Table of Content

12 January 2018, Volume 44 Issue 01

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CROP GENETICS & BREEDING · GERMPLASM RESOURCES · MOLECULAR GENETICS

Large Scale Detection of Powdery Mildew Resistance Genes in Wheat via SNP and Bulked Segregate Analysis

WU Qiu-Hong,CHEN Yong-Xing,LI Dan,WANG Zhen-Zhong,ZHANG Yan,YUAN Cheng-Guo,WANG Xi-Cheng,ZHAO Hong,CAO Ting-Jie,LIU Zhi-Yong

Acta Agron Sin. 2018, 44(01):  1-14.  doi:10.3724/SP.J.1006.2018.00001

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Large-scale detection of powdery mildew resistance genes is necessary for wheat germplasm innovation and breeding, especially via marker assisted selection. Illumina 90k iSelect SNP chip and Bulked Segregate Analysis (BSA) were applied to identify powdery mildew resistance gene in 36 wheat varieties (lines) from Henan province. SNP genotyping between 36 resistant bulks and 36 susceptible bulks revealed that single polymorphic SNP peaks were identified between 24 of the 36 bulk pairs, indicating single powdery mildew resistance gene may present in the 24 varieties (lines). Multiple polymorphic SNP peaks were found between other 12 resistant and susceptible bulks, indicating more than one powdery mildew resistance gene might be in these varieties (lines). Among the 36 bulk pairs, 26 showed the largest number of SNP enriched on chromosome 2AL, indicating the powdery mildew resistance genes, most likely on Pm4 locus, were in these 26 varieties (lines). A new marker Xwggc116 was developed and proved to be effective for detecting the powdery mildew resistance gene on 2AL. Overall, the combination of BSA and high-throughput SNP genotyping platform is highly effective for large scale powdery mildew resistance gene detection in wheat germplasm. There are a limited number of powdery mildew resistance genes (Pm2, Pm4, Pm21, and new 1BL/1RS translocation) in wheat varieties (lines) of Henan province, indicating very narrow genetic diversity of the powdery mildew resistance genes in wheat breeding program. Exploring and utilization of new diversified disease resistance genes are urgent for breeding new varieties with disease resistance.

Mapping of QTLs for Seed Dormancy in Oryza Rufipogon Griff.

SUN Ai-Ling,WU Hong-Ming,CHEN Gao-Ming,ZHANG Tian-Yu,CAO Peng-Hui,LIU Shi-Jia,JIANG Ling,WAN Jian-Min

Acta Agron Sin. 2018, 44(01):  15-23.  doi:10.3724/SP.J.1006.2018.00015

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Seed dormancy of rice is an important agronomic trait related to rice quality and quantity. Studies on genetics and molecular mechanisms of rice seed dormancy are of great significance in breeding fine rice varieties with moderate dormancy. In this research, a set of chromosome segment substitution lines (CSSLs), derived from an indica rice variety 9311 as the recurrent parent and the Oryza rufipogon Griff. as the donor parent, were used to detect the QTLs for dormancy of seeds at different storage dates after harvest. A total of 14 QTLs were detected on chromosomes 3, 4, 5, 6, 7, 10, 11, and 12. The lines with significantly stronger dormancy than the background parent 9311 were selected, showing the more dormancy loci in the lines the more strong dormancy. The F₂ population of the cross between Q14 and 9311 was used to verify the QTLs for seed dormancy. A significant dormancy locus qSD-7-2 was mapped on chromosome 7 between the markers RM180 and RM21323, its LOD was 18.49 and the phenotypic variation rate was 33.53%. On this major stable inherited QTL, the allele gene from Oryza rufipogon Griff. significantly increased the dormancy of seeds. These results are available for map-based cloning of major QTLs for seed dormancy, and provide the breeding materials for cultivating appropriate dormant rice varieties.

