GENE ACTION AND COMBINING ABILITY ESTIMATES FOR SOME WHITE PROMISING MAIZE INBRED LINES BY TOP CROSS SYSTEM

Abstract

Eleven white maize (Zea mays, L.) inbred lines isolated from different populations were topcrossed with each of three line testers, i.e Gm 4, Gm 21 and, Gm 22. All inbred lines and testers were developed at Gemmeiza Research Station from different genetic sources. The 33 topcrosses along with three checks, i.e. SC 10, SC 129 and SC 122 were evaluated at Sakha and Gemmeiza Research Stations during 2007 growing season. General (GCA) and specific (SCA) combining ability as well as other genetic parameters estimates were calculated for days to 50 % silking, plant height, ear height, number of ears/100 plants, ear length, ear diameter, number of rows/ear, kernels number per row and grain yield (ard/fad). Results indicated that ,there were highly significant differences among the evaluated 33 topcrosses for all studied traits across the two locations. Differences among inbred lines were highly significant for all traits. However, significant differences were detected among testers for silking date, ear height, ear length, ear diameter, rows/ear and grain yield. The interaction of both tested and tester inbred lines with locations was significant in case of silking date, ears/100 plants and grain yield. Significant interaction of lines x testers was detected for all traits except ear height and kernels number per row. Also, the locations interaction with lines and testers was highly significant for silking date, ears/100 plants and grain yield. The tested inbred lines and testers exhibited significant GCA effects vary greatly according to the studied traits. The variance magnitude due to GCA for tested and tester lines was higher than that due to SCA for all studied traits, except silking date, number of rows/ear. This indicates that additive genetic variance was the major source of variation responsible for the inheritance of these traits. Tester inbred line Gm 4 was the best general combiner for grain yield ability. Three single crosses i.e Gm- 304 x Gm- 4, Gm- 307 x Gm- 4 and Gm- 310 x Gm- 4 were significantly earlier and shorter than the commercial single crosses 10, 122 and 129. At the same time the grain yield ability for these three promising single crosses was equal to the best check sc 10 with no significant difference, better than the check Sc 122 and significantly higher than the commercial Sc 129. Therefore, these crosses should be released as new white earlier, shorter with high yield Potentiality relative to the three commercial check single crosses.