Functional properties of normal and waxy starches from maize, rice, potato, and cassava as well as the modified waxy maize starch COLFLO 67 were compared. The main objective of this study is to position the recently discovered spontaneous mutation for amylose-free cassava starch in relation to the other starches with well-known characteristics. Paste clarity, wavelength of maximum absorption (lambda(max)), pasting properties, swelling power, solubility, and dispersed volume fraction measurements and gel stability (acid and alkaline resistance, shear, refrigeration, and freeze/thaw stability) were evaluated in the different types and sources of starch included in this study. lambda(max) in the waxy cassava starch was reduced considerably in comparison with that of normal cassava starch (535 vs 592 nm). RVA peak viscosity of waxy cassava starch was larger than in normal cassava starch (1119 vs 937 cP) and assumed a position intermediate between the waxy potato and maize starches. Acid, alkaline, and shear stability of waxy cassava starch were similar to normal cassava except for alkaline pH, at which it showed a low effect. Gels from normal root and tuber starches after refrigeration and freeze/thaw had lower syneresis than cereal starches. Gels from waxy starches (except for potato) did not present any syneresis after 5 weeks of storage at 4 degrees C. Waxy cassava starch was the only one not showing any syneresis after 5 weeks of storage at -20 degrees C. Natural waxy cassava starch is, therefore, a promising ingredient to formulate refrigerated or frozen food.

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Cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) are currently two major viral diseases that severely reduce cassava production in large areas of Sub-Saharan Africa. Natural resistance has so far only been reported for CMD in cassava. CBSD is caused by two virus species, Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV). A sequence of the CBSV coat protein (CP) highly conserved between the two virus species was used to demonstrate that a CBSV-CP hairpin construct sufficed to generate immunity against both viral species in the cassava model cultivar (cv. 60444). Most of the transgenic lines showed high levels of resistance under increasing viral loads using a stringent top-grafting method of inoculation. No viral replication was observed in the resistant transgenic lines and they remained free of typical CBSD root symptoms 7 month post-infection. To generate transgenic cassava lines combining resistance to both CBSD and CMD the hairpin construct was transferred to a CMD-resistant farmer-preferred Nigerian landrace TME 7 (Oko-Iyawo). An adapted protocol allowed the efficient Agrobacterium-based transformation of TME 7 and the regeneration of transgenic lines with high levels of CBSV-CP hairpin-derived small RNAs. All transgenic TME 7 lines were immune to both CBSV and UCBSV infections. Further evaluation of the transgenic TME 7 lines revealed that CBSD resistance was maintained when plants were co-inoculated with East African cassava mosaic virus (EACMV), a geminivirus causing CMD. The innovative combination of natural and engineered virus resistance in farmer-preferred landraces will be particularly important to reducing the increasing impact of cassava viral diseases in Africa.

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Cassava (Manihot esculenta Crantz) is one of the most important sources of starch in the tropics. There is limited and contradictory information regarding cassava starch characteristics. The International Center for Tropical Agriculture (CIAT) holds in trust FAO's cassava germplasm collection. Starches from 3272 landraces (including 12 wild relatives) and 772 improved clones were extracted and analyzed over a period of several years. In most cases only one starch sample per genotype was analyzed. Average cyanogenic potential was 327 ppm but considerably higher in the landraces (340 ppm) than in improved clones (267 ppm). Average total and reducing sugars were slightly higher in improved clones (4.06 and 1.56%, respectively) than in landraces (3.68 and 1.25%, respectively). Amylose content was similar in both types of germplasm with an average of 20.7%. Average pasting temperature was 65.3°C. Maximum viscosity was 777.5 mPa s, breakdown was 298.1 mPa s, consistency was 155.8 mPa s and setback was ‐144.5 mPa s. The large sample of starches analyzed provides very robust information regarding the actual characteristics of cassava starch.