The Economic Impact in Developing Countries of ... - AgEcon Search

wheat yield, by dividing the sum of the zone-levelareas by the sum of the zone-level production foreach country from the CIMMYT data. A springbread wheat yield series was generated for eachzone and country, by multiplying the ratio of 1990zone-level yields to the national average with theFAO national average yield in each year from 1973to 1998. Zone yields were then multiplied by zoneareas for estimates of production by zone, whichwere aggregated over all the zones by countryincluded in each ME. This production estimate wasdivided by the corresponding area estimate tocalculate a zone-adjusted, area-by-country weightedaverage spring bread wheat yield by ME, from 1973to 1998 (Figure 2). 6Average yield levels thus estimated were thehighest in MEs 1, 2, and 5, and they have increasedin all MEs since 1973. Annual yield fluctuationswere evident in MEs 3 and 4b. Trend regressionswere fitted to the data to project yields to 2007.Embedded in these calculations is the assumptionthat, though overall average yields have changedover time, the ratio of spring bread wheat yield byproduction zone to national average has remainedconstant within countries.Yield (t/ha)4.0ME1 ME2 ME3 ME4a ME4b ME4c ME53.02.01.00.01973 78 83 88 93 98YearFigure 2. Average annual spring bread wheat yield byCIMMYT mega-environment from 1973 to 1998.With the parameter λy twe thus measure the lossesavoided through leaf rust resistance as a proportionof the observed yield of CIMMYT-related springbread wheat. However, these yields (y t) and thegrowth in annual wheat yields observed in Figure 2have resulted from both maintenance andenhancement research over the years. Thiscomplicates the estimation of the supply withmaintenance research but net of enhancementresearch (S 0) in Figure 1, and it demonstrates thedifficulties in separating the two components. Nodata or other systematic methods were available toseparate these inherent effects over all productionareas and years included in this study. Since S 0is infact never observed, it is difficult to estimate. We thuschose to apply the available data to estimate λy t, eventhough the production savings from maintenanceresearch may be overestimated. This would causeless distortion in the results than arbitrarilyattempting to disentangle the maintenance andenhancement effects in the yield series. The percentyield loss avoided (λ) through leaf rust resistance isfurthermore likely to remain the critical parameter inthe conceptual framework depicted in Figure 1.However, we included a sensitivity analysis to assessthe magnitude by which the production savings wereoverestimated in the base scenario. For this purpose,the enhancement and other effects were eliminatedfrom the yield series in ME 1 by drawing onCIMMYT trial data for northwestern Mexico (Sayreet al. 1998). This favorable wheat production area hasheavy disease pressure and represents a testingground for the major environment in whichCIMMYT-related spring bread wheat is grown (ME1). Considering that these trial results were availableonly over a relatively limited area and time period,however, we chose to apply them in a sensitivity testrather than in our base scenario.The data by Sayre et al. (1998) were generated fromreplicated trials including 15 popular CIMMYTrelatedbread wheat cultivars released between 1966and 1988 in the Yaqui Valley of northwestern Mexico.This set of cultivars provided an almost 30-yearhistorical perspective of germplasm improvement atCIMMYT. The genetic progress in reducing grainyield losses through leaf rust resistance breeding wassubsequently estimated over this time period. The6The 1997 yield by ME estimates obtained with this approach were compared to the 1997 point estimates of spring breadwheat yields independently estimated by Heisey et al. (2002). The latter are reported to be consistent with FAO estimatedyields. We calculated the 1997 area-weighted average yield over the study area at 2.85 t/ha, which was comparable to thearea-weighted average of 2.46 t/ha estimated by Heisey et al. (2002). Though slightly higher in most MEs, our yieldestimates were within a similar range, and the minor difference will not affect the overall results.18