Durum wheat ( Triticum durum Desf.) origin, cultivation, and 1 potential expansion in sub-Saharan Africa

19 Durum wheat is an important food crop in the world and an endemic species of sub-Saharan 20 Africa (SSA). In the highlands of Ethiopia and the oases of the South Sahara this crop has been 21 cultivated for thousands of years. Today, smallholder farmers still cultivate it on marginal lands 22 to assure production for their self-consumption. However, durum wheat is no longer just a staple 23 crop for food security but it has become a major cash crop. In fact, the pasta and couscous 24 industry currently purchase durum grain at prices 10 to 20% higher than bread wheat. Africa as a 25 whole of length and daytime temperatures always above 32°C. This review describes the ability of 32 releasing durum wheat varieties adapted to all growing conditions of SSA, from the oases of the 33 Sahara to the highlands of Ethiopia. This potential area of expansion for durum wheat production 34 in SSA is not linked to any breeding technology, but rather it remains dependent on the market 35 ability to purchase these grains at a higher price to stimulate farmer adoption. The critical 36 importance of connecting all actors along the semolina value chain is presented in the example of 37 Oromia, Ethiopia, and that success story is then used to prompt a wider discussion on the 38 potential of durum wheat as a crop for poverty reduction in Africa.

4 must be mentioned that the pasta industry in SSA often utilizes bread wheat flour for its 78 production, and typically only products from North Africa and developed countries meet the 79 international standard of 'pasta' by using 100% durum semolina [14]. Clearly, there is huge 80 agricultural and commercial scope for expanding domestic production and marketing of durum 81 wheat in SSA countries. Durum wheat and rice are the most lucrative among the cereals, with prices usually 20 to 40 % 84 higher than common wheat, millet, maize, and sorghum [16]. While durum wheat remains a 85 critical staple food for smallholder farmers in marginal lands, thanks to its exceptional adaptation 86 to climatic stresses, its large-scale production is tightly linked to its greater monetary return. In 87 the absence of governmental subsidies that push toward the cultivation of other crops, farmers 88 tend to prefer durum wheat as long as the market continues to guarantee additional profits. In this 89 regard, the existence of a strong value chain for the pasta, couscous, and bourghul industry is 90 quintessential to the success of durum wheat cropping.

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In this review, the current status of durum wheat production in SSA is discussed in comparison 93 to the needs of the local pasta industry to better understand the potential of its expansion through 94 the deployment of novel adapted varieties. Because of its industrial nature, durum wheat has 95 often been disregarded by SSA policy makers in favor of bread wheat as a more direct food 96 source. However, among the sustainable development goals set by the United Nations, "poverty 97 reduction" is considered as a strategic way to tackle famine, without causing nutritional deficits 98 due to mono-food diets. In this sense, durum wheat is at least as well suited as bread wheat in 99 improving livelihoods. Both aspects of durum wheat, as a "food security" staple food for 100 smallholder farmers, as well as a "poverty reduction" industrial crop will be considered here.   kolo (round and seasoned dough), and kinche (crushed kernels, cooked with milk or water and 175 mixed with spiced butter). Besides the role of grain in traditional food and processed products, 176 durum wheat straw is also greatly appreciated for its high palatability for livestock in the mixed 177 farming systems of the highlands of Ethiopia [42]. Ethiopia today cultivates 562,000 ha of durum 178 wheat [12], accounting for the vast majority of the cultivation of this crop in SSA ( Table 2). 179 Still, today's value represents just half of the land that was dedicated to durum wheat in 1967 system has been put in place, which rationalized also the previous work into a variety catalog, 208 which accounts today for 40 durum wheat cultivars (Fig. 1). In the last two decades, many 209 federal and regional agricultural research centers have become involved in durum wheat  remains very low [54], mainly because of the high cost of purchasing quality seeds, scarce access 226 to agriculture micro-credits, and a national seed system incapable of also reaching the more 227 remote areas [55]. To resolve some of these issues, international agricultural research centers and  Emmer wheat is recommended for mothers as a special diet to maintaining their health and 255 strength after childbirth because of its high protein content and digestibility [64]. In fact, its grain 256 protein content ranges from 8.5 to 21.5%, which is 5-35% higher than in grain from oats or 257 barley, and it has a very low glycemic index [63]. Emmer wheat is also a good source of resistance to leaf and stem rusts, powdery mildew, Septoria glume blotch, Fusarium head blight,  (Table 1). However, at the same time, pasta import increased two- the key element for the success and sustainability of the development process [72]. expanding to nearby Arsi and Shewa zones (Fig. 2)   This expansion into considering a pulse such as cowpea as part of the durum wheat production 391 system is, however, beyond the scope of this review and shall not be discussed further.

