are accustomed as a functional additive like- nano-zinc oxide, nano titanium dioxide, nano-
clay, titanium nitride nanoparticle in addition with nano clay. Packaging film introduced
with silicate nanoparticles keeps fresh of food by lowering oxygen flow, avoids leakage of
moisture outside the package, and also retard the growth of molds inside the refrigerator.

8. BIODEGRADABLE PACKAGING:

Globally, concerned that petrochemical based plastic substances have generated more interest in biodegradable or green packaging materials. The biodegradable plastics are those which degraded by the naturally occurring microorganisms like- bacteria, fungi, molds and algae. It satisfies principal requirement of an ideal candidate and includes many kinds of properties viz. as optical properties (transparency), migration resistance, barrier properties (against water vapor, light, gases and aromas), chemical and temperature resistance, retain sensory characteristics, welding and molding properties, antistatic properties, printing properties etc.

9. ACTIVE PACKAGING:

It is an innovative concept of food packaging in which product or environment both
associates to extend the durability of food although enhances safety and sensory properties.
The type of packaging allows active preservation of foods according to their requirements,
by alteration of atmosphere inside the package by removing unpleasant gases respectively.
Active system can be categorized on the basis of their functionality such as- Scavengers,
Regulators and Emitters; the internal environment may be adjusted by substances which
absorb (scavenge), release (emit) gases or vapors.

i. **Oxygen Scavengers:** It helps to retain quality of food by reducing food metabolism, lowers oxidative rancidity, inhibits growth of undesirable microorganisms, hinders the unwanted oxidation of labile pigments and vitamins, and retards enzyme discoloration. It provides surety of reducing oxygen level up to 0.01% whereas, non-metallic scavengers are those that uses organic reducing agents known as- catechol, ascorbate salts as well as ascorbic acid.

ii. **Carbon Dioxide Scavengers/Emitter:** There are various commercial sachet and labeled devices which can either scavenge or emits CO2. This is mainly applicable for freshly roasted and ground coffees that release notable volume of CO2.

iii. **Ethylene Scavengers:** Ethylene is a plant hormone which speeds up respiration rate ensuing senescence of horticultural products (vegetables, fruits and flowers.) Potassium permanganate (KMnO4) based ethylene (C2H4) scavengers are available in sachets to be placed inside packages, blankets, tubes that can be produced storage warehouses.

10. FLAVOR AND ODOUR ABSORBER PACKAGING:

The removal of odours from inside the food package may have both beneficial and detrimental effects; its function is to block the desirable odour from food product. Freshly packed foods like meats, poultry, cereals produce confinement odours. Very slight or generally insignificant but detectable deterioration odours mainly amino acid breakdown, lipid oxidation, anaerobic glycolysis etc. These odours are captured within gas barrier packaging so that when package opens it released or would be detected by consumers
therefore, these odors are remarkably harmless and do not signify any kind of spoilage.
Antioxidants are also including nowadays into polyolefin-processing additive package to
minimize the unwanted effects of odor. A small sachet carries certain harmless chemicals
that put inside the package mainly to absorb any undesirable odor or flavor from foods.
Silica and Ethylene vinyl alcohol are substantially used. The packaging has some exception
also that cannot be used in liquid foods or sometimes incidentally ingested by consumers.

CONCLUSION

Packaging is an art which represents particular product, good packaging or packaging material catches the attention of consumers towards a product. Various scientific as well as technological advances have brought revolutionary changes among packaging. Previously, people usually buy provisions, they used to carry various kind of bottles, vessels, gunny or jute bags. But nowadays, Packaging plays very crucial role in a modern economy. Numerous methods came which not only pack food products but also increases shelf-life, prevent from harmful microorganisms and provides a suitable environment to the food through various technologies.

