Table of Content

10 August 2018, Volume 44 Issue 8

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CROP GENETICS & BREEDING·GERMPLASM RESOURCES·MOLECULAR GENETICS

Mining Yellow-seeded Micro Effect Loci in B. napus by Integrated GWAS and WGCNA Analysis

Xiao-Hua XIAN,Jia WANG,Xin-Fu XU,Cun-Min QU,Kun LU,Jia-Na LI,Lie-Zhao LIU

Acta Agronomica Sinica. 2018, 44(8):  1105-1113.  doi:10.3724/SP.J.1006.2018.01105

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Brassica napus is one of the most important oil crops in the world, and developing yellow-seeded B. napus with improved qualities is a major breeding goal. The yellow-seeded minor genes were mined by genome-wide association study (GWAS) and weighted gene co-expression network analysis (WGCNA) with 520 representative varieties (or lines) and the transcriptional data at eight time points during the seed development. The 199 SNPs and 1826 nominally significant GWAS candidate genes were detected. Weighted gene co-expression network analysis was performed using the WGCNA R package to construct the resulting network composing eight distinct gene modules. Among them, the turquoise module and the blue module were related to the seed coat color based on gene function enrichment analysis. BnATCAD4, BnF3H, and BnANS, the key enzymes genes of phenylpropane metabolic pathway and flavonoid metabolic pathway were found in turquoise module. Through the characterization of module content and topology, we mined a number of micro effect genes based on known yellow-seed related genes mainly involved in the phenylpropanoid metabolic process, flavonoid metabolic process and proanthocyanidin biosynthetic process. This information of minor loci and candidate genes should be useful in the breeding for yellow-seeded B. napus.

Molecular Evaluation for Chromosome Segment Substitution Lines of Gossypium barbadense and QTL Mapping for Fiber Quality and Yield

Chao LI,Zhi-Kun LI,Qi-Shen GU,Jun YANG,Hui-Feng KE,Li-Qiang WU,Guo-Ning WANG,Yan ZHANG,Jin-Hua WU,Gui-Yin ZHANG,Yuan-Yuan YAN,Zhi-Ying MA,Xing-Fen WANG

Acta Agronomica Sinica. 2018, 44(8):  1114-1126.  doi:10.3724/SP.J.1006.2018.01114

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In the previous study, we developed a set of chromosome segment substitution lines (CSSLs) using G. hirsutum CCRI8 as the recipient parent and G. barbadense Pima 90-53 as the donor parent. In this study, we genotyped the BC₃F₅ generation of CSSLs with SSR markers, conducted QTL mapping for the fiber quality and yield traits and identified the stable QTLs in three different environments (Baoding, Qingxian, Luntai). The substituted segment number of the 182 CSSLs varied from one to fifteen, averaged 6.6. The length of introgressed segments ranged from 0.7 cM to 83.2 cM, and averaged 16.8 cM. The total length of the substituted fragment was 20 249.6 cM, background recoverage rate varied from 92.3% to 99.6%, and the average background recoverage rate was 96.2%. Fifty-nine QTLs related to fiber quality and yield traits were detected. Among them, 41 QTLs were related to fiber quality traits and each QTL explained 1.27% to 26.66% of the phenotypic variation. Eighteen QTLs for fiber yield-traits including boll weight and lint percentage were detected and each QTL explained 2.03% to 19.38% of the phenotypic variation. Fourteen stable QTLs were detected in multiple environments. Among them, four QTLs related to micronaire value and two QTLs related to fiber elongation both had enhancing alleles from G. barbadense Pima 90-53. Two boll weight QTLs had enhancing alleles from G. hirsutum CCRI8. The results provide a theoretical basis for QTL fine mapping, QTL interaction and molecular breeding for fiber quality and yield traits.

Major Quantitative Trait Loci Mapping for Tassel Branch Number and Construction of qTBN5 Near-isogenic Lines in Maize (Zea mays L.)

