International Journal of Horticulture, 2017, Vol.7, No.22, 180-204
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6.1 Selection methods for self- pollinated crops
Mass selection
: This is one of the oldest method of crop improvement. The best plants from the field or bulk are
selected and threshed together and the resulting bulk harvest is used to raise the crop for next generation. It is
practiced in mixed population of cultivars or land variety or unimproved strains. Generally, 500 to 1000 plants
are selected and bulked in the second year. Then the selected bulk is tested against the cultivar and the local
check and the superior one is released as cultivars in the following year. This technique is effective in ornamental
pepper.
Pureline selection:
Pureline selection is the progeny of a single homozygous plant of a self pollinated species. It
involves three steps:
Selection of a large number of superior individuals from a genetically variable population.
Raising of the self-progeny of each over several years under different environments. Unsuitable lines are
eliminated in each generation.
Replication of the trials to compare the remaining selections. This is done over several seasons, atleast three
years to compare them with each other and with existing commercial cultivars.
In Aster, AST-1 and AST-2 developed through pure line selection.
6.2 Selection methods in cross pollinated crops
Mass selection:
It is practiced to develop cultivars and for population improvement. In this method, a large
number of superior plants are selected and harvested in bulk and seeds are used to produce the next generation.
Mass selection is effective to improve qualitative characters as well as quantitative characters including yield. It
is practiced in sunflower and chrysanthemum for evolution of new cultivars.
Mass – pedigree method:
It is generally used for increasing seed set in introduced autotetraploids of self
incompatible crops. The individuals are selected in the population on the basis of certain increasing arbitrary
norms or selection indices.
Clonal selection:
A clone is a group of plants produced from a single plant asexually. All the individuals
belonging to a single clone are identical in genotype. The phenotypic variation within a clone is due to the
environment only and phenotype is due to the effects of genotype (G), the environment (E) and the genotypic x
environment interaction over the population mean. Clones are maintained easily through asexual means. In
general, clones are highly heterozygous and show loss in vigour due to inbreeding. Genetical variation within a
clone is due to mutation, mechanical mixture and segregation and recombination due to occasional sexual
reproduction. Selecting spontaneous mutants within a clone is called clonal selection. Hundreds of popular
ornamental plants grown in most part of the world originated from clonal variation and selection.
6.3 Clonal hybridization
Improvement of ornamental crops through clonal hybridization involves three steps:
Selection of parents
Production of F
1
hybrids and
Selection of superior clones
Large number of cultivars of perennial ornamental plants eg.
Bougainvillea, Chrysanthemum, Dahlia, Hibiscus,
Gladiolus, Rosa
etc. have been obtained by clonal hybridization.
Hybridization:
It is defined as the crossing of two or more plants which are genetically different from each other
to produce a new crop. Hybridization is effective to combine all the good characters in a single variety to create
genetical variation and to exploit the hybrid vigour.