REFERENCES

K.A. Mane (2016). A Review on Active Packaging: An Innovation in Food Packaging, *International Journal of Environment, Agriculture and Biotechnology*; Vol-1, Issue-3. http://dx.doi.org/10.22161/ijeab/1.3.34

P. Mahendra, D.Mridula(2019).Recent developments in food packaging technologies, Beverages and food world; 46(1): 21-25

M. Bhanu, K. Anu (2018), Anti-Microbial Food Packaging: Potentials and Pitfalls, *Front Microbiol*; 6

Luis Ruiz-Garcia, Jian-Ping Qian, and Xin-Ting Yang (2018), Food Packaging: A Comprehensive Review and Future Trends. *Comprehensive reviews in food science and safety*; 17.

Srilakshmi.B (2015). Food Science. 6th Edition. New Age International Publisher Limited https://en.wikipedia.org
# MALE STERILITY- THE GENETIC MECHANISMS AND IT'S TYPES

Aman Singh and Juhi Pandey

P.G. Scholar,

Department of Genetics and Plant Breeding, Acharya Narendra Deva University of Agriculture & Technology, Kumarganj, Ayodhya

## Introduction

Male sterility is characterized by inability to produce or release pollen grains in flowering plants. But they do produce viable eggs. In flowering plants, the first case of male sterility was reported by **J.K. Koelreuter** in 1763. Later on, numerous of male sterility was reported in Angiosperms. Male sterility have been also developed through genetic engineering (Rundfeldt 1960) and protoplast fusion (Pelletier et al. 1997). Male sterility were artificially induced through mutagenesis (Kaul 1998). Male sterility being used for development of hybrids in both tetraploid and diploid seed in various plants.

<figure><img src="image_38.png" /><figcaption>Figure1: Showing male sterile and male fertile flower</figcaption></figure>

* Male sterility occurs in many self-pollinated crops which hinders breeding and pollination.

* Male sterile plants have non-functional or non-viable pollen grains, which are formed through a chain of vital processes during microsporogenesis. The formation of non-functional pollens are due to mutation of any loci and they form under genetic control.
* Male sterility occurs naturally by mutations or can be artificially induced by physical or chemical mutagens. However, Ethidium Bromide is an effective chemical in inducing cytoplasmic male sterility.

* Pollen or anther abortion is another reason for male sterility.

## Types of Male Sterility

Male sterility is of three types, viz.

1) Genetic male sterility

2) Cytoplasmic male sterility

3) Cytoplasmic genetic male sterility

## 1. Genetic Male Sterility (GMS):

GMS is also called as nuclear male sterility. The pollen sterility that is caused by nuclear genes is termed as genic or genetic male sterility. This type of sterility has been reported in several crop plants like barley, wheat, maize, cotton, sorghum, lucerne, cucurbits, tomato and sugarbeet. Mostly sterility is caused by single gene but in some cases two or more genes also govern.

The male sterility alleles may occur spontaneously by mutation or by artificial means. A male sterile line may be maintained by crossing it with heterozygous male fertile plant, such a mating produces 1:1 male sterile and male fertile plants.

<figure><img src="image_39.png" /><figcaption>Figure2: Mechanism of Genetic Male Sterility</figcaption></figure>
## Utilization in Plant Breeding:

Genetic male sterility is usually recessive and monogenic thus utilized in hybrid seed production. It is used in both seed propagated crops and vegetatively propagated species. In this type of sterility progeny from crosses (msms X Msms) are used as a female and homozygous male fertile (MsMs) used as pollinator. The genotypes of msms and Msms lines are identical except for the ‘ms’ locus i.e they are isogenic lines and are known as male sterile (A) Maintainer B) Line respectively.

The female line possesses both male sterile and male fertile plants. Male fertile plants must be identified and removed before pollen shedding. This is done by identifying the male fertile plants in seeding stage either due to the pleiotropic effect of ms gene or due to phenotypic effect of closely linked genes.

Here the removal of male fertile plant from the female line is very costly and due to this cost of hybrid seed is higher. Therefore, GMS has been exploited commercially only in few crops by few countries. E.g. In USA it is used in castor while in India Arhar (cajanus cajan) hybrid is produced.

In cotton, GMS has been reported in upland, Egyptian and arboreum cottons. In tetraploid cotton, male sterility is governed by both recessive and dominant genes whereas, male sterility governed by recessive genes in practical plant breeding. The merits and demerits of GMS are presented below:

### Merits:

1) Large number of parents can be used in crosses, because all the genotypes have dominant genes for male sterility.

