Exploring true-seed based potato production systems

Summary

The introduction of true potato seeds (TPS) as starting material for seed and ware production has provided new pathways for cultivation of seed and ware tubers. Of these cultivation pathways, the use of field-transplanted, nursery-raised seedlings is currently the most efficient TPS-based system for production. This is mostly because direct sowing of TPS faces some major challenges and additional research to make this system work is still required. Additionally, the use of seedling tubers is dependent on successful production of tubers from either field-transplanted or directly sown seedling crops or under semi-controlled conditions. Even so, how a field-transplanting system would work and the factors that influence the success of the system have not been exhaustively researched and defined. Additionally, the consequences of the use of a seedling (or any TPS-based propagule) as opposed to seed tubers have also not been clearly defined. This thesis assessed the feasibility of the use of a field-transplanting system for seed or ware tuber production. Specifically, the differences between TPS- and tuber-grown plants were analysed and the implications of the differences between these propagules on crop growth, development and agronomy were assessed. Further, the effects of various agronomic factors on seedling growth in the nursery and to a lesser extent crop growth and development in the field were investigated. This thesis demonstrates that a field-transplanting system is a practical option for hybrid potato cultivation. Seed or ware tubers can be produced in the first generation from field-transplanted seedlings raised in greenhouse nurseries, especially when the various phases of the transplanting system are successfully executed. For nursery seedling production, when plug trays are utilised for seedling production, substrate type and volume, watering intervals and the levels of N and P in solution should be considered. Additionally, seedlings also respond variably to climatic factors such as temperature, light intensity and day light integral. Conclusively, attributes that define seedling vigour, such as leaf area or dry matter per unit stem length, should be used as selection criteria for transplantable seedlings to ensure successful field establishment and crop productivity under field conditions. Considering the differences between TPS-grown and tuber-grown plants, crop management factors and their application should be tailored to the cultivation system —in this case, the field-transplanting system. Agronomic consequences of field-transplanting, nursery raised seedlings have been highlighted in this study and specifically, the effects of the choice of bed, ridge or planting configurations during transplanting have been quantified and the possible implications of these choices have been reported. Ultimately, since direct sowing does not work to the current level of a field-transplanting system, the transplanting system remains the prospective method for production of seed and ware from hybrid TPS. The findings in this study and others, will still contribute to advancing the success of the field-transplanting system as well as inform on initiatives to ensure a possible direct sowing future in potato production. Finally, these findings will guide in the development of protocols for nursery seedling production and field cultivation of potato seedlings derived from TPS.