Table of Content

12 August 2020, Volume 46 Issue 8

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CROP GENETICS & BREEDING·GERMPLASM RESOURCES·MOLECULAR GENETICS

A large-scale screening of maize germplasm for resistance to multiple diseases in multi-plot demonstration for several years under natural condition

DUAN Can-Xing,DONG Huai-Yu,LI Xiao,LI Hong,LI Chun-Hui,SUN Su-Li,ZHU Zhen-Dong,WANG Xiao-Ming

Acta Agronomica Sinica. 2020, 46(8):  1135-1145.  doi:10.3724/SP.J.1006.2020.03003

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Disease is a major factor affecting maize production. The utilization of resistant cultivars is the most economical, safe, and effective method for controlling maize diseases. This research was finally conducted using 2000 maize germplasm accessions with extensive sources and rich genetic background to identify and evaluate the resistance to multiple diseases in multi-plot demonstration for several years under natural condition during 2016-2019. Nine diseases, including southern corn leaf blight, stalk rot, common smut, Curvularia leaf spot, southern rust, maize rough dwarf, northern corn leaf blight, gray leaf spot and head smut were investigated and evaluated in non-inoculated fields. The experimental data at 10 different sites from 2016 to 2019 showed that resistance identification under natural conditions was sensitive to environmental factors, with distinct differences among years and regions. The incidence of southern corn leaf blight was severe at multiple sites over these years and 11 maize accessions with stable resistance were screened out. Stalk rot, northern corn leaf blight, and gray leaf spot were relatively serious at several sites in four years, and 440, 356, and 423 resistant germplasm were screened out from 2000 accessions, respectively. These integrated data had considerable reference values. Curvularia leaf spot, common smut, and maize rough dwarf occurred heavily at only one plot while southern rust and head smut were not serious at all experimental sites, which should be studied further more. All in all, some maize germplasm resources with stable resistance to diverse diseases under different environments were screened out, such as JN15, 953, Shen 977, 68122, K21, SC24-1, 17MC7211, 17MC7223, Zheng 591, 161191, and so on. These results provide a significant reference for utilization and selection of germplasm for further precise inoculated identification.

Mechanism of BnaBZR1 and BnaPIF4 regulating photosynthetic efficiency in oilseed rape (Brassica napus L.) under poor light

FENG Tao,TAN Hui,GUAN Mei,GUAN Chun-Yun

Acta Agronomica Sinica. 2020, 46(8):  1146-1156.  doi:10.3724/SP.J.1006.2020.94198

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Double-low seed rape B. napus L. varieties XY881 and XY883 screened from the same parent Xiangyou 15 have significant differences in seed oil content, photosynthetic efficiency, and poor light sensitivity. Brassinazole-resistant 1 (BnaBZR1) and phytochrome interacting factor 4 (BnaPIF4) genes were cloned from XY881 and XY883, respectively, and their sequence structure, gene expression and gene function were analyzed. There were structural mutations in the BnaBZR1 and BnaPIF4 of XY883, causing differences in gene expression and regulation. The promoter of BnaBZR1 in XY883 had a 124 bp A/T-rich insertion mutation, and XY883 had a higher expression of BnaBZR1 than XY881, and fewer expression changes under low light and 2,4-epibrassinolide(2,4-BL) treatment. Splicing differences of BnaPIF4 in the 5'-UTR region were found in XY883, and the alternative splicing resulted in three 5'-UTRs of 424 bp (U01), 239 bp (U02), and 332 bp (U03). Under the induction of low light and 2,4-BL treatments the changed of three alternative spliced BnaPIF4 transcripts in XY883 had significant differences. The three 5'-UTRs combined with the CDS of BnaPIF4 were transformed into Arabidopsis thaliana. There was no significant difference in BnaPIF4 gene expression, but a significant difference in protein expression, indicating that the 5'-UTR mutation of BnaPIF4 affects protein synthesis. Transgenic BnaPIF4 Arabidopsis thaliana showed a phenotype with increased plant height, narrow leaves, and decreased photosynthesis. Co-transformation whit BnaBZR1 could attenuate the decrease in photosynthesis caused by BnaPIF4. The effects of BnaPIF4 and BnaBZR1 genes on Brassica napus L. were similar to those on Arabidopsis thaliana, while the phenotype was not as obvious as that of Arabidopsis thaliana, suggesting that BnaPIF4 is a negative regulator of photosynthesis in rapeseed, and BnaBZR1 can antagonize the negative regulation of photosynthesis by BnaPIF4, while is consistent with the regulation pattern and photosynthetic phenotype of the two genes in XY881 and XY883.

