The effects of preconditioning temperature and preconditioning period on the sensitivity of parasitic weed seeds to the synthetic germination stimulant GR24 were studied under laboratory and field conditions. The temperature during preconditioning of Orobanche cumana and Striga hermonthica seeds strongly affected the responsiveness of the seeds to the applied germination stimulant. Preconditioning at an optimal temperature (21°C for O. cumana and 30°C for S. hermonthica) rapidly released dormancy and increased the sensitivity to GR24 by several orders of magnitude. After reaching maximum sensitivity, prolonged preconditioning rapidly induced secondary dormancy, i.e. decreased sensitivity of O. cumana and S. hermonthica to GR24. The rapid change in sensitivity of preconditioned seeds to germination stimulants during prolonged preconditioning was particularly visible at low concentrations of GR24. GR24 at higher concentrations (0.1 and 1 mg l -1 ) usually induced high germination of both species, regardless of the preconditioning period. The striking similarities between the response of parasitic weed seeds to GR24, described here, and results in the literature on non-parasitic wild plant seeds are discussed. Our results show that parasitic weed seeds are highly sensitive to the germination stimulant for a short period of time only, and then enter into secondary dormancy relatively quickly. The similar germination pattern of S. hermonthica seeds preconditioned for prolonged periods of time under laboratory and field conditions suggests that the mechanism observed is of ecological significance.

In sub-Saharan Africa, more than 40% of children under five years of age suffer from vitamin A deficiency. Among several interventions in place to address vitamin A deficiency is biofortification, breeding vitamin A into key staple crops. Staple crops biofortified with beta-carotene, the precursor to vitamin A, are orange in color. Given the natural occurrence of high levels of beta-carotene in many sweet potato varieties, breeding progress for biofortified orange sweet potato (OSP) has been much faster than for the other vitamin A enhanced staples. Nearly 3 million households have been reached with OSP. This paper reviews key factors influencing the uptake of OSP, the breeding investment, five key delivery approaches that have been tested in the region and efforts to broaden government and other stakeholder engagement.

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Open Agriculture. 2017; 2: 83-90 and measured parameters, was most appreciated and was the farmers' first choice, followed by varieties TIB-440060 and 'Bela bela'. Keywords:Orange-fleshed sweetpotato, on-farm Demonstration, participatory varietal selection, sweetpotato IntroductionSweetpotato is cultivated in all the regions of Côte d'Ivoire for consumption and also as a source of income. It is a dicotyledonous plant called Ipomoea batatas (Lam.) that belongs to the family Convolvulaceae, and a tuberous root crop important for food security (Ermias et al. 2013). Globally it is among the important food crops in the world, after wheat, rice, maize, Irish potato, and barley and it ranks second following Irish potato in the world's root and tuber crops production and third after Irish potato and cassava in consumption in several parts of tropical Africa (Teshome et al. 2012). Sweetpotato is also a good source of calcium, ascorbic acid (vitamin C) and beta carotene (provitamin A). Varieties with orange flesh contain particularly high levels of beta carotene which is converted to vitamin A in the human body (Sakamoto et al. 1987); while there is moderate amount of beta carotene in yellow-fleshed and none in white-fleshed varieties (ACIAR, 2010 andStathers et al. 2013). Vitamin A is involved in building the body's immune system to defend against disease and blindness (WHO, 2014). According to the World Health Organization (WHO), vitamin A deficiency (VAD), which is associated with low consumption of products rich in vitamin A is common and is a serious health problem in many developing countries (including Côte d'Ivoire). According to FAO (2009) (OFSP) is hampered by the lack of genetic resources and planting material. To evaluate and release OFSP varieties, on-farm demonstration tests were conducted with women farmer groups in Bondoukou, Nassian, Korhogo and Bondiali in the north and northeast Côte d'Ivoire. Six varieties-'Kabode', 'Kakamega7' ('Irene'), 'Tacha', 'Bela Bela', 'Vita' and TIB-440060-were evaluated in comparison with locally grown varieties. The on-farm demonstration was laid out in a randomised complete block design with replicated three times per location. Assessments were made on yield, disease and pests; and consumer preference on attractiveness of skin color and flesh of the root (fresh and boiled), taste, texture and starchiness. Results showed that introduced varieties have generally recorded higher yields than the local varieties: Yields of about 25 t/ha have been recorded on the sites. The best average yield of about 15 t/ha, was recorded for TIB-440060 and 'Irene' varieties. Farmers' acceptance of OFSP varieties based on the attraction of their color, the dry matter content and taste was more than 90%. At the end of the sensory tests, 'Irene', which achieved the best compromise between all observed