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MALE-STERILITY
Several forms of pollination control
1. Manual emasculation
2. Use of male sterility
3. Use of self-incompatibility
4. Use of male gametocides
5. Use of genetically engineered “pollen killer” genetic
system
Male-sterility
Plant that do not produce viable, functional pollen grains
An inability to produce or to release functional pollen as a
result of failure of formation or development of functional
stamens, microspores or gametes
Phenotypic classes of sterility
• “Pollen sterility” in which male sterile individuals differ
from normal only in the absence or extreme scarcity of
functional pollen grains (the most common and the only
one that has played a major role in plant breeding)
• “Structural or staminal male sterility” in which male
flowers or stamen are malformed and non functional or
completely absent
• “Functional male sterility” in which perfectly good and
viable pollen is trapped in indehiscent anther and thus
prevented from functioning
Types of Male-sterility
 Genetic male sterility
 Cytoplasmic male sterility
 Environment sensitive genetic male sterility
 Chemical induced male sterility
 Genetically engineered male sterility
Cytoplasmic male-sterility
 CMS is the result of mutation in the mitochondrial
genome (mtDNA), which leads to mitochondrial
dysfunction.
 Stamen (anther and filament) and pollen grains are
affected
Cytoplasmic male-sterility
 The nuclear genetic control of CMS is predominantly
governed by one or more recessive genes, but can be
also dominant genes as well as polygenes
 The different mtDNA restriction endonuclease digestion
patterns are reflections of aberrant intra- or inter
molecular DNA recombination events in the mitochondrial
genome which have either modified existing genes or
related new genes some of which are more or less
related to the male sterile phenotypes
Cytoplasmic male-sterility
Origins:
1. Intergeneric crosses
2. Interspecific crosses
3. Intraspecific crosses
4. Mutagens (EMS, EtBr)
5. antibiotic (streptomycin and Mitomycin)
6. Spontaneus
CMS Characterization
It has been traditionally characterized by the restore
genes required to overcome the CMS and to provide
male sterile progeny in the male sterile system
CMS restoration is by nuclear genes, frequently
dominant in action, in many cases, few in number
The CMS restore genes temporarily suppress the
expression of the CMS permitting normal or near-normal
pollen production
Types
a. Autoplasmic
CMS has arisen within a species as a result of spontaneous
mutational changes in the cytoplasm, most likely in the
mitochondrial genome
b. Alloplasmic
CMS has arisen from intergeneric, interpecific or occasionally
intraspecific crosses and where the male sterility can be
interpreted as being due to incompatibility or poor co-operation
between nuclear genome of one species and the organellar
genome another
CMS can be a result of interspecific protoplast fusion
CMS mechanism of action
Abnormal behavior of the tapetum in the anther
Genetic determinant of CMS reside in mitochondria
Nuclear gene control the expression of CMS
CMS Limitations
Pleiotropic negative effect of the CMS on agronomic
quality performance of plants in the CMS cytoplasm
Enhanced disease susceptibility
Complex and environmentally unstable maintenance of
male sterility and/or male fertility restoration
Inability to produce commercial quantities of hybrid seed
economically because of poor floral characteristic of
cross pollination
CMS Utilization
 It provides a possible mechanism of pollination control in
plants to permit the easy production of commercial
quantities of hybrid seeds
 It consists of a male sterile line (the A-line), an isogenic
maintainer line (The B line), and if necessary also restore
line (the R-line)
 A lines are developed by back-crossing selected B-lines to
a CMS A-line for 4 – 6 times to generate a new A-line, B
and R-lines are developed by similar back cross
procedures using a CMS R-line as female in the original
cross and a new line as the recurrent parent in 4 – 6
backcrosses
CMS Utilization
Selfing the last backcross generation two
successive times and selection of pure breeding
male fertility restore line is required to complete
the development of the new R-lines developed
in the CMS
Current commercial hybrid seed production
relies entirely on the block method (alternating
strips of female and male genotypes
Fertility restoration in maize
Simple hybrid with cms and
