Anakha Mohan

2014.20.123

Distant Hybridization

• crossing between two genetically dissimilar parents.

• Interspecific Hybridization:- Crosses made between distantly related species.

• Intergeneric Hybridization:- Crosses made between distantly related genera.

Distant Hybridization/wide cross

History

Thomas Fairchild (1717) Karpechenko(1928)

Rimbu(1890)

Raphanobrassica

BrassicaRhaphanus

Inter-specific hybridization

Ex. Nerica, an upland rice for Africa.

• Oryza sativa (Asian upland rice): non-shattering, resistant to lodging, high yield potential

• Oryza glaberrima (African rice): drought tolerant, disease resistant, weed-suppressing

• Nerica rice combines the best of both species

•

Asian rice African rice

Nerica rice

• Triticale, a new cereal created in the lab.

• Intergeneric cross between wheat and rye.

• was produced by embryo rescue of the product of fertilization & chemicallyinduced doubling of the chromosomes.

• Embryo rescue becomes necessary when fertile offspring is never produced byan interspecific cross

Inter-generic cross

wheat Rye

Triticale

Hexaploid and Octaploid Triticale

Rye(secale cereale) Bread wheat(Triticum aestivum)

Diploid Sporophyte=14 Hexaploid sporophyte=42

Haploid gamete n=7 Triploid gamete 3n=21

Rye + Wheat =Triticale(4n=28) colchicine Triticale(8n=56)

Rye(secale cereale) Durum Wheat(T.turgidum)

Diploid sporophyte=14 Tetraploid sporophyte=28

n=7 2n=14

Rye + Wheat =Triticale(3n=21) colchicine Triticale(6n=42)

• when the desirable character is not found within the species.

• effective method of transferring desirable gene into cultivated plants.

• gives rise to three types of crosses viz. a) fully fertile, b) Partially fertile and c) Fully

sterile in different crop species.

Main features of Interspecific or Intergeneric hybridization

• . F1 hybrid between two genus are always sterile. The fertility has to be restored by

doubling of chromosome through colchicine treatment.

contd’

• colchicine is for inducing polyploidy in plant cells by inhibiting chromosome segregation during meiosis

• half the resulting gametes contain no chromosomes.

• other half contains double the usual number of chromosomes.

Colchicine

• lead to embryos with double the usual number of chromosomes.

• frequently results in larger, fast-growing, and in general more desirable plants than the normally diploid parents.

• this type of genetic manipulation is frequently used in breeding plants commercially.

Contd’

Disadvantages

• CROSS INCOMPATIBILITY

• HYBRID INVIABILITY

• HYBRID STERILITY

• HYBRID BREAKDOWN

Techniques to make wide crosses successful

• Selection of plants

• Manipulation of ploidy

• Bridge crosses

• Use of pollen mixture

• Manipulation of pistil

• Use of growth regulators

• Protoplast fusion

• Embryo rescue

Crop Character transferred Species transferred

from

Species transferred to

Cotton Jassid resistance

Blackarm resistance

G.Tomentosum

G.arboreum

G.Hirsutum

G.barbadense

Okra Resistance to YMV Abelmoschus manihot A. esculenta

Groundnut Resistant to leaf chewing insect Arachis monticola A.hypogea

Wheat Rust resistance Agropyron T. aestivum

Tobacco Resistant to mosaic virus N.repanda N. tabaccum

IMPROVING THE CROP PLANTS FOR

a). Disease and insect resistance

b). Improvement in quality

Crop Character transferred Species transferred from Species transferred to

Cotton Fibre lengthMale sterility

G. Thurberi &G. RaimondiiG. harkenssii

G. hirsutum

G. hirsutum

Potato Starch contentFrost resistance

Wild speciesSolanum acaule

Cultivated Spp.S. tuberosum

Tomato Carotenoid content LycopersiconWild Spp.

L. esculentum

Palm Oil quality Wild Spp. Cultivated Spp.

Rice, Oat & Rye Protein quality Wild Spp. Cultivated Spp.

Achievements

Hybrid varieties:

CO31 rice variety

Upland cotton – MCU-2, MCU-5, Khandwa1, Khandwa2

Napier grass- Jaywant and Yashwant

Interspecific hybrids in cotton- Varlaxmi, Savitri, DCH-32, NHB-12, DH-7,

DH-9

Prabhani Kranti variety of bhindi.

Embryo rescue methodearliest and successful forms of in-vitro culture technique.

nurtures the immature or weak embryo.

Plant embryos are multicellular structures that have the potential to develop into a

new plant.

widely used embryo rescue procedure is embryo culture.

wide hybridization crosses can result in small shrunken seeds which indicate that

fertilization has occurred, however the seed fails to develop.

Embryo culture.

(A)Proembryo dissected 3 to 5 days after pollination

(B) Proembryo culture on solid agar media

(C) Plantlet developing from embryo

(D) Plantlet transplanted into soil.