That root system architecture (RSA) has an essential role in nitrogen acquisition is expected in maize, but the genetic relationship between RSA and nitrogen use efficiency (NUE) traits remains to be elucidated. Here, the genetic basis of RSA and NUE traits was investigated in maize using a recombination inbred line population that was derived from two lines contrasted for both traits. Under high-nitrogen and low-nitrogen conditions, 10 NUE- and 9 RSA-related traits were evaluated in four field environments and three hydroponic experiments, respectively. In contrast to nitrogen utilization efficiency (NutE), nitrogen uptake efficiency (NupE) had significant phenotypic correlations with RSA, particularly the traits of seminal roots (r = 0.15-0.31) and crown roots (r = 0.15-0.18). A total of 331 quantitative trait loci (QTLs) were detected, including 184 and 147 QTLs for NUE- and RSA-related traits, respectively. These QTLs were assigned into 64 distinct QTL clusters, and ~70% of QTLs for nitrogen-efficiency (NUE, NupE, and NutE) coincided in clusters with those for RSA. Five important QTLs clusters at the chromosomal regions bin1.04, 2.04, 3.04, 3.05/3.06, and 6.07/6.08 were found in which QTLs for both traits had favourable effects from alleles coming from the large-rooted and high-NupE parent. Introgression of these QTL clusters in the advanced backcross-derived lines conferred mean increases in grain yield of ~14.8% for the line per se and ~15.9% in the testcross. These results reveal a significant genetic relationship between RSA and NUE traits, and uncover the most promising genomic regions for marker-assisted selection of RSA to improve NUE in maize.

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A genetic relationship between nitrogen use efficiency and seedling root traits in maize as revealed by QTL analysis

Root traits are important in improving nutrient and water use efficiency. Vertical root pulling resistance (VRPR) has been shown to be closely related to root system characteristics in maize (Zea mays L.). In the present study, two genetic populations derived from the same parents, one containing 218 recombinant inbred lines (RILs) and the other containing 187 advanced backcross BC4F3 lines, were genotyped using 184 SSR markers and evaluated for VRPR, grain yield (GY), stover yield (SY), and nitrogen uptake (Nup) under field conditions over 2 years. Our aims were (1) to locate QTLs associated with VRPR, SY, GY, and Nup, (2) to determine whether QTL detection is consistent between the BC4F3 and RIL populations, and (3) to identify backcross lines harboring favorable VRPR QTLs for use in future breeding programs. Using composite interval mapping (CIM), 12 and 17 QTLs were detected in BC4F3 and RIL populations, respectively. An important QTL region in bin 6.02 within the interval umc1006-umc1257 was found to control VRPR, SY, and Nup in both populations. These favorable alleles were contributed by the large-rooted parent Ye478. A significant positive correlation was detected between VRPR, SY, and Nup, but not between VRPR and GY. Backcross lines harboring VRPR QTLs could be useful germplasm for developing near isogenic lines (NILs) and for map-based cloning of genes controlling root growth.

Genetic analysis of vertical root pulling resistance (VRPR) in maize using two genetic populations

Mapping QTL for stem-related traits using RIL population with ultra-high density bin map can better dissect pleiotropic QTL controlling stem architecture that can provide valuable information for maize genetic improvement. The maize stem is one of the most important parts of the plant and is also a component of many agronomic traits in maize. This study aimed to advance our understanding of the genetic mechanisms underlying maize stem traits. A recombinant inbred line (RIL) population derived from a cross between Ye478 and Qi319 was used to identify quantitative trait loci (QTL) controlling stem height (SH), ear height (EH), stem node number (SN), ear node (EN), and stem diameter (SD), and two derived traits (ear height coefficient (EHc) and ear node coefficient (ENc)). Using an available ultra-high density bin map, 46 putative QTL for these traits were detected on chromosomes 1, 3, 4, 5, 6, 7, 8, and 10. Individual QTL explained 3.5–17.7% of the phenotypic variance in different environments. Two QTL for SH, three for EH, two for EHc, one for SN, one for EN, and one for SD were detected in more than one environment. QTL with pleiotropic effects or multiple linked QTL were also identified on chromosomes 1, 3, 4, 6, 8, and 10, which are potential target regions for fine-mapping and marker-assisted selection in maize breeding programs. Further, we discussed segregation of bin markers (mk1630 and mk4452) associated with EHc QTL in the RIL population. We had identified two putative WRKY DNA-binding domain proteins, AC209050.3_FG003 and GRMZM5G851490, and a putative auxin response factor, GRMZM2G437460, which might be involved in regulating plant growth and development, as candidate genes for the control of stem architecture.

Mapping quantitative trait loci associated with stem-related traits in maize (Zea mays L.).

Analysis of genetic structure and genetic relationships of partial maize inbred lines in China.

The conservation of water in agriculture requires an understanding of the mechanisms of plant–water relations. This study aimed to reveal hydraulic regulation strategies of maize (Zea mays L.) for maintaining the plant water balance during drought. The water relations of two maize inbred lines (Tian4 and 478) that differ in their resistance to drought in the field were investigated under well-watered conditions and osmotic stress induced with 10 % PEG 6000. The leaf transpiration rate and leaf water potential of 478 varied diurnally, but remained constant in Tian4, which is more drought resistant. Tian4 plants showed morphological, anatomical and physiological advantages that protected them from foliar water loss. The strategies of leaf hydraulics to regulate leaf water balance during the day and during short-term osmotic stress also differed between Tian4 and 478. The leaf hydraulic conductivity of Tian4 and 478 increased temporarily, but their root hydraulic conductivities were reduced under osmotic stress. However, the root hydraulic conductivity of Tian4 subsequently recovered. Lower and rapidly reduced leaf transpiration and the ability of root hydraulics to recover from short-term osmotic stress can help explain the strategies for plant water balance of drought-tolerant maize.

Hydraulic regulation strategies for whole-plant water balance of two maize inbred lines differing in drought resistance under short-term osmotic stress

The 478 maize inbred line was bred from two maize inbred lines 8112 and 5003.Plant shape of 478 is compact,and its plant height and ear height are lower,and inherited steadily.Furthermore,478 is high-resistant to many maize diseases and self-output.Because of its good characteristics,it is noticed by more and more maize breeding experts at home and oversea.According to the statistics,there have been 41 examined maize hybrid used 478 as parents by the province or nation,up to now,the 41 maize hybrids have covered at least 39570000 hectare plantation areas.Moreover,there have been 19 examined maize hybrids used its improved-line as parents,up to now,the 19 maize hybrids have covered at least 7960000 hectare plantation areas.

Zhang Yong-hui

Papers

Breeding Process and Utilization of Excellent Maize Inbred Line 478