ABSTRACT
Agriculture in the Old World started about 10,000 years ago, coinciding with the beginning of the Holocene. From this time up to the present, C3 cereals, such as bread (Triticum aestivum L.) and durum wheat (Triticum turgidum L. var. durum), as well as barley (Hordeum vulgare L.) have remained the outstanding crops in terms of area and food source (e.g., Evans, 1998). Relatively high cereal yields are suggested at the beginning of agriculture (Amir and Sinclair, 1994; Araus et al., 1999, 2001b), so t hat the yields believed to be attained then (the equivalent to ca. 1 Mg ha−1; see, for instance, Araus et al., 2001b and references therein) were quite similar to the averaged yields attained globally at the beginning of the twentieth century (Calderini and Slafer, 1998; Slafer and Satorre, 1999). This means that the increased demands produced by the growing population since the Neolithic (some 4-10 million people; Mine and Vandermeer, 1990; Evans, 1998) to 1900 (more than 1 billon people) were chiefly satisfied by the enlargement of the cultivated area. During the twentieth century, when Mendel’s laws were rediscovered and breeding started its period of scientifically based selection, increases in average yield were still not evident until around the 1950s (Calderini and Slafer, 1998; Slafer and Satorre, 1999). There was still a large increase in growing area as a response to the increased demand during the first half of the twentieth century (Slafer and Satorre, 1999). Since then, average yields increased dramatically in
only a few decades. This change, known as the Green Revolution, was due to the introduction of semidwarf varieties with improved harvest index (HI) and, consequently, higher yield potential* (Calderini et al., 1999a; Abeledo et al., 2001), which in turn were more responsive to management improvement (Calderini and Slafer, 1999). It allowed the interaction between genetic and management improvement to express a relative increase in average yields even greater than that in population during the second half of the twentieth century (Slafer and Satorre, 1999). Before the improvement in yield potential during the intermediate decades of the twentieth century, responsiveness to environmental amelioration has been limited. For instance, the increase in atmospheric CO2 concentrations from ca. 270 ppm before the beginning of the industrial revolution to the levels observed in 1950s (ca. 350 ppm) appears to have affected only marginally the yield levels of cereals (Slafer and Satorre, 1999).
