Based on its importance for smallholder farmers, the Gates Foundation has identified cassava as priority crop. To support cassava productivity, the foundation has launched several projects deciphering the genome sequence and to tackle major cassava diseases. Yield can be increased by expanding land use, improved crop management (especially the application of fertilizer or precision farming) and plant breeding. While increased land use will ultimately lead to higher emission of greenhouse gases and negatively affect biodiversity, improved crop management strategies are often not affordable by smallholder farmers.
Therefore, breeding for robustly high yielding cassava plants should be the prime strategy to support income of smallholder farmers. Compared to other crop plants, however, 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 over the last decades. This has mainly been achieved 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.
The Cassava Source-Sink (CASS) project brings 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, however, will be essential to achieve sustainable increases in cassava yield and will be critical for ensuring sufficient food supply in Sub-Saharan Africa (SSA). To achieve this we propose a three-pronged strategy, which is mainly based on proof-of-concept studies in other higher plant species including crops with comparable physiological backgrounds.
1. Understanding the metabolic processes limiting cassava yield and starch accumulation in storage roots under optimal growth conditions.
2. Exploration of the genetic space of total biomass and starch yield in a range of cassava genotypes and especially farmer-preferred varieties.
3. Engineering source-to-sink relations in transgenic cassava plants to increase total biomass and starch yield.
To accomplish this, leading experts in plant ecophysiology, molecular biochemistry and physiology, bioinformatics, biotechnology from Europe and the US have developed a research strategy to bring cassava physiology to the level of major crop plants and to team-up with cassava breeders and growers in SSA to work synergistically on the development of next generation cassava plants with elevated yield potential. This team of experts will deliver a unique database combining genomic, molecular, biochemical and phenotypic information required for in silico predictions and experimental testing of metabolic processes that limit cassava productivity.