The quikgro potato; an early maturing multiple stress tolerant potato crop for sub-Saharan Africa

Potato is a most important staple food and cash crop contributing both to food security and the local economy in countries of sub Saharan Africa (SSA) such as Kenya and Malawi. It is grown mainly by small holder farmers in the highland regions (>1500 m asl) since tuber development requires cool temperatures. Demand for potatoes is growing and the major challenge is to develop local varieties adapted to agronomic and environmental conditions found at lower altitudes to expand the production areas. Key to our proposal is to combine stress tolerance (biotic and abiotic) with the development of early maturing cvs (EMCs) (reaching full maturity in 60-70 days "the Quikgro potato" compared with over 100 days for most commercial varieties). We expect that EMCs will produce tubers that bulk quickly in warmer environments, mitigating the effect of short rainy seasons and droughts. EMCs will also be less susceptible to disease (due to a phenomenon called mature plant resistance; MPR) and the shorter growth cycle would allow potato to fit in rotation with other crops such as rice and wheat. Thus this innovation would have multiple benefits for the people of SSA.
Breeding potatoes to obtain germplasm with improved stress tolerances has proved very difficult as potato is tetraploid (it has 4 sets of each chromosome) and exhibits complex inheritance patterns making it a very long term process to achieve improvements in such genetically complex traits. Our approach is to avoid stresses by developing potato varieties that mature early (within 70 days) as our preliminary data indicates that this trait is controlled by a few dominant genes making it a more amenable breeding target.
Advances in understanding the control of tuber formation in potato have defined some of the components of day length signalling that lead to tuberisation such as the discovery of an additional version of the gene (StSP6A) that is associated with tuber formation under long days. Additionally, in transgenic tester lines, silencing of a gene encoding CEN1/TERMINAL FLOWER1, significantly decreases the time to both tuber and flower initiation. Thus the presence of a particular allelic variant impacts on the timing of tuber initiation providing a novel breeding strategy to develop early maturing potatoes. In further work (funded by ERA CAPS Hotsol BB/M004899/1) we have identified a gene that (designated StHot1) that confers extreme heat tolerance when tested in model systems.
Virus diseases are a major constraint of potato production systems in Kenya and Malawi. Mature potato plants are known to develop resistance to disease as they age (MPR). Our recent investigations (funded by BBSRC BB/L011840/1) have shown that resistance is induced at the onset of flowering, therefore, we hypothesise that early maturing plants will be more virus resistant. In addition, viruses can be controlled by natural resistance genes and previously we have identified natural resistance to potyviruses in the potato types (described above) that have also been studied for earliness and tuberisation. The resistance, has been genetically mapped and a marker developed. Using our network of established contacts, we introduced a virus resistant cultivar Mayan Gold containing this resistance to Kenya. Mayan Gold passed Kenyan National Performance Trials and since release has proved highly successful.
We will investigate the function of the newly identified gene targets to achieve proof of principle that EMC's will avoid both abiotic and biotic stresses. We shall screen a range of germplasm to test whether potato lines containing markers for earliness and stress tolerance will perform better in the African environment. Exchange with SSA scientists will enhance expertise in modern breeding and diagnostic technologies. Networks will be strengthened to engage all local stakeholders for knowledge exchange and feedback to translate findings into acceptable and practical outcomes.

