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Estimating genetic gains is vital to optimize breeding programs for increased efficiency. Genetic gains should translate into productivity gains if returns to investments in breeding and impact are to be realized. The objective of this study was to estimate genetic gain for grain yield and key agronomic traits in precommercial and commercial maize varieties from public and private breeding programs tested in (i) national performance trials (NPT), (ii) era trial and, (iii) compare the trends with the national average. The study used (i) historical NPT data on 419 improved maize varieties evaluated in 23 trials at 6-8 locations each between 2008 and 2020, and (ii) data from an era trial of 54 maize hybrids released between 1999 and 2020. The NPT data was first analyzed using a mixed model and resulting estimate for each entry was regressed onto its first year of testing. Analysis was done over all entries, only entries from National Agricultural Research Organization (NARO), International Maize and Wheat Improvement Center (CIMMYT), or private seed companies. Estimated genetic gain was 2.25% or 81 kg ha-1 year-1 from the NPT analysis. A comparison of genetic trends by source indicated that CIMMYT entries had a gain of 1.98% year-1 or 106 kg ha-1 year-1. In contrast, NARO and private sector maize entries recorded genetic gains of 1.30% year-1 (59 kg ha-1 year-1) and 1.71% year-1 (79 kg ha-1 year-1), respectively. Varieties from NARO and private sector showed comparable mean yields of 4.56 t ha-1 and 4.62 t ha-1, respectively, while hybrids from CIMMYT had a mean of 5.37 t ha-1. Era analysis indicated significant genetic gain of 1.69% year-1 or 55 kg ha-1 year-1, while a significant national productivity gain of 1.48% year-1 (37 kg ha-1 year-1) was obtained. The study, thus, demonstrated the importance of public-private partnerships in development and delivery of new genetics to farmers in Uganda. [ABSTRACT FROM AUTHOR]

Establishing detailed information on genetic diversity and relationships among maize (Zea mays L.) inbred lines in a breeding programme help ensure effective utilization of germplasm. Introgression of temperate maize germplasm into 12 tropical elite maize inbred lines using a common donor inbred line and different selection environments might disrupt the heterotic grouping system. Therefore, the objective of the study was to determine the effect of introgression on the clustering pattern of the newly introgressed inbred lines and to identify unique genotypes for breeding. A total of 76 introgressed inbred lines derived through pedigree crosses of introgression of 12 elite tropical inbred lines from three major heterotic groups N3, SC and P with a common donor temperate maize inbred line (08CED6_7_B) were used in the study. In addition to the derived 76 introgressed inbred lines, 26 temperate parental inbred lines and 21 elite tropical parental inbred lines with known heterotic group classification were also included in the study as references samples for heterotic groupings to give a total of 123 inbred lines for the study. Introgressed inbred lines derived from four generations of pedigree selection in three distinct environments in Zimbabwe and South Africa were characterised using 20 SSR markers. The 20 SSR markers proved very effective in discriminating the introgressed inbred lines according to genetic distance and clustering. A total of 83 alleles were detected with an average of 4.15 alleles per locus, and had an allelic diversity of 0.53 and PIC of 0.47. Introgression of temperate maize germplasm into tropical elite inbred lines did not disrupt heterotic groupings, because introgressed inbred lines remained genetically inclined towards the original heterotic groups from which they were derived. However, there were some introgressed inbred lines (14%), which did not show any inclination to any of the heterotic groups. Marked genetic difference noted within and across heterotic groupings for the introgressed inbred lines provides germplasm variation that can be exploited for inbred line development and hybrid formation, respectively. [ABSTRACT FROM AUTHOR]