CRISPR/Cas9-mediated editing of the thermo-sensitive genic male-sterile gene TMS5 in rice

CHEN Ri-Rong,ZHOU Yan-Biao,WANG Dai-Jun,ZHAO Xin-Hui,TANG Xiao-Dan,XU Shi-Chong,TANG Qian-Ying,FU Xing-Xue,WANG Kai,LIU Xuan-Ming,YANG Yuan-Zhu

Acta Agronomica Sinica. 2020, 46(8):  1157-1165.  doi:10.3724/SP.J.1006.2020.92059

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Thermo-sensitive genic male-sterile (TGMS) gene tms5 is most widely used in the two-line hybrid breeding system in China. To develop novel rice thermo-sensitive male sterile lines, we knocked out the TMS5 genes of six elite japonica and four indica rice varieties by using CRISPR/Cas9 gene editing technology. By analyzing the critical sterility-inducing temperature (CIST) of the newly TGMS lines, it was found that the CIST of japonica TGMS lines ZG75S, CYGS, YG0618S, ZG07S, T0361S, and 7679S were between 28°C and 32°C, the CIST of indica TGMS lines 2537S, 6150S and 6379S were between 24°C and 28°C, and the CIST of indica TGMS line 1109S was lower than 23.5°C. These results indicated that the CIST of tms5 mutant from different genetic background materials was different. The TGMS lines with lower CIST could be obtained by knocking out the TMS5 from different genetic background materials. A hybrid rice combination 1109S/8048 had high quality and high yield. The yield of 1109S/8048 was 13.1% higher than that of Fengliangyou 4. The creation of the TGMS 1109S and the high-yield cross combination 1109S/8048 provides a new way for high-yield breeding.

Optimization of test location number and replicate frequency in regional winter wheat variety trials in northern winter wheat region in China

ZHANG Yi,XU Nai-Yin,GUO Li-Lei,YANG Zi-Guang,ZHANG Xiao-Qing,YANG Xiao-Ni

Acta Agronomica Sinica. 2020, 46(8):  1166-1173.  doi:10.3724/SP.J.1006.2020.91069

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The rational allocation of the replicate frequency and test location number in regional crop trials are highly beneficial to the enhancement of both trial cost efficiency and new cultivar selection efficiency. The rationality of test location number and replicate frequency for national wheat regional trials in the Northern winter wheat region (NWWR) in China was evaluated by using historical experimental datasets during the last 10 years according to the dynamics of trial heritability and noise-signal quotient (Q) with the increase of test locations and replicates within trials in 2010-2019, proposing an optimal design scheme of the replicate frequency and test location number for the wheat planting region. The result indicated three replicates at current achieve 0.87 of the averaged within-trial heritability of single-trials in NWWR, and only 1.4 times of replicates on average was needed to achieve 0.75 of within-trial heritability, so three replicates were obviously sufficient to maintain enough test accuracy. The needed test location number to achieve 0.75 of cross-trial heritability was estimated as 11 for the irrigated group and 13 for the rainfed group in the one-year multi-locational trials in NWWR, while in the current wheat trials that was about 11 and 8 effective test locations, achieving a heritability level of 0.75 and 0.60, respectively. The irrigated group was exactly meet the trial accuracy requirement (H = 0.75), while the rainfed group was somewhat insufficient. Considering the importance of the regional wheat trials in recommending new varieties for registration and production, and the possible trial cancellation due to various abnormalities, the practical management should set a heritability level around 0.75, and maintain three replicates, with around 11 test locations for the irrigated group, and 13 locations for the rain-fed group. In order to increase heritability to the level of 0.80, about 16 test locations should be required.