ABA Biosynthesis Gene OsNCED3 Confers Drought Stress Tolerance in Rice

XU Xue-Zhong,WANG Ting,WAN Wang,LI Si-Hui,ZHU Guo-Hui*

Acta Agron Sin. 2018, 44(01):  24-31.  doi:10.3724/SP.J.1006.2018.00024

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NCED (9-cis-epoxycarotenoid dioxygenase), encoded by NCED gene family, is a rate limited enzyme responsible for the ABA biosynthesis in plants. It remains unknown whether OsNCED genes are responsible for controlling ABA levels during drought stress in rice. Among the five OsNCED genes, we found that OsNCED3 mRNA level was promptly induced by PEG-mimic drought stress and decreased by re-watering, with a tendency of well consistent with the variation of ABA content. Down-regulating of OsNCED3 gene expression in RNA interference (RNAi)-transgenic plants decreased the total biomass and showed a hypersensitive phenotype subjecting to drought stress, while the overexpression (OE)-transgenic seedlings increased the drought stress tolerance compared with the wild-type (WT). ABA contents in OsNCED3-OE leaves were higher than those in WT, meanwhile, OsNCED3-OE lines also increased the activities of anti-oxidative enzyme including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and expressions of stress/drought-related genes, i.e. dehydrin protein, LEA protein under drought stress. OsNCED3-RNAi lines showed an opposite tendency with the OsNCED3-OE plants. We therefore conclude that OsNCED3 gene plays an important role in controlling ABA level and drought stress resistance in rice.

Genome-wide Association Study of Grain Appearance and Milling Quality in a Worldwide Collection of Indica Rice Germplasm

FANG Ya-Jie,ZHU Ya-Jun,WU Zhi-Chao,CHEN Kai,SHEN Cong-Cong,SHI Ying-Yao,XU Jian-Long

Acta Agron Sin. 2018, 44(01):  32-42.  doi:10.3724/SP.J.1006.2018.00032

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Appearance and milling quality are two crucial properties of rice affecting their market acceptability. Understanding the genetic basis of rice grain quality could improve the efficiency of breeding for high quality. Here we carried out genome-wide association analysis using the 404K SNP genotype and data of grain appearance and milling quality for a diverse panel of 400 indica accessions selected from 3K Rice Genome Project collected in two environments. These were closely correlation between grain shape and quality (appearance and milling) of indica rice. The chalk trait reduced milled rice rate and high milled rice rate. In addition to grain shape, the phenotype value of appearance and milling quality traits was obviously affected by environments. Total of 39 QTL were detected which was significantly associated with grain appearance and milling quality in two environments and 17 of them were new QTL. Six new QTL (qMRR9, qGL2, qGL10, qGW1, qGLWR1, and qGLWR2.1) with minor or small effect were considered as stably expressed QTL because they were simultaneously identified in two environments. In addition, we found 21 QTL probably having multiple-effect in appearance and milling quality of indica rice. Combined with the results of previous studies, we concluded that qSW5, GSE5 and GS3 play important role in affecting appearance and milling quality. This research provides valuable information for cloning QTL controlling appearance and milling quality and breeding rice with high yield and good quality by molecular techniques.

Effect of Population Structure on Prediction Accuracy of Soybean 100-Seed Weight by Genomic Selection MA Yan-Song1,2,13, LIU Zhang-Xiong1, WEN Zi-Xiang3, WEI Shu-Hong4, YANG Chun-Ming5, WANG Hui-Cai6, YANG

MA Yan-Song, LIU Zhang-Xiong, WEN Zi-Xiang, WEI Shu-Hong, YANG Chun-Ming, WANG Hui-Cai6, YANG Chun-Yan, LU Wei-Guo, XU Ran, ZHANG Wan-Hai, WU Ji-An, HU Guo-Hua, LUAN Xiao-Yan, FU

