Nitrogen (N) is unevenly distributed throughout the soil and plant roots proliferate in N-rich soil patches.  However, the relationship between the root response to localized N supply and maize N uptake efficiency among different genotypes is unclear.  In this study, four maize varieties were evaluated to explore genotypic differences in the root response to local N application in relation to N uptake.  A split-root system was established for hydroponically-grown plants and two methods of local N application (local banding and local dotting) were examined in the field.  Genotypic differences in the root length response to N were highly correlated between the hydroponic and field conditions (r>0.99).  Genotypes showing high response to N, ZD958, XY335 and XF32D22, showed 50‒63% longer lateral root length and 36‒53% greater root biomass in N-rich regions under hydroponic conditions, while the LY13 genotype did not respond to N.  Under field conditions, the root length of the high-response genotypes was found to increase by 66‒75% at 40‒60 cm soil depth, while LY13 showed smaller changes in root length.  In addition, local N application increased N uptake at the post-silking stage by 16‒88% in the high-response genotypes and increased the grain yield of ZD958 by 10‒12%.  Moreover, yield was positively correlated with root length at 40‒60 cm soil depth (r=0.39).  We conclude that local fertilization should be used for high-response genotypes, which can be rapidly identified at the seedling stage, and selection for “local-N responsive roots” can be a promising trait in maize breeding for high nitrogen uptake efficiency.  

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most destructive diseases on wheat worldwide.  Wudubaijian, a wheat landrace released from Gansu Province in China since 1950, exhibits adult-plant resistance to stripe rust for several decades.  To elucidate the genetic basis of stripe rust resistance, Wudubaijian was crossed with the high susceptible cultivar Mingxian 169, and stripe rust tests of both parents and the F_2:3 lines were conducted in four environments of Yangling and Tianshui in 2015 and 2016, respectively.  The relative area under disease progress curve (rAUDPC) of Mingxian 169/Wudubaijian F_2:3 lines showed that the resistance of Wudubaijian was controlled by quantitative trait loci (QTL).  Combined with phenotypic data and molecular markers, two stable QTLs were identified in Wudubaijian.  QYrwdbj.nwafu-5A with the phenotypic variance of 15.02–40.26% was located between 5AS1–0.40–0.75 and 5AS3–0.75–0.98 of chromosome 5AS, and QYrwdbj.nwafu-2B.1 with the phenotypic variance of 9.54–10.40% was located in the bin C-2BS1–0.53 of chromosome 2BS.  Through the location of flanking markers and epistasis analysis, QYrwdbj.nwafu-5A may be a new major QTL that can be used in conjunction with other stripe rust resistance genes (QTLs).

Grain water relations play an important role in grain filling in maize.  The study aimed to gain a clear understanding of the changes in grain dry weight and water relations in maize grains by using hybrids with contrasting nitrogen efficiencies under differing nitrogen levels.  The objectives were: 1) to understand the changes in dry matter and percent moisture content (MC) during grain development in response to different nitrogen application rates and 2) to determine whether nitrogen application affects grain filling by regulating grain water relations.  Two maize hybrids, high N-efficient Zhenghong 311 (ZH311) and low N-efficient Xianyu 508 (XY508), were grown in the field under four levels of N fertilizer: 0, 150, 300, and 450 kg N ha^–1 during three growing seasons.  Dry weight, percent MC and water content (WC) of basal–middle and apical grains were investigated.  The difference in the maximum WC and filling duration of basal–middle and apical grains in maize ears resulted in a significant difference in final grain weight.  Grain position markedly influenced grain drying down; specifically, the drying down rate of apical grains was faster than that of basal–middle grains.  Genotype and grain position both influenced the impact of nitrogen application rate on grain filling and drying down.  Nitrogen rate determined the maximum grain WC and percent MC loss rate in the middle and the late grain-filling stages, thus affecting final grain weight.  The use of high N-efficient hybrids, combined with the reduction of nitrogen application rate, can coordinate basal–middle and apical grain drying down to ensure yield.  This management strategy could lead to a win–win situation in which the maximum maize yield, efficient mechanical harvest and environmental safety are all achieved. 

