Genetic gain in yield and agronomic characteristics of cowpea cultivars developed in the Sudan Savannas of Nigeria over the past three decades

Summary

A field study was conducted to determine the rate of genetic improvement in grain and fodder yields and associated agronomic and physiological changes of determinate and semi-determinate cowpea (Vigna unguiculata [L.] Walp.) genotypes developed in the Nigerian Sudan savannas between 1974 and 2004. Results showed that the grain yield of determinate cowpea ranged from 796 kg ha⁻¹ for cultivars released in the 1970s to 1,485 kg ha⁻¹ for cultivars released in the 2000s, with a corresponding genetic gain of 2.93% per year. The mean grain yield of semi-determinate cowpea ranged from 638 to 1,547 kg ha⁻¹ with a relative annual gain of 4.4%, suggesting that more progress was made in breeding semi-determinate cowpea cultivars for high grain yield. The fodder yield of determinate cowpea ranged from 1,493 kg ha⁻¹ for cultivars released in the 1970s to 2,332 kg ha⁻¹ for those released in 2000s, an average 1.74% genetic gain per year. For semi-determinate cowpea, fodder yield increased from 1,698 kg ha⁻¹ for older cultivars to 2,612 kg ha⁻¹ for modern cultivars, with a relative annual gain of 2.15%. The general gain in fodder yield for both cowpea types indicated that selection for dual‐purpose cowpea cultivars with increased fodder as well as grain yields has been successful. This study also revealed that genetic gains were made in the improvement of yield-related traits such as pods per plant, 100‐seed weight, total dry matter, and harvest index (HI) for both plant types. Remarkable progress has been made in increasing the total dry matter over the three-decade period. This trait was associated with grain yield (r = 0.60 for determinate cowpea and r = 0.53 for semi-determinate cowpea). Other traits correlated with grain yield were fodder yield, the number of pods per plant, HI for determinate cowpea and fodder yield, HI, and 100‐seed weight for semi-determinate cowpea. The strong relationship between grain and fodder yields confirmed how successful selecting for dual‐purpose cowpea cultivars had been.