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Genetic progress in grain yield: Genetic progress in grain yield of 10 Mexican and 5 Indian varieties was calculated from mean of two years data. Combined effect, including both released in India and Mexico, showed that progress in gram yield was 48 kg/ha/year or 0.54 % per year, and that absolute yield ranged from 8056 kg/ha by Pavon 76 (released in 1976) to 9968 kg/ha by Super Seri (named in 1999). Indian varieties released during 1982 and 1995 enhanced grain yield @ 22.7 kg/ha/year or 0.25 %, and Mexican cultivars released during 1976 and 1999 increased grain yield @ 57 kg/ha/year in absolute term or 0.63 % per year in relative term (Fig. 1 and Fig. 2). Yield potential progress (1982 to 1995) by Indian varieties was slower, probably due to inclusion of Indian varieties released during 13 years period only, as compared to CIMMYT, Mexico genotypes released during last 25 years. Our finding was in corroboration with observation of Bell et al. (1995) who have mentioned that genetic gain was 0.7 % per year during 1968 to 1993 (study of 50 experiments). At CIMMYT, Ortiz Monasterio et al. (1997) also calculated genetic gain @ 89 kg/ha/year or 1.9 % per year at 300 kg N/ha application by using varieties released between 1950 and 1985. This was higher due to inclusion of tall varieties like Yaqui 50 and Nainary 60 and crop was not prevented from lodging. Lodging susceptibility of tall varieties at such higher N rates (300 kg/ha) was another factor for higher genetic gain. In another study at the same place, genetic gain in grain yield was 67 kg/ha/year in absolute term and 0.88 % per year in relative term, where eight semi-dwarf varieties included, the earliest from Pitic 62, released in 1962 to Bacanora 88 released in 1988 (Sayre et al. 1997). In this case also genetic gain was a little higher than our findings, because the oldest variety was Pitic 62, which was released just after advent of Norin 10 dwarfing genes.

Therefore, it can be considered that yield potential progress in spring wheat genotypes under irrigated, high N use, disease free and lodging control condition was raised substantially during the last quarter of 20th century. So, it will be futile to preclude that genetic progress was stagnated but certainly slowed down as compared to green revolution era. Furthermore, this gain in grain yield will be undoubtedly higher under farmer's field condition due to development of higher disease resistant and lodging tolerant varieties.

Acknowledgments

Senior author is greatly thankful to Dr. S. Rajaram, Director, Wheat Program (CIMMYT), Mexico and Dr. S. Nagarajan, former Project Director (Wheat), Karnal, India for providing financial and technical support to do research work at CIMMYT, Mexico.

References

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