As a critical food crop, sweetpotato (Ipomoea batatas (L.) Lam.) is widely planted all over the world, but it is deeply affected by Sweetpotato Virus Disease (SPVD).  The present study utilized short tandem target mimic (STTM) technology to effectively up-regulate the expression of laccase (IbLACs) by successfully inhibiting the expression of miR397.  The upstream genes in the lignin synthesis pathway were widely up-regulated by feedback regulation, including phenylalanine ammonialyase (PAL), 4-coumarate-CoAligase (4CL), hydroxycinnamoyl CoA:shikimatetransferase (HTC), caffeicacid O-methyltransferase (COMT), and cinnamyl alcohol dehydrogenase (CAD).  Meanwhile, the activities of PAL and LAC increased significantly, finally leading to increased lignin content.  Lignin deposition in the cell wall increased the physical defence ability of transgenic sweetpotato plants, reduced the accumulation of SPVD transmitted by Bemisia tabaci (Gennadius), and promoted healthy sweetpotato growth.  The results provide new insights for disease resistance breeding and green production of sweetpotato. 

Nitrogen (N) is a critical element for plant growth and productivity that influences photosynthesis and chlorophyll fluorescence. We investigated the effect of low-N stress on leaf photosynthesis and chlorophyll fluorescence characteristics of maize cultivars with difference in tolerance to low N levels. The low-N tolerant cultivar ZH311 and low-N sensitive cultivar XY508 were used as the test materials. A field experiment (with three N levels: N0, 0 kg ha^–1; N1, 150 kg ha^–1; N2, 300 kg ha^–1) in Jiyanyang, Sichuan Province, China, and a hydroponic experiment (with two N levels: CK, 4 mmol L^–1; LN, 0.04 mmol L^–1) in Chengdu, Sichuan Province, China were conducted. Low-N stress significantly decreased chlorophyll content and rapid light response curves of the maximum fluorescence under light (F_m´), fluorescence instable state (F_s), non-photochemical quenching (q_N), the maximum efficiency of PSII photochemistry under dark-adaption (F_v/F_m), potential activity of PSII (F_v/F_o), and actual photochemical efficiency of PSII (ΦPSII) of leaves. Further, it increased the chlorophyll (Chl) a/Chl b values and so on. The light compensation point of ZH311 decreased, while that of XY508 increased. The degree of variation of these indices in low-N tolerant cultivars was lower than that in low-N sensitive cultivars, especially at the seedling stage. Maize could increase Chl a/Chl b, apparent quantum yield and light saturation point to adapt to N stress. Compared to low-N sensitive cultivars, low-N tolerant cultivars maintained a higher net photosynthetic rate and electron transport rate to maintain stronger PSII activity, which further promoted the ability to harvest and transfer light. This might be a photosynthetic mechanism by which low-N tolerant cultivar adapt to low-N stress.

