This article was written by Jorge Luis Alonso G., an information consultant specializing
in the potato crop.
Researchers from Solynta and Wageningen University and Research (WUR) recently published a scientific review in the journal Plants titled “Converting Hybrid Potato Breeding Science into Practice“. The research team provides an overview of the latest and most relevant research on diploid hybrid potatoes.
This article is a summary of its contents.
Introduction
Emerging research on diploid potato is advancing with the intention to translate findings into practical breeding programs that cater to the needs of farmers and end-users. Emphasizing the advantages of hybrid breeding — the favored method for plant improvement — the approach benefits both farmers and commercial breeders by offering a uniform crop with superior traits while also facilitating intellectual property protection.
Typically, a hybrid breeding program is bifurcated into parent line development and hybrid assessment programs, thereby focusing on acquiring beneficial alleles, selecting marketable traits, and evaluating regional adaptability and yield stability. Although this approach simplifies the selection process for trait improvement, it simultaneously introduces complexity into the design of the breeding program.
The successful realization of a commercial hybrid breeding program involves the interplay of high-quality inbred lines, hybrid development, and assessment across diverse market segments. Specifically, for Hybrid True Potato Seed (HTPS), the starting material varies from traditional seed tubers, leading to modifications in the cropping system.
To reach farmers, it is imperative that new varieties undergo registration and certification for marketing. Current strategies and remaining gaps are discussed in the following sections.
Inbred Line Development
Breeding programs begin with a germplasm pool that produces parent lines for hybrids via an inbred line development process. Inbred lines are cultivated from a diverse gene pool; despite the limited number of “founders”, the genetic diversity is considerable. This process adapts to changing market needs and growing conditions.
A major challenge in diploid potato breeding is self-incompatibility (SI), a trait common in wild potato relatives that hinders self-fertilization. The S-locus inhibitor (Sli) gene promotes self-compatibility (SC) and is introduced into the breeding program. Several methods to enhance SC in diploid potatoes are being explored.
Traits can be mapped following the development of inbred populations, for marker-assisted selection. Traits chosen in tetraploid breeding programs are present in diploid potato germplasm. High-quality reference genomes are needed for accurate trait mapping, and modern analytical tools are used in conjunction with SC germplasm and well-assembled genomes.
Inbreeding depression, mainly caused by the exposure of recessive deleterious alleles post self-pollination, is another hindrance to line development. Techniques such as recurrent selection and pedigree line development can manage inbreeding depression and maintain beneficial alleles. Hybrid breeding programs exploit heterosis, combine alleles at the same locus, and manage traits for specific markets.
Trait introgression in a breeding program involves the quick introduction of new traits. Methods like phenotypic selection or marker-assisted selection are used, and SNP markers are used to accurately select traits with high heritability. Strategies may involve improving select parent lines or the entire breeding pool, based on the program and market value.
The quality of an inbred line can be improved by incorporating market-specific traits. Resistance genes, for instance, can be added through marker-assisted breeding. Furthermore, male sterility is used in hybrid breeding for cost-effective seed production. While this affects the logistics of a breeding program, it leads to more efficient seed production.
Advancements in genetic research have enabled diploid inbred potato lines’ development. Genetically modified organisms (GMOs) and CRISPR-based editing can accelerate trait introgression and add value to a hybrid breeding program. While these technologies are regulated in the EU, they are gaining traction in the US market. The challenge now lies in efficiently utilizing available selection tools.
Hybrid Development and Evaluation
The development of hybrid crops involves a complex process including creating inbred lines, hybrid creation, evaluation, and large-scale hybrid development programs. Germplasm evaluation is used in various breeding stages like parental pool improvement and hybrid test crossing.
Hybrid performance prediction and parent classification are managed through genetic models and test-crosses. Using general and specific combining ability (GCA and SCA) estimators has improved the understanding of the value of parental lines in hybrid breeding.
Field trials are used for hybrid evaluation, comparing hybrids against commercial cultivars in traits like yield potential, dry matter percentage, and tuber shape. Factors such as soil conditions and plot dimensions, which can influence results, are accounted for to ensure genetic differences are observed.
As hybrid breeding grows, quicker methods to predict field traits are needed, particularly for crops grown from seedling tubers like potatoes.
Cropping Systems
Hybrid True Potato Seed (HTPS) breeding offers innovative potato production methods with multiple cultivation pathways leading to different cropping systems. Crop growth, development, and management can vary significantly depending on the starting materials used.
