The genetic basis of heterosis for grain yield and its components was investigated at the single- and two-locus levels using molecular markers with an immortalized F(2) (IF(2)) population, which was developed by pair crosses among recombinant inbred lines (RILs) derived from the elite maize hybrid Yuyu22. Mid-parent heterosis of each cross in the IF(2) population was used to map heterotic quantitative trait loci. A total of 13 heterotic loci (HL) were detected. These included three HL for grain yield, seven for ear length, one for ear row number and two for 100-kernel weight. A total of 143 digenic interactions contributing to mid-parent heterosis were detected at the two-locus level involving all three types of interactions (additive x additive = AA, additive x dominance = AD or DA, dominance x dominance = DD). There were 25 digenic interactions for grain yield, 36 for ear length, 31 for ear row number and 51 for 100-kernel weight. Altogether, dominance effects of HL at the single-locus level as well as AA interactions played an important role in the genetic basis of heterosis for grain yield and its components in Yuyu22.

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A set of recombinant inbred lines (RIL) derived from Yuyu22, an elite hybrid widespread in China, was used to construct an immortalized F 2 (IF 2 ) population comprising 441 different crosses. Genetic linkage maps were constructed containing 10 linkages groups with 263 simple sequence repeat (SSR) molecular markers. Twelve and ten quantitative trait loci (QTL) were detected for plant height in the IF 2 and RIL populations respectively, using the composite interval mapping method, and six same QTL were identified in the two populations. In addition, ten unique heterotic loci (HL) located on seven different chromosomes were revealed for plant height using the mid-parent heterosis as the input data. These HL explained 1.26%-8.41% of the genotypic variance in plant height heterosis and most expressed overdominant effects. Only three QTL and HL were located in the same chromosomal region, it implied that plant height and its heterosis might be controlled by two types of genetic mechanisms. maize, plant height, heterotic loci, QTL, detection

Plant height is an important trait for maize breeding because it is related to planting density and lodging resistance. It is influenced by many qualitative genes and quantitative trait loci (QTL). In this study, the genetic basis of plant height and its related traits were dissected, using simple sequence repeat (SSR) markers with a maize population of 294 recombinant inbred lines (RIL). Correlation results showed that plant height had a significant positive correlation with leaf number, average internode length and internode number. Increased plant height was affected most by average internode length. Six QTL for plant height were detected, which were consistent with those reported in previous studies. Moreover, eight QTL for leaf number, seven for internode number and six for average internode length were identified. Four of six QTL detected for average internode length were located on the same chromosomal region as the QTL affecting plant height and shared common molecular markers. This latter result strongly suggests that average internode length was the main contributor to plant height in maize. KeywordsPlant height Á Average internode length Á QTL Á Maize (Zea mays L.) Abbreviations QTL quantitative trait loci RIL recombinant inbred line SSR simple sequence repeats LOD logarithm of odds PH plant height LN leaf number IN internode number AIL average internode length

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