Use Of Male Sterility In Plant Breeding

Pollen grains which are non-functional called Male sterility . Male sterility may be broken down into three categories: cytoplasmic, genetic, and genetic cytoplasmic male infertility.

(a) Genetic male sterility

This particular form of male sterility develops in plants owing to mutation of the fertility locus, which is located on chromosomes inside the nucleus, much like any other morphological qualities, including mono and oligogenic traits. Cytoplasm is not responsible for bringing about sterility in this instance. Only one of the three genotypes that might exist for this locus is male sterile.

Fertile (R-line) = RR
Fertile (B-line) = Rr
Sterile (A-line) = rr

Sterility maintenance

Fertile and sterile progenies are produced in equal numbers when AxB lines are crossed. The fertile plants must be rapidly removed before the pollen grains shed in order to maintain the sterile line. By employing marker genes, it is possible to eliminate fertile plants at an early stage of plant development.

Fertility restoration

A-line and R-line can be crossed to create fertile lines. It can be employed for the preservation of variety, genetic research, and the generation of hybrid seeds.

(b) Cytoplasmic male sterility

The fertile cytoplasm is converted into a sterile one as a result of mitochondrial mutation or other cytoplasmic causes that are not related to the nucleus. Not involved are nuclear genes. Furthermore, only two genotypes, one of which is sterile and the other fertile, are feasible when there are only two types of cytoplasm, sterile and fertile. (F – B Line) designates the fertile cytoplasm, while (S – B Line) designates the sterile cytoplasm (f – A line).

Sterility maintenance

Cytoplasmic sterility can be maintained as follows due to two different sorts of genotypes:

Fertility restoration

Restoring fertility is not possible since there is no third genotype that can serve as an R-line. This does not, however, cover every use for cytoplasmic sterile lines.

Uses

This kind of sterility is only helpful in crops if the seed is not the desired end result since restoration is not possible. This is crucial for horticultural crops whose vegetative components have a marketable use.

(c) Cytoplasmic-genic male sterility

Such sterility results from the interplay of one or more nuclear genes and sterile cytoplasm with conditioned sterility. In essence, cytoplasmic genic sterility is cytoplasmic sterility with a mechanism for fertility restoration. The (R) gene, which is present in the nucleus, restores fertility.

The fertility or sterility of such plants is determined by the interaction of nuclear gene(s) and cytoplasmic factors. Based on these combinations, a maximum of six different genotype types are possible, only one of which is sterile.

Sterility maintenance

Only the [(rr) f] genotype can keep the A-line sterile, as shown by their genetic makeup and cytoplasm.

Fertility restoration

This is accomplished by choosing restorer lines that, when crossed with an A-line, may produce all viable offspring. The only restorer or R-line genotypes are [(RR) F] and [(RR) r] out of the six potential genotypes. All fruitful progenies are produced by them.

Uses

In crops where seed is the intended end result, cytoplasmic-genic male sterile lines are of tremendous value in using hybrid vigour.

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