Identification of an Aux/IAA regulator for flesh firmness using combined GWAS and bulked segregant RNA-Seq analysis in watermelon

Watermelon is a highly cultivated fruit crop renowned for its quality properties of fruit flesh.Among various quality factors,fruit flesh firmness is a crucial quality parameter influencing the fruit texture,shelf life and its commercial value.The auxin/indole-3-acetic acid(Aux/IAA)plays a significant role in fruit development and ripening of non-climacteric fruits.However,the regulatory mechanism of Aux/IAA in controlling fruit flesh firmness and ripening in watermelon remains unknown.In this study,we employed an integrative approach combining genome-wide association study(GWAS)and bulked segregant RNA-Seq analysis(BSR-Seq)to identify an overlapping candidate region between 12776310 and 12968331 bp on chromosome 6,underlying an auxin-responsive gene(Aux/IAA)associated with flesh firmness in watermelon.Transcriptome analysis,followed by real-time quantitative reverse transcription PCR(qRT-PCR),confirmed that the expression of Aux/IAA was consistently higher in fruits with high flesh firmness.The sequence alignment revealed a single base mutation in the coding region of Aux/IAA.Furthermore,the concomitant Kompetitive/Competitive allele-specific PCR(KASP)genotyping data sets for F2 population and germplasm accessions identified Aux/IAA as a strong candidate gene associated with flesh firmness.Aux/IAA was enriched in the plant hormone signal transduction pathway,involving cell enlargement and leading to low flesh firmness.We determined the higher accumulation of abscisic acid(ABA)in fruits with low flesh firmness than hard flesh.Moreover,overexpression of Aux/IAA induced higher flesh firmness with an increased number of fruit flesh cells while reducing ABA content and flesh cell sizes.Additionally,the allelic variation in Aux/IAA for soft flesh firmness was found to exist in Citrullus mucosospermus and gradually fixed into Citrullus lanatus during domestication,indicating that soft flesh firmness was a domesticated trait.These findings significantly enhanced our understanding of watermelon fruit flesh firmness and consequently the watermelon fruit quality.

Enhancer of Shoot Regeneration 2(ESR2)regulates pollen maturation and vitality in watermelon(Citrullus lanatus)

Watermelon(Citrullus lanatus)holds global significance as a fruit with high economic and nutritional value.Exploring the regulatory network of watermelon male reproductive development is crucial for developing male sterile materials and facilitating cross-breeding.Despite its importance,there is a lack of research on the regulation mechanism of male reproductive development in watermelon.In this study,we identified that ClESR2,a VIIIb subclass member in the APETALA2/Ethylene Responsive Factor(AP2/ERF)superfamily,was a key factor in pollen development.RNA insitu hybridization confirmed significantClESR2 expression in the tapetum and pollen during the later stage of anther development.The pollens of transgenic plants showed major defects in morphology and vitality at the late development stage.The RNA-seq and protein interaction assay confirmed that ClESR2 regulates pollen morphology and fertility by interacting with key genes involved in pollen development at both transcriptional and protein levels.These suggest that Enhancer of Shoot Regeneration 2(ESR2)plays an important role in pollen maturation and vitality.This study helps understand the male reproductive development of watermelon,providing a theoretical foundation for developing male sterile materials.

Additional far-red light promotes adventitious rooting of doubleroot-cutting grafted watermelon seedlings

Root regeneration is an important factor influencing the healing rate of graft union and the survival of double-root-cutting grafting.To date,little information is available on how to enhance root regeneration of rootstock in grafted watermelon(Citrullus lanatus)seedlings.In this study,the effects of different light treatments on root regeneration were determined.This revealed that addition of far-red light(Fr)could significantly expedite root formation in the rootstock.Moreover,the results of transcriptome analysis revealed that plant hormone pathway and auxinrelated genes were greatly induced by Fr,especially for auxin-response proteins(including CmIAA11,CmIAA17,and CmAUX28),Small auxinup RNA genes(including CmSAUR20 and CmSAUR50)and the auxin efflux transporter(CmPIN3).In addition,the expression of Phytochrome Interacting Factor(PIFs),such as CmPIF1,CmPIF3 and CmPIF7,was remarkably increased by Fr.These genes may act together to activate auxinrelated pathways under Fr treatment.Based on the results of HPLC-MS/MS analysis,the concentrations of different auxin-types in adventitious root were significantly influenced by Fr.Furthermore,the better growth of rootstock root displayed superior vasculature transport activity of the graft union with Fr treatment,which was determined by the acid magenta dyeing experiment.Therefore,all the results suggested that Fr could induce AR formation in rootstocks,which may be associated with the auxin accumulation by regulating the transcriptional level of auxinrelated and PIF genes.The findings of this study demonstrated a practicable way to shorten the healing period of graftings and improve the quality of grafted watermelon seedlings,which will provide a theoretical basis for the speeding development of industrialized seedlings production.