Acta Agron Sin. 2018, 44(01):  43-52.  doi:10.3724/SP.J.1006.2018.00043

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Hundred-seed weight is an important yield component and has positive relationship with soybean yield under certain conditions. The genetic gain of 100-seed weight based on traditional breeding or markers assisted-selection is limited because it is controlled by plenty of small effect genes. Genomic selection offers an approach to accelerate the soybean 100-seed weight breeding. However, the effect of population structure on soybean 100-seed weight prediction accuracy has not been elaborated. In our study 280 soybean varieties with phenotypic data evaluated in multi-location in 2008–2012 and 5361 SNPs genotype were used to explore the effect of population structure on 100-seed weight prediction accuracy. The best linear unbiased prediction of 100-seed weight of each variety was calculated according to mixed linear model. Ridge regression best linear unbiased prediction and five-fold cross validation were used to estimate the 100-seed weight prediction accuracy. Our research showed that the range of 100-seed weight, which was from –0.15 to 0.75. Hundred-seed weight prediction accuracy was affected by population structure significantly. The prediction accuracy within subset (0.24 to 0.75) was higher than that between subsets (?0.15 to +0.29). When the genetic distance between subsets increased from 0.1566 to 0.2201, the 100-seed weight prediction accuracy was decreased by 27.87%. Compared with random sampling training population, the training population composed based on genetic structure improved 100-seed weight prediction accuracy by 2.34%. In summary we are clear about the soybean 100-seed weight genomic selection accuracy and the effect of population structure on genomic selection accuracy. The genomic selection is an efficient method to improve the soybean breeding.

Cloning and Characterization of Heat Shock Transcription Factor Gene TaHsfB2d and Its Regulating Role in Thermotolerance

ZHAO Li-Na,LIU Zi-Hui,DUAN Shuo-Nan,ZHANG Yuan-Yuan,LI Guo-Liang,GUO Xiu-Lin

Acta Agron Sin. 2018, 44(01):  53-62.  doi:10.3724/SP.J.1006.2018.00053

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Heat shock transcription factors (Hsfs) are key components of heat shock signal transduction pathways involved in the activation of Hsp genes in response to heat stress in plants. There are at least 56 members in wheat Hsf family. Eleven of them belong to class B, among which 5 members belong to subclass B2. In this study, TaHsfB2d was isolated from wheat (Triticum aestivum L.) young leaves treated by heat shock at 37°C for 1.5 h using homologous cloning methods. Sequence analysis showed that the coding sequence (CDS) of TaHsfB2d was 1191 bp encoding a protein of 396 amino acids. The amino acid sequence analysis demonstrated that TaHsfB2d contained a DNA-binding domain (DBD) and nuclear localization signal (NLS). TaHsfB2d protein sequence shared 90%, 85% and 80% identities with the proteins from predicted protein of Hordeum vulgare, HsfB2c of Hordeum vulgare and Brachypodium distachyon, respectively. The qRT-PCR results showed that TaHsfB2d was expressed in multiple tissues and organs of wheat, and the relative expression level of TaHsfB2d was higher in roots at anthesis stage. TaHsfB2d was up-regulated by 37°C heat shock (HS), salicylic acid (SA) and H₂O₂ in leaves. Furthermore, HS significantly enhanced the expression of TaHsfB2d pretreated with SA or H₂O₂, the up-regulation expression of TaHsfB2d by HS was significantly inhibited by the combined treatment of 150 μmol L^–1 DPI and 20 mmol L^–1 DMTU, and the up-regulation expression by SA was completely inhibited. Through transient reporter assay with onion (Allium cepa L.) epidermal cells, we found that TaHsfB2d localized in the nuclei. Yeast overexpressing TaHsfB2d showed stronger growth potential than the control cells overexpressing pYES2 after HS at 50°C for 45 min, and overexpression of TaHsfB2d had no effect on the growth and development of yeast cells. The results revealed that TaHsfB2d perhaps plays a key role in regulating the response to HS through SA signal pathway in plants, which was dependent on existence of H₂O₂. These results will provide theoretical basis for analysing biological functions and regulating mechanism of TaHsfB2d further.

Genetic Diversity Analysis and Comprehensive Assessment of Phenotypic Traits in Introduced Potato Germplasm Resources in Arid and Semi-arid Area

