ObjectivesThe difference of QTL mapping in ear traits of maize treated with and without nitrogen input is helpful to identify the major QTL specific expression, which will provide theoretical basis for maize nitrogen efficient molecular breeding.

MethodsThe experimental materials used in a two-year's field experiment were one hundred and fifty recombinant inbred lines (RILs, the F₇generation), which were derived from the dominant maize inbred lines Xu178 (high nitrogen use efficiency) and K12 (low nitrogen use efficiency). In the field experiment, all the RILs were supplied with and without N, and the phenotypes were authenticated in five ear traits including ear length, ear diameter, row number per ear, kernel number per row and grain yield per plant in total. The breeding values of each trait under different nitrogen levels were estimated using the best linear unbiased prediction (BLUP) which based on mixed liner model (MLM) combining with the phenotype data in two years. Then the QTL analysis of the five traits with and without N supply was conducted utilizing the inclusive composite interval mapping method from the software of QTL IciMapping V4.0.

ResultsThe ear length, ear diameter and row number per ear were similar in both nitrogen levels, but the kernel number per row and grain yield per plant were dramatically declined without N input. Twenty QTLs for ear traits were detected in the experiment, eleven from treatment with N supply (2 for ear length, 1 for ear diameter, 2 for row number per ear, 1 for kernel number per row and 5 for grain yield per plant) and nine from treatment without N supply (1 for ear length, 1 for ear diameter, 2 for row number per ear, 1 for kernel number per row and 4 for grain yield per plant). These QTLs distributed on all the chromosomes except chromosome 2. Five "consistency QTLs" were detected in the experiment, they are qEL7a, qED7a, qRNE9b, qGYP1a, and qGYP6arespectively. These 5 QTLs had high phenotypic contribution rate, which contribute more than 10.00% under both the nitrogen supply conditions. Four specific expression QTLs were detected in treatment without N, they are qRNE9a, qKNR6a, qGYP3a and qGYP8a respectively, in which the phenotypic contribution of qRNE9aand qGYP3awas more than 10.00%, they were major QTLs. In both N supply treatments, the genes controlling different traits were closely linked or the same gene had phenomenon of pleiotropism, which was consistent with the high correlation of ear traits.

ConclusionThe specific expression of genes controlling ear traits will change greatly under different nitrogen supply levels, which will bring about difference in ear traits in maize. The expression of the five consistency major QTLs and two low-N major QTLs is beneficial to strengthen the resistance of maize to low nitrogen stress. These QTL enriched region may exist some key genes controlling ear traits in maize, which is worth of further research.