| dc.description.abstract | Striga (Striga hermonthica) and low nitrogen are major yield reducing factors in maize production in Uganda. Four Striga resistant inbred lines, four low nitrogen stress tolerant inbred lines and two inbred line testers of heterotic group A and B were crossed in a 10 x 10 half-diallel mating design. Out of the 45 hybrids, 42 hybrids were successful in generating adequate F1 hybrid seed. Consequently, the 42-single cross- experimental hybrids were evaluated in a 6 x 7 alpha-lattice design, during the first season of 2018 (2018A). The trials were planted on-farm under natural Striga infestations in Kasese and Bukedea districts; 3-metre plots were used with three replications. In each location, two levels of nitrogen (i.) no nitrogen added, and (ii.) 70 kg N/ha added. Data on Striga emergence, Striga damage syndrome and grain yield were recorded. The General combining ability (GCA) of the parents and Specific combining ability (SCA) of hybrids for resistance to Striga, and grain yield were estimated. Additive and non-additive gene actions conditioned the inheritance of resistance to Striga under low (no nitrogen added) and optimum (70kg N/ha) nitrogen. However, non-additive gene action was predominantly controlled Striga emergence and additive gene action mainly controlled Striga damage syndrome. Parental line TZISTR1146 consistently combined well for resistance to Striga hermonthica (basing on Striga emergence and Striga damage rating) under low and optimum nitrogen environments. Hybrids TZISTR1146/CML443, and CML395/CML312 exhibited resistance to Striga hermonthica under both low and optimum nitrogen environments.
The successful 42 FI hybrids generated from ten inbred lines plus three checks (1=nitrogen use efficient, 2=local varieties) were evaluated at National Crop Resource Research Institute (NaCRRI) in Namulonge. Two levels of nitrogen (i.) no nitrogen added, and (ii.) 70 kg N/ha added (control check) were used. The 45 hybrids were evaluated in a 9 x 5 alpha-lattice design, during 2018 season A. Data on grain yield, Anthesis-silking interval, stay green characteristics, number of ears per plant, plant and ear height, ear and plant aspect were collected and analyzed. Basing on the selection index, 23 hybrids exhibited tolerance to low soil nitrogen but were not high yielding compared to the best check.For stability assessments, the performance of the 42 experimental hybrids was compared to that of seven checks (2 commercial and 5 local) in the same experimental sites as in study two and a 7 x 7 alpha lattice design was used under each nitrogen level. The trial was conducted in 2018 A, with three replications. Genotype main effect and genotype by environment interaction (GGE) Biplot and Additive Main Effects and Multiplicative Interaction (AMMI) models were used in this study to measure the magnitude of G x E interactions for resistance to Striga, and grain yield amongst the genotypes. Hybrids CML395/CML443 (G36), TZISTR1146/CML395 (G18), TZISTR1146/CML443 (G22) and CML550/CML536 (G30) were high yielding and stable across all the six environments under study. Also, hybrids CML550/CML536 (G30) and TZISTR1146/CML443 (G22) performed well in grain yield and were stable across Striga infested environments. Similarly, hybrids TZISTR1003/TZISTR1146 (G2), TZISTR1199/CML544 (G14), TZISTR1146/CML395 (G18), TZISTR1004/CML550 (G23), TZISTR1146/TZISTR1004 (G16), TZISTR1146/CML550 (G17), SC403 (G45) and TZISTR1003/TZISTR1199 (G1) were resistant to S. hermonthica and hybrid TZISTR1003/TZISTR1146 (G2) was the stable across the Striga infested environments.
Selection of the parents from these present materials and hybridisation are possible. This study recommends parent TZISTR1146 to be used in breeding new high yielding Striga resistant maize varieties. The low nitrogen tolerant hybrids should be further evaluated for their performance in grain yield. The significant hybrid by environment interaction for grain yield and resistance to S. Hermonthica across environments suggested that breeding for specific locations is preferred to breeding for broad adaptation in Uganda | en_US |
