Accepted version

26 Cassava (Manihot esculenta Crantz) is the staple food source for over 850 million people 27 worldwide. Cassava contains cyanogenic glucosides and can be toxic to humans, causing 28 paralysing diseases such as konzo, and even death if not properly processed. Konzo 29 epidemics are often associated with times of drought. This may be due to a greater reliance 30 on cassava as it is drought tolerant, but it may also be due to an increase in cyanogenic 31 glucosides. Episodic droughts are forecast to become more common in many cassava32 growing regions. We therefore sought to quantify the effect of water-stress on both yield and 33 cyanogenic glucoside concentration (CNc) in the developing tubers of cassava. Five month34 old plants were grown in a glasshouse and either well-watered or droughted for 28 days. A 35 subset of droughted plants was re-watered half way through the experiment. Droughted plants 36 had 45% fewer leaves and lower tuber yield, by 83%, compared to well-watered plants. CNc 37 was 2.9-fold higher in the young leaves of droughted plants, while CNc in tubers from 38 droughted plants was 4-fold greater than in tubers from well-watered plants. Rewatered 39 plants had a similar biomass to control plants, and lower CNc than droughted plants. These 40 findings highlight the important link between food quality and episodic drought. 41