Identification of heterotic pattern in tropical inbred maize lines using broad-based synthetic testers

For a hybrid program it is crucial to obtain information about combining ab ility and heterotic patterns among its germplasm. A line x tester analysis including 23 partially inbred lines (S-2 to S-4) derived from seven late wh ite CIMMYT populations and pools test crossed to four synthetics were done to (i) examine the combining ability of the 23 lines and (ii) identify supe rior top-cross hybrids. The 92 crosses were evaluated during 1988, 1989, an d 1992 for grain yield, plant height, and days to 50% silking in six enviro nments; Venezuela (VE), Colombia (CO), and Mexico (PR1, PR2, PR3, and TL). Mean grain yield across environments was 5.66 Mg ha(-1), ranging from 3.67 Mg ha(-1) in PR1 to 7.75 Mg ha(-1) in CO. The ANOVA for grain yield showed significant GCA effects for lines in all environments except: in PR3 and TL , and significant GCA effects for testers in all environments except in PR1 . SCA effects for grain yield were significant in all environments except i n VE. The analysis for grain yield combined over the six environments showe d significant GCA effects for both lines and testers, and significant SCA e ffects. Significant GCA x environment interactions (GCA x E) were found for both line and tester and SCA (line x environment x tester) effects. In all six environments and across environments Line 11 (L11) and Line 23 (L23) s howed significant positive GCA effects. Tester 2 (T2) was a high performing tester with significant positive GCA effects across environments and in fo ur of the six environments. Across environments ten crosses were identified with significant positive SCA effects. All of them are inter-population cr osses and the four crosses with highest SCA effects are crosses between fli nt and dent germplasm. The best performing top-cross hybrids were identifie d. In all environments and across environments the best performing top-cros s hybrids were higher yielding than the checks. The highest yielding top-cr oss hybrid across environment was L23 x T1, a flint x dent cross with signi ficant positive SCA effects. The superior top cross hybrids identified thro ugh this study have significant potential to be released as cultivars in th e developing countries where production of conventional hybrids like single and three-way crosses are difficult due to lack of well-developed seed ind ustry.