Identification and virulence test of a new pathogen that causes verticillium striping on rapeseed in northwestern China

Five stems of rapeseed with abundant black microsclerotia were collected from Huangyuan County of Qinghai Province,China,and fungal isolates were obtained from the stems.They were identified based on morphology,molecular features and specific PCR detection.The results showed that the 10 fungal isolates belonged to Verticillium longisporum lineage A1/D3.One of the 10 isolates(HW7-1)was tested for virulence on three species of rapeseed,including B.napus Zhongshuang 9,B.rapa Qingyou 9 and B.juncea Tayou 2 by conidia inoculation of HW7-1 on roots of young seedlings.Control seedlings were inoculated with V.dahliae conidia or water alone.The seedlings of these treatments were transplanted in culture mix and incubated in a growth chamber(20℃).Results suggested that the control seedlings of three cultivars appeared quite healthy,while the seedlings inoculated with HW7-1 turned yellowing leaves,seedling stunting or even death after 22 days post-inoculation.V.longisporum was re-isolated from he yellow leaves,thus fulfilling Koch's postulates.Moreover,compared to the control treatments,inoculation with HW7-1 caused flowering delay and seed yield reduction on Tayou 2 with production of microsclerotia on the stems.To our knowledge,this is the first report of V.longisporum lineage A1/D3 on rapeseed in northwestern China.

Mapping winter rapeseed in South China using Sentinel-2 data based on a novel separability index

Large-scale crop mapping using remote sensing data is of great significance for agricultural production, food security and the sustainable development of human societies. Winter rapeseed is an important oil crop in China that is mainly distributed in the Yangtze River Valley. Traditional winter rapeseed mapping practices are insufficient since they only use the spectral characteristics during the critical phenological period of winter rapeseed, which are usually limited to a small region and cannot meet the needs of large-scale applications. In this study, a novel phenology-based winter rapeseed index(PWRI) was proposed to map winter rapeseed in the Yangtze River Valley. PWRI expands the date window for distinguishing winter rapeseed and winter wheat, and it has good separability throughout the flowering period of winter rapeseed. PWRI also improves the separability of winter rapeseed and winter wheat, which traditionally have been two easily confused winter crops. A PWRI-based method was applied to the Middle Reaches of the Yangtze River Valley to map winter rapeseed on the Google Earth Engine platform. Time series composited Sentinel-2 data were used to map winter rapeseed with 10 m resolution. The mapping achieved a good result with overall accuracy and kappa coefficients exceeding 92% and 0.85, respectively. The PWRI-based method provides a new solution for high spatial resolution winter rapeseed mapping at a large scale.

Development of a target capture sequencing SNP genotyping platform for genetic analysis and genomic breeding in rapeseed

Rapeseed(Brassica napus)is an oil crop grown worldwide,making it a key plant species in molecular breeding research.However,the complexity of its polyploid genome increases sequencing costs and reduces sequencing accuracy.Target capture coupled with high-throughput sequencing is an efficient approach for detecting genetic variation at genomic regions or loci of interest.In this study,588 resequenced accessions of rapeseed were used to develop a target capture sequencing SNP genotyping platform named BnaPan50T.The platform comprised 54,765,with 54,058 resequenced markers from the pan-genome,and 855 variant trait-associated markers for 12 agronomic traits.The capture quality of BnaPan50T was demonstrated well in 12 typical accessions.Compared with a conventional genotyping array,BnaPan50T has a high SNP density and a high proportion of SNPs in unique physical positions and in annotated functional genes,promising wide application.Target capture sequencing and wholegenome resequencing in 90 doubled-haploid lines yielded 60%specificity,78%uniformity within tenfold coverage range,and 93%genotyping accuracy for the platform.BnaPan50T was used to construct a genetic map for quantitative trait loci(QTL)mapping,identify 21 unique QTL,and predict several candidate genes for yield-related traits in multiple environments.A set of 132 core SNP loci was selected from BnaPan50T to construct DNA fingerprints and germplasm identification resources.This study provides genomics resources to support target capture sequencing,genetic analysis and genomic breeding of rapeseed.

