SYNTHETIC AND COMPOSITE VARIETY

PRESENTED BY: Pawan NagarReg. no.: 04-2690-2015M.Sc.(Fruit Science)

SYNTHETIC VARIETIES

The possibilities of commercial utilization of synthetic varieties in maize was first suggested by Hayas and Garber in 1919.

Synthetic varieties have been of great value in the breeding for those cross – pollinated crop, where pollination control is difficult. E .g Alfalfa, cloves, forage crop species etc.

Even in maize improvement synthetic varieties are becoming increasingly important ,and in India there had been a considerable emphasis on synthetic development.

Synthetic varieties

Defination: A Variety which is produced by crossing in all combination number of inbred lines that combine well with each other. Once synthesized, a synthetic is maintained by open-pollination in isolation is referred as synthetic variety.

A synthetic varieties can developed from inbreds, clones, and open pollinated varieties.

The end products of recurrent selection, which are already tested for GCA are generally, used to constitute synthetic varieties.

Generally 5-8 good general combining inbreds are used to constitute a synthetic variety.

Synthetic variety consists of several heterozygous initially. Since subsequently the variety is maintained by open pollination, some degree of selfing occurs resulting in fixation of some genes.

A result in later generation synthetic variety consists of several heterozygotes. Thus a synthetic variety has a heterogeneous population.

Step in development in synthetic varieties:

Development of synthetic variety consists of three major steps. i.e. 1) Evaluation of lines for GCA.2) Production of synthetic variety,3) Multiplication of synthetic variety.

1) Evaluation of Lines for GCA:

The lines that make up a synthetic variety may be inbred lines, clones, open pollinated variety of short term inbred lines.

Inbred lines are evaluated for general combining ability because synthetic variety exploit that portion of heterosis which is produced by GCA. 

There are three different methods of evaluating, which is produced by GCA. There are three cross, Polycross and single cross . In top cross, the inbreds are crossed with a common tester and the progeny are evaluated in replicated trials for general combining ability of yield and yield contributing characters.

In Polycross, selected inbreds are allowed to intermated by open pollination in isolation and in single cross all possible single crosses are made among selected inbreds.

These crosses are evaluated for GCA of yield in replicated that using local variety as a check

Thus, inbred lines with good GCA are identified and finally selected for development of synthetic variety.

2) Production of Synthetic Variety: A synthetic variety may be produced in one of the following two

ways:

a) Equal amount of seed from the parental lines (syno) are mixed and planted in isolation. Open- pollination is allowed and produce crosses in all combinations. The seed from this population is harvested in bulk; the population raised from this seed is the Syn1 generation.

b) All possible crosses among the selected lines are made in isolation Equal amount of seed from each cross is composite to produce the synthetic variety. The population derived from this composited seed is known as synthetic one generation. 

c)Multiplication of Synthetic Variety:

After a synthetic variety has synthesized. It is multiplied in isolation for one or more generation, before its distribution for cultivation This is done to produce commercial quantities and is a common practical in most of the crops. E. g Grasses, Clover, Maize.

In heterozygosity as a consequences of random mating. However, there would net be a noticeable decline in the subsequent generations produced by open – pollination (syn3, syn2, syn5, etc). Since the zygotic equilibrium for any gene is reached after one generation of random mating.

The synthetic varieties are maintained by open pollinated, seed, and may be further improved through population improvement, particularly recurrent selection.

Method 1: Equal seed from all the parental lines is mixed and planted in isolation. Open-pollinated seed harvested as the synthetic variety.(syn1)

Method 2: The parental lines are planted in a crossing block ,and all possible intercrosses are made among them .Equal seed from all the crosses is mixed to produce the synthetic varieties.(syn2)

Heterogeneous

Synthetic variety can be developed by using clones, inbreds or OPV i.e. open pollinated variety.

Cross pollination is must .

Maintained by open pollination.

Unlike composite variety, exact reconstitution of synthetic variety is possible .

More adaptive to varying growing conditions as compared to hybrids. Less uniform as compared to hybrids .

Less attractive as compared to hybrids .

Show some amount of heterosis as compared to OPV .

Have better disease resistance

Features of Synthetic Variety

Constituent genotypes can be two to ten. This number means a lot to achieve maximum heterosis. Heterosis increases with increase in number of contributing genotypes, but only up to 6 genotypes. Decreases when number increases to 10.

Farmer can use his own saved seed for 4 years as there is no reduction in yield up to that period, after that seed should be replaced .

Low yielder than single cross hybrids or double cross hybrids but yield higher than inbreds.