2) Only female parent of a good hybrid has to be converted.

3) GMS generally does not have undesirable agronomic characters.

4) It is possible to develop the varieties from segregating population of GMS.

### Demerits:

1) GMS is less stable. Sometimes, sterile plants become fertile under low temperature conditions.

2) In GMS, the lines segregate into male sterile and fertile plants in 1: 1 ratio.

3) To convert any genotype into GMS (ms5ms6) there is selfing after each backcross to isolate recessive genes. Therefore more number of generations are produced.

4) It requires more area as 50% of the population is fertile.

5) Low quantity of seeds are produced.

6) If fertile plants are not properly rogued out there could be admixture.

## 2. Cytoplasmic Male Sterility (CMS):

It occurs due to the occurrence of non-nuclear genes or cytoplasmic genes. This type of male sterility is determined by the cytoplasm. Since cytoplasm of the zygote comes from the egg cell, the progeny of such male sterile plants will always be male sterile. This type of male
sterility is important in certain ornamental species where the vegetative part is of economic value. The cytoplasm of zygote comes mainly from the egg cell and due to this progeny of such male sterile plants would always be male sterile.

CMS may be transferred to any plant by using that strain as a pollinator (recurrent parent) in a backcross programme. After 6-7 backcrosses the nuclear genotype of male sterile line would become 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 maintainer line or B line as it is used to maintain the male sterile line is also known as the A line.

<figure><img src="image_40.png" /><figcaption>Figure3: Showing Cytoplasmic Male Sterility</figcaption></figure>

## Utilization in Plant Breeding

CMS has limited application. Hybrids cannot be developed by this method, where seed is the economic product. But in some cases hybrids can be produced as in certain ornamental species or asexually propagated species like sugarcane, potato, and forage crops.

## 3. Cytoplasmic Genetic Male Sterility (CGMS)

This is a case of cytoplasmic male sterility for which a nuclear gene for restoring fertility in male sterile line is known Jones and Davis first discovered this type of male sterility in 1944 in onion. This type of male sterility has provision for restoration of fertility, which is not possible in cytoplasmic male sterility. The fertility is restored by the R gene (s) present in the nucleus. This is the case of cytoplasmic male sterility, where a nuclear genes restoring fertility in the male sterile line is known. The fertility restore gene 'R' is dominant and found in certain strains of the species. This genes restores male fertility in the male sterile line, hence is known as restorer gene.

This system includes A, B, and R lines. A line is a male sterile line, B is similar to 'A' except for it is a male fertile and R is restorer line as it restores the fertility in the F1 hybrid. Since B line is used to maintain the fertility factor thus referred as maintainer line. The plants would be male sterile line due to the presence of male sterile cytoplasm if the nuclear genotype is RR, but it could be male fertile if the nucleus is RR or Rr. New male sterile lines can be
produced following the same procedure as in the case of cytoplasmic system, but the nuclear gene constitution of the pollinator strain used in transfer must be the fertility would be restored. Development of new restorer strain is somehow indirect. Firstly a restorer strain (R) is crossed with male sterile line. The resulting male fertile plants are used as the female parent in repeated backcrosses with the strain (C) used as the recurrent parent to which transfer of restorer gene is to be done. In each generation, male sterile plants are rogued and the male fertile plants are selected as female for back crosses. This acts as selection device for the restores gene R during the backcross programme. At the end of back cross programme a restorer line isogenic or nearly similar to the strain 'C' would be obtained.

<figure><img src="image_41.png" /><figcaption>Figure4: Showing Cytoplasmic Genetic Male Sterility</figcaption></figure>

**Utilization in Plant Breeding:**

Cytoplasmic genetic male sterility is widely used for hybrid seed production of both seed propagated species as well as vegetatively propagated species. It is used commercially to produce hybrid seed in maize, bajra, cotton, rice, sunflower, jowar, etc.

Thus, the combination of both nuclear genes and cytoplasmic factors determines the fertility or sterility in such plants. The merits and demerits of CGMS are presented below:

**Merits**

1) In CGMS system, CMS is highly stable and is not affected by environmental factors.