National Protection Zone for Rapeseed Production and Industrial Cluster of Rape in Hubei Province

Hubei Province is the main winter rapeseed producing area in China,and has the national advantage and characteristic industrial cluster of rape.The protection zone for the production of important agricultural products of rapeseed in Hubei Province also ranks first as that in Hunan Province.This paper studied the winter rape industry,the important agricultural product production protection zone of rapeseed,the provincial double-low high-quality rape protection zone and the industrial cluster of rape in Jianghan Plain in Hubei Province,and analyzed the main problems existing in the development of rapeseed production protection zone and industrial cluster of rape.Finally,it came up with strategies including promoting national rape varieties,overcoming the problem of rape"agricultural chip",promoting the"rice+rape"rotation model,and strengthening the protection of intellectual property rights of brand marks.

Influence of two-stage harvesting on the properties of cold-pressed rapeseed(Brassica napus L.)oils

Rapeseed(Brassica napus L.)harvesting method is critical since it significantly determines the seed yield,oil quality,and industrial efficiency.This study investigated the influences of harvesting methods on the quality of cold-pressed rapeseed oil of two varieties.Oil color,peroxide value(POV),tocopherol content,fatty acid composition,and polarity of total polyphenols(PTP)contents of two rapeseed varieties in Huanggang and Xiangyang were compared through artificially simulated combined harvesting and two-stage harvesting.Results showed significant differences in the quality of rapeseed oil between the two harvesting methods.The red value(R-value),POV,total tocopherol contents,linoleic and linolenic acid content,and PTP content of the pressed rapeseed oil prepared by the combined harvesting method were about 27.6,5.7,15.8,2.0,0.5,and 28.6%lower than those of the oil produced from the two-stage harvesting method,respectively.Xiangyang and Huayouza62 performed better in the two regions and two varieties,respectively.To sum up,the rapeseed oil obtained 41–44 days after final flowering of combined harvesting,35 days after final flowering,and six days of post-ripening of the two-stage harvesting had the best quality.

Quick and Accurate Counting of Rapeseed Seedling with Improved YOLOv5s and Deep-Sort Method

The statistics of the number of rapeseed seedlings are very important for breeders and planters to conduct seed quality testing,field crop management and yield estimation.Calculating the number of seedlings is inefficient and cumbersome in the traditional method.In this study,a method was proposed for efficient detection and calculation of rapeseed seedling number based on improved you only look once version 5(YOLOv5)to identify objects and deep-sort to perform object tracking for rapeseed seedling video.Coordinated attention(CA)mechanism was added to the trunk of the improved YOLOv5s,which made the model more effective in identifying shaded,dense and small rapeseed seedlings.Also,the use of the GSConv module replaced the standard convolution at the neck,reduced model parameters and enabled it better able to be equipped for mobile devices.The accuracy and recall rate of using improved YOLOv5s on the test set by 1.9%and 3.7%compared to 96.2%and 93.7%of YOLOv5s,respectively.The experimental results showed that the average error of monitoring the number of seedlings by unmanned aerial vehicles(UAV)video of rapeseed seedlings based on improved YOLOv5s combined with depth-sort method was 4.3%.The presented approach can realize rapid statistics of the number of rapeseed seedlings in the field based on UAV remote sensing,provide a reference for variety selection and precise management of rapeseed.