Zi-Ju DAI,Xin-Tao WANG,Qing YANG,Yan WANG,Ying-Ying ZHANG,Zhang-Ying XI,Bao-Quan LI

Acta Agronomica Sinica. 2018, 44(8):  1127-1135.  doi:10.3724/SP.J.1006.2018.01127

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Tassel branch number (TBN) is a principal component of maize tassel-related traits important for modern maize breeding and production. To understand the genetic basis of tassel branch number, we adopted 288 markers exhibiting polymorphisms between Zheng 58 and Chang 7-2 to construct the genetic linkage map, and conduct quantitative trait loci (QTLs) analysis using sets of 188 recombinant inbred line (RIL) families derived from the elite maize inbred lines vz. Zheng 58 × Chang 7-2. Five major QTLs controlling tassel branch number within five different chromosomes respectively were validated by using the inclusive composite interval mapping method (ICIM) based on phenotypic data collected in two years. Because qTBN5 located on chromosome bin 5.05 was found to be an important QTL, qTBN5 near-isogenic lines (qTBN5-NILs) were developed by backcrossing and marker-assisted selection, and qTBN5 was further mapped in 13.2 Mb intervals. These findings will advance our understanding of the inheritance basis of TBN, and also facilitate the fine mapping and molecular breeding programs in maize.

Preliminary Study on Resistance of Different Mungbean Varieties to Callosobruchus chinensis (L.)

Hong-Min WANG,Xiao-Fang CHENG,Yan-Ping FAN,Hai-Xia ZHENG,Yao-Wen ZHANG,Xian-Hong ZHANG

Acta Agronomica Sinica. 2018, 44(8):  1136-1141.  doi:10.3724/SP.J.1006.2018.01136

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To clarify the effective component in mungbean seeds against bruchid (Callosobruchus chinensis L.), we identified the bruchid resistance of 13 mungbean varieties via in-house artificial feeding method, and the insect-resistant components in mungbean were investigated. Six mungbean varieties including B18, B20, B23, B27, A22, and Jinlyu 7, were found to be highly resistant to bruchid, showing seed-damage rates lower than 10%, whereas, the remaining seven varieties were highly susceptible with seed-damage rates higher than 90%. There was no significant difference in egg-hatch rate among all varieties. However, the developmental duration, the adult-emergence rate ,and the bodyweights of both male and female adults varied significantly between the resistant and susceptible varieties. Moreover, seed coat had no effect on the resistance to bruchid because samples with or without seed coat showed no significant difference in the rates of egg-hatch, adult emergence, and seed damage. The resistance test with synthetic mungbean indicated that the adult-emergence rate declined from 30.48% to 0 when the protein component of resistant mungbean varieties increased from 25% to 50%. In contrast, the increase of starch proportion had no effect on theadult emergence rate. Therefore, we conclude that seed proteins play an important role in bruchid resistance in mungbean.

QTL Mapping for Shelling Percentage and Plant Height in Cultivated Peanut (Arachis hypogaea L.)

Wei-Gang CHEN,Jian-Bin GUO,Zhi-Jun XU,Bo-Lun YU,Xi-Ke QIU,Li HUANG,Yan-Bin SONG,Yu-Ning CHEN,Xiao-Jing ZHOU,Huai-Yong LUO,Nian LIU,Xiao-Ping REN,Hui-Fang JIANG

Acta Agronomica Sinica. 2018, 44(8):  1142-1151.  doi:10.3724/SP.J.1006.2018.01142

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Peanut yield is greatly influenced by shelling percentage (SP) and plant height (PH). Marker-assisted selection for shelling percentage and plant height improvement can be facilitated by detecting additive and epistatic QTLs, understanding their interactions with environment, as well as the genetic relationship between SP and PH. In a four-year experiment, the variations of SP and PH were evaluated with the recombinant inbred line population derived from the cross between Yuanza 9102 and Xuzhou 68-4. QTLs associated with SP and PH were analyzed using a high density linkage map and QTLNetwork 2.0 software. The results showed that SP and PH were negatively correlated (P < 0.01). Thirteen and eight additive QTLs were identified for SP and PH, respectively. Major loci qSPA05.2 and qSPA09.1 for SP and major locus qPHA09.1 for PH were repeatedly detected in three or four years. Six pairs of epistatic QTLs for SP and five pairs of epistatic QTLs for PH were identified, and they all had interaction effects with environment. qSPA09.1 and qPHA09.1 were located in the same interval (Ad91I24-AGGS2492) on chromosome A09. The additive effect of this locus for SP variation decreased from 14.37% to 5.50% after eliminating the PH effect, suggesting the pleiotropism of qSPA09.1 for SP and qPHA09.1 for PH.