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A third country relying on the Senegal River for irrigation is Mali, whose production is 394 concentrated along this and the Niger River. The total irrigable land is estimated at 340,000 ha

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[81] with a potential to further expand. The vast majority of the land is utilized for the production 396 of rice and maize during the warm months. Wheat is cultivated during winter on just 10,000 ha, 397 of which a very small portion is durum wheat ( Table 1) The situation in Nigeria is no different than that observed for the Senegal River countries, even 412 though, with over 80,000 ha farmed to wheat in 2013, it is already the largest bread wheat 413 producer in West Africa ( grain to be converted into pasta for the national and export market (€ 41 million EUR worth).

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Hence, the local industry could certainly benefit from an increase in national production.

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Considering that the area cultivated with rice exceeds 2.9 million ha and that irrigation water is    or drip irrigation, such as in the regions of east of Morocco and Algeria [97]. In these cases, 508 water is pumped as needed, and wheat is often cultivated among date palms with the moisture 509 used by both cultures. In most other cases, large quantities of water are available only during 510 specific times of the year, and to collect it in sufficient amounts for cultivation, it is necessary to 511 build temporary dams with clay, sand, and stones. The dam is then opened at the beginning of 512 the winter and as the water recedes, holes are dug into the mud and cereal grains are placed 513 inside (Fig 3). Growing on residual moisture and with high temperatures, the yields rarely 514 exceed 0.5 t ha -1 , while under pumped irrigation yields of 4 to 5 t ha -1 are common [98].  adaptation. Furthermore, the oases represent fragile ecosystems, where land availability is 531 dependent on rainfall and maximum yields per unit of land are more critical than anywhere else.

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In that sense, the introduction of modern agronomy and irrigation practices, in integration with 533 targeted breeding efforts could deliver true game changers. Alternatively, the reduced available 534 land surface could be used as an advantage to generate very exclusive durum products. In fact, 535 the 'rarity' could be exploited through well integrated value chains to deliver products at 536 elevated prices on the occidental markets, as is already the case for the oases dates. Considering 537 that oases produce less than 5% of their needs in cereals [95], and the rest is purchased from 538 neighboring towns, the possibility of generating larger incomes would be a suitable strategy to 539 tackle famine. In that sense, the already high value of durum grains could be further exploited via 540 smart-marketing to increase the revenues. Canada, USA, and Turkey ( Table 1). North Africa already cultivates durum wheat on 2.9 million 547 ha, and the area for further expansion is limited. This opens an opportunity for SSA to gain 548 access to an € 3.7 billion annual market by filling part of the grain needs of NA. The current area 549 dedicated to wheat cultivation in SSA is limited to 2.6 million ha, mostly in Ethiopia, South 550 Africa and Sudan. In Ethiopia, new interest has sprung toward the promotion of industrial crops 551 such as durum wheat to provide the local manufacturers with prime raw material without the 552 need of relying on expensive imports. In addition, urbanization has shifted the food habits of 553 many countries, and pasta has gained steadily in appreciation by African consumers.

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Furthermore, the case presented for cultivation of durum wheat in rotation with rice along the 555 Senegal River, matches what is already customary on over 10 million ha of wheat-rice or wheat-556 rice-rice rotations in India [80]. In that sense, there is large potential for wheat expansion on the 557 9.1 million ha of rice land in SSA. Since further expansion of the wheat areas will require 558 additional investments and will face the risk of reduced yields, it appears logical to seek the 559 wheat type that would provide the maximum monetary return for unit of land converted. Durum