SELECTION OF NEW HYBRID COMBINATIONS OF YELLOW MAIZE FOR HIGH YIELD AND RESISTANCE AGAINST LATE WILT DISEASE VIA LINE × TESTER ANALYSES UNDER DIFFERENT ENVIRONMENTAL CONDITIONS

Forty two new inbred lines of yellow maize were top-crossed with two testers at Sakha Agricultural Research Station during 2006 summer season. The resultant 84 top-crosses were divided into two sets where each set included 42 top-crosses with two commercial checks. All genotypes were evaluated under two different experimental conditions in 2007 growing season. The first experiment was conducted at both Sakha and Mallawy Stations to be evaluated for grain yield (GY) and number of days to mid-silking (DS) and the second experiment was cultivated under artificial infection by the pathogen Cephalosporium maydisunder two levels of nitrogen fertilizer to assess the resistance to late wilt disease (RLW%). The best seven top-crosses for yielding ability with resistance against late wilt disease were selected from the two sets and evaluated at four locations i.e. Sakha, Gemmiza, Sids and Mallawy Stations for GY, DS and RLW% traits during the 2009 growing season.
The mean squares were significant or highly significant due to lines (L) for DS, GY and RLW%. Moreover, mean squares due to testers (T) and L x T interaction were significant or highly significant for RLW% in the two sets except for T in set-2. It appeared that DS and GY in set-2 could be mainly controlled by additive genes, while, GY of set-1 and RLW% of the two sets were mainly controlled by non-additive genes.
Inbred lines Sk10 in set-1 and Sk23 in set-2 were identified to be the best combiners for earliness, grain yield and resistance to late wilt disease simultaneously. Meanwhile, top-crosses Sk3 x SC162 and Sk14 x SC166 in set-1 showed favorable genes for yielding ability with high RLW%. It was noticed that 12 top-crosses in set-1 and two top-crosses in set-2 were significantly increased for grain yield over the best checks and had high resistance to late wilt disease.
Results of evaluation trail for best top crosses across the four locations indicated that the mean performances of the seven crosses i.e. Sk23 x SC162, Sk10 x SC162, Sk11 x SC166, Sk17 x SC166, Sk19 x SC162, Sk17 x SC162 and Sk18 x SC162 significantly surpassed the commercial check in grain yield by 3.15, 2.75, 2.56, 2.54, 2.52, 2.16 and 1.37 ton/ha, respectively. At the same time, they also exhibited high resistance to late wilt disease. This result emphasized the obtained result from top-cross trails, indicating that these promising yellow three way crosses stabilized yield and resistant to late wilt disease in different environments and would be very essential and valuable in maize improvement programs.