Improving Fiber Yield and Quality in the Short Season Cotton Variety Jinmian 11 by Introducing FBP7::iaaM

Xiao-Yan DING,Juan ZHAO,Shan-Shan QIAN,Xing-Ying YAN,Yan PEI

Acta Agronomica Sinica. 2018, 44(8):  1152-1158.  doi:10.3724/SP.J.1006.2018.01152

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Short season cotton is of particular importance for sustainable development of cotton production in China where has a huge population and limited arable land resources. Usually, early maturity is associated with lower yield and poor quality. We previously developed a novel transgenic cotton material with improved fiber yield and quality by spatiotemporal manipulation of auxin biosynthesis in cotton ovule epidermal cells. In this study, we introduced FBP7::iaaM into a short season cotton variety Jinmian 11, which has low lint percentage and high macronaire value, through backcross breeding. A consecutive two-year field experiment indicated that the transgenic-homozygous backcrossed progeny (JBC4) exhibited a significant improvement in fiber yield and fiber fineness. Compared with Jinmian 11, lint percentage and lint yield of JBC4 increased by 12.8% and 56.3%, respectively, and meanwhile, the micronaire value decreased by 10.7%. Our data demonstrate a significant potential of the FBP7::iaaM transgenic in the yield and quality improvement for short season cotton.

Functional Characterization of Soybean Cystatins Gene GmCYS2

Dan-Xia KE,Kun-Peng PENG,Yan JIA,Shuo ZENG,Ying-Zhi WANG,Jing-Yi ZHANG

Acta Agronomica Sinica. 2018, 44(8):  1159-1168.  doi:10.3724/SP.J.1006.2018.01159

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CYS (cystatin) plays an important role in nodulation, nodule development and senescence. In this study, we cloned a soybean CYS family gene GmCYS2, which had the highest similarity with pigeonpea (Cajanus cajan) CYS, shown by amino acid sequence alignment and phylogenetic tree analysis. The gene encoding protein was expressed and purified in vitro. Enzyme activity inhibition experiment of recombinant protein GmCYS2 showed that the cathepsin inhibitory activity of GmCYS2 protein on L and B classes was higher than that on H class, and cathepsin inhibitory activity in nodule extract from nodule at 30 d was generally higher than that at the 60 d. In addition, the plant overexpression vector was constructed and the GmCYS2-overexpression composite plants were obtained by Lotus japonicus hairy root transformation method. Overexpression of GmCYS2 increased the number of nodules in Lotus japonicus plants and up regulated the expression levels of symbiotic marker genes. These results suggest that GmCYS2 protein can inhibit the enzyme activity and positively regulate the symbiotic nodulation of Lotus japonicus.

Screening and Comprehensive Evaluation of Germplasm Resources with Tribenuron-methyl Tolerance at Germination Stage in Rapeseed (Brassica napus L.)

Qian WANG,Cui CUI,Sang YE,Ming-Sheng CUI,Yu-Feng ZHAO,Na LIN,Zhang-Lin TANG,Jia-Na LI,Qing-Yuan ZHOU

Acta Agronomica Sinica. 2018, 44(8):  1169-1184.  doi:10.3724/SP.J.1006.2018.01169

