Methods of Plant Breeding in Self and Cross-Pollinated Crops: Pedigree Method, Bulk Method, and Backcross Method - Merits and Demerits of Each Method
Introduction:
Plant breeding plays a vital role in developing improved varieties of crops with desirable traits such as higher yield, disease resistance, and improved quality. Breeders employ various methods to achieve these goals, and the choice of method depends on the crop type and breeding objectives. In this blog post, we will delve into the three main methods of plant breeding in self and cross-pollinated crops: the pedigree method, bulk method, and backcross method. We will explore the merits and demerits of each method, providing a comprehensive understanding of their applications and limitations.
Table of Contents:
I. Pedigree Method
A. Definition and Basic Principles
B. Steps Involved
1. Selection of Parents
2. Cross-Pollination
3. Selection of Offspring
4. Repeated Cycles of Selection
C. Merits of the Pedigree Method
D. Demerits of the Pedigree Method
II. Bulk Method
A. Definition and Basic Principles
B. Steps Involved
1. Selection of Initial Population
2. Mass Selection and Hybridization
3. Continuous Selection
C. Merits of the Bulk Method
D. Demerits of the Bulk Method
III. Backcross Method
A. Definition and Basic Principles
B. Steps Involved
1. Selection of Recurrent Parent
2. Cross-Pollination and Selection of Offspring
3. Repeated Backcrossing
C. Merits of the Backcross Method
D. Demerits of the Backcross Method
IV. Comparison of Methods
A. Key Factors to Consider
B. Merits and Demerits Compared
C. Selection of Appropriate Method
V. Conclusion
I. Pedigree Method:
A. Definition and Basic Principles:
The pedigree method is a systematic approach to plant breeding that involves controlled hybridization and selection of desirable traits in successive generations. It is predominantly used for self-pollinated crops, such as wheat, rice, and barley.
B. Steps Involved:
1. Selection of Parents:
- Breeders select superior parental lines based on desired traits.
- These parents should possess complementary or desirable traits to be incorporated into the offspring.
2. Cross-Pollination:
- Controlled cross-pollination is performed between the selected parents.
- This step ensures the transfer of desired genes from both parents to the offspring.
3. Selection of Offspring:
- After pollination, the resulting seeds are grown to produce the first filial generation (F1).
- The F1 plants are evaluated for desired traits, and the best individuals are selected as parents for the next generation.
4. Repeated Cycles of Selection:
- The process of selection, cross-pollination, and evaluation is repeated for several generations.
- This continuous cycle helps in accumulating and stabilizing the desired traits in the breeding population.
C. Merits of the Pedigree Method:
1. Precise Selection: The pedigree method allows breeders to make precise selections by evaluating each generation for the desired traits.
2. Trait Accumulation: With each successive generation, the frequency of desirable traits increases, leading to improved varieties.
3. Genetic Control: The pedigree method provides greater control over the genetic composition of the breeding population.
D. Demerits of the Pedigree Method:
1. Time-consuming: The pedigree method requires multiple generations of selection and evaluation, making it a time-consuming process.
2. Narrow Genetic Base: Continuous self-pollination can result in a reduced genetic diversity within the breeding population, limiting the potential for further improvement.
3. Inbreeding Depression: Inbreeding depression, the loss of vigor and productivity due to excessive inbreeding, can occur if not managed carefully.
II. Bulk Method:
A. Definition and Basic Principles:
The bulk method, also known as mass selection, is a plant breeding technique primarily used for self-pollinated crops. It involves the random mating of a population followed by the selection of superior individuals in subsequent generations.
B. Steps Involved:
1. Selection of Initial Population:
- A diverse population of plants is selected as the initial breeding population.
- The population should possess a range of genetic variation for the traits of interest.
2. Mass Selection and Hybridization:
- The selected population is allowed to self-pollinate freely, ensuring random mating.
- Seeds are collected in bulk from the entire population, creating the bulked seed.
3. Continuous Selection:
- The bulked seed is sown, and the resulting plants are evaluated for the desired traits.