Production is less costly as compared to hybrid varieties.

Merits of Synthetic Varieties:

1) Synthetic varieties offer a feasible means of utilizing heterosis in crop species where pollination control is difficult. 

2) Farmers can use the grain produced from a synthetic varieties as see to raise the

next crop.

3) In variable environments synthetic are likely to do better than hybrid variety. 

4) The cost of seed in synthetic variety is relatively lower than hybrid varieties. 

5) Seed production in case of synthetic variety required less skill operation than hybrid. 

6) The performance of synthetic varieties can be considerably improved through population improvement without reducing variability, whichis not possible with hybrids

Merits, Demerits and Achievement of Synthetic Varieties:

1) The performance of synthetic variety is usually lower than best single or double cross hybrid. 

2) Synthetic variety can be produced and maintained only in cross-pollinated crop. 

3) The performance of synthetic variety is adversely affected to relatively poorer GCA.

. Demerits of Synthetic Varieties:

Factors determining the performance of synthetic varieties:

Decline in Heterozygocity

Decline in syn2 performance

Enhancing the performance of syn2

Increase the number of parental line

Increasing the performance of syn1

Improving the performance of parental line

Synthetic varieties have been developed in cross- pollinated crops like maize, pearl millet, sunflower, Sugarbeet, alfalfa, lucerne, etc.

In India synthetic varieties have been evolved in pearl millet at ICRISAT and in Sugarbeet at pantnagar.

Ex. Sugarbeet- plant synthetic – 3, Cauliflower- synthetic -3, bajara- ICMS-7703.

Achievements of Synthetic Varieties:

COMPOSITE VARIETY:

In cross pollinated crops, the mixture of genotype from several sources is maintained bulk from one generation to the next is referred as composite variety.

Or

Composite variety is a variety derived from advance generation of random mated out standing lines (Germplasm inbreds, varieties, hybrids, advance generation lines).

Mixing the seeds of several phenotypically outstanding lines produces a composite variety and encouraging open pollination to produce crosses in all combinations among,the mixed lines.

The lines used to produce a composite variety are rarely tested for combining ability with each other like synthetic composite are commercial varieties and are maintained by open – pollination in isolation.

The line used a produce a composite variety are rarely tested for combining ability with each other.

Mixing the seeds of various genotypes, which are similar in maturity height, seed size, colour, etc. develops composite varieties.

The variety is maintained by open pollination. Farmers can use their own seed for 3 to 4 years.

The yields of composite verities cannot be predicted in advance ,which is contrast to synthetic; this is because of yield of all f1 among the component lines are not available .Like synthetic, composite are commercial varieties are maintained by open pollination in isolation . Another type of population , called germplasm complexes are produced by mixing seeds from several lines or populations of diverse genetic origin.

There is no restriction to the number of lines included in the development of composite , but the line possessing desirable characteristics should be selected like earliness, insect resistance, drought and frost resistance can be included in the development.

The seeds of desired selected lines mixed together and random mating is allowed for 4-5 generations.

Such uniform population is tested in replicated trials, across environment along with standards checks and high yielding stable type can be released as composite variety.

The combining ability of lines used in composite are not tested, whereas in synthetic each of the component is tested for its combining ability.

Procedure for Development Composite Variety:

Heterogeneous

Relevant to cross pollinated species only Can be developed from open pollinated variety any other heterozygous variety .

Farmer can use his own saved seed for 3 to 4 years, after that seed should be replaced .

There can be two or more constituent genotypes .

Features of Composite Variety

In India six composite varieties of maize like Amber, Jawahar, Kisan Vikram, sona and Vijay have been released in 1967.

Subsequently number of composite has been released in Bajara and other crops.

Some of the released composite of maize are Co-1 , NLD , Renuka and Kanchan, Diara-3 etc, while in Bajara released composite are WCC-75, RCBIC-9, ICTP-8203.

Achievement of Composite Varieties:Achievement of Composite Varieties:

SYNTHEIC VARIETIES COMPOSITE VARIETIES

Crossing in all combination of number of lines that combine well with each other.

Mixing the seeds of several phenotypically outstanding lines it and encouraging open pollination to produce crosses in all combination among the lines.

4-10 numbers of parents are involved

It is tested for GCA. Not tested for GCA.

Cost of seed is less than hybrid.

It shows less heterosis than hybrid. It shows more heterosis than synthetic

Reconstituted is done. Reconstituted is never done.

Maintenance of variety easy. Maintenance of variety is difficult but easy .

Prediction of performance possible. Prediction of performance is not possible.

Many parents are involved.

Cost of less than composite variety.

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