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The purpose of this study is to explore the characteristics of tribenuron-methyl tolerance in different genotypes of Brassica napus, and establish the evaluation system for screening and breeding new cultivars with tribenuron-methyl tolerance. The germination vigor was measured on the third day after treatment and the germination rate, shoot length, root length, dry weight, as well as fresh weight were measured on the seventh day. The identification of tolerance at germination stage was performed by tribenuron-methyl tolerance comprehensive evaluation value (T), average subordinative function value (ASF) and weight tribenuron-methyl tolerance coefficient (WTC) in correlation analysis, frequency analysis, principal component analysis, grey analysis, cluster analysis and stepwise regression analysis. Based on the variance analysis of relative root length index in 11 tested materials, we determined the optimum treatment concentration (25 mg kg ^-1) for selecting and evaluating the tolerant germplasm resources to tribenuron-methyl in napeseed. Under the optimum concentration, the single factor variance analysis showed significant differences in root length, shoot length, germination rate, germination vigor and fresh weight among 241 accessions of Brassica napus. The clustering analysis according to T value exhibited that the tested cultivars were roughly divided into five tribenuron-methyl tolerance grades, including three in grade I, 30 in grade II, 198 in grade III, six in grade IV, and four in grade V. We conclude that the varieties (lines) with strong tribenuron-methyl tolerance at germination stage are Xiwang 106, SWU95, and WH-33, which could be used as the germplasm materials for the study on tolerance breeding and mechanism. Furthermore, the root length, fresh weight and germination rate could be used as index traits to evaluate the tolerance of rapeseed germplasm resources during germination stage.

Genetic Analysis of Plant Height and Stem Diameter in Common Buckwheat

Ying-Shuang LI,Dan HU,Jiao NIE,Ke-Hui HUANG,Yu-Ke ZHANG,Yuan-Li ZHANG,Heng-Zhi SHE,Xiao-Mei FANG,Ren-Wu RUAN,Ze-Lin YI

Acta Agronomica Sinica. 2018, 44(8):  1185-1195.  doi:10.3724/SP.J.1006.2018.01185

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Common buckwheat (Fagopyrum esculentum M.) is susceptible to lodging, and plant height and stem diameter are recognized as important traits for lodging resistance. In this study, we developed the P_l, P₂, F_l, F₂, B_l, and B₂ populations from the reciprocal crosses between Youqiao 2 (YQ2, lodging-resistance) and Ukraine daliqiao (UD, lodging-susceptible) and analyzed the genetic effects of plant height and stem diameter. The heredity of both traits optimally fitted to the genetic model for two major genes with additive-dominance-epistatic effects plus polygenes with additive-dominance effects. For plant height in the orthogonal combination, additive effects of both two major genes were -1.39 and the dominant effects were -6.59 and -7.91. Heritability values of the major genes in B₁, B₂, and F₂ were 45.73%, 63.49%, and 81.12%, and those of polygenes were 27.41%, 0.95%, and 0, respectively. For plant height in the back cross, additive effects of both two major genes were -1.63 and the dominant effects were -7.03 and -4.19, respectively. Heritability values of the major genes in B₁, B₂, and F₂ were 41.51%, 66.18%, and 81.81%, and those of polygenes were 11.19%, 0, and 0, respectively. For stem diameter in the orthogonal combination, the two major genes had 0.03 and 0.03 of additive effect and -0.50 and -0.08 of dominant effect. Heritability values of the major genes in B₁, B₂ and F₂ were 37.26%, 48.80%, and 72.10%, and those of polygenes were 11.18%, 0, and 0, respectively. For stem diameter in the back cross, the two major genes possessed -0.15 and -0.15 of additive effect and -0.30 and -0.16 of dominant effect. The estimated heritability values in B₁, B₂, and F₂ were 76.22%, 47.12%, and 82.51%, respectively, for the major genes and 0, 14.53%, and 0, respectively, for the polygenes. These results suggest that plant height can be selected in early generations because the heritability of major genes plus polygenes was larger than 80%, whereas proper cultivation practice may enhance lodging resistance of buckwheat because the heritability of major genes plus polygenes was lower than 80%.