Research progress and strategies for multifunctional rapeseed： A case study of China

Rapeseed(Brassicanapus),is an important source of edible oil,animal fodder,vegetables,condiments and biodiesel,and plays a significant role in securing edible oil production worldwide.However,in countries with comparatively low levels of agricultural mechanization,such as China,increasing costs of labor and agricultural inputs are decreasing rapeseed profitability,and hence the area of rapeseed under cultivation.If the value of rapeseed crops is not further increased,the rapeseed growing area will continue to decrease,potentially jeopardizing oil production.Therefore,full exploitation of the existing and potential value of rapeseed is desirable.Different rapeseed products are already utilized in different ways,with more applications currently underutilized.As well as oil extraction from the seeds,the shoot and leaves can be used as vegetables,the roots to absorb soil cadmium for pollution remediation,the flowers for sightseeing and as a source of nectar,the pollen for extracting flavonoids and useful amino acids,the seeds/seed meal for extracting isthiocyanates and other important sulforaphane compounds,the straw and seed meal for fodder,and immature whole plants for green manure.This review summarizes recent research on ways to explore the potential holistic value of rapeseed,by taking the example of multifunctionality of rapeseed in China.

Radical-scavenging activity,ACE-inhibiting capability and identification of rapeseed albumin hydrolysate

Albumin derived from rapeseed was hydrolyzed sequentially using alcalase and flavorzyme to produce antioxidant peptides.To identify antioxidant peptides,rapeseed albumin hydrolysate(RAH)was fractionated using size exclusion chromatography(G-25).The antioxidant activity and angiotensin I-converting enzyme(ACE)inhibiting activity of rapeseed peptides(RSP)purified from RAH were evaluated.The results revealed that RSP-4 had the highest ABTS radical-scavenging activity(TEAC value=0.24)and ACE-inhibiting capacity(IC50=0.19 mg/mL)compared to other fractions.Moreover,RSP-4 was identified as PFDSYFVC(977 D)by electrospray ionization(ESI)mass spectrometry and tandem mass spectrometry(MS/MS).©2013 Beijing Academy of Food Sciences.Production and hosting by Elsevier B.V.All rights reserved.

Rapeseed research and production in China

Rapeseed(Brassica napus L.) is the largest oilseed crop in China and accounts for about 20% of world production.For the last 10 years,the production,planting area,and yield of rapeseed have been stable,with improvement of seed quality and especially seed oil content.China is among the leading countries in rapeseed genomic research internationally,having jointly with other countries accomplished the whole genome sequencing of rapeseed and its two parental species,Brassica oleracea and Brassica rapa.Progress on functional genomics including the identification of QTL governing important agronomic traits such as yield,seed oil content,fertility regulation,disease and insect resistance,abiotic stress,nutrition use efficiency,and pod shattering resistance has been achieved.As a consequence,molecular markers have been developed and used in breeding programs.During 2005–2014,215 rapeseed varieties were registered nationally,including 210 winter-and 5 spring-type varieties.Mechanization across the whole process of rapeseed production was investigated and operating instructions for all relevant techniques were published.Modern techniques for rapeseed field management such as high-density planting,controlled-release fertilizer,and biocontrol of disease and pests combined with precision tools such as drones have been developed and are being adopted in China.With the application of advanced breeding and production technologies,in the near future,the oil yield and quality of rapeseed varieties will be greatly increased,and more varieties with desirable traits,especially early maturation,high yield,high resistance to biotic and abiotic stress,and suitability for mechanized harvesting will be developed.Application of modern technologies on the mechanized management of rapeseed will greatly increase grower profit.