Detection of QTLs controlling cold tolerance at bud bursting stage by using a high-density SNP linkage map in japonica rice

JIANG Shu-Kun,WANG Li-Zhi,YANG Xian-Li,LI Bo,MU Wei-Jie,DONG Shi-Chen,CHE Wei-Cai,LI Zhong-Jie,CHI Li-Yong,LI Ming-Xian,ZHANG Xi-Juan,JIANG Hui,LI Rui,ZHAO Qian,LI Wen-Hua

Acta Agronomica Sinica. 2020, 46(8):  1174-1184.  doi:10.3724/SP.J.1006.2020.92066

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Direct seeded rice (DSR) has received much attention because of its time- and labour-saving and low-input demand. However, the long-term cultivation method of seedling-transplantation has led to loss of some low-temperature-tolerant genes expressed at the bud stage. It has made many currently popular rice varieties unsuitable for direct seeding production. Therefore, it is important to identify cold-tolerance genes at the bud stage and to provide genes for subsequent molecular marker assistant breeding. In this study, we used a recombinant inbred line population constructed by cross of Lijiangxintuanheigu (LTH) and Shennong 265 (SN265) and its linkage map containing 2818 markers to detect cold tolerance QTLs at the bud stage. A total of five QTLs were detected on rice chromosomes 1, 3, 9, and 11. All the cold tolerance alleles were from the cold-tolerant parent LTH. The LOD values of these QTLs ranged from 3.05 to 24.01, and the phenotypic variations ranged from 8.0% to 53.5%. Among them, the major QTL qCTB11b was located in a 790 kb interval of 21.24 Mb to 22.03 Mb on the long arm of chromosome 11. Subsequently, the “selective mapping” strategy was used for QTL verification and pyramiding effect analysis. Genetic improvement of cold tolerance at the bud stage would be achieved through pyramiding more QTLs. These results not only promote people’s understanding of the genetic basis for cold tolerance at the bud stage in rice but also provide theoretical basis and technical guidance for genetic improvement of DSR varieties.

Functional identification of maize cation/proton antiporter ZmNHX7

ZHANG Ling-Xiao,JIAO Zhen-Zhen,BU Hua-Hu,WANG Yi-Ru,LI Jian,ZHENG Jun

Acta Agronomica Sinica. 2020, 46(8):  1185-1194.  doi:10.3724/SP.J.1006.2020.93062

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Plant cation/proton antiporters can maintain intracellular ion homeostasis and resist ion toxicity. In this study, a gene encoding a maize cation/proton antiporter was cloned and named as ZmNHX7. The coding sequence of ZmNHX7 was 3411 bp, encoding a protein with 1136 amino acids. ZmNHX7 is ubiquitously expressed in various tissues of maize, With higher expression level in roots and stems at the V7 stage. The expression of ZmNHX7 was induced by NaCl and LiCl stresses. In phylogenetic tree ZmNHX7 showed a close relation with AtNHX7 and AtNHX8 of Arabidopsis thaliana. ZmNHX7 was located in cell membrane and nuclear membrane by confocal laser scanning microscopy analysis of the lower epidermis of tobacco leaves. When ZmNHX7 gene was transformed into the Arabidopsis thaliana T-DNA insertion mutant nhx8, the transgenic complementary lines could restore the tolerance of nhx8 to Li⁺. These results indicate that ZmNHX7 encodes a plasma membrane cation/proton antiporter of maize, which plays an important role in reducing the toxicity of Li⁺ to plants and maintaining intracellular ion homeostasis.

Discovery and analysis of NBS-LRR gene family in sweet potato genome

HUANG Xiao-Fang,BI Chu-Yun,SHI Yuan-Yuan,HU Yun-Zhuo,ZHOU Li-Xiang,LIANG Cai-Xiao,HUANG Bi-Fang,XU Ming,LIN Shi-Qiang,CHEN Xuan-Yang

Acta Agronomica Sinica. 2020, 46(8):  1195-1207.  doi:10.3724/SP.J.1006.2020.94163

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The NBS-LRR gene families possess the most abundant resistance genes in plants. Members of the NBS-LRR gene families contain nucleotide-binding site (NBS) and leucine-leucine repeat (LRR) domains. The genome of sweet potato (Ipomoea batatas) cultivar has been sequenced but the genes have not been annotated yet. In this study, we predicted the exons of sweet potato genome and obtained the proteins sequences, which were then used to identify and analyze genes of NBS-LRR family. There were 379 genes within NBS-LRR family, amounting to 0.212% of the total genes of sweet potato. The number of the N type, NL type, CNL type, TNL type and PN type was 120, 103, 133, 22, and 1, respectively. All of the chromosomes had NBS-LRR family genes but varied in number and 60.9% of them were clustered. NBS-LRR genes included 15 conservative domains and the genes were conservative within N terminal domain. The results provide references for further studies on the function of NBS-LRR family genes and resistance breeding of sweet potato.