TILLAGE & CULTIVATION·PHYSIOLOGY & BIOCHEMISTRY

Compensation Effect of Nitrogen Fertilizer on Photosynthetic Characteristics and Yield during Cotton Flowering Boll-setting Stage under Non-sufficient Drip Irrigation

Hong-Liang SHI,Qing-Qing YAN,Ju-Song ZHANG,Chun-Yan LI,Hai-Tao DOU

Acta Agronomica Sinica. 2018, 44(8):  1196-1204.  doi:10.3724/SP.J.1006.2018.01196

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Cotton cultivar ‘Xinluzhong 54’ was used to study the compensation effect of nitrogen fertilizer on photosynthetic characteristics and yield and its mechanism during cotton flowering boll-setting stage under non-sufficient drip irrigation, so as to provide a theoretical basis for the efficient use of water and fertilizer for cotton in arid area. Split plot experiment design was used, the main area included total drip irrigation amount of 2800 m ³ ha ^-1 (non-sufficient drip irrigation) and 3800 m ³ ha ^-1 (conventional drip irrigation), the secondary area had four nitrogen (pure N) levels (0, 150, 300, and 450 kg ha ^-1). Under the same nitrogen fertilizer treatment, the leaf area index (LAI) of cotton at flowering and boll-setting stage, net photosynthetic rate (P_n), transpiration rate (T_r), accumulation and allocation of photosynthate, boll number of single plant, single boll weight and seed cotton yield of non-sufficient drip irrigation treatment were lower than those of conventional drip irrigation treatment, while seed cotton yield rate and drip irrigation water productivity were higher. Under the same drip irrigation amount, with the increase of nitrogen fertilizer amount, LAI of cotton at flowering and boll-setting stage and photosynthate accumulation increased first and decreased then, showing a trend of N450>N300>N150>N0, and T_r, P_n, allocation proportion of photosynthate to reproductive organ, boll number of single plant, single boll weight, seed cotton yield, seed cotton yield rate and drip irrigation water productivity showed a trend of N300>N450>N150>N0. The compensation effect of increasing nitrogen fertilizer under non-sufficient drip irrigation condition increased first and decreased then with the increase of nitrogen fertilizer amount, the compensation effect of N300 treatment was most significant, P_n of cotton flowering and boll-setting stage P_n increased by 10.9% averagely, the allocation proportion of photosynthate translocated to reproductive organ increased by 10.7%, boll number of single plant, single boll weight, seed cotton yield rate and drip irrigation water productivity increased by 5.0%, 8.0%, 7.1%, and 7.5%, respectively. The influence of nitrogen fertilizer on photosynthetic characteristics and yield components of cotton at flowering and boll-setting stage was greater than that of water. The compensation effect was the maximum when nitrogen fertilizer increased to 300 kg ha ^-1 under non-sufficient drip irrigation condition, though the yield decreased by 1.3% compared with conventional drip irrigation treatment. Therefore, in natural ecological conditions of South Xinjiang, 300 kg ha ^-1 nitrogen application with non-sufficient drip irrigation is suitable for cotton at production with better, LAI, T_r, P_n and photosynthate accumulation and translocated compensation effect to reproductive organ, as well as the maximum yield compensation effect and water conservation of 26.3%.

Effects of Water Deficit at Flowering Stage on Yield and Quality of Fresh Waxy Maize

Long-Jian SHI,Zhang-Rong WEN,Shi-Bo ZHANG,Jue WANG,Wei-Ping LU,Da-Lei LU

Acta Agronomica Sinica. 2018, 44(8):  1205-1211.  doi:10.3724/SP.J.1006.2018.01205