YU Bin, YANG Hong-Yu,WANG Li,LIU Yu-Hui, BAI Jing-Pin, WANG Di, ZHANG Jun-Lian

Acta Agron Sin. 2018, 44(01):  63-74.  doi:10.3724/SP.J.1006.2018.00063

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In China, potato is a kind of foreign crop lacking germplasm resource，especially the varieties grown in arid and semi-arid areas. Therefore, it is an effective way to rich the germplasm resource by introducing potatoes abroad. In this study, the Shannon-Wiener’s diversity index and comprehensive score (F-value) were used to investigate the genetic diversity of 119 introduced potato clones from Peru International Potato Center about 10 phenotypic traits (emergence rate, plant height, stem diameter, leaf area, growth period, tuber number per plant, yield per plant, commodity rate, dry matter content and tuber length-width ratio). The genetic diversity of growth period was the most abundant among these phenotypic traits in 119 potato clones. Stem diameter, leaf area, growing period, tuber number per plant, yield per plant, commodity rate, dry matter content and tuber length-width ratio had significant effects on comprehensive value of phenotypic traits, and could be used to evaluate the potato germplasm resources on the drought farming. The F-value was significantly correlated with the economic characters (yield per plant, commodity rate and dry matter content), which can be used as the main evaluation index of potato germplasm resources. CIP393228.67 and CIP385561.124 in arid area and CIP304350.95, CIP392797.22, and CIP388615.22 in semi-arid area showed high and stable yield characteristics. These 119 introduced potato clones are rich in genetic diversity with good comprehensive evaluation, they could effectively complement potato germplasm resources and be beneficial to potato breeding in China.

Cloning, Location and Expression of BrSIZ1 in Brassica rapa L. subsp.rapifera ‘Tsuda’

LUO Yun, MA Xuan, GU Jun-Chen, YAN Hai-Fang*

Acta Agron Sin. 2018, 44(01):  75-81.  doi:10.3724/SP.J.1006.2018.000075

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SIZ1, a SUMO E3 ligase involved in post-translation of proteins in plant cells, plays a role in protein interaction、location and response to environmental stresses. In order to elucidate the expression profile of SIZ1 in Tsuda, cDNA of SIZ1 gene was isolated from Tsuda. This gene was named BrSIZ1 (GenBank accession number KY441465). BrSIZ1 was 2754 bp in full length cDNA and 2571 bp in full length open reading frame (ORF), encoding a peptide with 856 amino acids. A BrSIZ1-GFP expression vector was constructed to analysis the subcellular localization. BrSIZ1-GFP was localized to nucleus, indicating that BrSIZ1 may play an important role in the nucleus. Quantitative-PCR analysis showed that the BrSIZ1 was expressed meetly in leaf and secondly in young seedling and red root epidermis, showing tissue specificity. The expression of the BrSIZ1 was induced by UV-A light in the root epidermis. The transcript level of BrSIZ1 was up-regulated when treated with temperature of 4°C or 37°C in young seedling.

TILLAGE & CULTIVATION · PHYSIOLOGY & BIOCHEMISTRY

Physiological Mechanism on Drought Tolerance Enhanced by Exogenous Glucose in C₄-pepc Rice

ZHANG Jin-Fei, LI Xia, HE Ya-Fei,XIE Yin-Feng

Acta Agron Sin. 2018, 44(01):  82-94.  doi:10.3724/SP.J.1006.2018.00082

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In order to investigate the intrinsic mechanism of glucose participated in drought tolerance in plants, the effects of glucose were studied using the phosphoenolpyruvate carboxylase (C₄-pepc) rice (PC) and “Kitaake” (WT) rice lines in pot experiments and hydroponics experiments respectively. The changes of photosynthetic parameters, total soluble sugar and sugar components contents, Ca²⁺ and NO contents, hexokinase activity, transcript levels of sucrose nonfermenting-1(SNF1)-related protein kinases 3 (SnRK3s) and calcitonin B-like (CBL) of the functional leaves in rice lines were measured. Agronomic traits of the wild type (WT) and PC were recorded in the mature period. In pot experiment, the treatment of 3% glucose with drought during tillering stage had no significant effect on agronomic traits of the tested rice. During the booting stage, the plant height, panicle number per plant, filled grain number per panicle and grain yield per plant in PC were significantly higher than in WT (P < 0.05). In the hydroponics experiment with 1% glucose combined with 12% (m/v) polyethylene glycol 6000 (PEG-6000) to simulate drought stress, the photosynthetic parameters such as net photosynthetic rate (Pn), stomatal conductance (Gs) and carboxylation efficiency (Ce) significantly increased in PC than in WT. Similarly, the contents of sucrose and fructose of leaves in PC lines were significantly higher than those in WT. It was noteworthy that hexokinase (HXK) activity and the relative gene expression of CBL and SnRK3.1/SnRK3.4/SnRK3.21 in PC lines under the treatment with 1% glucose and 12% PEG were significantly lower than those under 12% PEG treatment alone. Intriguingly, the NO contents of PC under the corresponding treatments were significantly increased (P < 0.05). In addition, the photosynthetic parameters were significantly correlated with the glucose content, HXK activity and SnRK3.16 transcript level respectively in PC lines. It is suggested that PC can decrease the expression of CBL and SnRK3s gene by increasing glucose, participate the stomatal regulation via NO, maintain relative water content, keep stable photosynthetic capacity, and therefore confer drought tolerance.