restoration
CMS line (A-line)
CMS, rfrf
Large amounts
of CMS line
S
F
x
rr
S
rr
S
Rr
rr
x
Maintainer line (B-line)
N, rfrf
F
RR
Fertile F1 hybrid
CMS, Rfrf
Male line (C-line)
N and RfRf
Nuclear male sterility
 Originated through spontaneous mutation or mutation
by ionizing radiation and chemical mutagens such as
ethyl methane sulphonate (EMS) and ethyl imine (EI) or
by genetic engineering, protoplast fusion
 can probably be found in all diploid species
 Usually controlled by mutations in genes in the single
recessive genes affect stamen and pollen development,
but it can be regulated also by dominant genes
Morphology
 Variable (complete absence of male
reproductive organs to the formation of normal
stamen with viable pollen that fail to dehisce)
 It is not distinguishable from parent fertile
plants with the exception of flower structure
 Male sterile flowers are commonly smaller in
size in comparison to the fertile
 The size of stamens is generally reduced
Determining factor
 Temperature (TGMS)
Changing the optimal temperature can induce sterility
(23°C)
 Photoperiod (PGMS)
It has a strong influence (Photoperiod sensitive)
Changing the growth habit can stimulate the sterility
(23°C - 29°C)
Cytological Changes
 Breakdown in microsporogenesis can occur at a
number of pre-or postmeiotic stages
 The abnormalities can involve aberration during
the process of meiosis, in the formation of
tetrads, during the release of tetrad (the
dissolution of callose), at the vacuolate
microspore stage or at mature or near-mature
pollen stage
Use of genic male sterility in
hybrid programs
 Male sterile plants of monoecious or
hermaprodite crops are potentially useful in
hybrid program because they eliminate the labor
intensive process of flower emasculation
Hybrid seed production with GMS
and restoration
Male sterile line
msms
Male sterile line
msms
X
X
Male fertile line
MsMs
Maintainer line
Msms
Seed for harvested in bulk from male sterile line
Maintenance plot
Plants with
Msms and
msms
genotypes
Harvest seed
only from sterile
plants
Hybrid seed production plot
Female rows
Msms & msms
male rows
Female rows
Msms & msms
Remove fertile plants
from rows before
anthesis, harvest seed
from sterile plants
Cytoplasmic-genetic male sterility
• A case of cytoplasmic male sterility where a
nuclear gene for restoring fertility in the male
sterile line is known.
• The fertility restorer gene R is dominant.
Various Genotypes and Phenotypes
S
rr
F
Cytoplasm sterile
Nuclear gene non restorer
Cytoplasm fertile
Nuclear gene non restorer
rr
S
RR
S
Rr
Cytoplasm sterile (Male fertile)
Nuclear gene restorer in homozygous RR or heterozygous
Rr state
The effect of sterile cytoplasm is negated by the restorer
gene
CHEMICAL INDUCED
MALE-STERILE
Biochemical means of producing
male sterile plants
 Feminizing hormones
 Inhibitors of anther or pollen
development
Inhibitors of pollen fertility
Chemical hybridizing agent (CHA)
 Could be used in the large scale commercial
production of hybrid seed
Are applied to plant only at certain critical
stage of male gametophyte development
The logic of chemical hybridization






High degree of efficacy and developmental selectivity
Persistence during the development of flower or spikes
Low cost
Acceptable levels of toxicity to people and the environment
Low general phytotoxicity
Agronomic performance of hybrid seed produced is not
inferior to equivalent crosses produced by genetic methods
CHAs and pollen development
 There are at least 4 classes of chemical agents:
a. Plant growth regulators and substances that disrupt floral
development
b. Metabolic inhibitors
c. inhibitors of microspore development
d. inhibitors of pollen fertility
Plant growth regulators and substances
that disrupt floral development
 Plant hormones/hormones antagonists
a. auxins and auxin antagonists (NAA, IBA, 2,4-D, TIBA,
MH)
b. Gibberellins and antagonist (GA3, GA4+7, CCC: 2chloroethyl-trimethyl ammonium chloride)
c. Abscisic acid
 Other substances
a. LY195259
b. TD1123
Metabolic Inhibitors
 There are halogenated aliphatic acids (alpha, betadichloroisobutyrate and 2,2-dichloropropionate salts) and
arsenicals (methanearsonate salts)
 They affect mitochondrial protein by reducing the
efficiency of normal metabolic processes
Inhibitors of microspore development
 Copper chelators
 Ethylene
 Fenridazon
 Phenylcinnoline carboxylates (SC-1058, SC-1271
and SC-2053)
Inhibitors of pollen fertility
 Azetidine-3-carboxylate (A3C, CHA™)