A newly proposed development scale accommodates these differences, tracking growth from seeds. Transplanting hybrid potato seedlings in the field could revolutionize potato production, but the process depends on factors like nursery management, field conditions, and crop management. Transplanting density, timing, and stage influence yield and tuber size.
Despite promising yield levels, the system has challenges like extended growing periods affecting tuberization, bulking, and harvest timing. Seedling tubers, despite being technically demanding with longer cycles, have higher yields. However, traditional seed tubers may remain popular due to their convenience.
Developing new HTPS cropping systems is complex, and breeding companies need to provide technical support and information to growers, adapting to evolving contexts.
Variety Registration and Marketing
Hybrid True Potato Seed Varieties (HTPS) pose regulatory issues in the EU relating to variety registration, Plant Variety Rights, and marketing. The current regulatory structures, designed for clonal tuber-propagated potato varieties, fall short in addressing distinctiveness, uniformity, and stability testing for HTPS.
The certification and marketing standards for HTPS seeds, seedlings, and tubers need revising. Seed tubers from HTPS need to be included in the existing certification scheme and minimum standards for seed germination, purity, and health should be established. The EU Temporary Experiment aims to amend these regulations by 2024. Import restrictions on HTPS seeds from outside the EU could increase seed costs and complicate logistics.
To facilitate sustainable potato cultivation, governments should adapt regulations regarding DUS testing, Plant Variety Rights applications, and certification and marketing. By doing so, the availability of improved potato varieties for European farmers and consumers could be expedited
Implementation
Implementing a hybrid breeding program requires a focus on operational excellence and product management.
Operational excellence involves executing experiments as planned and delivering timely results based on a preset protocol, which enables effective decision-making and collaboration. This is crucial for processes like SNP marker-assisted breeding, which involves numerous coordinated steps, requires teamwork across different teams and locations, and needs automation for handling large sample volumes. Cultivating a culture of trust and transparency, and defining tasks and responsibilities, enhances program quality.
The breeding program must also manage market pull, driven by customer demand, and technology push, driven by internal discoveries. While the initial focus is on technology push, market pull becomes more important as the program matures. Clear articulation of market demands leads to product profiles based on market size and resource allocation. Efficient information management, communication, and decision-making about resource allocation are crucial aspects of product management in a breeding program.
Societal Context and Future Outlook
The successful implementation of hybrid potato breeding relies on societal acceptance, added value for the user, and appropriate legislative structures, as emphasized by recent public and private sector stakeholder discussions. It’s noted that government frameworks are key to promoting fair futures for all involved in this innovation. The Rathenau Institute suggests that the availability of diverse genetic material, backed by government support for scientific progress, is critical to the potato value chain.
Public funding, particularly from the USA, China, and the Netherlands, is crucial to investigating fundamental scientific issues associated with hybrid diploid potato breeding. While this knowledge can benefit private entities, large-scale fundamental research often necessitates significant investment, usually accessible only to large corporations. Therefore, public funding is essential to supporting a range of private players.
Despite ongoing efforts, challenges such as yield stability under abiotic stress persist. This issue is paramount given the unstable climate and the demand for sustainable agriculture. On a positive note, two major potato processors, Simplot and AVEBE, are investing in hybrid breeding in response to diverse food product demands.
Challenges to overcome include transitioning from primarily scientific hurdles to registration, commercialization, and development of robust agronomic methods for potato cultivation.
The authors address specific challenges at three levels:
- Protecting varieties and facilitating germplasm exchange. Rapid adaptation of policies enables breeders to share germplasm, leading to faster genetic progress and expanding farmers’ access to high-quality varieties. Variety protection increases breeders’ confidence that they will receive a fair return on their investment.
- Extend research and development of agronomic practices to potato-growing areas outside Europe. In regions such as Africa and Asia, HTPS has immense potential to increase yields and strengthen food security. To realize this potential, they are working to formulate, develop and disseminate crop management knowledge.
- Advancing the development of high-yielding, resilient hybrids. The potato is particularly sensitive to abiotic stresses, especially heat and drought. Research is therefore underway to develop traits to mitigate the effects of abiotic stress. Basic research is needed to understand the interactions between tuber dynamics and the environment.
Source: de Vries, M. E., Adams, J. R., Eggers, E., Ying, S., Stockem, J. E., Kacheyo, O. C., van Dijk, L. C., Khera, P., Bachem, C. W., Lindhout, P., & G., E. A. (2023). Converting Hybrid Potato Breeding Science into Practice. Plants, 12(2), 230. https://doi.org/10.3390/plants12020230
Cover photo: Credit and courtesy Solynta