Identification and selection for anti-browning potato varieties (lines)

CHEN Ming-Jun,SHU Qi-Qiong,XU Jian-Fei,LUO Xiao-Bo,LEI Zun-Guo,JIN Li-Ping,LI Fei

Acta Agronomica Sinica. 2020, 46(8):  1208-1216.  doi:10.3724/SP.J.1006.2020.94183

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Potato tuber is easy to be damaged and caused browning, which will affect its nutrition, sense quality and safety. Different potato varieties have different resistances to browning. In this study, 27 different potato germplasm resources,were used to measure four indexes including polyphenol oxidase (PPO), browning degree (BD), browning index and after cooking darkening (ACD), for indentifying and selecting anti-browning potato varieties (lines). The 27 materials could be divided into four groups. High anti-browning, group including 09306-82 and 13041-52 had high resistance to browning. Anti-browning group, included Yanshu 4, Q 8, 12-1, Chunshu 3, 19-1, 14018-142, Atlantic, Longshu 12, Weiyu 5, Lishu 6, Chunshu 5, and Zaodabai, had some obvious deficiencies in the related anti-browning indicators. Medium anti-browning group, including 09001-136, Zhongshu 5, Longshu 4, Dongnong 310, Qingshu 9, 15-1, Yunshu 505, BF006, Minshu 1, and Qianyu 8, had poor resistance to browning. Easy browning group, containing Chunshu 6 and Favorita, had very weak resistance to browning. The selected varieties (lines) with very high or high resistance to browning can be used in potato breeding for browning resistance , providing variety support for potato processing industry, and the easy browning materials can be used to study the browning mechanism of potato.

Effects of OsRPK1 gene overexpression and RNAi on the salt-tolerance at seedling stage in rice

LI Jing-Lan,CHEN Xin-Xin,SHI Cui-Cui,LIU Fang-Hui,SUN Jing,GE Rong-Chao

Acta Agronomica Sinica. 2020, 46(8):  1217-1224.  doi:10.3724/SP.J.1006.2020.92060

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OsRPK1 is a leucine-rich repeat receptor-like protein kinase (LRR-RLK) gene in rice, and its expression level decreases evidently after temporarily increasing under salt stress. Previous studies have shown that the overexpression of OsRPK1 can significantly reduce the abiotic stress tolerance of Arabidopsis. In this study, OsRPK1 gene was overexpressed and RNA interfered in rice. The salt tolerance of the 35S:OsRPK1 rice seedlings was significantly lower than that of the control plants. The OsRPK1-RNAi rice seedlings exhibited higher salt tolerance than the wild-type plants. The proline content of OsRPK1 overexpressed plants was lower than that of the wild type, MDA content and relative conductivity were significantly higher than those of the wild type, while the proline content of OsRPK1-RNAi rice plants was significantly higher than those of wild type, MDA content and relative conductivity were significantly lower than those of wild type. The results of this study indicate that OsRPK1 plays an important role in salt tolerance of rice. The changes of proline content and the damage degree of cytoplasmic membrane may be the internal reasons for the salt-tolerance variations of the transgenic rice lines. This study lays a foundation for further elucidating the resistance mechanism of OsRPK1 gene, which is very important for cultivating salt-tolerance rice by adjusting the expression of OsRPK1 gene.