Heat stress seriously affects wheat production in many regions of the world.  At present, heat tolerance research remains one of the least understood fields in wheat genetics and breeding and there is a lack of effective methods to quantify heat stress and heat tolerance in different wheat cultivars.  The objective of this study was to use various wheat cultivars to evaluate stress intensity (δ) and a new method for quantification of heat tolerance and compare this technique with three other currently utilized methods.  This new parameter for heat tolerance quantification is referred to as the heat tolerance index (HTI) and is an indicator of both yield potential and yield stability.  Heat treatments were applied in a controlled setting when anthesis had been reached for 80% of the wheat.  The stress intensity evaluation indicated heat shock was the main factor associated with kernel weight reduction while grain yield reduction was mainly associated with chronic high temperature.  The methods evaluation showed that a temperature difference of 5°C from natural temperatures was a suitable heat treatment to compare to the untreated controls.  HTI was positively correlated with yield under heat stress (r=0.8657, δ₂₀₁₀=0.15, in 2009–2010; r=0.8418, δ₂₀₁₁=0.20, in 2010–2011; P<0.01), and negatively correlated with yield reduction rate (r=–0.8344, in 2009–2010; r=–0.7158, in 2010–2011; P<0.01).  The results of this study validated the use of HTI and temperature difference control for quantifying wheat heat tolerance that included the yield potential and the stability of different wheat cultivars under heat stress.  Additionally, 10 wheat cultivars showed high HTI and should be further tested for their heat confirming characteristics for use in wheat heat tolerance breeding.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most damaging diseases to wheat in the world.  The cultivation of resistant varieties of wheat is essential for controlling the powdery mildew epidemic.  Wheat landraces are important resources of resistance to many diseases.  Mapping powdery mildew resistance genes from wheat landraces will promote the development of new varieties with disease resistance.  The Chinese wheat landrace Baiyouyantiao possesses characteristic of disease resistance to powdery mildew.  To identify the resistance gene in this landrace, Baiyouyantiao was crossed with the susceptible cultivar Jingshuang 16 and seedlings of parents and F₁, BC₁, F₂, and F_2:3 were tested with Bgt isolate E09.  The genetic results showed that the resistance of Baiyouyantiao to E09 was controlled by a single recessive gene, tentatively designated PmBYYT.  An Illumina wheat 90K single-nucleotide polymorphism (SNP) array was applied to screen polymorphisms between F₂-resistant and F₂-susceptible DNA bulks for identifying the chromosomal location of PmBYYT.  A high percentage of polymorphic SNPs between the resistant and susceptible DNA bulks was found on chromosome 7B, indicating that PmBYYT may be located on this chromosome.  A genetic linkage map of PmBYYT consisting of two simple sequence repeat markers and eight SNP markers was developed.  The two flanking markers were SNP markers W7BL-8 and W7BL-15, with genetic distances of 3 and 2.9 cM, respectively.  The results of this study demonstrated the rapid characterization of a wheat disease resistance gene and SNP marker development using the 90K SNP assay.  The flanking markers of gene PmBYYT will benefit marker-assisted selection (MAS) and map-based cloning in breeding wheat cultivars with powdery mildew resistance.

Even though the impact of Bacillus thuringiensis (Bt) cotton on pesticide use has been well documented, all previous studies focus on the mean value of pesticide use.  Using seven unique waves of panel data collected between 1999 and 2012 in China, we show that Bt cotton adoption has not only caused a reduction of the mean value of pesticide use, but also a reduction of the standard deviation of pesticide use.  We conclude that Bt technology adoption has also contributed to the stability of pesticide use in cotton production.  We believe that this contribution is theoretically and practically relevant because of the long length of our unique dataset.

Soil salinity causes the negative effects on the growth and yield of crops. In this study, two sweet potato (Ipomoea batatas L.) cultivars, Xushu 28 (X-28) and Okinawa 100 (O-100), were examined under 50 and 100 mmol L^–1 NaCl stress. X-28 cultivar is relatively high salt tolerant than O-100 cultivar. Interestingly, real-time quantitative polymerase chain reaction (RT-qPCR) results indicated that sweet potato high-affinity K⁺ transporter 1 (IbHKT1) gene expression was highly induced by 50 and 100 mmol L^–1 NaCl stress in the stems of X-28 cultivar than in those of O-100 cultivar, but only slightly induced by these stresses in the leaves and fibrous roots in both cultivars. To characterize the function of IbHKT1 transporter, we performed ion-flux analysis in tobacco transient system and yeast complementation. Tobacco transient assay showed that IbHKT1 could uptake sodium (Na⁺). Yeast complementation assay showed that IbHKT1 could take up K⁺ in 50 mmol L^–1 K⁺ medium without the presence of NaCl. Moreover, Na⁺ uptake significantly increased in yeast overexpressing IbHKT1. These results showed that IbHKT1 transporter could have K⁺-Na⁺ symport function in yeast. Therefore, the modes of action of IbHKT1 in transgenic yeast could differ from the mode of action of the other HKT1 transporters in class I. Potentially, IbHKT1 could be used to improve the salt tolerance nature in sweet potato.