2) In CGMS system, CMS 'A' line produces only male sterile plants.

3) Conversion of a genotype in CGMS system 'A' line is quicker and direct.

4) CMS requires less area for maintenance.

5) The quantity of seed produced is more.

6) There is no chance of admixture.

**Demerits**

1) In CGMS, only limited number of crosses can be made due to availability of limited number of restorers.

2) In CGMS, both male and female parents of the hybrid need to be converted.
3) CMS is solely controlled by cytoplasmic genes and hence it may have some adverse effect on other characters.

4) It is not possible to breed a variety from CMS line.

## Maintenance of Male Sterility

As already mentioned in cotton, two types of male sterilities are used. Maintenance procedure for each type is given below.

### Maintenance of GMS Lines

GMS lines is maintained by sib-mating between fertile and sterile plants. The pollination is done by hand. The identification of sterile plants is easy by trained eyes and thus 50% plant population is to be rogued out.

### Maintenance of CMS Lines

The CMS line referred to as 'A' line is maintained by crossing to its counter 'B' line (Isogenic Line).

* The 'B' line, a sterility maintainer line, is maintained by selfing.

* The 'R' line, a fertility restorer line, is maintained by selfing.

## Conversion into Male Sterile Lines

The potential female parents of hybrids can be converted into male sterile lines. To convert in GMS, four to five backcrosses are done followed by alternate selfing. Finally, a line which is heterozygous for sterility and showing 1: 1 segregation is selected having all the characters of the recurrent parent. The local genotypes with good agronomic characters can be converted into CMS line by performing five to six backcrosses. Similarly, the desired male parents can be converted into restorer lines by five to six backcrosses along-with a 'Rf' factor. Finally, a homozygous line for 'Rf' factor is selected. So many promising varieties and elite germplasm lines have been converted into CMS and restorer lines and few in GMS background also.

There are three important sources of male sterility viz. interspecific crosses, spontaneous mutations and induced mutations. These are briefly discussed as follows:

### 1.Interspecific Crosses

The cytoplasms of three diploid species, viz. G. anomalum, G. harknessii and G. arboreum combine with nuclear genes of G. hirsutum and produce male sterility.

The cytoplasm of G. arboreum and G. anomalum are less stable as they are temperature-sensitive. The cytoplasm of G. harknessii and genome of G. hirsutum interaction produce stable and dependable cytoplasmic male-sterility in cotton over all environments, though some inappropriate results on ginning outturn, micronaire value and bacterial blight susceptibility have been reported.

Very recently, a new male sterility system of cytoplasmic nuclear genic male sterility has been developed by interspecific cross using a synthetic allopolyploid between G.
*anomalum* x *G. thurberi* at Akola. The new male sterility system avoids the tiresome work of insertion of R genes into cultivated species / genotypes which is the main impotent step of CGMS.

## 2. Mutations

Male sterility caused by mutagens has been reported in nearly 35 crop species including cotton. In *G. arboreum*, the first spontaneous male sterile mutant was described in variety DS-5 developed at Haryana Agricultural University, Hisar. The gene is termed as *ams1*. The semi and complete male sterility has been achieved by various workers from the crops that are treated with X-rays, gamma rays and Ethyl Methane Sulphonate (EMS).

## 3. Induction of Male Sterility by Male Gametocides

Male sterility can also be obtained through the use of chemicals, which are commonly known as male gametocides. Some common examples of the chemicals used for induction of male sterility is FW 450 (Sodium B Dichloro-iso-butyrate) or MH-30 (Maleic hydrazide) and Ethidium bromide (a potential mutagen).

## Development of MS Based Hybrids

The main application of Male sterility is the development of hybrids. All the three types of male sterility are used for crop improvement. In India, few hybrids in cotton have been developed by using the GMS system. **CPH2 (Suguna)** was the first male sterile hybrid released in 1975 from CICR Regional Station, Coimbatore. However, this GMS based hybrid did not spread much because of lack in seed production efforts. The *G. harknessii* cytoplasmic male sterility possesed fertility restoration gene sources and were used in developing the hybrid CAHH 468 (PKV Hy-3).

