Q&A: Methods for estimating genetic gain in sub-Saharan Africa and achieving improved gains.

Regular measurement of realized genetic gain allows plant breeders to assess and review the effectiveness of their strategies, allocate resources efficiently, and make informed decisions throughout the breeding process. Realized genetic gain estimation requires separating genetic trends from nongenetic trends using the linear mixed model (LMM) on historical multi-environment trial data. The LMM, accounting for the year effect, experimental designs, and heterogeneous residual variances, estimates best linear unbiased estimators of genotypes and regresses them on their years of origin. An illustrative example of estimating realized genetic gain was provided by analyzing historical data on fresh cassava (Manihot esculenta Crantz) yield in West Africa (https://github.com/Biometrics-IITA/Estimating-Realized-Genetic-Gain). This approach can serve as a model applicable to other crops and regions. Modernization of breeding programs is necessary to maximize the rate of genetic gain. This can be achieved by adopting genomics to enable faster breeding, accurate selection, and improved traits through genomic selection and gene editing. Tracking operational costs, establishing robust, digitalized data management and analytics systems, and developing effective varietal selection processes based on customer insights are also crucial for success. Capacity building and collaboration of breeding programs and institutions also play a significant role in accelerating genetic gains.

Evaluation of Soybean Entries in the Pan-African Trials for Response to Coniothyrium glycines, the Cause of Red Leaf Blotch.

Red leaf blotch (RLB), caused by the fungus Coniothyrium glycines, is an important disease of soybean known to cause yield losses across soybean-growing regions in Africa. Fungicides are one option to manage this disease, but utilization of host resistance may be a better option suited for smallholder soybean farmers in Africa. Fifty-nine soybean entries were evaluated for RLB severity in nine field locations in Ethiopia, Kenya, Uganda, and Zambia. Disease incidence was 100% and disease severity differed (P < 0.01) among entries at eight of the nine locations. Mean severity ratings ranged from 1.4 to 3.2 based on a 0-to-5 scale, with higher disease severities recorded in Ethiopia followed by Zambia. Eight of the 59 entries were common to all nine locations and had severity ratings ranging from 1.6 to 2.9. The cultivar SC Signal had the lowest RLB severity ratings in the combined analysis over locations. Based on correlations of weather variables to RLB severity, mean rainfall from planting to 30 days before assessment date had a positive correlation (r = 0.70; P = 0.035), as did mean morning maximum wind speed (r = 0.88; P = 0.016). Other variables, such as temperature and relative humidity, did not correlate to RLB severity. This is the most comprehensive report to date on the occurrence of RLB in the region, which for the first time demonstrates an association between rainfall and wind speed with RLB severity. It also represents the first extensive report evaluating soybean genotypes for resistance against RLB in multiple environments.

Evaluation of Foliar Diseases for Soybean Entries in the Pan-African Trials in Malawi and Zambia.

Soybean production has expanded worldwide including countries in sub-Saharan Africa. Several national and international agencies and research groups have partnered to improve overall performance of soybean breeding stocks and have introduced new germplasm from Brazil and the United States with the goal of developing new high-yielding cultivars. Part of this effort has been to test improved soybean lines/cultivars accumulated from private and public sources in multilocational trials in sub-Saharan Africa. These trials are known as the Pan-African Soybean Variety Trials, and the entries come from both private and public breeding programs. The objective of this research was to evaluate entries in the trials that include commercial cultivars or advanced experimental lines for the incidence and severity of foliar diseases. All trials were planted in December 2018 with six located in Zambia and one in Malawi. Plants were evaluated during the reproductive growth stages using a visual pretransformed severity rating scale. Foliar disease ratings were recorded for three bacterial diseases, six fungal diseases, one oomycete, and viruses. The overall occurrence of most of the diseases was high except for soybean rust and target spot, which were only found at two and one location, respectively. However, disease severity was generally low, although there were differences in disease severity ratings among the entries at some of the locations for brown spot, downy mildew, frogeye leaf spot, red leaf blotch, and soybean rust.