Heterosis and combining ability of high oil corn

Three high oil corn varieties; DA-HO-8-1-C1-F2 (DA-HO), Alexander Synthetic Cycle 23 (AHO), and Illinoils High Oil (IHO) were intercrossed and extracted S1 lines from them. These three varieties were crossed with inbred lines of corn Breeding Project of Kasetsart University (Ki). They were made diallel cross among them that made in total 60 hybrids in 1995-96. Downy mildew testing was conducted in parent groups; DA-HO, AHO, IHO and Ki. Their downy mildew infections were 2.8-20.8, 13.5-33.4, 12.8-39.5 and 0-4.4 percent. The susceptible downy mildew check variety (Tuxpeno) was 49.6 percent. The diallel cross of high oil corn DA-HO, AHO and IHO had downy mildew infection 14.7-37.4 percent. The DA-HO, AHO and IHO were crossed with Ki had infection 2.0-22.9, 8.6-27.6 and 9.0-29.2 percent. The DA-HO-S1, AHO-S1 and IHO-S1 were crossed with Ki that possessed downy mildew infection 2.9-23.8, 0.9-46.3 and 7.6-39.8 percent, Tuxpeno had 23.8 percent infection. The mean grain yield of parents DA-Ho, AHO, IHO and Ki group were 4,594, 3,725, 3,406 and 2,988 kg/ha and the mean grain yield of experiment was 3,575 kg/ha. The range oil content of parent was 5.0-6.9 percent and its mean was 6.2 percent, Ki 32 gave the highest oil content 6.9 percent. Ki 27xIHO produced the highest yield 9,138 kg/ha, with 9 percent higher than check variety Suwan 3701 (8,394 kg/ha). The mean grain yield of experiment was 7,350 kg/ha Ki 21 x DA-HO and Ki 21 x AHO-S1-3 produced the highest 8.1 percent oil content that 31 percent higher than check variety KOSX 3501. The mean oil content of the experiment was 6.7 percent. The highest oil per unit area was Ki 21 x DA-HO 644 kg/ha (yield 7,769 kg/ha, oil 8.1 percent). The heterosis of hybrid yield produced 2-231 percent which Ki 21 x IHO-S1-1 gave the highest 231 percent (yield 7,494 kg/ha). The heterosis of oil in hybrids was found -20 to 30 percent, and Ki 21 x DA-HO produced highest oil heterosis 30 percent (oil 8.1 percent). The combining ability of high oil hybrids was found that Ki crossed with high oil varieties (Ki x DA-HO) gave highest mean yield 7,744 kg/ha and their oil content was found that Ki x DA-HO and Ki x IHO gave highest mean oil content 6.5 percent. The highest mean grain yield (8,544 kg/ha) came from the cross of Ki 27 with high oil varieties whereas the highest mean oil content (7.3 percent) derived from the cross of Ki 21 with the high oil varieties. The Ki 27 and Ki 21 had high general combining ability for yield and oil content. The cross of high oil S1 lines with Ki 32 produced highest mean grain yield 7,356 kg/ha and with Ki 21 gave highest mean oil content 7.0 percent. The high oil varieties were made diallel cross and was found that DA-HO x IHO hybrid produced highest yield and oil content in the group (7,225 kg/ha and oil 75 percent). The good agronomic characters of hybrids viz. loging resistance, less foliar diseases and rotten ear came from the crosses of high oil materials with the Ki. The tendency of potential inbred lines to make a cross with high oil varieties and lines to produce high yield and high oil hybrids were Ki 21, Ki 27 and Ki 32. The high oil varieties and their lines to develop inbred lines and high oil hybrids were varieties and S1 lines from DA-HO crossed with AHO and IHO but should not made hybrid between AHO and IHO because they have close genetic relationship.