QTL mapping for ear leaf stay-green in maize under high and low N conditions

Objectives Stay-green of maize leaves is closely associated with the grain yield and quality. In this study, QTLs for ear leaf stay-green in maize were identified by using single segment substitution lines (SSSLs) to provide theoretical support for the fine mapping and cloning of major QTLs.

Methods Two years field experiments with a randomized complete block design were conducted, and a total of 172 maize SSSLs from a cross between a N-efficient inbred line Xu178 and a N-inefficient inbred line Zong3 were used as test materials. Nitrogen levels of 240 kg/hm² (high) and 75 kg/hm² (low) were applied for each material. The SPAD values of 10 days-old ear leaves after silking were measured to evaluate their stay-green feature. The T-test method was used to analysis the phenotype differences between SSSL and Xu178, and the QTLs for stay-green were mapped in the SSR genetic linkage map at P < 0.01.

Results In the genome range, 53 QTLs for ear leaf stay-green were detected under the two nitrogen levels and effectively resulted in contribution rates of –2.45% to –22.65%. These QTLs were unevenly distributed in all the 10 chromosomes of maize, up to 14 QTLs were detected in chromosome 1, while only one QTL was detected in chromosome 7. Under high nitrogen condition, a total of 29 QTLs were detected, and in which six QTLs including qhnSG1d, qhnSG2a, qhnSG3a, qhnSG4a, qhnSG8b and qhnSG10c were detected simultaneously under the two-year experimental condition. Here, qhnSG8b and qhnSG10c represented QTLs with high N-specific characteristics, and effective contribution rates were –4.47%, –9.17%, –9.46% and –5.05% in two years, respectively. Under low nitrogen condition, a total of 16 QTLs were detected, and 2 QTLs of which, qlnSG1f and qlnSG2b, were detected repeatedly under the two-year experimental conditions. qlnSG1f was a low N-specific QTL, and made effective contribution rates of –9.70% and –10.85% in two years, respectively.

Conclusions The high N-specific stay-green QTL is localized in the segment of umc1077−umc2350 and the low N-specific stay-green QTL is localized in the segment of umc1013−umc2047.