Net energy of corn,soybean meal and rapeseed meal in growing pigs

Background: Two experiments were conducted to estimate the net energy(NE) of corn, soybean meal, expel er-pressed rapeseed meal(EP-RSM) and solvent-extracted rapeseed meal(SE-RSM) using indirect calorimetry and to validate the NE of these four ingredients using pig growth performance.Methods: In Exp.1, 24 barrows(initial BW = 36.4 ± 1.6 kg) were allotted to 1 of 4 diets which included a corn basal diet,a corn-soybean meal basal diet and two rapeseed meal diets containing 20% EP-RSM(9.5% ether extract) or SE-RSM(1.1% ether extract) substituted for corn and soybean meal. The design allowed the calculation of NE values of corn,soybean meal and rapeseed meals according to the difference method. In Exp.2, 175 growing pigs(initial BW = 36.0± 5.2 kg) were fed 1 of 5 diets for 28 d, with five pigs per pen and seven replications(pens) per treatment in order to validate the measured energy values. Diets were a corn-soybean meal diet and four diets including 10% or 20% EP-RSM and 10% or 20% SE-RSM.Results: The NE of corn, soybean meal, EP-RSM and SE-RSM were 12.46, 11.34, 11.71 and 8.83 MJ/kg DM, respectively. The NE to ME ratio of corn(78%) was similar to tabular values, however, the NE to ME ratios of soybean meal(70%) and rapeseed meal(76%) were greater than tabular values. The greater NE value in EP-RSM than in SE-RSM is consistent with its higher EE content. Increasing EP-RSM or SE-RSM did not affect the growth performance of pigs and the caloric efficiency of NE was comparable for al diets.Conclusions: The NE of EP-RSM was similar to soybean meal, and both were greater than SE-RSM. The DE, ME and NE values measured in Exp.1 are confirmed by results of Exp. 2 with comparable caloric efficiencies of DE, ME or NE for all diets.

Development and molecular analysis of a novel acetohydroxyacid synthase rapeseed mutant with high resistance to sulfonylurea herbicides

With the increasing promotion of simplified rapeseed cultivation in recent years,the development of cultivars with high resistance to herbicides is urgently needed.We previously developed M342,which shows sulfonylurea herbicide resistance,by targeting acetohydroxyacid synthase(AHAS),a key enzyme in branched-chain amino acid synthesis.In the present study,we used a progeny line derived from M342 for an additional round of ethyl methane sulfonate mutagenesis,yielding the novel mutant DS3,which harbored two mutations in AHAS genes and showed high sulfonylurea resistance.One mutation was the substitution Trp574 Leu,as in M342,according to Arabidopsis protein sequencing.The other site was a newly recognized substitution,Pro197 Leu.A KASP marker targeting Pro197 Leu was developed and reliably predicted the response to sulfonylurea herbicides in the F2 population.The combination of Trp574 Leu and Pro197 Leu in DS3 produced a synergistic effect that greatly increased herbicide resistance.Analysis of the protein structures of AHAS1 and AHAS3 in wild-type and single-gene mutant plants revealed three-dimensional protein conformational changes that could account for differences in herbicide resistance characteristics including toxicity tolerance,AHAS enzyme activity,and AHAS gene expression.

Exogenous strigolactones promote lateral root growth by reducing the endogenous auxin level in rapeseed

Strigolactones(SLs)are newly discovered plant hormones which regulate the normal development of different plant organs,especially root architecture.Lateral root formation of rapeseed seedlings before winter has great effects on the plant growth and seed yield.Here,we treated the seedlings of Zhongshuang 11(ZS11),an elite conventional rapeseed cultivar,with different concentrations of GR24(a synthetic analogue of strigolactones),and found that a low concentration(0.18μmol L–1)of GR24 could significantly increase the lateral root growth,shoot growth,and root/shoot ratio of seedlings.RNA-Seq analysis of lateral roots at 12 h,1 d,4 d,and 7 d after GR24 treatment showed that 2301,4626,1595,and 783 genes were significantly differentially expressed,respectively.Function enrichment analysis revealed that the plant hormone transduction pathway,tryptophan metabolism,and the phenylpropanoid biosynthesis pathway were over-represented.Moreover,transcription factors,including AP2/ERF,AUX/IAA,NAC,MYB,and WRKY,were up-regulated at 1 d after GR24 treatment.Metabolomics profiling further demonstrated that the amounts of various metabolites,such as indole-3-acetic acid(IAA)and cis-zeatin were drastically altered.In particular,the concentrations of endogenous IAA significantly decreased by 52.4 and 75.8%at 12 h and 1 d after GR24 treatment,respectively.Our study indicated that low concentrations of exogenous SLs could promote the lateral root growth of rapeseed through interaction with other phytohormones,which provides useful clues for the effects of SLs on root architecture and crop productivity.

