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Combining Ability Analysis for Northern Leaf Blight Disease Resistance on Tanzania Adapted Inbred Maize Lines

Tulole Lugendo Bucheyeki, Pangirayi Tongoona, John Derera and Suzan Nchimbi- Msolla

Northern leaf blight (NLB) disease incited by Exserohilum turcicum has increased in incidence and severity. Inbred lines combining ability and its interactions to the environment are required for the development of NLB disease resistance. The specific objectives were to estimate the combining ability for NLB disease resistance, determine maternal effects, and determine the heterosis in the F1 hybrids by using a full 11 × 11 diallel cross. The resulting 110 F1 hybrids with the 11 parents were evaluated together with 9 commercial varieties at three Agricultural Research Institutes: Tumbi, Uyole and Selian which represent diverse environments. Breeding materials were planted in 13 × 10 alpha lattice design with two replications per site. Top ten experimental hybrids in each site had negative mid parent heterosis for NLB disease severity. Heterosis for NLB disease severity ranged 94-362%. The overall mid parent heterosis means for yield across sites was 152%. Maternal effects had non-significant (P>0.005) influence on the inheritance of the NLB disease severity. Mean sum of squares for GCA was highly significant (P<0.001) on disease severity indicating additive gene action. Mean sum of squares for SCA were highly significant on disease severity and yield implying non-additive gene action. The mean squares for reciprocals effects were highly significant for yield and non-maternal effects sums of squares had significant effect (P<0.05) on yield. The GCA effects contribution was high for disease severity (91%) and lesion number (85%). With the exception of CML 395 and KS03-0B15-12 parents which were susceptible, all GCA effects were negative implying the contribution to disease resistance in their progenies. Due to preponderance of the additive gene action, recurrent selection could be used to improve the resistance of inbreeds while the non-additive gene action could be exploited in breeding for disease resistant high yielding hybrids.