Mapping of QTLs for root morphology and nitrogen uptake of maize under different nitrogen conditions

ObjectivesThere is a strong relationship between maize root morphology and nitrogen uptake capacity. In this study, QTLs for maize root morphology and plant nitrogen uptake were identified using single segment substitution lines (SSSLs) to provide support for fine mapping and cloning of major QTLs controlling maize root morphology and nitrogen uptake.

Methods150 maize SSSLs derived from a cross between a N-efficient inbred line Xu178 and a N-inefficient inbred line Zong 3 were used for solution culture. Ca(NO₃)₂ was used as nitrogen source and high nitrogen level (4 mmol/L NO₃^–) and low nitrogen level (0.05 mmol/L NO₃^–) were supplied for each line, and each N level had six seedlings. After 20 days culture, seedlings were harvested, and the biomass and nitrogen contents of shoots and roots were analyzed respectively. Total root length (TRL), root surface area (RSA), root volume (RV), root average diameter (RAD) and root tip numbers (RTN) were determined from the root images using WinRHIZO. According to the results of the T-test of the phenotype values of SSSL and Xu178, QTLs for each trait were mapped in the SSR genetic linkage map when P value was less than 0.001.

ResultsUnder the high N level, all root traits were significantly correlated with each other except that between RAD and either TRL or RTN, and the plant nitrogen uptake was significantly correlated with all the root morphology related traits. Under the low N level, all the root morphology traits were strongly correlated with plant nitrogen uptake except for RAD, and the RSA showed the most significant correlation. Under the high N level, 102 QTLs were detected including 40 QTLs for root morphology traits, 34 QTLs for plant biomass and 28 QTLs for plant nitrogen uptake. Under the low N level, 85 QTLs were detected including 47 QTLs for root morphology traits, 22 QTLs for plant biomass and 16 QTLs for plant nitrogen uptake. Most of the QTLs for N uptake coincided in cluster with those for root morphology. Several QTLs for root morphology and nitrogen uptake were mapped in the same substituted segment region. Under the high N condition, five high N-specific QTLs clusters containing several root morphology traits and nitrogen uptake were detected in SSSL lines of 1428, 1376, 1282, 1266 and 1473. The single QTL additive effect contribution was from –43% to 84%. Moreover, several QTLs for root morphology and nitrogen uptake were identified in the SSSL lines of 1419 and 1314 under the LN condition, with the additive effect contribution from –32% to 55%.

ConclusionsIn the present study, several LN-specific QTLs were mapped in substituted segment of bnlg182–bnlg2295 in line 1419 and umc1013–umc2047 in line 1314, in which some QTLs related to nitrogen use efficiency of maize were detected in previous researches. It was indicated that there were some major QTLs for maize root morphology and plant nitrogen uptake located in the two regions which would play important role in maize nitrogen uptake efficiency. The present research serves as a basis for the major QTLs fine-mapping and candidate genes cloning.