Response of Membrane Fatty Acid Composition and ATPase Activity in Brassica rapa L. to Temperature in North China

FANG Yan,SUN Wan-Cang,WU Jun-Yan，LIU Zi-Gang,DONG Yun,MI Chao,MA Li,CHEN Qi,HE Hui-Li

Acta Agron Sin. 2018, 44(01):  95-104.  doi:10.3724/SP.J.1006.2018.00095

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Brassica rapa L. cultivars Longyou 7 (cold tolerant) and Tianyou 2 (cold sensitive) were used to investigate the variations of membrane fatty acid composition and ATPase activity at the temperatures of 25°C, 10°C, 2°C, and –5°C. There was the same membrane fatty acid composition in leaf and root of two cultivars under temperature stresses, with linolenic acid as the main component of unsaturated fatty acid in leaf, but linoleic acid in root. With decrease of treatment temperatures, the content of unsaturated fatty acid in leaf initially decreased at 10°Cand 2°C, then increased at –5°C.The content of unsaturated fatty acid rose up gradually in root of Longyou 7, but reduced in Tianyou 2. At low temperature(2°C, –5°C), the ratio of U/S and IUFA in Longyou 7 were significantly higher than those in Tianyou 2.The activity of ATPase was gradually increased in Longyou 7 than in Tianyou 2. It suggested there are differences in membrane lipids in response to temperature for two winter rapeseed cultivars, the increase of unsaturated fatty acid content and ATPase activity is the main cause sustaining winter rapeseed cultivars to overwinter.

Effects of Rotational Tillage on Nutrient Storage Capacity and Cd Content in Tilth Soil of Double-cropping Rice Region

TANG Wen-Guang, XIAO Xiao-Ping, ZHANG Hai-Lin, HUANG Gui-Lin, TANG Hai-Ming, LI Chao, LIU Sheng-Li,WANG Ke

Acta Agron Sin. 2018, 44(01):  105-114.  doi:10.3724/SP.J.1006.2018.00105

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It is important significance to construct and improve the quality paddy layer, promote the sustainable grain yield by studies on the soil structure, nutrient and heavy metal contents in double cropping paddy fields under different tillage measures. The long-term located experiments with five tillage treatments including no tillage (NT-NT), conventional tillage (CT-CT), rotary tillage (RT-RT), conventional tillage-no tillage (CT-NT), and rotary tillage-no tillage (RT-NT) were conducted in double-cropping rice paddy from 2005. The tilth soil depth, soil bulk density, soil carbon, nitrogen, phosphorus, potassium, nutrients pool and heavy metal Cd content in different tillage treatments were analyzed. The results showed that NT-NT had higher soil bulk density, however, RT-RT, CT-CT, CT-NT and RT-NT reduced it to a ideal interval. Soil organic carbon, active organic carbon, total nitrogen, available nitrogen, available phosphorus, available potassium and Cd content of CT-NT and RT-NT in 0-5 cm topsoil were significantly lower than those of NT-NT, showing that nutrients and Cd were aggregated to the surface layer of soil and decreased with increasing frequency of farming. Soil nutrient contents of CT-NT and RT-NT were significantly higher than those of NT-NT in 5?10 cm topsoil, but lower than those of RT-RT, CT-CT in 10?20 cm topsoil, demonstrating that the rotational tillage was beneficial to accumulate nutrients, especially in middle soil layer. The order of topsoil thickness, total available nutrients pool and Cd content showed RT-RT>CT-CT>CT-NT, RT-NT>NT-NT, therefore, topsoil layers would shallow, total available nutrients pool, soil total Cd and available Cd would shrink gradually with reducing tillage frequency. Our results indicated that long-term with no tillage, conventional tillage or rotary tillage all have certain drawbacks, no-tillage reduces soil Cd content and soil nutrients pool, conventional tillage or rotary tillage increases soil nutrients pools and soil Cd content. Therefore, the reasonable soil rotational tillage could improve soil structure, promote soil nutrient accumulation, and increase soil nutrients pool, reduce soil Cd content and improve the soil environment.

