Sorghum [Sorghum bicolor (L.) Moench] is the fifth most important cereal grain after maize, rice, wheat and barley in the world (FAOSTAT, 2017). It has been cultivated for centuries as a staple food crop in much of sub-Saharan Africa and Asia. It has remarkably wide adaptation and tolerates high temperatures and drought stress. It grows under high radiation, inadequate and erratic rainfall and in soils of poor structure, low fertility and low water holding capacity.
Sorghum is an important source of food and feed, particularly in the arid and semi-arid regions where other cereal crops such as maize and wheat fail to grow (Duodu et al., 2003; Reddy et al., 2004). Considering recent climate changes, sorghum production could reduce the expected food shortages (Abdalla and Gamar, 2011). In developing countries, including Ethiopia, more than 500 million people consume sorghum as their principal food source (Burke et al., 2013).
Sorghum is a gluten-free cereal used as a whole grain or processed into flour to provide essential nutrients including carbohydrates, protein, vitamins and minerals, and nutraceuticals such as antioxidants, phenolics and cholesterol-lowering waxes (Taylor et al., 2006; Perazzo et al., 2014).
In Ethiopia a total of 4.34 million tons of sorghum is being produced per annum. The mean yield level in the country is estimated at 2.37 t. ha-1. The crop is the major food cereal after maize and tef in terms of number of growers, area coverage and grain production in the country (CSA, 2016). It is utilized in various forms, such as for making the local bread, „„Injera‟‟, and for the preparation of local beverages such as, „„tela‟‟ and „„areki‟‟. Grain from some sorghum varieties is cooked as a roasted or boiled grain. Sorghum stalks are used as feed for animals, and as housing and fencing material. The crop is highly adapted to the lowland and drier parts of Ethiopia owing to its considerable drought resilience.
Despite its ability to grow in the arid and semi-arid areas of sub-Saharan Africa including in Ethiopia, the yield and quality of sorghum is affected by a wide array of production constraints such as the use of low yielding traditional varieties, which keep its productivity low. Drought, infestations by Striga hermonthica and soil salinity are the major stresses that limit sorghum production and productivity in the world (Zhu-Salzman et al., 2004). Among these, drought
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stress and Striga damages are the most important production constraints to sorghum production in Ethiopia (Gebretsadik et al., 2014). Drought is a major constraint in sorghum production worldwide and is considered as the most important cause of yield reduction in crop plants (Sabadin et al., 2012; Besufekad and Bantte, 2013), especially in water-limited areas of the world including parts of eastern and southern Africa. Striga infestation is often linked with poor soil fertility, resulting in poor harvests and consequently of hunger (Ejeta, 2007). The impact of Striga is more pronounced in areas under moisture and nutrient stresses.
In sorghum, there are two primary types of drought responses including pre-flowering and post- flowering, which are under the control of two different sets of genetic mechanisms. Pre- flowering refers to the stage from panicle differentiation to flowering, while post-flowering refers to the stage between flowering to grain development (GS-3) (Burke et al., 2010). Pre- flowering drought tolerance responses of sorghum includes reductions in panicle size, seed number, and grain yield. Post-flowering drought tolerance encompasses rapid premature senescence, which leads to reductions in seed size, yield loss and stalk lodging (Sanchez et al., 2002; Burke et al., 2010).
Much research effort has been spent trying to understand drought tolerance mechanisms in sorghum in order to breed for drought tolerant genotypes that will tolerate the frequent moisture deficit events in Ethiopia. These studies have recommended a number of soil and moisture conservation practices, which include tillage operations, tie-ridging and mulching to reduce the effects of drought (Teshome et al., 1995). Efforts have also been made to develop early maturing sorghum varieties that are adapted to areas where regular moisture scarcity is detrimental to sorghum production. In Ethiopia, more than 51 early maturing sorghum varieties are currently available for use in such environments (ABoA, 2017; SARC, 2017). However, most of these varieties were not readily adopted by farmers for varied reasons. Firstly, planting dates for these varieties are mismatched with what the farmers are currently using; mid-April to mid-May is the normal sorghum planting time, particularly in north eastern Amhara Region. Secondly, farmers highly expect two most important benefits at the same time from sorghum crop, i.e., grain yield and above ground biomass to their livestock. Thirdly, farmers believe that post-flowering drought recovery capacity of long and medium-maturing sorghum landraces is better than early maturing ones.
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Despite the long-term efforts made to breeding for tolerance to drought in sorghum, advances made in developing improved varieties with adequate levels of drought tolerance using indigenous landraces combined with farmers‟ and market-preferred grain, and above ground biomass traits have been limited. Farmers still prefer to plant local sorghum landraces rather than introduced varieties because local landraces produce larger volumes of biomass for animal fodder, fuel, and construction material in good cropping seasons. Therefore, sorghum breeding programs should ensure that the new varieties satisfy the preferences of the farmers through participatory variety selection to create sustainable adaptation of the released varieties and their production packages. This explains why this breeding study was preceded by a survey using a structured questionnaire to collect information on impact of drought, and on farmer‟s varietal and trait preferences of sorghum in north eastern Ethiopia. This information was gathered through participatory rural appraisal (PRA).
In Ethiopia sorghum remains a subsistence crop with limited industrial value. It is the third most important cereal next to tef and maize on the basis of area cultivated and production amount (CSA, 2016). In the Oromia Special and North Wello Zones, sorghum is the first major cereal crop in terms of area coverage and amount produced whereas it is the second next to tef in area coverage in the South Wollo Zone (CSA, 2015). Because of its drought tolerance, high biomass production for cattle feed, relatively better productivity during good rainy seasons, and its provision of continuous supply of food starting from mid-September, farmers rely heavily on sorghum cultivation yearly.
In the study zones, April is the ideal sorghum planting time. Farmers start to harvest green heads for food around September or in the „Meskel‟ season (coinciding with the celebration of the Finding of the True Cross. At this time sweet stem sorghum varieties reaches the middle of the grain filling stage, at this point the stems can be chewed as an important food source (“Gulbet”).
Farmers often grew a mixture of varieties (locally referred to as „Wajera‟) so that in some areas medium maturing local landraces of grain and sweet sorghum could be ready for family consumption before September 11. It was believed that eating sweet sorghum stalks before September 11 would increase the likelihood of catching malaria. Some stands of the sweet sorghum varieties were left in sorghum fields up to grain physiological maturity to be used for porridge preparation and as a seed source in the coming production year. Heads of sorghum at
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grain filling are roasted and eaten, which is locally termed as „mashella eshet‟, „tibese‟ or
„lemete‟. These are the most common food types around September and October when sorghum reaches the soft dough stage. Depending on the maturity period farmers have access to “mashela eshet” until harvest.
Participatory rural appraisal is one of the most effective and popular way to gather information in rural areas. The basic concept of PRA is to learn from rural communities. It is a bottom-up approach developed in the early 1990s and stands on the principle that local communities are creative, capable and can do their own investigations, analysis and planning (Chambers, 1992).
Therefore, the objectives of this study were to determine the impact of drought on sorghum production and productivity over time and space, and to identify farmers‟ production constraints and coping strategies when dealing with drought in north eastern Ethiopia.
2.3 Materials and methods