Evaluation of Promiscuous Soybean Genotypes at Chitedze, Malawi.

A total of 60 genotypes that comprised 56 IITA bred promiscuous materials under West Africa conditions and four varieties from Malawi were evaluated for their agronomic performance at Chitedze Research Station using a randomized complete block design with two replications in 2008 and three replications in 2009. Only phosphorous at a rate of 30 kg ha^-1 was applied in both years and no Rhizobium inoculation was made. Combined analysis of variance showed that genotypes differed significantly for grain and fodder yields, days to flowering and maturity, 100-seed weight, harvest index and rust score. Mean grain yield ranged from 388 kg ha^-1 (TGx 923-2E) to 1704 kg ha^-1 (TGx 1903-3F). The top three high yielding genotypes were TGx 1903-3F, TGx 1740-2F, and TGx 1835-10E followed by Nasoko and Makwacha. Fodder yield ranged from 1.8 t ha^-1 (TGx 1908-1F) to 4.5 t ha^-1 (TGx 1955-4F) and the overall mean was 3.3 t ha^-1. The IITA promiscuous genotypes gave substantially higher fodder yields in Malawi. In contrast, four varieties from Malawi gave a mean fodder yield of 2 – 2.3 t ha^-1, lower than the population mean. Flowering and maturity dates showed a range of 47-78 and 108-142 days, respectively. With the exception of Magoye (a widely grown local variety in southern Africa), Malawi released varieties (Nasoko and Makwacha) flowered relatively early (less than 50 days) and matured early (less than 115 days). From the best IITA genotypes TGx 1740-2F and TGx 1835-10E exhibited a similar pattern of phenological development with that of the Malawi varieties. Genotypes also showed highly significant differences for 100 seed weight that ranged from 12 – 21 g.  Malawi released varieties showed a significantly bigger seeds (19 – 21 g per 100 seeds) as compared to all IITA genotypes. Most of the IITA genotypes (more than 40) showed 100 seed weight of 15 g or below and as the result the population mean was 14 g. This is not unexpected because IITA genotypes were selected for smaller seed size during breeding mainly to improve seed viability under high temperature conditions in West Africa. Difference for harvest index was also highly significant among the genotypes and this trait ranged from 0.11 for TGx 1927-5F to 0.43 for TGx 1903-3F with the experimental mean of 0.23. Soybean rust was noted in all the genotypes, but some genotypes showed resistance to this disease by showing reddish brown (RB) reaction. Genotypes showed a highly significant difference for rust score and it ranged from 3% – 24% with an experimental mean of 16%. High rate of rust incidence was noted on Makwacha (24%), Nasoko (21%) and TGx 1830-20E (22%). The rust susceptible variety in Nigeria, TGx 1485-1D, showed a fairly high rust infection of 19%. The rust resistant variety TGx 1835-10E under Nigeria condition also showed a low rust incidence (12%) under Malawi condition. Though not agronomically superior, genotypes such as TGx 1961-1F and TGx 1894-3F have showed resistance to the disease, which may be considered in the breeding program.