Quantitative trait loci identification reveals zinc finger protein CONSTANS-LIKE 4 as the key candidate gene of stigma color in watermelon(Citrullus lanatus)

Stigma color is a critical agronomic trait in watermelon that plays an important role in pollination.However,there are few reports on the regulation of stigma color in watermelon.In this study,a genetic analysis of the F2 population derived from ZXG1553(P1,with orange stigma)and W1-17(P2,with yellow stigma)indicated that stigma color is a quantitative trait and the orange stigma is recessive compared with the yellow stigma.Bulk segregant analysis sequencing(BSA-seq)revealed a 3.75 Mb segment on chromosome 6 that is related to stigma color.Also,a major stable effective QTL Clqsc6.1(QTL stigma color)was detected in two years between cleaved amplified polymorphic sequencing(CAPS)markers Chr06_8338913 and Chr06_9344593 spanning a~1.01 Mb interval that harbors 51 annotated genes.Cla97C06G117020(annotated as zinc finger protein CONSTANS-LIKE 4)was identified as the best candidate gene for the stigma color trait through RNA-seq,quantitative real-time PCR(qRT-PCR),and gene structure alignment analysis among the natural watermelon panel.The expression level of Cla97C06G117020 in the orange stigma accession was lower than in the yellow stigma accessions with a significant difference.A nonsynonymous SNP site of the Cla97C06G117020 coding region that causes amino acid variation was related to the stigma color variation among nine watermelon accessions according to their re-sequencing data.Stigma color formation is often related to carotenoids,and we also found that the expression trend of ClCHYB(annotated asβ-carotene hydroxylase)in the carotenoid metabolic pathway was consistent with Cla97C06G117020,and it was expressed in low amounts in the orange stigma accession.These data indicated that Cla97C06G117020 and ClCHYB may interact to form the stigma color.This study provides a theoretical basis for gene fine mapping and mechanisms for the regulation of stigma color in watermelon.

Effects of Functional Organic Materials on Morphological Indexes,Quality and Yield of Watermelon

[Objectives]This study was conducted to explore suitable organic compound application models for watermelon growth.[Methods]With watermelon hybrid material"M22×P18"as the test material,the effects of four functional organic materials,namely garlic straw treatment(T_(1)),onion straw treatment(T_(2)),garlic straw+sheep manure treatment(T_(3))and onion straw+chicken manure treatment(T_(4)),on the morphological indexes,yield and quality of watermelon were investigated.[Results]Different functional organic materials had different effects on morphological indexes,yield and quality of watermelon.The morphological indexes,nutritional quality indexes and yield of watermelon treated with garlic straw and sheep manure compound(T_(3))and onion straw and chicken manure compound(T_(4))were significantly higher than those treated simply with garlic straw(T_(1))and onion straw(T_(2)),and T_(3)performed relatively better.Compared with treatment T_(2),T_(3)showed a stem diameter,vine length and leaf number increasing by 43.05%,46.69%and 40.77%respectively,central sugar and side sugar contents increasing by 11.72%and 21.90%respectively,and a yield increasing by 42.91%,with significant differences from T_(2).[Conclusions]This study provides technical support for high-quality and high-yielding cultivation of watermelon.

Effects of Functional Organic Materials on Fresh Weight,Quality,Single-melon Weight and SPAD Value of Watermelon

[Objectives]This study was conducted to explore a functional organic material formula suitable for watermelon cultivation with high quality,high yield and high efficiency.[Methods]Four treatments were set in the experiment,namely four functional organic materials,garlic straw treatment(T_(1)),onion straw treatment(T_(2)),garlic straw+sheep manure treatment(T_(3))and onion straw+chicken manure treatment(T_(4)),to investigate the effects of different functional organic materials on fresh weight,quality,single-melon weight and SPAD value of watermelon.[Results]The effects of different functional organic materials on fresh weight,quality,single-melon weight and SPAD value of watermelon were quite different.The fresh weight,quality,single-melon weight and SPAD value of watermelon were higher in treatment T_(3)applying garlic straw and sheep manure and treatment T_(4)applying onion straw and chicken manure than in treatment T_(1)applying garlic straw and treatment T_(2)applying onion straw.Specifically,the fresh weight of whole plant was the highest in treatment T_(3),followed by treatment T_(4),and the values of the two treatments increased by 12.83%and 5.94%respectively compared with treatment T_(1);the weight of single melon was the highest in treatment T_(3),followed by treatment T_(4),and the values of the two treatments increased by 42.45%and 31.77%respectively compared with treatment T_(2);and the SPAD values of treatments T_(3)and T_(4)were significantly higher than those of treatments T_(1)and T_(2),and the value of treatment T_(3)was the largest.[Conclusions]This study provides theoretical support for the popularization and application of fertilization techniques combining organic fertilizers and reduced chemical fertilizers for watermelon.