The information of single nucleotide polymorphisms (SNPs) is quite unknown in sweetpotato.  In this study, two sweetpotato varieties (Xushu 18 and Xu 781) were sequenced by Illumina technology, as well as de novo transcriptome assembly, functional annotation, and in silico discovery of potential SNP molecular markers.  Tetra-primer Amplification Refractory Mutation System PCR (ARMS-PCR) is a simple and sufficient method for detecting different alleles in SNP locus.  Total 153 sets of ARMS-PCR primers were designed to validate the putative SNPs from sequences.  PCR products from 103 sets of primers were different between Xu 781 and Xushu 18 via agarose gel electrophoresis, and the detection rate was 67.32%.  We obtained the expected results from 32 sets of primers between the two genotypes.  Furthermore, we ascertained the optimal annealing temperature of 32 sets of primers.  These SNPs might be used in genotyping, QTL mapping, or marker-assisted trait selection further in sweetpotato.  To our knowledge, this work was the first study to develop SNP markers in sweetpotato by using tetra-primer ARMS-PCR technique.  This method was a simple, rapid, and useful technique to develop SNP markers, and will provide a potential and preliminary application in discriminating cultivars in sweetpotato.

Sweetpotato (Ipomoea batatas (L.) Lam.) breeding is challenging due to its genetic complexity. In the present study, interval mapping (IM) and multiple quantitative trait locus (QTL) model (MQM) analysis were used to identify QTLs for starch content with a mapping population consisting of 202 F1 individuals of a cross between Xushu 18, a cultivar susceptible to stem nematodes, with high yield and moderate starch, and Xu 781, which is resistant to stem nematodes, has low yield and high starch content. Six QTLs for starch content were mapped on six linkage groups of the Xu 781 map, explaining 9.1-38.8% of the variation. Especially, one of them, DMFN_4, accounted for 38.8% of starch content variation, which is the QTL that explains the highest phenotypic variation detected to date in sweetpotato. All of the six QTLs had a positive effect on the variation of the starch content, which indicated the inheritance derived from the parent Xu 781. Two QTLs for starch content were detected on two linkage groups of the Xushu 18 map, explaining 14.3 and 16.1% of the variation, respectively. They had a negative effect on the variation, indicating the inheritance derived from Xu 781. Seven of eight QTLs were co-localized with a single marker. This is the first report on the development of QTLs co-localized with a single marker in sweetpotato. These QTLs and their co-localized markers may be used in marker-assisted breeding for the starch content of sweetpotato.

Stripe rust (yellow rust), caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most devastating diseases of wheat throughout the world. H9020-1-6-8-3 is a translocation line originally developed from interspecific hybridization between wheat line 7182 and Psathyrostachys huashanica Keng and is resistant to most Pst races in China. To identify the resistance gene(s) in the translocation line, H9020-1-6-8-3 was crossed with susceptible cultivar Mingxian 169, and seedlings of the parents, F1, F2, F3, and BC1 generations were tested with prevalent Chinese Pst race CYR32 under controlled greenhouse conditions. The results indicated that there is a single dominant gene, temporarily designated as YrH9020a, conferring resistance to CYR32. The resistance gene was mapped by the F2 population from Mingxian 169/H9020-1-6-8-3. It was linked to six microsatellite markers, including Xbarc196, Xbarc202, Xbarc96, Xgpw4372, Xbarc21, and Xgdm141, flanked by Xbarc96 and Xbarc202 with at 4.5 and 8.3 cM, respectively. Based on the chromosomal locations of these markers and the test of Chinese Spring (CS) nullitetrasomic and ditelosomic lines, the gene was assigned to chromosome 6D. According to the origin and the chromosomal location, YrH9020a might be a new resistance gene to stripe rust. The flanking markers linked to YrH9020a could be useful for marker-assisted selection in breeding programs.