Response of leaf carbon metabolism and dry matter accumulation to density and row spacing in two rapeseed(Brassica napus L.)genotypes with differing plant architectures

Biological yield indicates the potential for increasing yield.Leaf carbon metabolism plays an important role in the biomass accumulation of rapeseed(Brassica napus L.).Field experiments with the hybrid HZ62(with a conventional plant architecture)grown in 2016–2017,and HZ62 and accession 1301(with a compact plant architecture)grown in 2017–2018 were conducted to characterize the physiological and proteomic responses of leaf photosynthetic carbon metabolism to density and row spacing configurations.The densities were set at 15×10;ha^(-1)(D1),30×10^(4)ha^(-1)(D2),and 45×10^(4)ha^(-1)(D3)(main plot),with row spacings of 15 cm(R15),25 cm(R25),and 35 cm(R35)(subplot).Individual and plant population biomass accumulation was greatest at R25,R15,and R15 for D1,D2,and D3,respectively,for both genotypes.In comparison with D1 R25,the individual aboveground biomass of HZ62 decreased by60.2%,whereas the population biomass increased by 31.9%,and the individual biomass of genotype1301 decreased by 54.0%and the population biomass increased by 53.9%at D3 R15.Leaf carbon metabolic enzymes varied between genotypes at flowering stage.In contrast to D1 R25,at D3 R15 the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase(Rubisco)and sucrose phosphate synthase(SPS)and the contents of starch,sucrose and soluble sugars in leaves were significantly decreased in HZ62 and increased in genotype 1301.The activities of fructose-1,6-bisphosphatase(FBPase)decreased,in consistency with the abundance of fructose-bisphosphate aldolase in HZ62.In contrast,sucrose synthase(Su Sy)activity appeared to decrease in both genotypes,but a significant increase in abundance of a protein with sucrose synthase was found in the 1301 genotype by proteomic analysis.With increased density and reduced row spacing,the expression of most key proteins involved in carbon metabolism was elevated,and enzyme activity and carbon assimilate content were increased in 1301,whereas HZ62 showed the opposite trend,indicating that the compact plant type can accumulate more population biomass with denser planting.

Mapping rapeseed planting areas using an automatic phenology-and pixel-based algorithm(APPA) in Google Earth Engine

The timely and rapid mapping of rapeseed planting areas is desirable for national food security. Most current rapeseed mapping methods depend strongly on images with good observations obtained during the flowering stages. Although vegetation indices have been proposed to identify the rapeseed flowering stage in some areas, automatically mapping rapeseed planting areas in large regions is still challenging.We developed an automatic phenology-and pixel-based algorithm(APPA) by integrating Landsat 8 and Sentinel-1 satellite data. We found that the Normalized Rapeseed Flowering Index shows unique spectral characteristics during the flowering and post-flowering periods, which distinguish rapeseed parcels from other land-use types(urban, water, forest, grass, maize, wheat, barley, and soybean). To verify the robustness of APPA, we applied APPA to seven areas in five rapeseed-producing countries with flowering images unavailable. The rapeseed maps by APPA showed consistently high accuracies with producer accuracies of 0.87–0.93 and F-scores of 0.92–0.95 based on 4503 verification samples. They showed high spatial consistency at the pixel level with the land cover Scientific Expertise Centres(SEC) map in France,Crop Map of England in United Kingdom, national-scale crop-and land-cover map of Germany, and Annual Crop Inventory in Canada at the pixel level. We propose APPA as a highly promising method for automatically and efficiently mapping rapeseed areas.