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In order to clarify the influence of water deficit at flowering stage (tasseling silking stage) on yield and quality of fresh waxy maize (harvest at 23 d after silking), the fresh ear/grain yield and kernel components, pasting and thermal properties were measured using Suyunuo 5 and Yunuo 7. The soil moisture content was controlled by negative-pressure water supply and controlling pot device, and the relative soil moisture content for control and drought treatments was 80% and 60%, respectively. The drought at flowering stage decreased grain number, weight and volume, leading to the yield loss of fresh ear and grain. Under water deficit condition, grain starch content was increased, while protein content was increased in Yunuo 7 and unchanged in Suyunuo 5. For protein components, globulin contents was not affected by drought, while albumin, zein and glutenin contents were decreased when plants suffered water deficit at flowering stage. The starch granule size was reduced by drought for both varieties in both years, while starch iodine binding capacity for both varieties was decreased in 2015 and not affected in 2014 by drought. The peak, trough and final viscosities of grains were increased in Yunuo 7 and decreased in Suyunuo 5. Under drought condition, the grain peak gelatinization temperatures were decreased, retrogradation enthalpy and percentage were increased, while gelatinization enthalpy was only increased in Yunuo 7 in 2014. In conclusion, drought at flowering stage decreases fresh ear/grain yield, increases grain starch content, decreases protein content, starch granule size and the proportion of long chains in amylopectin, and increases the grain retrograde, while viscosities in response to water deficit are dependent on varieties (increases in Yunuo 7 and decreases in Suyunuo 5).

Effects of CO₂ Concentrations on Stomatal Traits and Gas Exchange in Leaves of Soybean

Fei LI,Liang LIU,Hao ZHANG,Qing-Tao WANG,Li-Li GUO,Li-Hua HAO,Xi-Xi ZHANG,Xu CAO,Wei-Jia LIANG,Yun-Pu ZHENG

Acta Agronomica Sinica. 2018, 44(8):  1212-1220.  doi:10.3724/SP.J.1006.2018.01212

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Seven concentrations treatments (400, 600, 800, 1000, 1200, 1400, and 1600 μmol mol ^-1) were designed to investigate the effects of atmospheric CO₂ concentrations on the stomatal traits and leaf gas exchange of soybean. We found that elevating CO₂ concentrations significantly decreased the stomatal density of adaxial side and the stomatal area index of both the adaxial and abaxial sides. Meanwhile, the spatial distribution pattern analysis of stomata with the Ripley’s K function showed that the spatial distribution pattern of stomata on leaf surfaces of soybean was highly scale-dependent. The most regular distribution pattern of stomata on the abaxial surface was found under the CO₂ concentration of 400 μmol mol ^-1, and the increase of CO₂ concentration resulted in irregular distribution pattern of stomata on the abaxial surface of soybean leaves. In contrast to the abaxial surface, elevating CO₂ concentrations made the spatial distribution pattern of stomata more regular on the adaxial leaf surface, which was evidenced by lower minimal Lhat(d) values under elevated CO₂ concentrations than those under CO₂ concentration of 400 μmol mol ^-1. Although the response of stomatal traits to atmospheric CO₂ concentration was obviously different between the adaxial and abaxial surfaces of leaves, soybean plants could alter leaf gas exchange through adjusting the morphological traits and the spatial distribution pattern of stomata. These results may be helpful for further understanding potential mechanisms concerning about the elevating CO₂ effect on the leaf gas exchange of soybean plants from the view of stomatal traits.

Relationship between Lipid and Flag Leaf Senescence Induced by Low Nitrogen Stress during Grain Filling of Wheat

Qian LI,Ling-Yun QI,Li-Na YIN,Shi-Wen WANG,Xi-Ping DENG

Acta Agronomica Sinica. 2018, 44(8):  1221-1228.  doi:10.3724/SP.J.1006.2018.01221

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Nitrogen (N) deficiency induces flag leaf senescence at the grain-filling stage of wheat resulting in yield decrease. In this study, we carried out a field experiment to investigate the relationship between N-deficiency-induced flag leaf senescence and lipid change using wheat variety ‘Changhan 58’. Under the low-N (120 kg ha ^-1) condition, the photosynthetic rate, chlorophyll content, total N content, and contents of all lipid components of flag leaf at 14 days after flowering were significantly lower than those under normal-N (180 kg ha ^-1) condition, while the DGDG/MGDG ratio in low-N treatment increased. The content of unsaturated fatty acids, such as C18:3 and C18:2 decreased significantly, whereas the contents of saturated fatty acids, such as C16:0, increased significantly, leading to the reduction of index of unsaturated double bounds. In addition, thylakoid protein packing density also decreased under N-deficiency condition. These results indicate that N-deficiency-induced leaf senescence is characterized with lipid degradation and components changes, which result in negative effects on reductions of membrane permeability, chlorophyll content and photosynthetic rate. Simultaneously, the DGDG/MGDG ratio of plants is adjusted in response to N deficiency to alleviate damages of membrane function caused bby lipid degradation.

