description
- 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.