Maize (Zea mays L.) root morphology exhibits a high degree of phenotypic plasticity to nitrogen (N) deficiency, but the underlying genetic architecture remains to be investigated. Using an advanced BC 4 F 3 population, we investigated the root growth plasticity under two contrasted N levels and identified the quantitative trait loci (QTLs) with QTL-environment (Q Â E) interaction effects. Principal components analysis (PCA) on changesofroottraitstoNdeficiency(DLN-HN)showedthatroot length and biomass contributed for45.8%inthesamemagnitude and direction on the first PC, while root traits scattered highly on PC2 and PC3. Hierarchical cluster analysis on traits for DLN-HN further assigned the BC 4 F 3 lines into six groups, in which the special phenotypic responses to N deficiency was presented. These results revealed thecomplicated root plasticity of maizein response to N deficiency that can be caused by genotypeenvironment (G Â E) interactions. Furthermore, QTL mapping using a multi-environment analysis identified 35 QTLs for root traits. Nine of these QTLs exhibited significant Q Â E interaction effects. Taken together, our findings contribute to understanding the phenotypic and genotypic pattern of root plasticity to N deficiency, which will be useful for developing maize tolerance cultivars to N deficiency.Keywords: Genotype-environment interactions; nitrogen stress; quantitative trait locus; root morphology; root plasticity; Zea mays L. Citation: Li P, Zhuang Z, Cai H, Cheng S, Soomro AA, Liu Z, Gu R, Mi G, Yuan L, Chen F (2016) Use of genotype-environment interactions to elucidate the pattern of maize root plasticgqy to nitrogen deficiency.

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Selecting optimum planting time (PT) in maize–soybean relay intercropping system (MSRI) is important to obtain higher intercrop yields because planting time decides the co‐growth duration and competitive ability of intercrop species in MSRI. However, little is known on how planting time (co‐growth duration) changes the interspecific interaction resulting in a seed‐yield difference between intercropping and sole cropping system. Therefore, this field study was initiated to determine the effects of changing co‐growth duration on competitive interactions, growth, and yield of intercrop species under MSRI. The sole soybean and relay‐cropped soybean were planted on PT1 (15–20 May, 90 days of co‐growth duration in MSRI); PT2 (5–10 June, 70 days of co‐growth duration in MSRI); and PT3 (25–30 June, 50 days of co‐growth duration in MSRI) to generate different size‐asymmetric competition between component crops in MSRI. Results showed that sole soybean produced the mean highest (2.93 t/ha) seed yield under PT2, and the mean lowest (2.51 t/ha) seed yield under PT1. However, in MSRI, PT3 increased the soybean yield by 29.1% and 13.3% compared to PT1 and PT2, respectively. The PT3 also increased the maize yield by 7.4% and 2.9% than PT1 and PT2, respectively, and it reduced the yield differences of maize and soybean between relay intercropping and sole cropping systems. In MSRI, decreased co‐growth duration promoted the soybean plants to achieve the higher crop growth rate, and biomass accumulation, which ultimately improved the soybean resilience toward size‐asymmetric competition created by maize plants. Furthermore, as compared to PT1 and PT2, planting time PT3 significantly increased the competitive ratio (by 10.1% and 17.3%, respectively) of soybean plants. Overall, the PT3 achieved the average highest land equivalent ratio of 1.63, which is significantly higher than PT1 (by 12.3%) and PT2 (by 10.6%). In conclusion, this study implied that in MSRI, the determination of proper soybean planting time (co‐growth duration) is one of the most critical factors to reduce the competition between the intercrops and to obtain higher crop yields.

Ferrum and zinc are essential microelements for rice. However, rice growing in lowland or acid soil is easily subjected to ferrous iron and zinc toxicities which harm plant growth and finally result in deduction of biomass and yield in production. The aim of this study was to identify quantitative trait locus (QTL) underlying ferrous iron toxicity tolerance (FTT) and zinc toxicity tolerance (ZTT) of rice using a reciprocal advanced backcross introgression lines, which was derived from the cross between Lemont (japonica) and Teqing (indica), and 308 evenly distributed single nucleotide polymorphism (SNP) markers developed from the two parents. A total of 42 putative QTLs affecting shoot height (SH), shoot dry weight (SDW), and root dry weight (RDW) under control and stress conditions and for the relative value of the stress to the control were detected, the alleles at most loci improving the tolerance of ferrous and zinc toxicities were from Lemont. Among them, only four QTLs (9.5%) were detected under the two backgrounds, indicating the expression of most QTLs is specific to genetic background. Nine QTLs were detected from the same genetic background affecting the tolerance of both ferrous and zinc toxicities, in which QSdw5 was expressed under the two backgrounds with the same direction and similar quantity of gene additive effect, suggesting that there is a genetic overlap between FTT and ZTT at seedling stage in rice. It is likely, therefore, to improve Teqing's FTT and ZTT by introgressing and pyramiding Lemont favorable alleles at the overlapping QTLs via marker-assisted selection.