Male Sterility

  • Male sterility :- Presence of non-functional pollen grains and absence of functional pollen grains. (while female gametes function normally).
  • It occurs in nature sporadically due to mutation.
  • Male sterility enforces cross pollination.
  • Male sterility can be exploited as a tool to eliminate the need for emasculation for producing hybrid seed.
  • A-Line - Male sterile line
  • B-Line/maintainer Line - Isogenic Line of A-line with male Fertility.
  • R-Line/Restorer Line - A line which restores Fertility when crossed with CGMS-line.
  • There are three basic kinds of male sterility based on the origin of the abnormality:-
    1. True male sterility:- This is due to unisexual flowers that lack male sex organs (Dioecy and monoecy), or bisexual flowers with abnormal or non-functional microspores (leading to pollen abortion).
    2. Functional male sterility:- The anthers fail to release their contents even though the pollen is fertile.
    3. Induced male sterility:- Plant breeders may use chemicals to induce sterility.
  • True male sterility is classified into three groups : - (1) Genetic Male Sterility (GMS) (2) Cytoplasmic Male Sterility (CMS) (3) Cytoplasmic – Genetic Male sterility (CGMS)
(1) Genetic (Nuclear, Genic) Male Sterility (GMS)

  • Caused by nuclear genes.
  • GMS is usually recessive & Monogenic.
  • Generally governed by a single recessive gene (ms).
  • However, male sterility in alfalfa has been reported to be under the control of two independently inherited genes.
  • Dominant genes governing male sterility are also known in safflower.
  • It consists two types lines via A-line & B-line
  • A-Line-ms-Female parent (sterile)
  • B-Line-Ms- it is used to maintain A-Line(male parent)(fertile).
  • ms – Male sterile , Ms – Normal anthers
  • The genetically male sterile line (msms) can be maintained by crossing them with a heterozygous male fertile (Msms) (pollen source) plants.
  • Such a mating produces 1:1 male sterile (msms) and male fertile (Msms) plants.
  • The progeny from ms ms x Ms ms crosses are used as female, and are inerplanted with a homozygous male fertile (Ms Ms) pollinator.
  • 50% fertile rouged out before flowering. This is done by identifying the male fertile plants in seedling stage either due to the pleiotropic effect of the ms gene or due to the phenotypic effect of a closely-linked gene.
  • GMS can be used for the production of hybrid seeds in both seed propagated crops & vegetatively propagated species.
  • 50% plants are fertile which have to be removed every year. This increase the cost of hybrid seed.
  • In USA, it is being successfully used in Castor.
  • In India, it is being used for hybrid seed production of Arhar.
  • Molecular markers (including SCAR,STS, RAPD) associated with male sterility have also been found in some plant species.
(2) Cytoplasmic Male Sterility (CMS)

  • Male sterility is controlled by the cytoplasm (Mitochondrial and chloroplast genes) but may be influenced by nuclear genes.
  • A cytoplasm without sterility genes is described as normal cytoplasm, while a cytoplasm that causes male sterility is called a sterile cytoplasm or said to have CMS.
  • The cytoplasm of a zygote comes primarily from egg cell, the progeny of such male sterile plants would always be male sterile.
  • Nuclear genotype of male sterile line would be almost identical to that of the recurrent pollinator strain.
  • The male sterile line is maintained by crossing it with the pollinator strain used as the recurrent parent in the backcross programme since its nuclear genotype is identical with that of this new male sterile line. such a male fertile line is known as the maintainer line or B line as it is used to maintain the male sterile line is also known as the A line.
  • CMS is useful for ornamental or vegetatively propagated crops where vegetative parts are of economic value.
  • F1 of CMS line is always male sterile, therefore, it cannot be used for crops where seed is the economic part.
  • This system has real advantages in breeding ornamental species because all the offspring is male sterile, hence allowing them to remain fruitless. By not fruiting, the plant remains fresh and in bloom for a longer time.
(3) Cytoplasmic – Genetic Male sterility (CGMS)

  • Both Genetic & Cytoplasmic factors are involved
  • Nuclear gene restore the fertility in male sterile Line.
  • Fertility Restorer gene ‘R’ is dominat & restores male fertility in the male sterile line, hence it is known as restorer gene.
  • Plant would be male sterile in the presence of male sterile cytoplasm if the nuclear genotype were rr, but would be male fertile if the nucleus were Rr or RR.
  • The nuclear genotype of the pollinator strain used in such a transfer must be rr, otherwise the fertility would be restored.
  • The development of new restorer strains is somewhat indirect. First, a restorer strain (say R) is crossed with a male sterile line (A).
  • The resulting male fertile plants are used as the female parent in repeated backcrosses with the strain (C) (used as the recurrent parent), into which the transfer of restorer genes(s) is desired.
  • In each generation, male sterile plants are discarded, and the male fertile plants are used as females for backcrossing to the strain C.
  • This acts as a selection device for the restorer gene R during the backcross programme.
  • At the end of backcross programme, a restorer line isogenic to the stain C would be recovered.

About Author / Additional Info:
I am currently pursuing Ph.D. in Plant Breeding and Genetics from MPUAT-Udaipur (Raj.)