Parameter Optimization in APSIM-Based Simulation Model for Yield Formation of Dryland Wheat Using Shuffled Frog Leaping Algorithm

Zhi-Gang NIE,Guang LI,Cui-Ping LUO,Wei-Wei MA,Yong-Qiang DAI

Acta Agronomica Sinica. 2018, 44(8):  1229-1236.  doi:10.3724/SP.J.1006.2018.01229

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The rapid and accurate estimation of model parameters is an important prerequisite for the application of yield formation model. In the process of localization parameters calibration for yield formation based on APSIM (agricultural production systems simulator) model of dryland wheat, there are some deficiencies such as large scale, long time consuming, a lack of precision and low efficiency. In this study, intelligent algorithm was used to remedy the deficiencies. We collected and analyzed the field experimental data in Mazichuan village, Lijiabao town, Anding district, Dingxi city from 2002 to 2005, and Anjiagou village, Fengxiang town, Anding district, Dingxi city from 2015 to 2016, and the historical and meteorological data in Anding district, Dingxi city from 1971 to 2016. According to the characteristics of the yield formation model for parameters nonlinearity and multidimensional change, making full use of the intelligent strategy of advanced group rotation and global information exchange in shuffled frog leaping algorithm and the self-organization, self-learning intelligent algorithm characteristics, the estimation parameters more difficult to obtain in the model of the dryland wheat yield formation based on APSIM platform were optimized and tested by correlation analysis method. This optimization method could use frog intelligent group biology evolution learning strategy to estimate the yield formation model parameters of dryland wheat. Compared with the method of attempting to eliminate the error, which is used in the localization parameters calibration of APSIM platform usually, the accuracy of simulation output was significantly improved. The root mean square error (RMSE) reduced from 79.13 kg ha ^-1 to 35.36 kg ha ^-1, the normalized root mean square error (NRMSE) decreased from 5.97% to 2.63%, and the model effectiveness index (M_E) increased from 0.939 to 0.989. This method has strong global optimization ability, reasonable calculation quantity, and fast convergence speed.

Identification of Salt Tolerance and Screening for Its Indicators in Sweet Potato Varieties during Seedling Stage

Wen-Xue DUAN,Hai-Yan ZHANG,Bei-Tao XIE,Bao-Qing WANG,Li-Ming ZHANG

Acta Agronomica Sinica. 2018, 44(8):  1237-1247.  doi:10.3724/SP.J.1006.2018.01237

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Eighteen sweet potato varieties were selected as the test material. The control and treatment groups were established via saline soil cultivation in seedling stage. The treatment group received 200 mmol L ^-1 NaCl. Fourteen physical traits were observed in each treatment, which were fresh stem leaf weight, fresh root weight, dry stem leaf weight, dry root weight, relative leaf conductivity, F_v/F_m, SPAD value, superoxide dismutase (SOD) activity, malondialdehyde (MDA) content, proline content, root vigor, root Na ⁺ content, root K ⁺content, and Na ⁺/K ⁺ ratio. A comprehensive analysis of the salt tolerance of different varieties was conducted via correlation analysis, principal component analysis, clustering analysis, and stepwise regression of the salt tolerance efficiency of each index. Principal component analysis narrowed down the 14 single indexes in the salt-stressed seedling stage of sweet potatoes to five independent comprehensive indexes. Subordinate function analysis was conducted to obtain the comprehensive assessment value (D-value) of salt tolerance of different varieties in seedling stage. In clustering analysis, the 18 sweet potato varieties were divided into four salt tolerance types, including four salt-sensitive, three weak salt tolerant, seven moderate salt-tolerant, and four high salt-tolerant. On the basis of this division, stepwise regression method was used to establish a regression equation for salt tolerance assessment of sweet potatoes in seedling stage. Eight physiological indexes were selected (fresh stem leaf weight, fresh root weight, dry stem leaf weight, leaf SPAD value, SOD enzyme activity, MDA content, proline content, and Na ⁺/K ⁺ ratio) for the same assessment purpose. This paper presents the germplasm information for selection and breeding of new salt-tolerant sweet potato varieties. The results could serve as a basis for subsequent assessment of seedling stage salt tolerance of sweet potatoes and further studies on their salt tolerance mechanism.

