Abstract: Four cycles of modified S1-HS (MS1-HS) alternant recurrent selection to improve grain yield of ZZ4 maize (Zea mays L.) population have been completed in northern China. In 2001, 30 NCⅡ testcrosses and 11 parents (including six testing lines and five populations for each cycle) were tested at four locations. Analysis of variance indicated that significant progress（p﹤0.05）was achieved for major agronomic traits of populations and testcrosses. MS1-HS alternant recurrent selection was effective for increasing grain yield of testcrosses, heterosis and general combining ability. The average yield increase of testcrosses to MS1-HS alternant recurrent selection in ZZ4 was 6.7%-8.1% per cycle. Increased yield of testcrosses was accompanied with increased heterosis. The average gain for mid-parent yield heterosis of testcrosses to MS1-HS alternant recurrent selection in ZZ4 was 211 -248 kg·ha-1per cycle. The GCA of grain yield and ear traits all increased cycle by cycle. The MS1-HS alternant recurrent selection seemed to be less effective to improve special combining ability (SCA). ZZ4 and Huangzao4 or Dan340 lines may be the most efficient herterosis pattern after comparing the yield of hybrids and heterosis between improved population and the 6 testing lines.

Key words: Maize (Zea mays L.), Population improvement, Modified S1-HS alternant recurrent selection