Everything you need to know about synthetic and composite varieties of crops.
Q. 1. What is inbred line?
Ans. In allogamous species, a true breeding line obtained by continuous inbreeding is called inbred line.
Main features of inbred line are given below:
(i) It is relevant to cross pollinated species
(ii) It is true breeding
(iii) It is homozygous and homogeneous
(iv) It is obtained by continuous inbreeding
Q. 2. What is synthetic variety?
Ans. A variety which is developed by inter-mating in all possible combinations a number of inbred lines with good general combining ability and mixing their seeds (seeds of F1s) in equal quantity is referred to as synthetic variety. It is relevant to cross pollinated species.
Q. 3. What are base materials used for developing synthetic variety?
Ans. A synthetic variety can be developed from inbreds, clones arid open pollinated varieties. The end products of recurrent selection which are already tested for gca are used to constitute synthetic variety.
Q. 4. Why synthetic varieties are developed?
Ans. The basic concept in the development of synthetic variety is exploitation of heterosis. In the development of synthetics, heterosis is partially exploited, because some degree of inbreeding takes place due to open pollination in later generations.
Q. 5. What is genetic constitution of a synthetic variety?
Ans. Initially, a synthetic variety consists of several heterozygotes. A synthetic variety is maintained by open pollination, some degree of selfing occurs resulting in fixation of some genes. As a result in later generations, a synthetic variety consists of several heterozygotes and homozygotes.
Q. 6. What type of variance is exploited in synthetic varieties?
Ans. Synthetic varieties exploit more of additive gene action than dominance gene action.
Q. 7. How many inbreds are used to constitute a synthetic variety?
Ans. Generally, 5-8 good general combining inbred lines are used to constitute a synthetic variety.
Q. 8. After how many years a synthetic variety is reconstituted?
Ans. A synthetic variety can safely be grown for a period of 4-5 years without reduction in yield potential. After a period of five years, it would be desirable to reconstitute the synthetic variety. Farmers can use their own seeds upto five years.
Q. 9. What are main features of synthetic variety?
Ans. Main features of synthetic variety are given below:
(i) They are relevant to cross pollinated species.
(ii) They are maintained by open pollination.
(iii) They exploit more of additive variance.
(iv) In later generations, they consist of several heterozygotes and homozygotes.
(v) Synthetics have wider adaptability.
Q. 10. What is yield level of synthetic variety?
Ans. The yield of synthetic variety is always higher than open pollinated variety but lower than the yield of single and double cross hybrids.
Q. 11. What is difference between mass selected variety and synthetic variety?
Ans. Main difference between mass selected and synthetic varieties are given below:
(i) In mass selected variety, component genotypes are selected on the basis of phenotypic performance, whereas component lines of synthetic variety are selected on the basis of gca.
(ii) Development of synthetics involves inter-mating among selected lines which is not in ease of mass selection,
(iii) Synthetics have better buffering capacity to environmental changes,
(iv) Synthetics are more tolerant to insects and diseases.
Q. 20. What are demerits of synthetic varieties?
Ans. Main demerits of synthetic varieties are given below:
(i) The produce of synthetic varieties is generally less uniform and less attractive than hybrids,
(ii) The yield of synthetic varieties is poorer than single or double cross hybrids.
Q. 21. Why yield of synthetics is poorer than hybrids?
Ans. The yield of synthetics is poorer than hybrids, because in synthetics heterosis is partially exploited, whereas in hybrids heterosis is fully exploited.
Q. 22. Why heterosis is partially exploited in synthetics?
Ans. In synthetics, heterosis is partially exploited because some level of inbreeding takes place due to open pollination in later generations.
Q. 23. Why synthetics have better resistance to diseases?
Ans. Synthetic varieties have better resistance to plant diseases due to their heterogeneous nature and broad genetic base.
Q. 24. What is a composite variety?
Ans. In cross pollinated species, a variety which is developed by mixing the seed of various genotypes (in equal quantity) which are similar in maturity, height, seed size, colour etc. is called composite variety.
Q. 25. What are main features of composites?
Ans. Main features of composites are given below:
(i) Component genotypes are open pollinated.
(ii) They are relevant to cross pollinated species.
(iii) They are maintained by open pollination.
(iv) The exploit heterosis partially.
(v) Exact reconstitution is not possible.
(vi) Highly adaptable to environmental changes.
Q. 26. Is it possible to reconstitute a composite variety?
Ans. It is not possible to reconstitute a composite variety, because such variety is developed from heterozygous genotypes.
Q. 27. Cite examples of composite variety.
Ans. Composite varieties have been developed in maize.
Important composite varieties of maize are given below:
Q. 28. What is composite variety of Brassica campestris?
Ans. The composite variety of Brassica campestris is composite 1.
Q. 29. What are similarities between synthetics and composites?
Ans. Main similarities between synthetics and composites are given below. Both are:
(i) Polymorphic and stable
(ii) Relevant to allogamous species
(iii) Mixture of several homozygotes and heterozygotes
(iv) Both have broad genetic base.
Q. 30. What steps are involved in the development of composite variety?
Ans. Development of a composite variety consists of the following important steps:
(i) Selection of heterozygous base material.
(ii) Inter-mating among selected genotypes to get F1s.
(iii) Evaluation of F1 crosses.
(iv) Mixing in equal quantity parental seeds of superior crosses.
Q. 31. What are similarities and dissimilarities between synthetic and composite varieties?
Ans. Comparison of synthetic and composite varieties is presented below in Table 17.1.