Effects of Conventional Urea Combined with Slow-release Urea Application on Phosphorus Uptake, Translocation and Distribution in Mechanically Transplanted Rice with Different Plant Spacings

WANG Hai-Yue,JIANG Ming-Jin,SUN Yong-Jian*,GUO Chang-Chun,YIN Yao-Zhu,HE Yan,YAN Tian-Rong,YANG Zhi-Yuan,XU Hui,MA Jun

Acta Agron Sin. 2018, 44(01):  115-125.  doi:10.3724/SP.J.1006.2018.00115

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Spilt-plot design with plant spacing (16, 18, and 20 cm with 30 cm-row spacing, respectively) as main plot and slow-release urea application rate (36, 66, 96, and 126 kg ha^–1) combined with 54 kg ha^–1 of conventional urea as subplot was arranged. In the present study P accumulated amount of rice plant at the main growth stages, P absorption and P uptake rate during various growth stages, P translocation amount of stem-sheath, and the P translocation rate and P conversion rate of leaf at the grain-filling stage were significantly affected by the slow-release urea application rate. Ninety-six kg ha^–1 of slow-release urea combined with 54 kg ha^–1 of conventional urea significantly improved P uptake, translocation and redistribution under the plant spacing of 18 cm, which is a best cultural practices for mechanically transplanted rice with the highest yield of 11 463.8 kg ha^–1 in Southwest. A relatively high plant density (208.4 thousand plants per hectare) was established when the plant spacing was 16 cm. In addition, a higher total P accumulation amount of plant was achieved under 126 kg ha^–1 of slow-release urea, resulting in improved P redistribution and high grain yield. The relatively lower plant density (166.7 thousand plants per hectare) was due to the larger plant spacing under the conditions of 20 cm-plant spacing and 126 kg ha^–1 of slow-release urea. Although P accumulated amount decreased, P translocation from stem-sheath and leaf to panicle increased, resulting in increased P accumulation in panicle and grain yield. Furthermore, a relatively high correlation between P translocation amount (especially the P translocation amount of stem-sheath from heading stage to maturity stage) and grain yield (r = 0.72**) under a certain plant spacing combined with the slow-release urea, could be beneficial to improving grain yield.

Effects of Drought Stress at Different Growth Stages on Endogenous Hormones and Its Relationship with Storage Root Yield in Sweetpotato

ZHANG Hai-Yan,DUAN Wen-Xue,XIE Bei-Tao,DONG Shun-Xu,WANG Bao-Qing,SHI Chun-Yu,ZHANG Li-Ming

Acta Agron Sin. 2018, 44(01):  126-136. 

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Field experiments were conducted under a rain exclusion shelter using two sweetpotato (Ipomoea batatas (L.) Lam) cultivars (Jishu 21, drought-tolerant, and Jizishu 1, drought-sensitive) with four drought stress treatments during the whole growth period (DS), root branching stage (DS1), the intermediate stage (storage root initiation) (DS2), and the final stage (storage root bulking) (DS3). A sep-arate well watered experiment was as a control (WW). Compared with the control, the fresh and dry weight of two cultivars in all treatments decreased significantly in three years. The dry weight of DS treatment had the highest decrease, with an average of 44.62% and 56.21% for Jishu 21 and Jizishu 1, respectively. The impact of DS1 was the second, with an average decrease of 32.03% and 44.03% for Jishu 21 and Jizishu 1, respectively, followed by DS2, with an average decrease of 30.41% and 39.39%, respectively. The impact of DS3 was the lowest, with an average decrease of 13.66% and 17.88%, respectively. The impact of drought stress on dry weight of Jishu 21 was lower than that of Jizishu 1. The drought stress significantly inhibited the growth of aboveground part, and the formation and bulking of storage roots. Number of leaves per plant, vine length, dry weight of aboveground and underground parts, and starch content were decreased under drought stress, compared with the control. DS had the highest impact, followed by DS1 and DS2; DS3 had the lowest impact. GA, IAA, and ZR contents in leaves and roots of both cultivars decreased, while ABA content increased. There were significant positive correlations between dry weight of aboveground part and GA, IAA, and ZR contents in leaves, dry weight of underground part and GA, IAA, and ZR contents in storage roots. However, ABA content in leaves and storage roots was negatively correlated with dry weight of aboveground part and underground part, respectively. In summary, drought stress applied during different growth stages reduced the yield of fresh and dry roots. The earlier the application of drought stress, the greater influence on levels of endogenous hormones and storage root yields. Root branching stage of sweetpotato is most sensitive to drought stress.

