Introduction

• Cultivated species of Cotton- 2 types

Tetraploids

• Gossypium hirsutum (2n = 52)
• Gossypium barbadense (2n = 52)

Diploids

• Gossypium arboreum (2n = 26)
• Gossypium herbaceum (2n = 26)

• Hybrids between the cultivated species of same ploidy level are fertile.
• Four intra specific hybrids (one in each species) and two inter specific hybrids of same deployed no. between Gossypium hirusutum x Gossypium barbadense and Gossypium arboreum x Gossypium herbaceum.
• Totally 6 different types of hybrids are theoretically possible.

• Four types of hybrids are only developed for commercial cultivation,
• Intraspecific hybrids in Gossypium hirsutum and Gossypium arboreum.
• Interspecific hybrids between tetraploids viz., Gossypium barbadense and Gossypium hirsutum and diploids G. arboreum x G.herbaceum.
• Interspecific hybrids between G.barbadense and G. herbaceum could not be released.

• India is the pioneer country for cultivation of hybrid cotton on commercial scale.
• Other countries where hybrid cotton is grown on commercial scale include China and Vietnam (ICAC, 1997).
• In china, hybrid cotton is cultivated on 3.3 Lakh hectares and in Vietnam about 70% of total cotton area is covered by hybrids.
• In India, hybrid cotton is cultivated on 40% of total cotton area. Efforts are being made to develop cotton hybrids in countries like USA, Pakistan, Uzbekistan and Israel.
• There is an International Cotton Advisory Committee (ICAC), Washington USA, that advises on various matters of cotton research and marketing.
• In India, research on hybrid cotton is carried by two types of organizations, viz.,
• Public research centres, and
• Private Seed Companies.

• Public research centres include Cotton research Institutes of the Indian Council of Agricultural Research and Cotton Research Stations of State Agricultural Universities.
• There are two ICAR Institutes where research on hybrid cotton is carried out.
• The first is Central Institute for Cotton Research (CICR), Nagpur and second is Central Institute for Research on Cotton Technology (CIRCOT), Mumbai.
• CIRCOT helps in evaluation of cotton hybrids in terms of fibre properties and spinning capacity.
• There are 13 research centres where research on hybrid cotton is carried out.
• These are located at Ludhiana, Hisar, Sirsa, Srinagar, New Delhi, Khandwa, Akola, Surat, Nagpur, Dharwad, Guntur and Coimbatore.

• Research on hybrid cotton is also carried out by various private seed companies.
• There are several private seed companies which are actively engaged in the development of high yielding and superior quality hybrids in cotton and several other field crops.

The list of some private seed companies is given below

• Maharashtra Hybrid Corporation (MHYCO), Jalna (Maharashtra).
• Nath Seed Company Private Limited, Aurangabad (Maharashtra)
• Mahendra Seed Company, Jalna (Maharashtra)
• Vijay Seed Company, Jalna (Maharashtra)
• Ankur Seed Company, Nagpur (Maharashtra)
• Hindustan Lever Limited, Mumbai (Maharashtra)
• Pioneer Seed Compnay, Hyderabad (A.P)
• Nagarjuna Agriculture Research and Development Institute, Secunderabad, Hyderabad (A.P.)
• Proagro Seed Company, New Delhi.
• The main function of these private seed companies is to develop superior hybrids in cotton and several other field crops.
• These companies also take up the hybrid seed production work of various commercially cultivated cotton hybrids.

Classification of Hybrids

• In cotton, different types of hybrids are developed for commercial cultivation which can be classified into various groups on the basis of
• species involved
• ploidy level or chromosome number, and
• method of hybrid seed production.
• A brief classification of cotton hybrids on the basis of these criteria is presented below:
• On the basis of species involved, cotton hybrids are of two types, viz.,
• Intraspecific hybrids, and
• Interspecific hybrids.

• A hybrid between genetically different genotypes of the same species is referred to as intraspecific hybrid. It is also known as intervarietal hybrid. Intraspecific hybrids are always fertile. In cotton, intraspecific hybrids have been released for commercial cultivation in G.hirsutum at tetraploid level and in G.arboreum at diploid level. The main features of intraspecific cotton hybrids are presented below:
• Intraspecific hybrids have been released in two species so far i.e., in G.hirsutum at tetraploid level and in G.arboreum in diploid level.
• Most of the Intraspecific hybrids have been developed by conventional method i.e., by hand emasculation and pollination method and very few have been evolved through the use of male sterility.
• Intraspecific hybrids of above two species can be cultivated both under irrigated and rainfed conditions. Intra arboreum hybrids are highly tolerant to sucking pests and drought conditions.
• Several intraspecific hybrids have been developed in G.hirsutum and very few in G.arboreum.
• The fiber quality and yield potential of intra-hirsutum hybrids is better than intra-arboreum hybrids.
• Intra-hirsutum hybrids have superior medium, long and extra long staple.
• The spinning potential of intra-hirsutum hybrids varies from 40s to 60s, whereas in intra-arboreum hybrids spinning capacity of 15-20 counts is observed.
• In G.hirsutum, one hybrid has been developed through the use of genitic male sterility (Suguna) and three hybrids through the use of cytoplasmic genitic male sterility system (PKVHy 3, PKVHy 4 and MECH 4) so far.
• Both intra-hirsutum and arboreum hybrids have wider adaptability.
• All the Intraspecific hybrids developed in G.hirsutum and G.arboreum are single cross hybrids.
• In G.hirsutum, first intraspecific hybrid was released in 1970 under the name H 4 from Main Cotton Research Station, Surat of the Gujarat Agricultural University. H 4 is the world's first cotton hybrid released for commercial cultivation. First intra-arboreum hybrid was released in 1994 under the name LDH 11 from Cotton Research Station of the Punjab Agricultural University, Ludhiana.
• Intraspecific hybrids do not have problems of neps and motes.

