Hybrid seed production

What is hybrid cultivar?

Hybrid cultivar is the first generation offspring of a cross b/w inbred line parents with different genotypes

How hybrid cultivar differs from a cultivar produced by hybridization as in breeding of self pollinated crops?

Steps involved in hybrid cultivar production Development of inbred line. Crossing pairs of unrelated inbred lines. Producing seed for distribution

History Koelreuter 1763 (hybrid tobacco) Darwin in 1877 concluded that effect of cross fertilization is beneficial and vice versa. 1880 Beal reported that hybrids were more productive than open pollinated variety. Produced hybrid in the same way as done today.

History 1909 G.H. Shull proposed a method for producing hybrid cultivar of corn Revolutionized corn breeding. Edward M. East also reported inbreeding of corn in 1909 Unable to describe a clear procedure for inbred lines utilization

Limitations The cost of producing corn would limit its use at that time. (seed produced on weak and un productive inbred plants) Jones in 1918 solved that problem by proposing double cross hybrid cultivar.

Characteristics of double cross Economically feasible More seed on vigorous and productive single cross female plant. Abundant pollen production by single cross male parent.

History 1952 Shull recalled when he concieved the hybrid concept. 1906 his concept was that selfing had deleterious effect and crossing has advantageous affects

Cont…. It may be assumed that correct field practice in breeding of corn must have as its objective the maintenance of such hybrid combinations as proved to be most productive and vigorous and give all desired qualities of ear and grain.

Inbreeding Any system of mating that leads to an increase in homozygosity.

Inbreeding in cross-pollinated crops Three ways Self-fertilization Half-sib mating Full-sib mating

Self-fertilization Rapid approach Heterozygosity reduced to one half with each successive self-fertilization. Restricted in crops having self incompatibility or sex organs on separate plants.

Sib-mating Half-sib mating: Mating b/w plants having one parent or one pollen source in common. Full-sib mating: Mating between plants within the progeny of a single plant.

Homozygosity achieved slower than self- fertilization. Ten generations of full-sib mating = 3 generations of self-fertilization.

Hybrid Vigor or Heterosis It is increase in size, vigor or productivity of a hybrid plant over the average or mean of its parents

Theories Accumulation of favorable dominant genes. Inbred A X Inbred B AABBccddEE aabbCCDDEE AaBbCcDdEE Heterozygosity being superior to homozygosity.

Heterozygosity being superior to homozygosity.

Breeding single-cross hybrid cultivar The single-cross hybrid cultivar is the product of a cross between two inbred lines or pure-line cultivar. Began with research of Shull in corn in 1909.

Inbred line Development An inbred line is a homozygous breeding line developed and maintained by self- pollination. Heterozygous plants may have been selected by the breeder from Natural population of a cross-pollinated species. F2 progeny from a cross b/w homozygous parental lines.

Combining Inbred lines. The ability of the inbred line to transmit desirable performance to the hybrid progeny is referred to as combining ability.

General combining ability It is the average contribution that the inbred makes to hybrid performance in a series of hybrid combinations in comparison to the contribution of other inbred lines to hybrid performance in the same series of hybrid combinations. Additive gene action

Specific combining ability. Is the contribution of an inbred line to hybrid performance in a cross with a specified inbred line, in relation to its contributions in crosses with an array of specified inbred lines. Non-additive gene action