TILLAGE & CULTIVATION·PHYSIOLOGY & BIOCHEMISTRY

Critical nitrogen dilution curves and nitrogen nutrition diagnosis of spring maize under different precipitation patterns in Weibei dryland

LIU Peng-Zhao,SHI Zu-Jiao,NING Fang,WANG Rui,WANG Xiao-Li,LI Jun

Acta Agronomica Sinica. 2020, 46(8):  1225-1237.  doi:10.3724/SP.J.1006.2020.03007

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The excessive nitrogen (N) applications, large rainfall variations and poor water-nitrogen couplings are main problems to efficient nitrogen fertilizer uses in spring maize production of Weibei dryland. Critical nitrogen dilution curves under different rainfall scenarios in Weibei dryland were constructed in this study to analyze the feasibilities of diagnosing and evaluating nitrogen nutritional conditions in terms of nitrogen nutrition index (NNI), which would provide a theoretical basis for reasonable nitrogen fertilizations application of dryland maize in response to different rainfalls. The experiment design using Zhengdan 958 (ZD958) and Shaandan 8806 (SD8806) as tested materials was five treatments level, N applied at 0(N0), 75(N1), 150(N2), 270(N3), and 360(N4) kg hm^-2 in 2016 and 2017, and at 0(N0), 90(N0), 180(N2), 270(N3), and 360(N4) kg hm^-2 in 2018 and 2019, respectively. It was rainy at the ear stage and dry at the grain stage in 2016 and 2018, whereas dry at the ear stage and rainy at the grain stage in 2017 and 2019. Critical nitrogen dilution curve models for spring maize with two precipitation patterns were constructed and verified using the data collected in the four-year position nitrogen fertilization experiment. The results showed that: (1) increased nitrogen fertilizer application significantly increased aboveground biomass and plant N concentrations, and there were significantly different among different treatments. Both critical nitrogen concentrations (N_c) and aboveground biomass conformed the exponential relations with the two precipitation patterns, but there were differences between the parameters of the models for these relations (a. Rainy at the ear stage: N_c = 35.98DM^-0.35; b. Dry at the ear stage: N_c = 35.04DM^-0.23). The relatively stable model had a linear correlation between the fitted and actual plant N concentrations, which shown that the RMSE and n-RMSE were 1.03 and 5.75% at the ear stage over the rainy years and 1.53 and 6.78% at the ear stage in the dry years, respectively. (2) at the different growth stages, NNI were increased with the increased application, and there were differences in the optimal nitrogen application under different precipitation conditions. The optimum N rate in the form of basal fertilizers was 150-180 kg hm^-2, and in the form of top dressing fertilizers was 45-75 kg hm^-2 at the ear stage in the rainy years. The nitrogen nutrition index (NNI) was significantly correlated with relative nitrogen uptake (RN_upt), as were relative aboveground biomass (RDW) and relative yield (RY). When the NNI was 1.02 at the ear stage in the rainy years, the maximum RY was 0.95; and when the NNI was 1.08 at the ear stage in the dry years, the maximum RY was 0.92. The critical nitrogen dilution curve model and nitrogen nutrition index model constructed in this study were able to accurately predict nitrogen nutrition conditions from jointing stage to maturity stage under the two precipitation patterns of spring maize. They would provide an important guidance for nitrogen diagnosis and fertilization application in maize growing stage.

Tillering characteristics and its relationships with population productivity of japonica rice Nanjing 9108 under salinity stress

WEI Huan-He,GE Jia-Lin,ZHANG Xu-Bin,MENG Tian-Yao,LU Yu,LI Xin-Yue,TAO Yuan,DING En-Hao,CHEN Ying-Long,DAI Qi-Gen

Acta Agronomica Sinica. 2020, 46(8):  1238-1247.  doi:10.3724/SP.J.1006.2020.02001