Screening of Soil Antagonistic Bacteria for Watermelon Fusarium Wilt

[Objective] The aim of this study was to screen bacteria strains with stable antagonistic effect against watermelon fusarium wilt from soil and investigate the biological control of watermelon fusarium wilt by applying the antagonistic bacteria strains into soil.[Method] Actinomycete strains,fluorescent bacteria strains and bacillus strains were isolated from soil samples by the dilution-plate method,then its resistance was screened respectively by the improved confront culture method after colonies were purified.Finally,bacteria strains with better antagonistic effect were identified.[Result] 29 bacteria strains with stable antagonistic effect against watermelon fusarium wilt were screened from 39 soil samples,which contained 15 fluorescent bacteria strains,5 bacillus strains and 9 actinomycete strains.Furthermore,three antagonistic bacteria strains of FM2,FM3 and FM4 with the strongest antagonism were identified primarily.[Conclusion] According to cultural characteristics,morphological observation,biochemical and physiological tests,FM2 belongs to bacillus subtilis,while FM3 and FM4 belong to micrococcus.

AFLP Fingerprint and SCAR Marker of Watermelon Core Collection

The identification of germplasm is an important step for effective utilization of the available germplasm. In previous studies, isoenzyme, RAPD and SSR techniques had been used to conduct the genetic identification of watermelon ( Citrullus lanatus (Thunb.) Mansf.), but their effectiveness was limited due to the extremely narrow genetic background among watermelon genotypes. In this research, amplified fragment length polymorphism (AFLP), which was reported as a reliable technique with high efficiency in detecting polymorphism, was used to conduct genetic analysis and variety identification of thirty genotypes of watermelon core collection that represent a wide range of breeding and commercially available germplasm. As a result, a DNA fingerprint based on 15 bands amplified with four primer combinations was developed. In this fingerprint, each genotype has its unique fingerprint pattern and can be distinguished from each other. Furthermore, in or der to facilitate the utilization of AFLP marker in practice, one specific AFLP band of genotype 'PI296341' coming from fragment amplified by primer combination E-AT/M-CAT was successfully converted into a sequence characterized amplified region (SCAR) marker.

Benefit of Interplanting Sugarcane with Watermelon and Soybean

This study was conducted to investigate the effects of interplanting of sugarcane with watermelon and soybean on agronomic traits, yields, quality and benefit of crops, so as to provide reference for extension of the interplanting mode of sugarcane with watermelon or soybean. There were 4 treatments： CK1 （sole planting of sugarcane, no fertilization）, CK2 （sole planting of sugarcane, applying chemical fertilizers）, T1 （interplanting sugarcane with watermelon, applying chemical fertilizers ＋ cow dung）, and T2 （interplanting sugarcane with soybean, applying chemical fertilizers ＋ cow dung）. The results showed that compared with CK2, the sugarcane yield of treatment T1 reached 2.5 t/hm2, the watermelon yield was 1.02 t/hm2, and the total economic benefit increased by 3090 Yuan/hm2; the sugarcane yield in treatment T2 decreased by 7.61 t/hm2 （but not significant）, and the soybean yield was 0.35 t/hm2, and the total economic benefit increased by 720 Yuan/hm2; and the total sugar content in watermelon flesh was 8.59%, and the crude protein content in soybean was 36.15%, satisfying the quality indexes of the same agricultural products. Compared with sole planting of sugarcane, sugarcane plus watermelon or soybean interplanting mode improved economic benefit, treatment T1 showed economic benefit far higher than treatment T2, and is suitable for sugarcane regions with good water and fertilizer conditions and enough labor, and the T2 mode has simple operation, and is suitable for large-area extension.

Mixed Substrate Soilless Cultivation Techniques for Mini Watermelon in Spring Greenhouse of Beijing Area

Watermelon, as a traditional dominant crop in Beijing, has obvious indus- trial advantages. The mixed substrate soilless cultivation techniques developed by the Beijing Agricultural Technology Extension Station for mini watermelon in spring greenhouse can effectively solve the problem of continuous cropping in facility wa- termelon, and they are conducive to green, safe and efficient development of water- melon industry for fixed nutrient solution formula, automatic water and fertilizer irri- gation, stable product quality and facilitating large-scale and standardized production.

