A Review of the Evidence - Search CIMMYT repository

In the same trial, no statistically significant difference was detected between theperformance of the advanced-generation hybrids and the three OPVs. Based on this finding,Pérez Rodas (1997) concludes that in cases in which F1 hybrid seed is unavailable orunaffordable, recycling of hybrids would be rational.Zambezi et al. (1997) and Kumwenda et al. (1996, 1997) describe a series of on-farm trialscarried out in Malawi with the objective of evaluating the effects of seed recycling on twosingle-cross hybrids (MH12 and MH16), one three-way-cross hybrid (NSCM41), and twotop-cross hybrids (MH17 and MH18). One landrace (LFM) and one improved OPV(Chitedze Composite C, or CCC) were also included for comparative purposes. Between theF1 and F2 generations, recycled hybrids suffered marked declines in yield (Table 19).Averaged across three levels of fertilization, inbreeding depression was greater in thesingle-cross hybrids (24-33%) than in the three-way crosses (22%) or in the top crosses (16-21%). A much greater degree of inbreeding depression was observed in the unfertilizedtreatments. An additional generation of recycling (from F2 to F3) produced less inbreedingdepression in both the single-cross and the top-cross hybrids; in several cases, F3 plantsoutyielded F2 plants, especially in unfertilized treatments.In this trial, many of the advanced-generation hybrids maintained their yield advantageover the improved OPV and the landrace. In general the top-cross hybrids toleratedrecycling better than the other types of hybrids, although one of the recycled single crossesalso yielded well, particularly in the F3 generation (Figure 5). After one year of recycling,the recycled top crosses significantly outperformed the landrace, and after two years ofrecycling, they outperformed both the OPV and the landrace. In addition to showing thatYield (kg/ha)9,0008,0007,0006,0005,0004,0003,0002,0001,000Third-generation seed (F3), y,y,y,y, y,y,y,yy,y,y,y,y,,yy,,y,y,y,yy,y,y,, , y,y,,yy,,y,y,y,yy,y,y,, , y,y,,yy,,y,y,y,yy,y,y,,y,y,,yy,,,,,,,,,,y,y,y,yy,y,y,, , y,y,,yy,,y,y,y,yy,y,y,, , y,y,,yy,,y,y,y,yy,y,y,, , y,y,,yy,,y,y,y,yy,y,y,, , y,y,,yy,,,,,,,,,,,,,,,,,,0,,,y,,HE-9103 HE-9101 HE-9122 HB-85 HB-9126 HE-9124 HA-46 HA-28 ICTA LM-7442 LM-7442 LM-7843DC DC DC (DC) DC DC TWC (TWC) B1(OPV) (OPV) (OPV) (OPV)Figure 4. Effects of seed recycling on yields of selected maize cultivars, Guatemala.Source: Pérez Rodas (1997).Note: DC = double-cross hybrid, TWC = three-way-cross hybrid, and OPV = open-pollinated variety43Commercial seed (F1)Second-generation seed (F2)