Cassava, also known as manioc, provides the basic diet for more than half a billion people. It is the most important food source throughout much of the tropical belt of Sub-Saharan Africa and the the third largest source of food carbohydrates in the tropics globally, after rice and maize. Yet its inherent yield capacity and harvest index are significantly lower than other crops such as potato or sweet potato.
An interdisciplinary research project led by FAU scientists aims to determine ways to increase the total biomass and starch yield of the cassava plant. The Bill & Melinda Gates Foundation, which combats disease, hunger and poverty in the developing world, has awarded $10 million in funding over a five-year period to the project, entitled Metabolic engineering of carbon pathways to enhance yield of root and tuber crops. Leading experts in plant ecophysiology, molecular biochemistry and physiology, biotechnology and cassava breeding will team up to improve cassava productivity. International project partners include ETH Zurich (Switzerland), MPI-MPP (Golm, Germany), the University of Kaiserslautern (Germany), Boyce Thompson Institute for Plant Research (Urbana, USA) and the University of Illinois (USA).
Project coordinator Prof. Dr. Uwe Sonnewald, Chair of Biochemistry at FAU, said: "The greatest challenge is to bring together computer scientists, plant scientists and breeders, to combine progress in each field with the common goal to improve plant productivity and to secure future food supply for a growing world population. So far, cassava has not significantly benefited from major advances in modern plant biochemistry and physiology. A better understanding of cassava physiology and biochemistry will be essential to achieve sustainable increases in cassava yield and will be critical for ensuring sufficient food supply in Sub-Saharan Africa."
Compared to other crop plants, little is known about cassava source-to-sink relations which are major determinants of final crop yield. In other crop plants, such as wheat or rice, grain yield has substantially been increased in recent decades. This has been achieved mainly by shifting biomass from shoots to grains, thereby increasing harvest index. The physiological basis for increased yield and improved biomass allocation can be attributed to improved photosynthetic carbon assimilation in source tissues (mainly mature leaves), long-distance transport of assimilates (through the phloem ) and their utilization in sink tissues. Significant technological breakthroughs, such as Systems Biology, Next Generation Sequencing, Computing, and their implementation in plant science are major drivers of yield improvements in crops.
To achieve a sustainable increase in cassava yield, the research project will follow a three-pronged strategy based on studies of comparable crops. Firstly, to understand the metabolic processes limiting cassava yield and starch accumulation in storage-roots under optimal growth conditions; secondly, to explore the genetic space of total biomass and starch yield in a range of cassava genotypes and especially farmer-preferred varieties; and thirdly, to engineer sink-to-source relations in transgenic cassava plants to increase total biomass and starch yield.
Researchers will deliver a unique database combining genomic, molecular, biochemical and phenotypic data for in silico predictions and experimental testing of metabolic processes that limit cassava productivity. Molecular tools will be developed for the spatial and temporal engineering of cassava source-to-sink relationship to increase starch production. Engineering efforts will be complemented by validation and evaluation of transgenic and existing cassava genotypes as well as farmer-preferred varieties with improved productivity and increased storage root starch content for breeders and farmers. In addition to increasing the inherent productivity of cassava, the project will also characterize the different developmental stages of cassava roots, providing basic information that will be invaluable to cassava researchers.
While this stage of the work is focused on achieving proof of concept, any promising transgenic materials with high potential to increase yields will be transferred to Africa-based partners. Following proof of concept, additional work will support partners in Africa as they utilize those transgenic materials to develop higher-yielding varieties for farmers, including support managing the regulatory system.