- Superior individuals are selected as parents for the next generation, and the process is repeated over multiple generations.
C. Merits of the Bulk Method:
1. Cost-Effective: The bulk method is relatively inexpensive compared to other breeding methods as it does not require individual plant selection.
2. Genetic Variation: The random mating in the bulk method helps maintain a high level of genetic variation within the population.
3. Adaptability: The bulk method is suitable for breeding populations with complex traits influenced by multiple genes.
D. Demerits of the Bulk Method:
1. Lack of Precision: Since the selection is based on the overall performance of the population, it may be challenging to target specific traits accurately.
2. Dilution of Desired Traits: Unwanted or detrimental traits can also be bulked along with the desired traits, potentially diluting the genetic improvement.
3. Slow Progress: The bulk method typically takes longer to achieve the desired improvements compared to the pedigree method.
III. Backcross Method:
A. Definition and Basic Principles:
The backcross method is commonly used for breeding in cross-pollinated crops, such as maize, tomato, and cotton. It involves repeated hybridization between a recurrent parent and a selected donor parent to introduce a specific trait while retaining the genetic background of the recurrent parent.
B. Steps Involved:
1. Selection of Recurrent Parent:
- The recurrent parent is typically a commercial variety or an elite line with desirable agronomic characteristics.
- It serves as the genetic background into which the desired trait will be introgressed.
2. Cross-Pollination and Selection of Offspring:
- The recurrent parent is crossed with the donor parent, which possesses the desired trait.
- The resulting F1 plants are evaluated, and individuals expressing the desired trait are selected.
3. Repeated Backcrossing:
- Selected F1 plants are crossed back to the recurrent parent over multiple generations.
- Each backcross generation involves selection for the desired trait and discarding individuals without the desired trait.
C. Merits of the Backcross Method:
1. Genetic Background Preservation: The backcross method allows breeders to transfer a specific trait while preserving the genetic background of the recurrent parent.
2. Precision: The method enables precise incorporation of the desired trait by selecting individuals expressing the trait at each generation.
3. Rapid Improvement: The backcross method can achieve rapid improvement by focusing solely on the introgression of a single trait.
D. Demerits of the Backcross Method:
1. Genetic Linkage Drag: The donor parent may carry unwanted genes linked to the desired trait, leading to the unintentional transfer of undesirable traits.
2. Increased Cost: The backcross method requires multiple generations of crossing and selection, which can be costly and time-consuming.
3. Reduction in Genetic Diversity: Continuous backcrossing can reduce the genetic diversity of the resulting population, increasing the risk of vulnerability to diseases or environmental changes.
IV. Comparison of Methods:
A. Key Factors to Consider:
When choosing a breeding method, several factors should be considered:
- Crop Type: Different methods are more suitable for self-pollinated or cross-pollinated crops.
- Breeding Objective: The specific traits being targeted and the level of precision required.
- Genetic Diversity: The available genetic variation within the breeding population and the desired level of genetic improvement.
- Cost and Time Constraints: The resources available for the breeding program and the urgency of achieving the breeding goals.
B. Merits and Demerits Compared:
- The pedigree method offers precise selection but has a narrow genetic base and requires significant time investment.
- The bulk method is cost-effective and maintains genetic diversity but lacks precision and may dilute desired traits.
- The backcross method enables precise incorporation of desired traits but can introduce genetic linkage drag and may reduce genetic diversity.
C. Selection of Appropriate Method:
The selection of the breeding method depends on the specific breeding goals, available resources, and the characteristics of the crop being targeted. Breeders often employ a combination of methods to exploit their individual strengths and overcome their limitations.
V. Conclusion:
Plant breeding methods play a crucial role in developing improved varieties of crops. The pedigree method, bulk method, and backcross method offer distinct approaches to achieving breeding objectives in self and cross-pollinated crops. Each method has its merits and demerits, and the choice of method depends on various factors. Understanding the principles, advantages, and limitations of these methods empowers breeders to make informed decisions and effectively contribute to the enhancement of agricultural productivity and sustainability.
