A Review of the Evidence - Search CIMMYT repository

As a general rule, we propose that the OPV recycling factor (c) be assigned a value of 4.This implies that on average OPV seed will be recycled three times and that on average thearea planted to recycled seed in the second, third, and fourth year will be equal to the areaplanted to commercial seed in the first year (i.e., no “multiplying up” effect). In some cases,these assumptions will result in an underestimation of the total area planted to improvedOPVs, i.e., whenever the area planted to recycled seed in the second, third, and/or fourthyears exceeds the area planted in the first year to commercial seed. However, in many casesthis “multiplying up” effect will be offset at least in part by the fact that advancedgenerationOPV seed does not perform as well as commercial seed.Estimating productivity gains attributable to adoption of MVsEstimating productivity gains associated with MV adoption is complicated by at least fourfactors:(1) Productivity gains may be expressed in many different ways. Although productivity isoften expressed in terms of grain yield per unit land area, this is not always an appropriatemeasure. In some instances, the benefits of improved germplasm are reflected in earliermaturity, enhanced grain quality, improved quantity or quality of fodder, or bettertolerance of biotic or abiotic stresses (which may allow the crop to be grown in places or attimes where it could not be grown before, even if the grain yield remains unchanged).(2) Productivity gains will vary depending on the type of MV adoption that is taking place.For example, yield gains will differ greatly (both in absolute and relative terms) dependingon whether farmers are replacing a landrace with an improved OPV, a landrace with ahybrid, an older improved OPV with a newer improved OPV, an improved OPV with ahybrid, an older hybrid with a newer hybrid, and so forth.(3) Productivity gains will vary depending on environmental factors, includingagroclimatic conditions and farmers’ management practices. The same MV may deliversignificant productivity gains in favorable production conditions and modest productivitygains in unfavorable production conditions.(4) Productivity gains can change through time as a result of seed recycling. As we haveseen, when farmers recycle their seed, grain yield and other productivity measures canchange dramatically from one generation of plants to the next as a result of deliberateselection pressure or inadvertent genetic change.Because of these four factors, the size of the productivity gains associated with the adoptionof maize MVs can vary tremendously. In subsistence-oriented cropping systems wherefarmers are adopting MVs and improved crop management practices for the first time, it isnot unheard of to witness yield increases of 100% or more. In modern commercialproduction systems in which farmers regularly replace high-yielding single-cross hybrids, ayield increase of only 2-3% might be considered satisfactory.60