Development of New Variety

• In plant breeding various types of cultivars are developed and released for commercial cultivation.
• The development of new variety depends mainly on two factors, viz.:

(1) Mode of reproduction of the crop species, and

(2) Method of breeding used for development of a variety.

• Some varieties are developed by selection without hybridization such as pure-line variety, mass selected variety and clonal variety. Development of some varieties involves hybridization and selection. This includes varieties that are developed by pedigree, bulk and backcross methods including multiline cultivars.
• After release, all these varieties remain under cultivation for several years. The seed of some varieties has to be produced every year afresh such as hybrid varieties and triploids in seed propagated species (i.e. watermelon). Some varieties are developed by special breeding techniques such as mutant and transgenic varieties.

A brief description of different types of varieties which are developed in plant breeding is presented below:

I. Pure-Line Variety:

• It is developed in self-pollinated crops by pure-line selection. The progeny of a single homozygous plant obtained by selfing is called pure-line. The variety is released from a single best progeny. The base population, which is used for development of pure-line variety is always a heterogeneous population. A pure-line variety is a homozygous and homogeneous population.

ii. Mass Selected Variety:

• It is developed in both self- and cross-pollinated species. However, mass selection is more common in cross pollinated crops than in self-pollinated ones. In self- pollinated crops, a mass selected variety consists of several pure-lines. In other words, it is a mixture of several pure-lines.
• Thus, it is homozygous but heterogeneous population. In cross pollinated species, a mass selected variety is a mixture of several homo and heterozygotes. Thus, it is a heterozygous and heterogeneous population. A mass selected variety has broad genetic base and wide adaptation.

iii. Clonal Variety:

• It is developed in asexually propagated crops such as potato, sugarcane, sweet potato, etc. The progeny of a single best clone is released as a cultivar. Such varieties are heterozygous but homogeneous, because all the plants of a clone have exactly the same genotype. Clonal cultivars have wide adaptation than pure-line cultivars. A heterogeneous base population is used for development of clonal variety.

iv. Synthetic Variety:

• A synthetic variety is developed in cross pollinated crops such as maize. For development of synthetic variety, first good general combining inbreds are identified. All inbreds with good general combining ability are intermated in all possible combinations and hybrid seed is obtained.
• The hybrid seed of all combinations is mixed together in equal quantity to constitute a synthetic variety. Thus initially, a synthetic variety consists of several heterozygotes. This is maintained by open pollination which allows some degree of selfing. Hence in later generations, a synthetic variety consists of several homo and heterozygotes.
• Thus, synthetic variety has a heterogeneous population and wide adaptation. The yield level of synthetic variety is always higher than open pollinated variety but lower than the yield of single and double cross hybrids.

v. Composite Variety:

• It is developed in cross pollinated species. It is developed by mixing the seed of various open pollinated genotypes which are similar in height, maturity, seed color, seed size, etc. Thus, composite variety has a heterozygous and heterogeneous population. It consists of several homozygotes and heterozygotes. Such varieties are highly adaptable to environmental fluctuations.

vi. Multiline Variety:

• It is developed in self-pollinated crops. A multiline variety is a mixture of several isogenic lines, related lines or unrelated lines. Each component line has different gene for disease resistance. Such varieties are homozygous but heterogeneous and have very good buffering capacity due to broad genetic base.

vii. Mutant Variety:

• A mutant variety is developed through induced mutagenesis. Mutant varieties are generally developed in self-pollinated and asexually propagated species and rarely in cross pollinated species. A mutant variety differs from parent variety in one or two characters. Such varieties are developed to induce disease resistance, earliness, dwarfness and achieve improvement in quality.

viii. Transgenic Variety:

• A variety which is developed by the technique of genetic engineering is called transgenic variety. Such varieties are developed to solve specific problems that are difficult to be solved by conventional methods of plant breeding. Transgenic varieties with herbicide resistance, insect resistance and improved quality have “been developed in several crop plants. Such varieties can be developed in all the three groups of crops viz. self-pollinated, cross pollinated and asexually propagated.

ix. Pedigree, Bulk and Backcross Bred Varieties:

• Pedigree and bulk bred varieties are developed in self-pollinated species. Such varieties are developed from the progeny of a single best homozygote. Hence varieties developed by pedigree and bulk methods are homozygous and homogeneous and have narrow genetic base.
• Backcross method is used both in self- and cross-pollinated species for improvement of oligogenic character such as disease resistance. Backcross bred variety is similar to parent variety except for the gene which has been transferred into parent variety.

x. Hybrid Variety:

• The F1 population that is used for commercial cultivation is called hybrid variety. Hybrid varieties are developed both in cross and self-pollinated species. However, hybrid varieties are more common in the cross-pollinated species than in self-pollinated species. Hybrids are of different types, viz., intervarietal hybrids (single, three way and double cross hybrids) and interspecific hybrids. Hybrids are heterozygous but homogeneous. For hybrid varieties, fresh seed has to be produced every year.
• All the varieties discussed above are used for commercial cultivation. These varieties can be divided into different groups on the basis of several criteria.

The main criteria which are used for classification of varieties include:

(1) Country of origin,

(2) Area of adaptation,

(3) Genetic constitution,

(4) Use of seed,

(5) Evolution techniques, etc.