Godfree Chigeza IITA-Tanzania
Despite positive trends in soybean production, average soybean yields in Africa of approximately 1.1 t/ha are much lower than the global average of nearly 2.5 t/ha. Most of the constraints to the crop’s production are due to the impact of climate change, which tends to be greater in sub-Saharan Africa than in other regions. Impact includes erratic rainfall patterns and annual totals; shifts in the rainy season; an increase in dry spells and hot weather conditions, which lead to crops being exposed to drought conditions; and increased prevalence and sporadic occurrences of pests and diseases. These constraints pose new challenges for breeders to develop and disseminate new soybean varieties with improved yield potential as well as tolerance to multiple stresses to safeguard yield in the event of adverse climatic conditions.
Developing high-yielding, multiple stress tolerant soybean varieties through multidisciplinary partnerships is at the core of IITA’s soybean breeding program. The specific objectives include: (i) developing well coordinated and characterized soybean trait pipelines that include drought tolerance, rust resistance, phosphorus use efficiency, and high biological nitrogen fixation (BNF); (ii)accelerating cultivar development pipelines by putting together the must-win traits; (iii) establishing an effective breeding management and bioinformatics database for soybean; and (v) capacity and capability building through training postgraduate students and mentorship of breeders in the national agricultural research systems (NARS).
During the 2017 season, germplasm acquisition, introgressions, and evaluation of preliminary and advanced soybean trials were done both in Nigeria and southern African countries in a well-defined and structured high-level process that delineates effective delivery of diverse varieties from IITA to the NARS and private seed companies.
Germplasm acquisition and introgression
Evaluating rust resistance lines for yield and introgression of Rpp rust resistance genes into IITA elite lines
Acquisition of new germplasm during 2017 included evaluating some rust resistant lines from the USDA germplasm collection at Ibadan, Nigeria. Results from the evaluation indicated that only one known rust resistant accession PI635999 (Rpp 3&4) was moderately adapted to tropical conditions. The other known rust resistant accessions were not adapted. Crosses between the rust lines and IITA were developed and marker-assisted selection (MAS) will be used to select the resistant progenies from the crosses.
Preliminary and advanced variety trials
During the 2017 season, preliminary variety trials and advanced variety trials were planted in Malawi, Mozambique, Nigeria, and Zambia to determine the performance of varieties under different environmental conditions, which included drought and low soil phosphorus conditions. The trials consisted of 30–40 lines per set including checks. Genotypes exhibited significant differences for several agronomic and disease traits. On average, the best five experimental genotypes showed a significant yield advantage of between 5 and 16% better than the best commercial check (Fig. 2). As per product concept, experimental lines yielding greater than 5% compared to the best check will be advanced to the next stage of evaluation if other agronomic traits such as resistance to shattering, lodging, diseases, and having an acceptable seed size meet the criteria. For example, in Ghana, TGx 1844-22E distributed through Soybean International Trials (SIT) and having excelled in the advanced trials in Nigeria in 2015, is going through variety registration, https://mailchi.mp/illinois/have-a- look-atsils-latestmonthly-digest?e=807cdd1b85, providing farmers with a wide range of choices to use multiple stress tolerant varieties to improve their production.