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Grain rate (GR) is a very important trait in maize ( Zea mays L.) breeding program related to yield. To realize its genetic basis, a recombinant inbred line (RIL) population and different nitrogen (N) regimes were used to map the quantitative trait loci (QTLs) for GR in maize. As a result, two QTLs were identified under high N regime and could explain a total of 14.84% of phenotypic variance. Due to additive effect, the QTL on chromosome 6 could decrease 0.029 of GR, while the QTL on chromosome 9 could increase 0.0203 of GR. Under low N regime, one QTL was mapped on chromosome 6 and could account for 9.52% of phenotypic variance, and owning to additive effect, the QTL could make GR decrease by 0.0234. The result in comparison with previous studies showed that the three QTLs in this present study were new quantitative loci associated with GR in maize. These results were beneficial for understanding the genetic basis of GR in maize. Key words : Maize ( Zea mays L.), grain rate, quantitative trait locus, recombinant inbred line, nitrogen.

Nitrogen (N) deficiency will severely affect many metabolic pathways and physiological progresses during maize ( Zea mays L.) growth and change of anthesis-silking interval (ASI) is one of the most serious consequences. To realize the genetic basis of ASI, a recombinant inbred line (RIL) population consisting of 239 RILs, derived from the cross between Mo17 and Huangzao4, was used to identify the quantitative trait loci (QTLs) controlling ASI under different N environments. As a result, 6 QTLs were detected under high N environment on chromosome 3, 6, 7 and 8 and could explain total 53.67% of phenotypic variance. While, under low N environment, only 3 QTLs were identified on chromosome 6, 7 and 8, and they could account for total 31.87% of phenotypic variance. The two QTLs Qasihn6-1 and Qasihn3-1 , identified under high N environment, were quite near to their linked marker Phi077 and Bnlg197, respectively, with less than 1 cM of genetic distance. These results are beneficial for understanding the genetic basis of ASI in maize.

Nitrogen (N) deficiency affects severely many metabolic pathways and physiological progresses during maize (Zea mays L.) growing stage, and change of days to pollen shed (DPS) is one of the most serious consequences. To realize the genetic basis of DPS, a recombinant inbred line (RIL) population from the cross between Mo17 and Huangzao4 was used to identify the quantitative trait loci (QTLs) controlling DPS under two N regimes. As a result, 2 QTLs were detected, of which the QTL identified under both N regimes was quite near to the marker Nc134, with 0 centiMorgan (cM) of mapping distance between them, it could account for 15.36% and 10.39% of phenotypic variance under high and low N regimes respectively, and could make maize flower with ahead of time about 1 d duo to its additive effect. The other QTL, identified only under low N regime, was close to marker Bnlg1129 with 8.6 cM of maping distance between them, could explain 12.39% of phenotypic variance and increase DPS for 0.8 d owing to its additive effect. These results are beneficial for understanding the genetic basis of DPS in maize.