Genome-wide association study identifies novel loci and candidate genes for drought stress tolerance in rapeseed

Rapeseed(Brassica napus)is one of the most important oil crops worldwide;however,drought seriously curtails its growth and productivity.Identifying drought-tolerant germplasm is an efficient strategy for addressing water shortages.Here,we phenotyped a panel of 264 B.napus accessions at full-bloom stage using water loss ratio(WLR)as drought-tolerant index.It identified 8 low-WLR and 6 high-WLR accessions,regarded as droughttolerant and drought-sensitive,respectively.Comparing with drought-sensitive accessions at the seedling stage,drought-tolerant accessions had shown better performance in maintaining fresh and dry weights,and performed the higher expression of drought-induced marker genes under drought stress.Subsequently,a total of 139 SNPs(single nucleotide polymorphisms)were identified associated with the WLR using a genome-wide association study(GWAS)among 264 B.napus accessions,with the largest number SNPs at chromosome A10,and 13 SNPs significantly were associated with the WLR(-log_(10)(p-value)>6).Furthermore,4 putative candidate genes(BnaC09.RPS6,BnaC09.MATE,BnaA10.PPD5 and BnaC09.Histone)were screened involving in drought tolerance in B.napus.Together,our results highlight the WLR's importance in drought tolerance and establish the foundation for improving WLR-associated drought tolerance in rapeseed.

Analysis on Technical Efficiency and Influencing Factors of Rapeseed Production

Based on micro survey data of 344 rapeseed farmers in 19 rapeseed counties of Hubei Province,with the aid of stochastic frontier production function model and efficiency loss model,this paper analyzed basic production situations,demographic characteristics of rapeseed farmers,technical efficiency loss,and main influencing factors. In Hubei Province,there are mainly following problems in rapeseed production: serious aging of rapeseed farmers; relatively scarce labors; the middle-aged and old farmers have higher technical efficiency level; with increase in farmer age,their technical efficiency firstly declines and then rises. In view of these situations,it came up with recommendations including raising educational level of rapeseed farmers to realize large scale economy and effectively reduce technical efficiency loss,and local government,specialized associations and agricultural machinery extension departments should provide proper technical guidance according to demands of farmers to reduce technical efficiency loss.

Optimizing agronomic practices for closing rapeseed yield gaps under intensive cropping systems in China

A yield gap analysis for rapeseed(Brassica napus L.) is critical to meeting the oil demand by identifying yield potential and yield constraints. In this study, potential yield(Y_p), attainable yield(Y_(att)), and actual yield(Y_(act)) for winter rapeseed were determined in five different zones of China. A boundary line approach was adopted to calculate Y_p, based on a large-scale field experimental database. A meta-analysis was conducted on the data obtained from 118 published studies to evaluate the effects of agronomic factors on rapeseed yield. The main results indicated that farmers only achieved 37–56% of the yield potential across the zones. The low altitude areas(L-URY) and lower reaches(LRY) of the Yangtze River Basin(YRB), China had high yield levels. The total yield gap was 1 893 kg ha^(–1), due to the agronomic management factors, environmental factors, and socioeconomic factors. The meta-analysis showed that weed control and drainage were the best management practices to improve yields(45.6 and 35.3%, respectively), and other practices improved yields by 17.1–21.6%. Consequently, to narrow the yield gap over the short term, the study could focus on techniques that are easily implemented to farmers.

Ultrastructural studies of seed coat and cotyledon during rapeseed maturation

Brassica napus L.(B.napus)is an important oil crop worldwide and it rapidly accumulates oil at late stage of seed maturation.However,little is known about the cellular mechanism of oil accumulation and seed color changes during the late stage of rapeseed development.Here,we analyzed the ultrastructure of seed coat,aleurone and cotyledon in embryos of B.napus from 25 to 70 days after flowering(DAF).The pigments,which were deposited on the cell wall of palisade cells in seed coat,determined dark black color of rapeseed.The chloroplasts degenerated into non-photosynthetic plastids which caused the green cotyledon to turn into yellow.The chloroplasts in aleurone and cotyledon cells respectively degenerated into remnants without inner and outer envelope membranes and ecoplasts with intact inner and outer envelope membranes.From 40 to 70 DAF,there were degraded chloroplasts without thylakoid,oil bodies contacting with plastids or protein bodies,big starch deposits of chloroplasts degrading into small particles then disappearing,and small endoplasmic reticulum(ER)in aleurone and cotyledon cells.Additionally,there were decreases of chlorophyll content and dramatic increases of oil content in rapeseed.These results suggested that the rapid oil accumulation was independent on the NADPH synthesized by photosynthesis of chloroplasts and probably utilized other sources of reductant,such as the oxidative pentose phosphate pathway during the late stage of rapeseed development.The triacylglycerol assembly presumably utilizes the enzymes in the plastid,cytosol or oil body of cotyledon and aleurone cells.

