Determining the Heterotic Group of the Nineteen Open Pollinated Maize Varieties from Their Topcrosses with Inbreed Line Testers in Uganda

Knowledge gap on heterotic patterns for yield limits maize breeding program from exploiting genetic potential of open pollinated maize varieties (OPVs) in Uganda. So this study was conducted to determine the heterotic group of the 19 OPVs using the specific combining ability effects of their topcrosses. The toptcrosses were evaluated in 4 Agro-ecologies of Uganda using 5x13 α-lattice design replicated twice per location to test the study hypotheses which was stated as all the 19 OPVs fall under divers heterotic groups. The results of this experiment indicated the presence of low variability for grain yield and thus the possibility of selection among the topcross hybrids that are adapted to the different agro ecologies of Uganda is low. An OPV parent was assigned to group A when its cross with inbred line tester A showed a large negative specific combining ability (SCA) value otherwise it was assigned to opposite heterotic group B. Other parents with lower magnitude of SCA were assigned as heterotic group AB. Based on this criterion, 3 parent OPVs (Longe 4, Longe 5RS and SUWAN) were assigned to the heterotic group A, 2 (SITUKA MI and Ambsyn 5) heterotic group B, and other remaining 14 OPVs were grouped under heterotic group AB. The expressed heterosis between female OPV Ambsyn 5 and SITUKA MI when testcrosses with in bred line tester A (CML536) and Longe 4, Longe 5RS and SUWAN with another tester B (CML202) could be exploited to produce topcrosses and OPV KC2014 as general combiner for yield.