The term Multiline Genetics is used for a variety is a composite of genetically identical lines, except that each line possesses a different gene for resistance to the disease. This is also called Multiline Varieties.
In the event of occurrence of a new race, some plants may be susceptible, but not all. This mix of susceptible and resistant plants should provide a buffering effect against rapid disease development and thus extend the life of resistance genes.
Self Pollinated Plants – Multiple Crossing
It is complex system of crossing in which 8 to 16 parents are systematically crossed to develop new hybrid variety. Ex. Barley. Multiple crosses are produced by crossing pairs of parents, pairs of F1 and pairs of F1’s of F1’ s , till all parents are included into a common progeny.
A X B CX D E X F G X H
AB X CD EF X GH
ABCD X EFGH
This method of breeding help to accumulate more and more gene quickly from several parents. But some times undesirable combinations may be brought together, since large number of parents are involved. This can be avoided by selecting the desirable combination before including in crossing programme during each generation. These procedures will require a longer time to reach the final cross. Ex. Self Pollinated Crop like Wheat and Rice are common examples.
Examples of Multiline Variety
- Kalyan sonaWheat variety Kalyan sona is the suitable example to explain the concept. This variety was originally resistant to brown rust. Later on became susceptible to new races of pathogen.Several pure lines with different resistance genes are produced through backcross breeding using one recipient or recurrent parent. The donor parents are the one with different genes for the disease resistance, every donor parent is used in separate back cross program. Because of this each line receives different gene for disease resistance according to the type of pathogen. Five to ten of such lines with different alleles for disease resistance are mixed to develop multiline variety. The lines to be mixed are determined by the races of the pathogen relevant to the area considered.
- MLKS11 (8 closely related lines)
- KML7404 (9 closely related lines)
Advantages of Multiline Variety
Merits of the multiline breeding are discussed below.
- At the time of disease outbreak, only one or few lines of the mixture get attacked, others remain resistant. So the loss to the farmer is comparatively less.
- Multiline varieties are more adaptive to environmental changes than individual pure line.
Disadvantages of Multiline Variety
Demerits of the multiline breeding are given below.
- Races of pathogen change as time goes on, so farmer has to change seeds every few years which contains seeds of lines resistant to new pathogen races.
- No improvement in yield or other characters
- Takes more time to develop new variety, in the due course of time new pathogen races may evolve.
- All the lines constituting multiline variety may get attacked by the new race of pathogen.
- Not suitable for cross pollinated crops
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