The bulk selection method is one of the techniques used to mate individuals from a genetically separated population until reaching a level of change that leads to specific homozygous traits.
Each generation of mating utilizes seeds derived from plant samples taken from the previous generation.
Initially, this technique was developed for the breeding of self-pollinating plants, but it can also be applied to populations originating from both self-crossing and crossbreeding.
Understanding the Concept of Bulk Selection
Please bear in mind that utilizing the breeding method through bulk populations is a highly cost-effective approach to producing homozygous lines that will undergo a selection process.
This approach holds significant advantages when applied in breeding for quantitative traits that require further selection in subsequent generations.
The bulk population method is also capable of providing initial selection by applying selective pressure to genotypes that may not be able to adapt optimally and have low agronomic value when the bulk population is formed.
These genotypes will be grown at a high density, resulting in intense competition among them, which in turn resembles natural selection. In terms of time, it takes approximately 3 to 4 years or more to develop multi-tolerant traits.
In this year, it is also possible to carry out crosses between selected parents resulting from evaluations. In the second year, the focus shifts to evaluating the F1 offspring generated from these parent crosses. This evaluation aims to identify physiological traits that can serve as selection criteria for the subsequent crosses.
Diallel crosses are also conducted in this year, with the goal of combining desired traits. In the third year, a restricted bulk approach is employed to form a bulk population. Selection is based on the evaluation results of physiological traits. The process of bulk population formation continues up to the fifth generation.
Following this stage, the selected lines undergo selection under various stress conditions to obtain promising strains. In the bulk method, there is no separation or selection in the initial generations. Plants with genetic variations are allowed to grow together in a single population, creating opportunities for crosses between different genotypes. This method requires less effort compared to the pedigree method.
Once the selection is completed, only the subsequent generations after many plants have become homozygous will be maintained.
During the growth phase within a mixed population, two things will occur. Firstly, natural selection will take place, where plants unable to withstand environmental pressures will struggle in growth or even die. Secondly, genetic enhancement can occur due to the possibility of crossbreeding between individuals.
The bulk selection process begins by combining Parent A and Parent B, then progressing through generations F1 to F4. F1 is planted in a greenhouse, while the bulk population is grown in the field. Selection is carried out on individual plants, as well as on the best rows or families, continuing to generations F5, F6, and F7. At this stage, plants are densely spaced.
In the F8 stage, yield testing is conducted as a part of the preliminary phase by comparing the released varieties (F9) with reference varieties. Multi-location trials are also performed to assess the yield potential of the developed varieties across various locations before being released to the public.
Advantages of Bulk Selection Method
There are several advantages to utilizing the bulk selection method in plant breeding, including:
- The process is relatively inexpensive and straightforward.
- Economical for plants with short life cycles.
- High-quality plants won’t be wasted.
- Several generations can be processed simultaneously.
Disadvantages of Bulk Selection Method
There are several drawbacks to implementing the bulk selection method in plant breeding, including:
- Lack of pedigree records from the start, leading to limited genetic information.
- Natural selection in the early generations can eliminate potentially valuable genotypes.
- Requires extensive land to produce mixed populations.
Steps of the Bulk Method
- F2 plants are cultivated in a large plot with hundreds to thousands of individuals. The plants can be placed relatively close together. After growth, seeds from selected plants are harvested and mixed together. These seeds will become the material for the next generation.
- The F3 generation is collectively harvested, and its seeds are evenly mixed. Some of the seeds will be used for the subsequent generation.
- This process continues until reaching the F5 generation. At this stage, a high percentage of homozygous individuals in the population is achieved before individual or manual selection is performed.
- Seeds from the selected plants are then sown in predetermined rows or plots. Individual/manual selection is carried out at this stage to obtain the desired strains.
- The expected strains will be tested in various locations to measure their adaptation and resilience to the environment.
Through this method, genotypes with desired traits can be generated through more efficient selection after the bulk generation process.
