🔗 Hybridization in Clonal Crops

This lesson covers core principles and exam-focused points from this topic in plant breeding.

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Clonal crops are generally improved by crossing two or more desirable clones, followed

by by selection in the F1 progeny and in the subsequent clonal generations. Once the F1 has

been produced, the breeding procedure is essentially the same as clonal selection. The

improvement through hybridization involves the following three steps:

1. Selection of parents,

2. Production of F1 progeny, and

3. Selection of superior cones.

Hybridization can be used only in such crops, which can reproduce sexually. In case of

those crops where sexual reproduction is lacking, mutagenesis or biotechnological

approaches can be applied.

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Selection of Parents

Selection of the parents to be used in hybridization is very important since the value of F1

progeny would depend upon the parents used for producing the F1. Parents are generally selected

on the basis of their known performance both as varieties and as parents in hybridization

programmes. The performance of a strain in hybridization programmes depends on its

prepotency and general combining ability. It would be highly desirable to know the relative

values of CGA and SCA in the crop to be improved. If GCA is more important, a small number

of parents with good should be used in hybridization programmes. On the other hand, when SCA

is more important, a large number of parents should be used to produce a large number of F1

families In an effort to find some outstanding crosses.

A recent suggestion is to partially inbreed the parents to be used in hybridization

programmes. Clonal crops show severe inbreeding depression, but it is expected that one

generation of selfing or 2-3 generations of sib-mating may not reduce vigour and fertility too

severely. Inbreeding may enable the breeder to identify plants that would have a greater

concentration of desirable alleles. These plants may be more prepotent as parents than the

highly heterozygous clones. The practice is gaining some favour with plant breeders.

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Production of F1 progeny

Generally, clonal crops are cross-pollinated and they may show self-incompatibility.

The selected parents may be used to produce single crosses involving two parents or an

equivalent of a polycross involving more than two parents.

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Selection among FI Families

When the breeding value of parents is not known, and the relative contributions of

GCA and SCA is not available, a large number of crosses have to be made in order to ensure

that at least some of the crosses would produce outstanding progeny in F,. This is particularly

true in a species where crop improvement has not been done or has been done at a small

scale. In such cases, it would be cumbersome to evaluate a large number of F, progeny is

detail. To avoid this, generally small samples of several F, populations are grown. The

general worth of individual F, populations is estimated visually. The presence of outstanding

individuals in the F, populations is also noted, and inferior F1’s are eliminated. Promising

F1’s with outstanding individuals are then grown at a much larger scale for selection. The

procedure is designed to save time, space and labor by planting only small populations of a

large number of crosses at the preliminary stage.

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Selection within FI Families

The selection procedure within FJ populations is essentially the same as that in the

case of clonal selection. The various steps involved in the breeding of clonal crops through

hybridization are briefly described below. From second year onward, these should be read

along with the steps described in clonal selection.

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First Year

Clones to be used as parents are grown and crosses are made to produce F1

progeny.

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Second Year

Sexual progeny from the cross, i.e., seedlings obtained from seeds, are grown.

Undesirable plants are eliminated. Few hundred t9 few thousand desirable plants are

selected.

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Third Year

Clones from the selected individual plants are grown separately. Poor and inferior

clones are eliminated. Up to 200 superior clones may be selected for preliminary yield trial.

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Fourth Year

A replicated preliminary yield trial is conducted in which suitable checks are

included for comparison. Few outstanding clones are selected for trials at several locations.

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Fifth to seventh year

Replicated yield trials are conducted at several locations. Suitable checks are

included for comparison. One or a few outstanding clones are identified and realsed as new

varities.

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Eighth year

The clones released as varities are multiplied and distributed among farmers.

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Summary Cheat Sheet

Quick Recall Points

• This lesson focuses on key plant breeding concepts, terminology, and exam-relevant applications.
• Review major definitions, classifications, and method-wise distinctions from the sections above.
• Revise tables and examples from this lesson for fast pre-exam recall.

Exam Traps

• Do not confuse similarly named breeding methods without checking their core selection logic.
• Pay attention to crop-specific examples because the same principle can behave differently by species.

References

1 source • [1]

[1]

Standard Plant Breeding Class Notes (GPBR211)

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