Plant Breeding Practices in Cotton (Gossypium spp)

Plant Breeding Practices in Cotton (Gossypium spp)

India possessed the flourishing expert trade in cotton and cotton fabrics in early historic time. India now grows largest acreage of cotton than any country in the world. In India cotton is cultivated from he lower Himalayas in north to the extreme southern tip, but 90% of the acreage is in southern India.

The per acre yield in India is low as cotton is planted mostly at beginning of monsoon and is dependent upon the destruction of monsoon and is dependent upon the low soil fertility , lack of fertilization and poor cultured. Practises, major states growing cotton are M.S, Gujarat, Karnataka, Punjab, M.P, Andhra, Rajasthan and Tamil Nadu in India.

Origin:

Cotton belongs to genus Gossypium. The genus has 35 diploid (ABCDEF genomes) and 6 tetraploid species out of these only two diploid and two tetraploid species are categorized as cultivated.

  
The new world tetraploid species are allapolyploids, which originated by hybridization between old world and the new world diploid species.

Diploid old world species X Diploid new world species
2n = 26 (AA)                        2n = 26 (DD)

F1 2n=26 (AD)
Chromosome doubled 4n=52 (AADD)
Tetraploid new world species

Gossypium hirsutum was first time introduced into Bombay in 1790 and most early introductions failed due to attack of Jassids and leaf minor. During recent years many agricultural varieties are developed. New varieties originated from crosses involving older varieties races or species.

The cultivated new world Allotetraploid cotton species dominate world cotton production Gossypium barbadense is known for extra log fine and strong fibre. Cultivated Gossypium hirsutum upland cotton accounts for major world production.

Hybridization:

Normally pollen shed directly on the stigma when anthers open. Pollen is rarely wind born, as it is heavy and sticky. Cross – pollination to the extent of 5 to 30 % is possible by insects, mostly honey bees.

For hybridization emasculation is done one day earlier of the flower opening. Corolla is removed by hand or cut away with scissors. The stamens are removed with forceps. Ripe anthers are collected from pollen parent in straw tube and slipped over emasculated stigma and stigma immediately enclosed with bract by wire. Similarly, ripe anthers can be rubbed on the stigma of the emasculated flower. The pollination is usually done a day after emasculation. The emasculation may be done
1) By taking circular cut at the base and piercing needle through staminal tube or 2) Removed of anthers by pointed forceps. It is also be done by thumb and nail method and instead of bagging small piece of straw tube inserted over stigma of emasculated flower and tied along with bracts with thread.

Breeding Objectives:

1. High yield and early maturity.
2. Resistant to disease and pests
3. Breeding for staple length, fiber strength , fineness of fiber.
4. Increased lint to seed ratio.

Breeding Methods:

1) Introduction :

Cambodia cotton in 1906 from America, Andrews from sea Island.

2) Pure Line Section:

Pure line selection is practised for maintainers of genetic purity of existing varieties and development of new by selection with in hybrid population. Pure lines varieties developed one Ganga-1, CC-2, MCU-5, SRT-1, Eknath, Sanjay.

3) Pedigree Method:

This method practised by crossing two complementing parental lines. In the early generations the individual both plant progenies are grown as in the self pollinated crops and selection is practised both between and within rows for favourable traits. In later segregating generations promising lines for plant type, insect pest and disease varieties. Varieties : Laxmi, PKV-81, KOP-203.

4) Heterosis Breeding:

India is created first country where hybrid cotton (H4) was used on commercial scale in 1970 on seed production by hand emasculation. Latter on number of hybrids were released for commercial cultivation.

E.g. H4- Gujarat 67 X American Nectariless (Irrigated)
Godavari – Buri Nectariless X MCU -5 (Rainfed)
NHH-44 – Becaneri Nermax X AC-738.
Varlaxmi – Laxmi X SB 1085 -6

Using cytoplasmic genetic male sterility can also produce the hybrid. so the tedious task of hand emasculation can be avoided but pollination is done manually to increase the seed set. Keeping of honeybee and also hand pollination used to facilitate pollination in hybrid seed production programmes. E.g. Hybrid AKH – 468 ( AK-32 X DHY-286-1)

Resistance Breeding:

When suitable donor parent available the resistant varieties are developed by back cross breeding.

Bacterial Blight:

PS-10 (Donor Parent)

Bollworms and Jassids:

Khandra-2, bari-1007 (Donor Parent)

Genetic Engineering (Biotechnology) :

Insect cause more damage to cotton than any other crop. Cotton growers need reliable insect control system that does not involve time consuming application, expensive chemicals and elimination of beneficial insect so Bilt in genetic resistance is the only solution.

The best source for these genes is the bacteria, Bacillus thuringiensis (Bt) products insecticides properties, which toxic to insects but is is non toxic to humans and animals. It is highly effective against most important cotton insects as budwarm, bollworm, pink bollworm etc. Monsanto agricultural company of America discovered to transfer single gene in cotton plant from Bt. The human and animal digest the protein smaller to other proteins. When gene come in contact of insect proteins degradation of proteins take place, causing the death of insect. Morasses of USA has developed the cotton variety resistant bollworm complex known as ‘Bolgard’ is completely resistant is in commercial use.