<table><thead><tr><td>MS Based Hybrids</td><td>Conventional Hybrids</td></tr></thead><tbody><tr><td>Planting ratio for female to male is 4: 1 or 3: 1</td><td>Planting ratio for female to male is 2:2.</td></tr><tr><td>Half day labours are required for pollination in case of GMS (few labours are required for identifying and roguing of fertile plants)</td><td>Full day labours are required for emasculation and pollination</td></tr><tr><td>For one kg seed production, one female labour required per day.</td><td>For one kg of seed production, three female labours are required for one day.</td></tr><tr><td>One female labour can pollinate 2000-3000 flowers</td><td>One female labour can emasculate and pollinate 200- 300 flowers.</td></tr><tr><td>Quantity of seed produced is more due to high Seed setting as there is no malformation in the female part.</td><td>Amount of seed produced is less as there are more chances of mechanical injury during emasculation.</td></tr><tr><td>Immature seed % is low.</td><td>Immature seed % is high.</td></tr><tr><td>Shedding % of crossed bolls is nearly negligible.</td><td>Shedding % of crossed bolls is more due to mechanical injury.</td></tr></tbody></table>
<table><tr><td>Self-pollinated bolls is negligible (chance only in GMS)</td><td>Self-pollinated bolls are high.</td></tr><tr><td>Spread of hybrids is rapid.</td><td>Spread of hybrids is slow.</td></tr><tr><td>Use of F2 seed as planting material is not possible.</td><td>Use of F2 seed, as planting material is possible.</td></tr></table>

Table: Difference between MS based and Conventional Hybrids

However, the genetic male sterility is not much followed by the seed producers because of the following reasons:

a. The 50% plants are to be rogued out at the time of crossing.

b. There is possibility of admixture if fertile plants are not properly rogued out.

c. The quantity of hybrid seed produced by GMS is less than that produced by CMS system.

Future Thrusts

➤ In case of cotton, now both genetic male sterility as well as cytoplasmic genic male sterility are available. In tetraploid and diploid cotton these are being used for developing MS based hybrids and some GMS based hybrids. The future research work on male sterility has to be forwarded towards following thrust areas:

➤ Identification of high yielding hybrids with already known threshold points of fertility conversion of different A-lines regarding temperature and photo-period.

➤ Attempts made to understand the molecular basis of sex reversion under different environments.

➤ Identify genes/QTLs responsible for controlling this character that will help in quick transfer of these genes into heterotic hybrid parents.

➤ In GMS, 50% population is male fertile and are identified only after flower initiation. Thus use of marker genes is essential in GMS for early identification and removal of fertile plants.

➤ The GMS is sensitive to temperature which sometimes become fertile at low temperature (below 16°C). Efforts are needed to identify temperature insensitive and highly stable GMS lines.

➤ Male sterility has been developed through genetic engineering in various crops. Efforts should be made to develop male sterile lines in cotton through genetic engineering.

➤ In CGMS system, the male sterile cytoplasm has some adverse effects on insect resistance and fibre quality. Hence, efforts should be made to eliminate undesirable effects of sterile cytoplasm.

➤ The cost of conventional hybrids seeds is very high (Rs. 600-1000) which cannot be afforded by small and marginal farmers. Hence, care should be given to develop MS based hybrids to provide hybrid seed to the farmers at much lower rate.
**Limitation**

Male sterility is useful in hybrid seed production. However, it has some disadvantages. It is very difficult to identify the male sterility line (when controlled by nuclear genes) before anthesis. Moreover, male sterility cannot be effectively used in those crops in which efficient natural pollen dispersal mechanism is lacking and flower morphology is not suitable for cross pollination. In some cases, GMS line becomes fertile under low or high temperature conditions. Moreover, sterile cytoplasm has adverse effects on yield components in some crops.

**Reference**

1. Essentials of Plant Breeding by Phundan Singh.

2. Methods and Principles of Plant Breeding by BD Singh.

3. Male Sterility in Flowering Plants by SK Dahiya.

4. Plant Breeding Theory & Practices by VL Chopra.