A set of 213 F 2:3 families were used to investigate the effects of nitrogen (N) on grain yield and the concentrations of three nutrient components in maize (Zea mays L.) kernels. A genetic linkage map was constructed using 189 SSR (simple sequence repeat) markers, spanning a total of 2003 cM, including 11 linkages, and the families were evaluated under high N and low N conditions at two farm locations. The results indicate that low N conditions may induce an increase in starch concentration, but a decrease in protein levels. Twenty-six quantitative trait loci (QTL) were detected for four measured traits in the two N treatments at both locations, including eight QTL for grain yield, seven QTL for oil content, six QTL for protein content and five QTL for starch content. The total number of QTL detected for the four measured traits under high N levels was greater than the QTL detected under low N conditions, and several QTL were identified that specifically expressed under different N conditions. These particular QTL could help provide greater understanding of the genetic basis of N-usage efficiency.

The effect of two different nitrogen treatments on five traits associated with yield and nutrient composition of stover were evaluated using a set of 213 F 2:3 families derived from two elite inbred lines Huang-C and Xu178. Evaluation of the phenotypes expressed under the two nitrogen conditions showed that low nitrogen conditions could increase acid detergent fiber (ADF) and neutral detergent fiber (NDF), and decreased crude protein content (CP), crude fat content (CF), and stover yield (SY), thereby negatively affecting the digestibility and quality of silage maize. Twenty-eight quantitative trait loci (QTL) were identified affecting the five measured traits under two nitrogen conditions, including four for ADF, five for NDF, five for CP, four for CF, and three for SY. Several QTL associated with ADF or NDF were detected under same nitrogen conditions, and were localized to the same chromosomal regions, especially the QTL qADF6 and qNDF6, qADF10 and qNDF10, were only detected under low nitrogen condition. These results suggested that ADF and NDF perhaps were controlled by several common genes, and that the nutritional content of stover may be influenced by additional genetic mechanisms when grown under conditions of low nitrogen.

For elucidating the genetic basis of N, P and K contents in kernels and stalks in maize under different nitrogen supply condition, a set of 203 F 2: 4 / F 2: 5 family lines, derived from an elite maize hybrid Nongda108, were tested under nitrogen plus (N+) and no nitrogen plus (N-) treatments in the field over two years, and a genetic linkage map was constructed with 199 SSR molecular markers, covered 2100.9 cm for 10 chromosomes with an average interval length of 10.82 cm. The results showed that low N stress not only affected N content in maize kernels and stalks, but also affected the absorption and transportation of P and K contents in some degree. A total of 34 quantitative trait locus (QTL) including 15 QTLs in kernels and 19 QTLs in stalks for N, P, K content were identified by means of the composite interval mapping method (CIM), of which, 13, 9 and 12 QTLs detected for N, P, K content, respectively. Each QTL could explain the variance of phenotype ranged in turn from 7.30 to 31.09%, 7.57 to 14.3% and 8.11 to 32.82% for three main mineral elements content. The QTL qNC4c, qPC9b, qKC10b as well as qNC4b, qPC5b, qKC6a were main contributing QTL for N, P, K contents in kernels and stalks. Out of these QTLs detected for N, P, K contents in kernels and stalks, the results also implied that the loci derived from Huang C played important roles in N, P, K absorption, while the loci from Xu178 played marked roles in N, P, K transportation from stalks to grains.