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This study was conducted to clarify the characteristics for occurrence of rice tillers, its dominant leaf positions, and panicle formation under salinity stress, and to provide a basis for the rational utilization and regulation of rice tillers for high-yield cultivation methods in tidal flat area. Conventional japonica rice Nanjing 9108 was used with three salinity treatments, namely, Control (CK, 0 salt concentration), Medium-salinity stress (MS, 0.15% salt concentration), and high-salinity stress (HS, 0.3% salt concentration) to compare the tillering and panicle formation characteristics and its contribution to population yield under salinity stress. As a result, the average yields (t hm^-2) of CK, MS, and HS were 9.7, 7.4, and 4.2 across two years, respectively; the number of panicles, spikelets per panicle, percentage of filled grains, and 1000-grain weight in MS and HS treatments were significantly lower than those in CK. Compared with CK, the number of tillers at jointing, heading, and maturity and percentage of productive tillers in MS and HS treatments were decreased. For CK, the primary tillers emerged from the 3rd leaf to 7th leaf on the main stem, with higher tiller emerging rate and more panicles from the 4th leaf to 6th leaf among them, and secondary tillers mainly emerged and earbeared from 1/4 and 1/5 tiller position; as for MS and HS, tillers are mainly primary ones emerging from the 4th to 6th leaf as the dominant position for the tiller occurrence and earbearing. The mean value of panicle length, total grains, grain density, and number of grains and its total grains on the primary and secondary branches in MS and HS treatments were both lower than those in CK. Our results suggest that, salinity stress caused lower number of panicles per plant, inferior growth of individuals and populations, smaller panicle types, and finally lower grain yield.

Canopy SIF synergize with total spectral reflectance optimized by the MDBPSO algorithm to monitor wheat stripe rust

BAI Zong-Fan,JING Xia,ZHANG Teng,DONG Ying-Ying

Acta Agronomica Sinica. 2020, 46(8):  1248-1257.  doi:10.3724/SP.J.1006.2020.01004

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In order to extract the characteristic parameters sensitive to wheat stripe rust from total spectral reflectance and improve the operation efficiency and estimation accuracy of the wheat stripe rust remote sensing detection model, this paper improved the traditional discrete binary particle swarm optimization (DBPSO) algorithm from two aspects: inertia weight and particle update method. The modified discrete binary particle swarm optimization (MDBPSO) algorithm was used to select the characteristic parameters for the severity of wheat stripe rust from the total spectral reflectance. The selected characteristic variables were combined with canopy solar-induced chlorophyll fluorescence (SIF) data as independent variables to construct wheat stripe rust estimation model. Random forest (RF) algorithm and back propagation (BP) neural network algorithm were used as model construction method to compare and analyze the accuracy of the feature parameter construction model extracted by the correlation coefficient (CC) analysis method and the DBPSO algorithm. The MDBPSO algorithm had faster convergence speed and higher optimization accuracy than the DBPSO algorithm. The number of iterations before and after the improvement was reduced from 395 to 156. The optimal fitness function (OFV) value decreased from 0.145 to 0.127. When the MDBPSO algorithm was used to select feature variables, the accuracy of the models constructed by the two methods of RF and BP neural networks was higher than that by CC analysis and DBPSO. The validation set determination coefficient (R²_V) between the predicted disease index (DI) value and the measured DI value of the RF algorithm was 9% and 3% higher than that of the CC analysis method and the DBPSO algorithm, the validation set root mean square error (RMSE_V) was reduced by 28% and 11%, respectively. The R²_V between the predicted disease index (DI) value and the measured DI value of the BP neural network algorithm was 13% and 6% higher than that of the CC analysis method and DBPSO algorithm, respectively, and the RMSE_V was reduced by 21% and 10% respectively. The MDBPSO algorithm can improve the remote sensing detection accuracy of wheat stripe rust. Among the three feature selection algorithms of MDBPSO, DBPSO, and CC analysis, the accuracy of the model constructed by the RF algorithm was higher than that by the BP neural network algorithm. The R²_V between the predicted DI value and the measured DI value of the RF model was at least 7% higher than that of BP neural network algorithm, with an average increase of 9%; RMSE_V had reduced by at least 15%, with an average reduction of 20%. The MDBPSO-RF model for wheat stripe rust remote sensing detection constructed by RF method using the characteristic parameters selected by the MDBPSO algorithm as independent variables is an appropriate model for wheat stripe rust remote sensing detection. The research results provide new ideas for further realizing large-area high-precision remote sensing monitoring of crop health.

