Breeding progress for grain yield and associated traits in medium and late maturing promiscuous soybeans in Nigeria

The rate of breeding progress of 10 medium and 11 late maturing promiscuous soybean varieties developed by IITA for the savanna zones of Nigeria from 1980 to 1996 was assessed at two locations in 2001 and 2002. The two maturity groups were evaluated in separate experiments using randomized complete block design with four replications. There were highly significant effects of variety on grain yield, fodder yield, and another set of eight traits both in the medium and late maturity groups. In the medium varieties, grain yield increased linearly from 1184 kg ha⁻¹ for an old variety TGx 1019-2EN to 1764 kg ha⁻¹ for TGx 1910-7F released in 1996. The annual rate of progress against year of release was 23.61 kg ha⁻¹ (1.99%). Modern varieties of the medium maturity group had high number of pods per plant, high harvest index, and reduced pod shattering. For late varieties, grain yield ranged from 1569 kg ha⁻¹ for an old variety Samsoy-2 to 2303 kg ha⁻¹ for a recently developed variety TGx 1910-14F. The annual rate of breeding progress during the improvement period of 16 years for late varieties was 22.23 kg ha⁻¹ or 1.42%. The overall yield of the late maturing varieties was 19% higher than the medium maturing varieties.