• The F1 progeny between two different species of the same genus is referred to as interspecific hybrid. This is also known as intrageneric hybrid. Development of fully fertile interspecific hybrids is possible only between those species that have complete chromosomal homology. In cotton, interspecific hybrids are fully fertile between G.hirsutum and G.barbadense and between G.herbaceum and G. arboreum. Main features of interspecific cotton hybrids are
• Interspecific hybrids have been released between G.hirsutum and G.barbadense at tetraploid level and between G.herbaceum and G. arboreum at diploid level.
• All the interspecific hybrids released for commercial cultivation so far both in tetraploid and diploid cottons have been developed by conventional method i.e., by hand emasculation and pollination.
• Intraspecific tetraploid hybrids are cultivated under irrigated conditions. They can not be grown under rainfed conditions because the G.barbadense parent in such hybrids is susceptible to drought conditions. However, interspecific diploid hybrids can be cultivated both under irrigated as well as rainfed conditions.
• Interspecific tetraploid hybrids are susceptible to sucking pests, whereas interspecific diploid hybrids are highly tolerant to sucking pests.
• Several interspecific hybrids have been released at tetraploid level and very few at diploid level.
• The interspecific tetraploid hybrids have better fiber quality and higher yield than interspecific diploid hybrids.
• Interspecific tetraploid hybrids usually have superior long staple, whereas the interspecific diploid hybrids have either medium or long staple.
• Interspecific tetraploid hybrids have better spinning capacity (70-80 counts) than interspecific diploid hybrids (20-40 counts)
• All the interspecific hybrids developed in tetraploid and diploid cotton so far are single cross hybrids.
• In tetraploid cotton, first interspecific hybrid was developed in 1972 under the name Varalaxmi from Cotton Research Station, Dharwad, University of Agricultural Sciences, Bangalore. In diploid cotton, first interspecific hybrid was released in 1985 from Main Cotton Research Station, Surat of the Gujarat Agricultural University for cultivation in Gujarat State.
• Interspecific tetraploid and diploid hybrids cover about 5% of the total cotton area and contribute about 8% to the national cotton production.
• Interspecific tetraploid and diploid hybrids are grown in central and south zones so far.
• Based on ploidy level:
• Cotton hybrids are of two types, viz.,
• Tetraploid hybrids, and
• Diploid hybrids.
• Those hybrids which are developed in tetraploid species are referred to as tetraploid hybrids and those produced in diploid species are known as diploid hybrids have been released for commercial cultivation. Brief description of tetraploid and diploid hybrids is presented below.

• Tetraploid hybrids are developed in G.hirusutum and G.barbadense. Tetraploid hybrids are of two types, viz., Intraspecific and interspecific. Intraspecific hybrids have been developed in G.hirsutum only.
• Intra-hirsutum hybrids have been released for commercial cultivation in all three zones. Intra-hirsutum hybrids can be cultivated both under irrigated and rainfed conditions.
• Interspecific hybrids have been released between G.hirsutum and G.barbadense for commercial cultivation in central and south zones. These hybrids are grown under irrigated conditions only.

• Diploid hybrids are developed between G.arboreum and G.herbaceum. Diploid hybrids are of two types, viz., Intraspecific and interspecific.
• Intraspecific hybrids have been developed in G.arboreum only. Intra-arboreum hybrids can be cultivated both under irrigated as well as rainfed conditions. Interspecific hybrids between G.herbaceum and G.arboreum have been released for commercial cultivation in central and south zones.
• Diploid hybrids have high degree of resistance to insect pests, diseases and drought conditions.
• The main drawback of diploid hybrids is that the hybrid seed production is a problem due to poor seed setting in crossed bolls.
• Based on method of hybrid seed production, hybrids are of two types, viz.,

• Hybrids which are developed by hand emasculation and pollination are referred to as conventional hybrids.

• Hybrids which are produced using either genetic male sterility or cytoplasmic genetic male sterility are referred to as non-conventional or male sterility based hybrids.

• Such hybrids are produced by hand emasculation and pollination method.
• Majority of cotton hybrids are developed by conventional method. Conventional hybrids have been developed in tetraploid and diploid cottons both at intraspecific and interspecific level.
• There are two main drawbacks of conventional hybrids.
• Firstly, the seed of such hybrids is very expensive because several laborers are engaged daily for emasculation process during crossing period.
• Secondly, hand emasculation causes some injury to the female part, resulting in poor hybrid seed setting.

• Such hybrids are developed through the use of either genic male sterility or cytoplasmic genitic male sterility.
• In cotton, very few hybrids have been developed through the use of male sterility.
• All the male sterility based hybrids have been released in G.hirsutum so far.
• The first hybrid was developed in 1978 under the name Suguna through the use of genic male sterility. Now three hybrids, viz., PKVHy 3, PKVHy 4 and MECH 4 have been developed through the use of cytoplasmic genic male sterility.
• There are two main advantages of male sterility based hybrids.
• Firstly, the seed of such hybrids is cheaper due to elimination of emasculation process.
• Secondly, the seed setting in such hybrids is higher because there is no mutilation of ovary due to elimination of emasculation process.
• However, the yield of presently released male sterility based hybrids is 10-15% lower than the conventional hybrid involving same parents.