The study of carbon budget on field-tobacco ecosystem

LIU Qing-Li,JIANG Yu-Zhou,ZOU Yan,ZHANG Yun-Gui,ZHANG Heng,SHI Jun-Xiong,LI Zhi-Hong

Acta Agronomica Sinica. 2020, 46(8):  1258-1265.  doi:10.3724/SP.J.1006.2020.94164

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The carbon balance of the agricultural ecosystem is of great significance for the assessment of the source and sink of the terrestrial ecosystem. In view of the particularity of the growth and management of flue-cured tobacco, the carbon budget of the field-tobacco ecosystem was studied in order to provide the basis for the improvement of tobacco field management and the estimation of agricultural carbon sink. In this study, the carbon budget was observed with single application of chemical fertilizer using the long-term positioning test station for three years from 2015 to 2017. The results showed that the average cumulative biomass of flue-cured tobacco, the average carbon content of tobacco plant, and the cumulative carbon sequestration were (5832.10 ± 537.32) kg hm^-2, (42.14 ± 0.05)%, and (2459.25 ± 233.78) kg hm^-2, respectively. The ratio of root carbon to plant carbon was higher, with an average of 24.94%. The wet deposition carbon and the dry deposition carbon were 115.32 kg hm^-2 and 6.54 kg hm^-2 respectively, both accounting for 20.01% of root carbon amount. The total carbon output in growing season was 2464.98 kg hm^-2, in which the CO₂ emission expenditure accounts for 98.99%, the runoff carbon expenditure 0.76%, and the leaching carbon accounts for 0.25%. The flue-cured tobacco ecosystem was a weak carbon sink to the atmosphere, with a carbon sink of 116.13 kg hm^-2. The total amount of carbon sequestration in flue-cured tobacco was relatively lower, whereas its root system had a relatively higher contribution to soil carbon.

Estimation of cotton Car/Chla ratio by hyperspectral vegetation indices and partial least square regression

YI Qiu-Xiang,LIU Ying,CHANG Cun,ZHONG Rui-Sen

Acta Agronomica Sinica. 2020, 46(8):  1266-1274.  doi:10.3724/SP.J.1006.2020.94157

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Estimating the ratio between carotenoid to chlorophyll a (Car/Chla) provides an additional avenue for the assessment of physiology and phenology of plant growth and development. With the aim of assessing cotton Car/Chla ratio from hyperspectral reflectance, a wide range of carotenoid (Car) and chlorophyll a concentrations, and leaf and canopy reflectance at cotton different growth stages were measured. The performance of a variety of Car/Chla ratio related vegetation indices and partial least square regression (PLSR) for Car/Chla ratio and Car estimation were tested. Among all tested vegetation indices, PRI (Photochemical Reflectance Index) and linear PRI models had the most significant correlations with Car/Chla ratio and Car, and could accurately estimate, Car/Chla ratio (R²_{leaf level} = 0.69 and R²_{canopy level} = 0.67) and Car concentration (R²_{leaf level} = 0.44 and R²_{canopy level} = 0.36). The best estimation of the Car/Chla ratio and Car was provided by PLSR models with R² > 0.80 between the estimated and measured value for Car/Chla ratio and R²= 0.74 for Car. Both reflectance indices and PLSR method were more successful for the estimation of Car/Chla ratio than for that of Car concentration, indicating the promising potential of Car/Chla ratio as a powerful indicator using for plant status monitoring by remote sensing. Besides, accuracy test of models using validation dataset highlighted the remarkable performance of PLSR for Car/Chla (R²_{leaf level} = 0.87 and R²_{canopy level} = 0.84) and Car (R²_{leaf level} = 0.73 and R²_{canopy level} = 0.74) estimated by hyperspectral reflectance at both the leaf and canopy levels. The results further prove the remarkable performance of hyperspectral reflectance for the estimation of Car/Chla ratio, and enrich the parameters for monitoring high temperature stress, water deficit stress, and nutrient stress and pest diseases by remote sensing in cotton.

