Partially inbred maize lines in topcrosses and hybrid performance

ABSTRACT In plant breeding programs, the selection of potential progenies in early generations of inbreeding is an essential step. Considering that, the adoption of topcrosses helps the breeder in the selection, this study aimed to verify the potential of S2 strains for synthesis of synthetic varieties and to obtain experimental information on yield and agronomic potential of topcross hybrids. As such, 75 topcross hybrids were generated from crossing 75 S2 lines with F2 generation of the commercial hybrid. The 75 hybrids were grown in a field, along with two commercial hybrids in a randomized complete block design with 4 replicates and in 4-meter plots. Flowering, plant height, height, diameter, length and weight in the ear, and grain yield traits were examined. Analysis of variance was performed, the combining ability was estimated, and, from the means, the Scott & Knott test was conducted. So, the topcross hybrids that distinguished themselves for grain yield were those composed by lines 67, 14, 44, and 69, presenting high CGA, therefore indicating good potential for producing synthetic or base population. For the other traits of agronomic interest that were assessed in maize, a potential for selection with different focuses was found: reduction of cycle and height and increase in length and diameter of the ear.

摘要
在植物育种项目中，对早期自交世代的潜在育种后代进行选择是至关重要的核心环节。鉴于顶交（topcross）育种技术可辅助育种者开展后代选择工作，本研究旨在验证S2株系用于合成品种培育的潜力，并获取顶交杂交种的产量与农艺性状潜力相关实验数据。
据此，本研究将75个S2株系与商用杂交种的F2代进行杂交，共获得75个顶交杂交种。将该75个杂交种与2个商用杂交种一同种植于田间，采用随机完全区组设计（randomized complete block design），设置4次重复，小区规格为4米。本研究测定了抽穗期、株高、穗部高度、穗直径、穗长、穗粒重以及籽粒产量等性状。随后开展了方差分析，估算了配合力（combining ability），并基于均值进行了Scott & Knott检验。
结果显示，由株系67、14、44及69组配得到的顶交杂交种籽粒产量表现突出，且具有较高的一般配合力（CGA），表明其具备培育合成品种或基础群体的良好潜力。针对本次评估的其他玉米农艺性状，本研究发现了具备不同选择导向的育种潜力：可通过选择缩短生育期与株高，同时增加穗长与穗径。