant cultivar cytoplasm interactions for seedling

vigor, vigor at heading stage, and spike length. C. F. Hayward (1975, unpublished) compared crosses of three restorer (male) lines with two male-sterile

(T. tinwpheevi) lines and their normal cytoplasmic (B line) counterparts. Hybrids

made on normal cytoplasm had yields 7.1% higher than their T . timopheevi

counterparts, although the magnitude differed considerably between crosses

(-3.5-22.0%). Mean heterosis levels averaged 19.9% in the normal cytoplasm

and 12.8% in the T. tinwpheevi cytoplasm.

Table IV

Interactions between the Genomes of T. dunun, T. aesh'vum, and T. tinropheevi and the

cytoplasms of Species of Aegilops, Tritieum, Secale, and Haynoldioa

Cytoplasm donor

Aegilops species

A. speltoides

A. bicornis

A. longissimae

A. sharonensisc

A. mutica

A. comosa

A. heldreichii

A. uniaristata

A. caudatac

A. umbellulata

A. squarrosa

A. cyIindrica

A. ventricosa

A. crassa

A. ovata

A. triaristata

A. biuncialis

A. columnaris

A. juvanalis

A. varzhbilis

A. kotschyii

A. triuncialisc

Triticum species

T. monoemcum

T. boeoticum

T. dicoccoides

T. dicmcum

T. dunun

T. aestivum

T. macho

T. dicoccoides var.


T. timopheevi

T. araraticum

T. zhukovskyi

Other species

Secale cereale

Haynaldia villosa


number (2n) and

genome symbol

Nucleocytoplasmic interactionsb

T. durum

T. aestivum

T. timopheevi

14, SS

14, SbSb

14, SISI

14, SISI

14, M'Mt

14, MM

14, MM

14, MUMU

14, CC

14, C U C U

14, DD

28, CCDD

28, DDM'JM'J


28, CUCuMM


28, W M M

28, CuCuMM



28, CuC'JSIS1


















28, AAGG

28, AAGG


14, RR

14, HH

"After Maan (1975) and Sasakuma and Maan (1978).

bF,male fertile; PF, partially fertile; S,male sterile; FS,female sterile; N, normal vigor; NN, near n o d vigor;

BN, below normal vigor; w.weak (markedly reduced vigor); Z, zygote elimination (nonviable seed); B, bushy

(stunted); E, early maturity; L, delayed maturity.

=Some evidence of intraspecific cytoplasmic variability has been obtained by using two 01 more accessions.



The effects of various nucleocytoplasmiccombinations involving the genomes

of common and durum wheat on a range of phenotypic characters were reviewed

by Maan (1973a,b, 1975) and Sage (1976). Sasakuma and Maan (1978) reported

on an extensive study in which the genomes of T. durum (selection 56-1) were

substituted into 22 cytoplasms, and the effects on pollen fertility, seed set,

heading date, and plant vigor were measured. Table IV represents the combined

data of Maan (1975), Sasakuma and Maan (1978), and some data supplied by S.

S. Maan (unpublished). It should be pointed out that the effects recorded are

those that were most easily observable. In the future, more precise measurements

may reveal different degrees of increased or reduced fertility and plant vigor. As

has already been reported for rice, different accessions within certain species

show nucleocytoplasmic interactions that differ sufficiently to suggest that

cytoplasmic differences are present; these are indicated in Table IV (S.S. Maan,

personal communication). The principal cytoplasmic effects resulting from various nucleocytoplasmic combinations included reduced vigor, delayed maturity,

pistilloidy, and nongerminating grain. Mukai and Tsunewaki (1979) also showed

that the degree of phenotypic deviation for a number of traits varied depending

on the cultivar or genome used. The literature on gene interaction indicates that

most genes do not act in isolation from other genes. Therefore, the alien

cytoplasms and nuclear genes controlling cytoplasmic effects from alien sources

may alter the phenotypic expression of various agronomic triats. Although no

yield-enhancing effects from nucleocytoplasmicinteractions have been reported,

the possibility of such an Occurrence should not be disregarded in the future as

increasing numbers of substitutions are made by hybrid breeders.




Although work to date has not revealed any relationship between CMS and

disease susceptibility in rice (Y. Y.Dong, unpublished data), the desirability of

hybrid rice and wheat breeders using more than one source of cytoplasmic male

sterility as a safeguard against potential disease epidemics is widely recognized.

Washington and Maan (1974) tested alloplasmic lines of T. aestivum (cultivars

Chris and Selkirk) and T. durum with three physiologic races of wheat leaf rust

(Pucciniu recondiru) at the seedling and adult plant stages. Although euplasmic

and alloplasmic Selkirk lines were resistant to all races at both stages, differences

were found in the cultivar Chris. Both forms were seedling susceptible,but adult

plants of euplasmic Chris were resistant, whereas certain alloplasmic lines were

susceptible or moderately susceptible to all races used. Other alloplasmic Chris

lines were susceptible to one race but not to the other two. These results indicate

that certain alien cytoplasms may alter the expansion of host nuclear genes for

resistance to certain physiologic races of leaf rust. Furthermore, the host parasite

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IV. Cytoplasmic–Genetic Male Sterility Systems in Rice and Wheat

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