RESEARCH NOTES

Comparative proteomic analysis of two wheat genotypes with contrasting grain softness index

LIU Pei-Xun,MA Xiao-Fei,WAN Hong-Shen,ZHENG Jian-Min,LUO Jiang-Tao,PU Zong-Jun

Acta Agronomica Sinica. 2020, 46(8):  1275-1282.  doi:10.3724/SP.J.1006.2020.91068

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Wheat is the crop most widely grown in the world and provides the daily protein and 20% food calories for 4.5 billion people. It is crucial to understand the genetic basis of grain hardness for improving wheat quality. In order to explore the molecular basis of the formation of wheat grain hardness, two wheat cultivars Chuanmai 66 and Shumai 969 with significant hardness difference in southwest wheat region were selected to analyze the proteins differential expression by TMT quantitative proteomics (tandem mass tags) and bioinformatic methods of function and pathway enrichment analysis. A total of 6020 effective proteins were identified and quantified, including 113 differentially expressed proteins (DEPs), of which 69 were up-regulated and 44 were down-regulated in soft wheat Chuanmai 66. These DEPs were enriched into 65 GO terms, including a biological process term, a cellular component term and six molecular function terms at extremely significant level. Based on the enrichment analysis, we suggested that nutrient reservoir activity proteins, enzyme inhibitor proteins and glutathione metabolism proteins might participate in the formation of wheat grain hardness, and grain hardness related proteins might mainly distribute in the extracellular region of cells and had defensive function. According to the phylogenetic analysis, it was inferred that puroindolines and its homologous proteins might be as not only wheat grain storage proteins, but also enzyme inhibitors regulating grain development. This study provides a basis for further exploring the genetic mechanism of wheat grain hardness.

Cloning and function analysis of a type 2 diacylglycerol acyltransferase (DGAT2) from Perilla frutescens

LU Geng,TANG Xin,LU Jun-Xing,LI Dan,HU Qiu-Yun,HU Tian,ZHANG Tao

Acta Agronomica Sinica. 2020, 46(8):  1283-1290.  doi:10.3724/SP.J.1006.2020.94192

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Diacylglycerol acyltransferase (DGAT) is a key enzyme in the final step of triacylglycerol (TAG) synthesis in plant. In seed oil of certain plants, DGAT2 can selectively accumulate more unsaturated fatty acids. In this paper, we successful cloned PfDGAT2 from Perilla frutescens and performed bioinformatics analysis. Real-time fluorescence quantitative analysis showed that PfDGAT2 was expressed in different organs, with the highest in seeds at 10 d after anthesis, the medium in roots, and gradual decrement in the middle and late stages of seed. Compared with the wild-type, the oil content of seeds in PfDGAT2 transgenic Arabidopsis was increased by 21.68%-77.89%. The fatty acid components of the four strains with the largest increase in seed oil content were analyzed. Compared with the control, linolenic acid (C18:3), arachidonic acid (C20:1), arachidonic acid (C20:2), docosaenoic acid (C22:1) increased significantly by 4.57%, 7.44%, 5.40%, and 0.37%, respectively. Palmitic acid (C16:0), stearic acid (C18:0), and linoleic acid (C18:2) were obviously reduced by 3.47%, 6.64%, and 4.83%, respectively. Oleic acid (C18:1) only decreased by 0.18% and arachidic acid (C20:0) by 1.91%. In conclusion that PfDGAT2 gene can not only increase the oil content, but promote the accumulation of unsaturated fatty acids such as linolenic acid and arachidonic acid, which provides a reference and theoretical basis for studying the synthesis and accumulation of unsaturated fatty acid in plants.

Identification of CRISPR/Cas9 knockout targets and tissue expression analysis of circadian clock genes GmLNK1/2, GmRVE4/8, and GmTOC1 in soybean

GAN Zhuo-Ran,SHI Wen-Qian,LI Yong-Li,HOU Zhi-Hong,LI Hai-Yang,CHENG Qun,DONG Li-Dong,LIU Bao-Hui,LU Si-Jia

Acta Agronomica Sinica. 2020, 46(8):  1291-1300.  doi:10.3724/SP.J.1006.2020.94169

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Circadian clock genes play an important role in improving crop yield. LNK1, LNK2, RVE4, RVE8, and TOC1 are important circadian clock genes in plants. Homologous genes of AtLNK1, AtLNK2, AtRVE4, AtRVE8, and AtTOC1 in soybean were found by evolutionary tree analysis. These genes were expressed in soybean roots, stems and leaves. The knockout vectors of these genes were successfully constructed by using CRISPR/Cas9 gene editing technology. Transformation system of soybean root hair and RT-PCR were used to identify 13 genes targets effectively. The results of this study provide important target informations for further obtaining soybean mutant materials, and a foundation for further studying the function of circadian clock genes.