Statistical Analysis of Durum Wheat Yield Under Semi-Warm Dryland Condition (Report‪)‬

Introduction Among all cultivated wheats, Triticum aestivum and Triticum durum are the most important cereal crops in the world. Durum wheat is a minor crop, grown on only 8 to 10% of all wheat cultivated area. In spite of its low acreage, durum wheat is an economically important crop because of its unique characteristics and end products. It is generally considered the hardiest of all wheats. Durum kernels are usually large, golden amber, and translucent. These characteristics, along with its protein content and gluten strength, make it suitable for manufacturing of diverse food products. Pasta is the most common durum's end product consumed in Europe, North America, and the former USSR. Products other than pasta are also made from durum wheat. Couscous, made from durum semolina, is consumed mainly in North Africa. Flat bread made from durum wheat and bulgur are part of the main diet in Jordan, Lebanon, and Syria. Durum wheat is one of the most extensively cultivated crops under dryland conditions in the Mediterranean environments, where water stress and high temperature are the main constraints limiting productivity (Araus et al., 2002), although this condition offers an opportunity for the production of high-quality durum (Borghi et al., 1997). Selection for genotypes with increased productivity under drought conditions has been an important aspect of many breeding programs. The biological basis for drought tolerance is still poorly understood. Also, drought stress is highly heterogeneous space (between and within sites), and time (over the seasons and years), and is unpredictable. This makes it difficult to identify or simulate a representative drought stress condition. In addition to the complexity of drought itself (Passioura, 2007), plant responses to drought are complex and different mechanisms are adopted by plants when they encounter drought (Jones, 2004). Different methods have been employed to identify crops that are productive under drought condition. Yield loss is the main concern of plant breeders, hence, they emphasize on yield performance under drought condition. But yield is a complex trait and is the result of environmental factors as well as interaction of many minor-effect characteristics by low heritability especially under dryland condition (Blum, 1988). So, yield improvement through direct selection method is difficult. The morpho-physiological trait based breeding approaches has merit over breeding solely on the basis of grain yield. If the morpho-physiological traits affecting yield are found as indirect selection criteria with higher heritability and easily and rapidly screened. The efficiency of selection will increase especially in early generations or when the yield may not be properly evaluated (Royo et al., 2003). A great number of physiological traits have the potential to improve crop performance under abiotic stress (Araus et al., 2002; Condon et al., 2004; Richards, 2006). The existence of correlation between different traits with grain yield under drought stress shows compatibility with drought conditions is not unexpected (Richards et al., 2003). Selection of drought tolerant genotypes in wheat requires a simple and nondestructive method (Gusta and Chen, 1987). The results of research by Moghadam et al. (1993) showed that although there are positive correlation between grain yield and some of its components, but the existence of negative correlations has caused different efficiency of selection for some components that are not in the same direction of increasing the wheat yield. Increase in one component usually causes the decreasing of other components. Furthermore, although a number of morpho-physiological traits have proved associated with yield of wheat under semi-arid conditions; their contribution to selection can be adversely affected by the fact that this association may be environment-specific. In modeling of durum yield, different statistical techniques have been used, includi