manihot esculenta 638 starch crops 171 cultivation 95 variedades 75 research 73 productivity 71 development 69 marketing 66 processing 59 economics 55 root productivity 54 fitomejoramiento 52 cultivars 48 production 47 cultivo 45 pests 45 mercadeo 43 varieties 42 cassava 40 cultivation systems 40 plant anatomy 40 uses 39 cassava products 38 processed products 38 drying 37 producción 37 roots 37 costs 36 plant breeding 36 cuttings 35