Composite varieties

Composite varieties
Composite varieties
    • In cross pollinated crops, the mixture of genotypes from several sources that is maintained in bulk from one generation to the next is referred to as composite variety.”
    • Composites are constituted by seed mixture of advanced generation material of intervarietal or inter racial cross.
Steps In Development of Composite Variety
    • Selection of base or parental material
    • Intermating of selected genotype.
    • Evaluation of crosses.
    • Mixing of parental material of superior crosses in equal quantity
Selection Of Base Material
    • In developing composite cultivars, open pollinated varieties or other heterozygous sources serve as the base material.
    • Several open pollinated varieties with similar maturity duration , height , seed colour are selected for this purpose.
Evaluation Of Crosses
    • All the single crosses are evaluated in replicated trials for yield performance in F1,F2,F3 & F4 generations using standard hybrid or open pollinated variety as a check.
    • Crosses exhibiting little or no inbreeding depression in F2,F3 &F4 generations are indentified & selected for the development of composite cultivar.
Intermating Selected Genotype
  • Selected genotypes are crossed in all possible combinations.
  • Total crosses to be made are equal to n(n-1)/2, where n is the no of varieties selected for intermating.
  • If there are 10 varieties would be 10(9)/2=45 single crosses.
  • Seed of each crosses harvested separatly.
Mixing Parental Seed of Superior Crosses
  • Parental seeds (of the superior crosses) is mixed in equal quantity to develop a composite variety.
  • Seed multiplication is carried out by open pollination in isolation for 1 or 2 generations.
  • Composite cultivars also exhibit more of additive gene action, because composites are constituted from the parents of only those crosses which exhibit little or no inbreeding depression in F2, F3 and F4 generations.
Features Of Composite Variety
    • Heterogeneous
    • Relevant to cross pollinated species only
    • Can be developed from open pollinated variety or 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
    • Evaluation for general combining ability (gca) as in synthetic variety production, is not carried out
    • Exact reconstitution of composite variety is not possible

Last modified: Monday, 2 April 2012, 10:06 PM