RESEARCH NOTES

QTL Mapping for Rice Appearance Quality Traits Based on a High-density Genetic Map in Different Environments

Qiang PENG,Jia-Li LI,Da-Shuang ZHANG,Xue JIANG,Ru-Yue DENG,Jian-Qiang WU,Su-Song ZHU

Acta Agronomica Sinica. 2018, 44(8):  1248-1255.  doi:10.3724/SP.J.1006.2018.01248

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To analyze the genetic basis of appearance quality of rice, explore QTL which controlled rice appearance quality related traits stably existing, a mapping population of 150 lines (recombination inbred lines, RIL), derived from a cross between rice varieties V20B and CPSLO17, was applied to analysis QTL location of appearance quality trait. The specific locus amplified fragment sequencing (SLAF-seq) technology was employed to construct a high-density genetic map in rice (Oryza sativa L.). A genetic map included 8602 markers on the 12 linkage groups was successfully constructed, which with an average distance of 0.29 cM between adjacent markers. The ICIM-ADD method of IciMapping 4.0 software was used to analyze QTL location for four appearance quality traits, including grain length (GL), grain width (GW), chalky grain rate, and chalkiness degree in three environmental conditions (Guiyang, Guiding, and Sanya). A total of nine QTLs for grain length (GL), six QTLs for grain width (GW), four QTLs for chalkiness size, three QTLs for chalkiness degree traits were detested in three environments. Five QTLs were repeatedly detected in multiple environments, of which the QTL qGW5-1 and qCha5-1 with the same localization interval (Marker1642127-Marker1514505 on chromosome 5) were repeatedly located in all three environments. In addition, the positioning interval of chalkiness QTL qCha5-2 (Marker1554573-Marker1554589) is the same as the chalkiness size QTL qCGP5-2. The sequence alignment found that the location interval of QTL qCha5-1 was only 51.5 kb, which was a new main effect QTL for chalkiness trait. These results lay the foundation for further exploiting candidate gene of appearance quality, which also contribute to the development of new molecular markers for rice appearance quality traits genetic improvement.

Identification of Maize Germplasm for Resistance to Pythium Stalk Rot

Yang YANG,Guo-Kang CHEN,Cheng GUO,Wei ZHANG,Su-Li SUN,Xiao-Ming WANG,Zhen-Dong ZHU,Can-Xing DUAN

Acta Agronomica Sinica. 2018, 44(8):  1256-1260.  doi:10.3724/SP.J.1006.2018.01256

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Pythium stalk rot is a serious disease in maize production. A total of 1213 maize accessions were screened for resistance to Pythium stalk rot from 2013 to 2016. Among the 1213 germplasm resources, 207 were highly resistant to Pythium stalk rot, accounting for 17.1% of total accessions screened, mainly from Inner Mongolia, Hebei, Shanxi Provinces of China and the United States, 159 were resistant to Pythium stalk rot, accounting for 13.1% of total accessions, mainly from Inner Mongolia, Yunnan, Shanxi Provinces of China and USA, showing that there are relatively abundant germplasm resistant to Pythium stalk rot in these maize accessions, and the level of resistance is related to geographical origin. In present study, 18.7% of maize inbred lines were highly resistant to Pythium stalk rot, whereas 10.6% of landraces were highly resistant to the same diseases, indicating higher level of resistance and more multiple resistance were in inbred lines than in landraces.