| The productive level of maize has had tremendous change dues to the using of maize heterosis, and yield increasing of40%—50%should be attributed to the popularization and application of hybrid. The United States is the country that takes the lead in the use of heterosis in maize, is the earliest country that carries out the division of heterosis groups, and is the country that builds the heterosis model of Reidxnon-Reid. The Reid Yellow Dent is very important germplasm of United States, its representative inbred lines are B73and PH6WC. Our country breeding practice shows the introduction of foreign germplasm in the United States and other countries has made great contribution for our country hybrid maize production, its contribution rate is close to60%. The introduction of exotic maize lines and its genetic improvement are very important methods to develop elite inbred lines. Exotic maize lines PH6WC, Zheng58and the second cycle-line were used as the experimental material in this study. Genetic studies on their ear characters were done in different density of45000,60000,75000,90000plant.hm-2. That is hopeful to provide theory reference for using of exotic maize lines and its genetic improvement.The tested inbred lines were divided into groups by heterosis group in the study. PH6WC of Reid group, C8605-2, Zheng58, Tie7922exotic lines etal. and their improved inbred lines J1684J1685and J1686were used as female parent, other groups were used as male parent for the incomplete diallel cross, the preparation of the incomplete diallel cross and their corresponding parents (augmented NCII) density levels in4randomized block experiment. Yield of panicle traits etal. were analysed from the point of heterosis, combining ability and correlation.The results are as follows:1. The heterosis of the kernel weight per plant (KWPP) shows the KWPP of all hybrid combination of F1showed obvious heterosis in4kinds of density. The combination of Zheng58×Chang7-2showed the highest heterosis (110.6%) in the lower density of45000plant.hm-2. The combination of PH6WC×PH4CV showed the highest heterosis (118.71%) in the density of60000plant.hm-2. The combination of J1686×A87showed the highest heterosis (97.18%) in the density of75000plant.hm-2. The combination of J1684×A87showed the highest heterosis (89.48%) in the higher density of90000plant.hm-2. All the results shows the improved inbreds of Reid showed more obvious heterosis in middle density. Improved inbreds of J1684, J1685and J1686are second cycle-line from PH6WC, C8605-2, Zheng58and7922. They inherit and surpass exotic lines of PH6WC and Zheng58in density-tolerance. Improved inbreds of1684, J1685and J1686are suit for density-tolerance breeding in productive practice.2. The general combining ability and genetic basis of improved inbreds of J1684, J1685and J1686were enhanced in the study. The general combining ability of J1685being successful improved inbreds showed stranger and its density-tolerance is higher than PH6WC and Zheng-58. J1684and J1686are also certain available in breeding practice.The heterosis analysis and combining ability of42combination were dealt with the hybridization model of Reid group as female parent with Lancaster, tangsipingtou and lvdahonggu as male parent.The general combining ability of parents ears characters showed the general combining ability of KWPP of J1685was the highest12.3318in the density of45000plant.hm-2, the general combining ability of KWPP of J1685was the highest15.9633in the density of60000plant.hm-2, the general combining ability of KWPP of J1685was the highest17.5569in the density of75000plant.hm-2, the general combining ability of KWPP of J1685was the highest12.736in the density of90000plant.hm-2The special combining ability of F1showed that the combining ability of KWPP of J1686xchang7-2, J1684×huangzao4, J1684×4CV and J1685×B1M were higher, they showed negative value in the length of ear top and were excellent combination of improved inbreds in the density of45000plant.hm-2. The combining ability of KWPP of J1685x4CV, J1686x4CV, J1684xA87, J1685xchang7-2and J1685xB1M was higher, they showed negative value in the length of ear top and were excellent combination of improved inbreds in the density of60000plant.hm-2. The combining ability of KWPP of J1684x4CV, J1684xA87, J1685x4CV, J1684×B1M and J1685×B1M, they showed negative value in the length of ear top and were excellent combination of improved inbreds in the density of75000plant.hm-2. The combining ability of KWPP of J1686xF349, J1685x4CV, J1685xB1M, J1684xA87, J1686xhuangzao4and J1685xchang7-2, they showed negative value in the length of ear top and were excellent combination of improved inbreds in the density of90000plant.hm-2The study result of heterosis showed the hybridization model of Reid×tangsipingtou and ReidxLancaster showed stronger heterosis in four kinds of density. The improved material of Reid had the same performance and conformed to the heterosis model of Reidxtangsipingtou and ReidxLancaster in the kinds of density in the experiment. The GCA effect analysis came to the same conclusion that proved improved inbreds of J1684, J1685and J1686conformed to the heterosis model of Reidxtangsipingtou and ReidxLancaster. The comprehensive evaluation of the ear characters and KWPP of Reid improved inbreds J1685was better than the exotic lines PH6WC and Backbone lines zheng58, was excellent density-tolerance breeding material.3. The result of path analysis showed the ear row number was the most important direct influence factor for KWPP in the density of45000plant.hm-2and the impact factor was0.3635. Kernel length was the most important direct influence factor for KWPP in the density of60000plant.hm-2and the impact factor was0.4553. Kernel length was the most important direct influence factor for kernel weight per plant in the density of75000plant.hm-2and the impact factor was0.6939. Kernel length was the most important direct influence factor for KWPP in the density of90000plant.hm-2and the impact factor was0.4695. |
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