Overall, the impacts of the Green Revolution have been mixed.

Positive impacts on yield have been achieved in Latin America with an increase of 132% (36% from improved varieties and 64% from other inputs) on 32% less land (Evenson and Gollin, 2003a). Negative effects on yield occurred in sub- Saharan Africa even though overall yield increased 11% (130% coming from improved varieties and -30% from other inputs), since 88% more land was used). In SSA and CWANA, MVs were released but not adopted throughout the 1960s and 70s (Evenson, 2003). In some cases, MVs lacked desired organolepic qualities or were not as well adapted as Traditional Varieties (TVs). However, in many cases the lack of adoption resulted from inadequate delivery of seeds to farmers (Witcombe et al., 1988). Poor seed delivery systems remain a major constraint in many parts of Africa (Tripp, 2001).

Plants

Domestication, intensive selection and conventional breeding have had major impacts on yield and production of staple food crops, horticultural crops and timber trees.

Yield per unit area of the world's staple food crops, especially cereals (rice, wheat and maize) have increased over the last 50 years (Figure 3-2), as a result of publicly and privately funded research on genetic selection and conventional breeding (Simmonds, 1976; Snape, 2004; Swaminathan, 2006). Increased wheat and barley yield in the UK (Silvey, 1986, 1994), and maize yield in the USA (Duvick and Cassman, 1999; Tollenaur and Wu, 1999), e.g., is attributed equally to advances in breeding and to improved crop and soil management. Gains in productivity between 1965 and 1995 were about 2% per annum for maize, wheat and rice (Pingali and Heisey, 1999; Evenson and Gollin, 2003a), though rates have declined in the last decade. Similarly, productivity measured as total factor productivity (TFP) also increased in rice, wheat and maize (Pingali and Heisey, 1999; Evenson, 2003a). The impact of crop improvement on non-cereals has been less well documented as these crops are often far more diverse, occupy smaller areas globally and are not traded as commodities. For example, in total legumes occupy 70.1 m ha globally, but there a greater diversity of legume species is used with clear regional preferences and adaptation (e.g., cowpeas, Vigna unguiculata, in West Africa; pigeon pea, Cajanus cajan, and mung bean, Vigna radiata, in India). Nonetheless, plant breeding has increased yields in many protein crops (Evenson and Gollin, 2003b).

Much of the increase in crop yield and productivity can be attributed to breeding and dissemination of Modern Varieties (MV) allied to improved crop management.

A number of studies (Pingali and Heisey, 1999; Heisey et al., 2002; Evenson and Gollin, 2003ab; Hossain et al., 2003; Raitzer, 2003; Lantican et al., 2005) have quantified the large impact (particularly in industrialized countries and Asia) of crop genetic improvement on productivity (Figure 3-2). Much of this impact can be attributed to IARC genetic research programs, both direct (i.e., finished varieties) and indirect (i.e., parents of NARS varieties, germplasm conservation). Benefit-cost ratios for genetic research are substantial: between 2 (significantly demonstrated and empirically attributed) and 17 (plausible, extrapolated to 2011) (Raitzer, 2003). Two innovations-rice and wheat MVs rice (47% and 31% of benefits, respectively) account for most of the impact. Benefits can also be demonstrated for many other crops. For example, an analysis of the CIAT bean (Phaseolus vulgaris) breeding program (Johnson et al., 2003) showed that 49% of the area under beans could be attributed to the CIAT breeding program, raising yield by 210 kg ha-1 on average and resulting in added production value of US$177 m. For Africa, where the breeding program started later, about 15% of the area is under cvs that can be attributed to CIAT, with an added value of US$26 million. The estimated internal rate of return was between 18 and 33%, with more rapid positive returns in Africa, which built upon earlier work in LAC.