Preparation and Tribological Behavior of Hydrophobic Lanthanum Borate Nanosheets in Rapeseed Oil

Oleic acid-capped lanthanum borate(abbreviated as OA/La BO_3·H_2O) nanosheets were prepared by the hydrothermal method. The microstructures of as-prepared OA/La BO_3·H_2O were characterized by means of SEM, TEM, EDS, FTIR and XRD, respectively. Moreover, the friction and wear properties of OA/La BO_3·H_2O as a lubricant additive in rapeseed oil were evaluated on a four-ball tribotester. The tribochemical characteristics of worn surfaces were investigated by SEM and XPS. The results showed that the hydrophobic OA/La BO_3·H_2O nanosheets exhibited their morphology with a diameter in the range of 100 nm to 300 nm and a thickness of about 25 nm, and displayed excellent dispersing stability in rapeseed oil. In the meantime, the rapeseed oil doped with OA/La BO_3·H_2O nanosheets markedly decreased the friction and wear of steel balls, and the optimal friction-reducing and antiwear ability of rapeseed oil was obtained at an OA/La BO_3·H_2O content of 1.0%. The outstanding tribological performance of OA/La BO_3·H_2O in rapeseed oil was attributed to the formation of a composite boundary lubrication film mainly composed of lubricious tribochemical species of B_2O_3, La_2O_3 and Fe_2O_3, and deposits of OA/La BO_3·H_2O nanosheets as well as the adsorbates of rapeseed oil on rubbed surfaces.

Effects of uniconazole rate on agronomic traits and physiological indexes of rapeseed blanket seedling

Mechanized transplanting of rapeseed(Brassica napus L.)blanket seedling is an innovative cultivation technology.Cultivating high quality blanket seedling to ensure high survival rate of seedling after transplanting is the key of the technology.The effects of different uniconazole rates of 0,0.5,1.0,1.5 and 2.0 mg/tray,spraying at one leaf and one heart stage,on selected agronomic traits,physiological indexes and survival rate of two rapeseed cultivars(‘Qinyou 100 and’Yangyou 90)were investigated in 2018 and 2019.Our results showed that the plant height decreased significantly with the increase of uniconazole rate.However,the collar diameter increased significantly with the increase of uniconazole rate up to 1.5 mg/tray,and the leaf area,dry weights of root and shoot increased with increased uniconazole rate up to 1.0 mg/tray.The root to shoot ratios,N concentrations of root and shoot with the uniconazole rates of 1.0 and 1.5 mg/tray were higher than those with other treatments.As uniconazole rate increasing,gibberellin(GA)and auxin(IAA)concentrations of root and shoot decreased,while abscisic acid(ABA)concentrations increased,and cytokinin(CTK)concentrations topped at uniconazole rate of 1.0 mg/tray and decreased thereafter.The seedling survival rates with 1.0 and 1.5 mg/tray were greatly higher than those in other treatments.Regression analysis suggested plant survival rate was positively related to CTK concentrations and negatively to GA concentrations of root and shoot.To achieve high survival rate after mechanized transplanting,our study revealed that the uniconazole applied at a rate of 1.0 mg/tray was recommended as the best,followed by 1.5 mg/tray.The findings would help to enhance qualities of rapeseed blanket seedling and to promote popularization of mechanized transplanting of rapeseed production.