RESEARCH NOTES

Suitable Maturity Period and Accumulated Temperature of Summer Maize in Wheat–maize Double Cropping System

REN Bai-Zhao**, GAO Fei**, WEI Yu-Jun, DONG Shu-Ting, ZHAO Bin, LIU Peng,ZHANG Ji-Wang*

Acta Agron Sin. 2018, 44(01):  137-143.  doi:10.3724/SP.J.1006.2018.00137

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Five summer maize hybrids Zhengdan 958 (ZD958), Xianyu 335 (XY335), Denghai 605 (DH605), Denghai 618 (DH618), and Denghai 661 (DH661) were used with treatments of four seeding dates on 21 May, 31 May, 10 June, and 20 June to explore the accumulated temperature and growth period of summer maize in wheat–maize double cropping system. There was no significant effect of seeding dates on the required accumulated temperature making physiological maturity, which mainly depended on the nature of varieties. DH618, XY335, ZD958, DH605, and DH661 had the growth period of 110, 112, 116, 116, and 121 d, and required accumulated temperature of 2800, 2880, 2945, 2950, and 3025°C d, respectively. In wheat–maize double cropping system, the largest possible growth period was 107120 d (from 15 June to 15 October), the accumulated temperature was about 2800°C d, which was difficult to meet the needs of production for main maize hybrids. The double late-cropping patterns were conducive to increasing grain yield. However, the growth period (about 120 d) of summer maize hybrids planted most popularly was too long to reach full maturity, resulting in serious grain damage when harvest by machinery. In conclusion, at present, the largest possible growth period and accumulated temperature are not possible to satisfy the needs of the production of main maize hybrids in wheat–maize double cropping system, even timely late harvest is still difficult to complete physiological maturity. Therefore, we need early-maturing (growth period ≤ 107 d) and high-yielding summer maize hybrids in the Yellew-Huaihe-Haihe Rivers Plain.

Pedigree Construction and SSR Analysis of Broomcorn Millet Mutant by ¹²C⁶⁺ Ion Beam Irradiation

LIU Tian-Peng, DONG Kong-Jun, DONG Xi-Cun, HE Ji-Hong, LIU Min-Xuan,REN Rui-Yu,ZHANG Lei,YANG Tian-Yu

Acta Agron Sin. 2018, 44(01):  144-156.  doi:10.3724/SP.J.1006.2018.00144

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To construct mutant library of physical mutation in broomcorn millet, applied five doses of ¹²C⁶⁺ ion beam at 50, 100, 150, 200, and 250 Gy to irradiate seed of Longmi 7 and Jinshu 9, and constructed two populations (M₅) consisting of 52 and 79 lines respectively with mixed pedigree method and system cluster. The field text showed that the emergence rate of M₁ decreased significantly with increasing ¹²C⁶⁺ dose, half lethal dose for M₁ from Longmi 7 and Jinshu 9 were 150 Gy and 100 Gy. M₄ at 100, 150 Gy produce a most abundant mutants. M₅ and M₆ Phenotypes were more stable than M₄, and plant height, yield traits, plant color and seed color showed significant difference. Nine M₆ lines from Longmi 7 and 11 M₆ lines from Jinshu 9 were detected with six pairs of SSR primer, compared with the parents, loci variant genotype number were 1-2 and 1-4, respectively, showing abundant genetic diversity in mutant populations.