Variety Blend in Plant breeding and Genetics

“Variety blend cultivar is a complex cultivar produce by a  mixture of genotype from different  sources to kept in BULK from one to next generation.”

Under reliable conditions of environment, blend varieties will give more yield than the average varieties of components. Mixture of genotypes having buffering effect against environmental interaction and genotype, then this will be more stable than a single cultivar over an area and years. The given advantage is tend to reduce as the number of varieties in blend increases. The yield of mixture will be less due to presence of highly yielding varieties in the mixture.

Blend variety cultivar will be less homogenous than the varieties of pure-line. While in making of a blend variety ensure that variety should not be mixed because it will badly affect the compatibility and qualities of  the variety.

  • MAIN FEATURES OF VARIETY BLEND CULTIVAR:-
  1. Base Material:

Blend varieties are produced by mixing the seed of different genotypes having similar colour, height, seed size etc. In isolation blend varieties are maintained by open-pollination. Farmer use their seed for 3-4 years.

  1. Genetic Concept:

To use heterosis in cross pollinated crops blend varieties are produced.

  1. Adaptation:

Blend varieties are stable and capable to harsh environment.

  1. Reconstitutions:

To maintain stability regularly, variety blend need to be reconstituted.

Variety blends produce by heterozygous genotypes, so these cannot be reconstitute. Because with the passage of time frequency of gene change in population of segregation.

  1. Genetic Constitute:

Due to several homozygous, blend variety constitute heterogeneous population.

  • NON-TRADITIONAL BREEDING PROCEDURES:

In breeding procedure, crosses involve between two parents to improve self-pollinated crops by following generations of segregation; yield testing started when purity reached at high degree. To start a new cycle of breeding, superior segregates crosses.

During the early year of this century, bulk-hybrid and pedigree procedures of selection developed. Later on back-cross and multiline procedures were added. By using two parents only opportunities of gene recombination by the fixed input and breaking of linkage-blocks are limited.

To overcome these limitations, breeders find many ways to increase the input of gene pool. This lead to modifications in traditional breeding systems, including early testing, large number of crosses and improvement of population.

  1. Large Numbers Of Crosses:

Parents may be chose to improve desired characters like resistance of seed against diseases and seed color in a hybridization breeding program. Yield like quantitative characters can be improve by selecting parents for cross. When it’s not easy to handle inheritance, it will be more difficult because complementary genes involved by the set of parents into yield cannot be identified by a single parent only.

When cross is made and segregation limits checked out then success of crosses can be easily determined. This led breeders to make crosses in large numbers to produce superior quality segregates. To ensure the presence of superior genotypic plants it is important to grow large numbers of  segregating population because their is no limitations of resources, the breeder must choose b/w limited number of population of large number of crosses or large number of population of limited number of crosses.

First one is often in favour because large number of crosses involved and increases the possibilities that cross combinations with greater potential will be made.

  1. Early Testing:

To find the superior segregate progenies it should be estimated from each cross after a cross is made. Testing size can be increased by increase in number of crosses. In the testing program to offset the growth, early testing is only a procedure; i.e cross estimation and yield trial selection from these crosses at early stage of generation.

Superior segregates may be carried out with the help of early testing or by eliminating the inferior segregation. Where constancy and homogeneity attained. In segregation generation, testing of yield and concerted selection may be used to decrease the size of population so that by F5 and F6 only few strains remained when it reach to its homozygous form.

In new crosses, lines of superior yield may be immediately use as a parents when these lined identified in early generation, even this is not in state of homozygosity, thus to complete the cycle of crossing generations are reduced.

By using superior lines as a parent in new crosses can be recycled into breeding system. In three barley program Mc proud observed that the cycle varies from 6.5 to 10.5 years. To complete cycle, reduce the time period to ensure the progress of breeders rapidly.

  1. Population Improvement :

To increase the constancy of genes with in a population, procedure of population improvement is designed. In population many intermating are required among the genotype.

Exemplary, to produce the next generation superior genotypes inter-crossed and separate from each cycle of mating. In cross pollinated crops by using population improvement method, desirable success can be achieved. To apply this method of population improvement for self pollinated crop is difficult because of numerous pollination that are important to make. Multiple crosses and male-sterile crosses are used to attain the principle of population improvement. Mostly two parents cross involved in hybridization. Where contrasting allele are present, in two cross gene parents combination will be limited in population segregation.

More than two parents are used to brought combination together by multiple crosses is called as Convergent Crosses.

By crossing pairs of parents multiple cross is produced.

C×D             E×F           F×G          H×I

CD        ×      EF            FG     ×     HI

CDEF×           FGHI

BCDEFGHI

Many combinations are formed by using this pattern. After the initial cross every seed which is produced called as a new hybrid. Disadvantage of this scheme is that many undesirable combinations also formed. In second, large numbers of hybrid seeds obtained and these are again crosses to obtained maximum genotype in the progenies.

By using sterile gene in barley and providing cross to self pollinated crops can eliminate the need of emasculation. Backcross technique is used to incorporate male-steri6gene into standard varieties. Iso-lines of male sterile gene which are produced can be pollinate from the varieties and bulk seed cross to make a composite cross.

Male sterile flowers can be pollinated with the help of male fertile plant thus within a population gene recombination can be further improve by taking seed from male sterile plants.

In barley, recurrent selection scheme facilitate by a male sterile and this is capable to other self-pollinated crops. By using genetic male sterile crosses can be made. The plants selected from a male-fertile plant are then hand pollinated during generation of segregation and seed produce by these crosses is use to plant the next generation.

REFERENCES:

www.slideshare.com

www.botanylibrary.com

Variety blend cultivar

Book: Breeding field crop by John M.Poehlam

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