In potato, tuber yield is highly sensitive to biotic and abiotic stresses which limit production in climatic zones experienced in sub-Saharan Africa and parts of Asia. Recent developments by researchers at St Andrews University and the James Hutton Institute have identified allelic variants that protect the plant from the harmful effects of heat and virus. Elevated temperature tolerance is achieved by the presence of an allele of an HSc70 gene that is expressed at much higher levels than other alleles at elevated temperature. Using a genetic approach, a locus has been defined that is associated with virus resistance. Our recent research has also characterised mature plant resistance to virus. An important part of our strategy to develop potatoes with combined heat and virus tolerance is to produce early maturing varieties that escape the effects of abiotic stress and will also be protected from virus by developing mature plant resistance earlier in the growing season. We have demonstrated that by silencing CENTRORADIALIS/TERMINAL FLOWER 1, transgenic lines tuberise and initiate flowers much earlier (by ca. 20 days) than controls. This finding will add an important element to published tuberisation models and will enable hypotheses about mature plant resistance to be tested.
KASP markers will be developed for allelic variants of the genes that impact on tuber maturity, heat tolerance and virus resistance. By extensive phenotyping and genotyping of potato populations in Malawi and Kenya we shall build quantitative genetic models relating allelic composition to phenotype and develop predictive tools to identify the most beneficial combinations of alleles. Outreach activities to crop scientists (including training of African scientists), stakeholders in the potato production and value chain and policy makers will amplify the impact of the research and opportunities for application.

Introduction: The underlying thrust of the proposed research is to develop a new concept that builds on our recent findings about tuberisation and stress tolerance in potato, the world's third most important food crop. Currently, a combination of biotic and abiotic stress decrease yields and constrain production to the cooler highland areas of sub-Saharan Africa (SSA). The outcomes of this project will be new knowledge, genes and alleles that can feed into a delivery framework that can be used in breeding programmes to increase tuber yield in warmer lowland environments.
Who might benefit from the proposed research? The DAC countries that will directly benefit from this foundation award are Malawi and Kenya. However, if the objectives of the proposal are realised then countries in SSA (such as Uganda, Tanzania, Rwanda, Zimbabwe, DRC) and Asia would benefit as 'Quikgro' potato is relevant to their production systems. Potato is an important food and cash crop in SSA grown predominantly by small holder farmers. In Malawi it contributes to food security especially during the hunger months (November to February) and in Kenya it is the second most important food crop after maize. Potato is a valuable alternative to reduce the dependence on maize as it is more nutritious (yielding 2-4 x the food quantity per ha than cereals, can meet the daily human dietary requirement of protein, vitamin C, zinc and iron, and uses water more efficiently). Therefore, the crop has strategic value in decreasing hunger and malnutrition. Furthermore, potato is not susceptible to commodity market speculation. In Kenya potato is cultivated by over 500,000 mostly small holder farmers with annual production worth about KSh50 billion. The industry has a strong multiplier effect, indirectly employing about 2.5 million people. National per capita consumption is expected to grow at 5.2% annually, with urban demand exceeding 7%, for the next 10 years to >40kg per capita by 2022. Thus potatoes have significant potential to contribute to food security and income generation but current yields of approx 20t/ha are far below the potential. Malawi has about 2 million small-holder farmers and there is a recognised over dependency on maize, potato is at the forefront of the Government's crop diversification efforts. The market for potato is expanding rapidly because of urbanization. This growing domestic market presents a valuable livelihood opportunity for smallholder farmers besides benefiting vulnerable low-income consumers. The annual national production statistics show potato production doubled from 527,830 MT in 2006 to 1,065,833 MT in 2015, and potato yield has increased by 33%, from 13.0 MT/ha to 17.3 MT/ha (a period which overlaps with Irish Aid's and the Scottish Government's (PI Torrance grant) first investments in strengthening the potato sector).
How might they benefit from this research? Maximum impact will be achieved as the project combines cutting edge research in the UK with an established network of scientists in Malawi (Mwenye/Demo) and Kenya (Were) working with farmers clubs and cooperatives. Each club represents several hundred farmers and other stakeholders in many counties and districts (at least 1000 in each country). The clubs are key centres for engagement, knowledge exchange and gaining information on farmer and industry preferences. Importantly, the networks of farmers associations are already established and growing (resulting in successful implementation and improved potato cultivation in previous projects). The associations and clubs will be boosted by the capacity building, knowledge exchange and demonstrations supported by this grant. The impact pathway will involve development of a delivery framework for technologies and a roadmap for further exploitation including plans for industry-led actions. This will positively impact on yields, farmers' incomes (and livelihoods) and growth across the whole value chain.