to 100% when the canopy is closed. Losses occur before canopy closure and towards physiological maturity due to senescence. A number of traits have been identified that may increase light interception during the early development period of the crop. The most important factors contributing to the differences in leaf area development are size of the embryo, specific leaf area (SLA), speed of germination, faster rate of leaf expansion, shallow crown depth, coleoptile tiller and absence of GA-insensitive major dwarfing genes24 Rht1 and Rht2. Semi-dwarf GA-sensitive dwarfing genes are available, which result in better emergence and early leaf area growth. A high SLA is one way that barley achieves its early growth advantage over wheat. But a higher SLA also results in lower assimilation rate, because of a likely reduction in the amount of photosynthetic machinery per unit leaf area associated with a higher SLA. The increase in leaf area, however, more than compensates for this reduction in photosynthesis through greater light interception early in crop development. Thus, for early growth stages of cereals, a high SLA results in higher net assimilation rate (NAR). After canopy closure a high SLA becomes a hindrance to photosynthesis24.