Stripe rust, caused by Puccinia striiformis Westend. f. sp. tritici (Pst), is a severe foliar disease of common wheat (Triticum aestivum L.) in the world. Resistance is the best approach to control the disease. The winter wheat cultivar Lantian 1 has high-temperature resistance to stripe rust. To determing the gene(s) for the stripe rust resistance, Lantian 1 was crossed with Mingxian 169 (M169). Seedlings of the parents, and F1, F2 and F2-3 progenies were tested with races CYR32 of Pst under controlled greenhouse conditions. Lantian 1 has a single partially dominant gene conferred resistance to race CYR32, designated as YrLT1. Simple sequence repeat (SSR) techniques were used to identify molecular markers linked to YrLT1. A linkage group of five SSR markers was constructed for YrLT1 using 166 F2 plants. Based on the SSR marker consensus map and the position on wheat chromosome, the resistance gene was assigned on chromosome 2DL. Amplification of a set of nulli-tetrasomic Chinese Spring lines with SSR marker Xwmc797 confirmed that the resistance gene was located on the long arm of chromosome 2D. Because of its chromosomal location and the high-temperature resistance, this gene is different from previously described genes. The molecular map spanned 29.9 cM, and the genetic distance of two close markers Xbarc228 and Xcfd16 to resistance gene locus was 4.0 and 5.7 cM, respectively. The polymorphism rates of the flanking markers in 46 wheat lines were 2.1 and 2.1%, respectively; and the two markers in combination could distinguish the alleles at the resistance locus in 97.9% of tested genotypes. This new gene and flanking markers should be useful in developing wheat cultivars with high level and possible durable resistance to stripe rust.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most widespread and destructive wheat diseases in many wheat-growing regions of the world. The winter wheat translocation line H9014-14-4-6-1 has all stage resistance. To identify stripe rust resistance genes, the segregating populations were developed from the cross between H9014-14-4-6-1 and Mingxian 169 (a wheat cultivar susceptible to all Pst races identified in China). The seedlings of the parents and F1 plants, F2, F3 and BC1 generations were tested with Pst races under controlled greenhouse conditions. Two genes for resistance to stripe rust were identified, one dominant gene conferred resistance to SUN11-4, temporarily designated YrH9014 and the other recessive gene conferred resistance to CYR33. The bulked segregant analysis and simple sequence repeat (SSR) markers were used to identify polymorphic markers associated with YrH9014. Seven polymorphic SSR markers were used to genotype the F2 population inoculated with SUN11-4. A linkage map was constructed according to the genotypes of seven SSR markers and resistance gene. The molecular map spanned 24.3 cM, and the genetic distance of the two closest markers Xbarc13 and Xbarc55 to gene locus was 1.4 and 3.6 cM, respectively. Based on the position of SSR marker, the resistance gene YrH9014 was located on chromosome arm 2BS. Amplification of a set of nulli-tetrasomic Chinese Spring lines with SSR marker Xbarc13 indicated that YrH9014 was located on chromosome 2B. Based on chromosomal location, the reaction patterns and pedigree analysis, YrH9014 should be a novel resistance gene to stripe rust. This new gene and flanking markers got from this study should be useful for marker-assisted selection (MAS) in breeding programs for stripe rust.

Sequence-related amplification polymorphism (SRAP) markers closely linked to stem nematode resistance gene were developed in sweetpotato, Ipomoea batatas (L.) Lam. Using bulked segregant analysis (BSA), 200 SRAP primer combinations were screened with the resistant and susceptible bulked DNA from the 196 progenies of an F1 single-cross population of resistant parent Xu 781×susceptible parent Xushu 18, 77 of them showed polymorphic bands between resistant and susceptible DNA. Primer combinations detecting polymorphism between the two bulks were used to screen both parents and 10 individuals from each of the bulks. The results showed that primer combination A9B4 produced 3 specific bands in the resistant plants but not in the susceptible plants, suggesting that the markers, named Nsp1, Nsp2 and Nsp3, respectively, linked to a gene for stem nematode resistance. Primer combination A3B6 also produced a SRAP marker named Nsp4 linking to the resistance gene. Amplified analysis of the 196 F1 individuals indicated that the genetic distance between these markers and the resistance gene was 4.7, 4.7, 6.3, and 9.6 cM, respectively.

The free putrescine (Put) content, the hydrogen peroxide (H2O2) content and the polyamine oxidase (PAO) activity in roots of Malus hupehensis Rehd. var. pinyiensis Jiang (PYTC) were significantly increased, and reached its peak at 1, 2 and 6 h, respectively, under cadmium treatment. The free spermine (Spm) and spermidine (Spd) contents were dramatically decreased, and reached the minimum value at 4-6 h, then remained relatively stable. The change in total free polyamines (PAs) content was consistent with that of free Put. The number of root dead cells was gradually increased after treatment for 24 h, and the typical characteristics of programmed cell death (PCD) were displayed at 48 h. Throughout the Cd treatment process, changes in PAs metabolism appeared to be prior to cell death increase, and the H2O2 content was always maintained at a high level. These results indicated that polyamines could initiate cell death by generating H2O2 in roots of Malus hupehensis Rehd. under CdSO4 stress.