Spatial Characteristic Analysis of the Comparative Advantage of Watermelon and Melon Production in Hainan Province

[Objective] This study investigated the spatial characteristics of counties （cities） with comparative advantages in watermelon and melon production to provide reference bases in formulating strategies for the development of watermelon and melon industries in Hainan Province. [Method] By using the sowing area, total yield, and yield per unit area of watermelon and melon in Hainan Province as research u- nits, the yield comparative advantage （YCA）, efficiency comparative advantage （E- CA）, scale comparative advantage （SCA）, concentration ratio comparative advantage （CRCA）, comprehensive comparative advantage （CCA）, ratio of yield per unit area （RYPA）, sowing area ratio （SAR）, and distribution characteristics of watermelon and melon were systematically analyzed. By referring to the agricultural statistic data of 18 counties （cities） in Hainan Province, indexes for each research unit （i.e., the YCA index, ECA index, SCA index, CRCA index, CCA index, RYPA index, and SAR index） were established and calculated to determine the comparative advantage of watermelon and melon production in Hainan Province. A spatial expression of the research result on a map was conducted by using GIS software. [Result] Seven counties （cities） exhibited comparative advantages in watermelon production, namely, Lingshui, Wanning, Wenchang, Dongfang, Sanya, Ledong, and Changjiang. The Eastern and Southern Hainan Provinces had CCAs, and the Western and Northern Hainan Provinces could be reserved for future development. For melon production, four counties （cities） exhibited comparative advantages, namely, Ledong, Lingshui, Sanya, and Dongfang. The Southern Hainan Province had CCA, whereas the West- ern Hainan Province could be reserved for later development. [Conclusion] The result has showed that establishing watermelon and melon as dominant agricultural prod- ucts is necessary for the future development of the industry and for the formulation of a layout of regions with advantages, where key support and construction should be provided preferentially with the aim to raise the yield, quality, and market com- petitiveness of products.

Effects of Exogenous Calcium(Ca) on the Growth of Watermelon Seedlings under NaCl Stress

[Objective] This study was conducted to reveal the effect of exogenous calcium （Ca） in mitigating the damage caused by NaCI stress to watermelon seedlings. [Method] To the liquid medium containing 100 mmol/L NaCI, CaSO4 was added to the final concentrations of 4, 6, 10 and 14 mmol/L. The morphological and physiological indices including plant height, stem diameter, number of leaves per plant, maximum leaf length, maximum leaf width, seedling fresh weight and dry weight, malondialdehyde （MDA） content, relative permeability of plasma membrane, ascorbic acid （AsA） content, free proline content, soluble sugar content and soluble protein content in leaves of the seedlings treated with above media for 10 d were measured. [Result] NaCI stress significantly inhibited the growth of watermelon seedlings. The membrane permeability and MDA content in leaves were significantly increased under NaCI stress, and the contents of proline, soluble sugar, soluble protein and AsA were increased to different extents. Exogenous CaSO4 influenced the morphological and physiological indices of seedlings under NaCI stress in a manner. Treated with 6 mmol/L CaSO4, the growth of seedlings under salinity was significantly improved; membrane permeability and MDA content were drastically reduced, the contents of proline, soluble sugar, soluble pro- tein and AsA in leaves were significantly increased. [Conclusion] Exogenous CaSO＋ alleviates lipid peroxidation and inhibition of seedling growth under NaCI stress by improving the abilities of antioxidation and osmotic adjustment, and 6 mmol/L CaSO4 showed the best effect.

Provincial Comparative Advantages of Watermelon Production in Guangxi Zhuang Autonomous Region

[Objective]This study aimed to clarify the spatial patterns of comparative advantage of watermelon production in Guangxi Zhuang Autonomous Region, to pro-vide theoretical basis for the development of watermelon industry in China. [Method] Based on the agricultural statistics data of Guangxi and al over China, yield com-parative advantage （YCA） index, efficiency comparative advantage （ECA） index, scale comparative advantage （SCA） index, concentration ratio comparative advantage （CRCA） index, comprehensive comparative advantage （CCA） index, ratio of yield per unit area （RYPA） index and sowing area ratio （SAR） index were established and calculated to determine the watermelon production comparative advantages in 31 provinces （cities） in China. Spacial patterns of the comparative advantages were produced by using GIS software. [Result] Nine provinces Shandong, Henan, Anhui, Hebei, Hubei, Jiangsu, Hunan, Zhejiang and Guangxi were the dominant regions in watermelon production al over the country. The Central and Eastern China showed the integrated comparative advantage in watermelon production, while the Southern, Northeastern, Northern and Northwestern China can be considered as the potential places for watermelon production in future. Southwest China gave more priority to watermelon production, so the comparative advantages kept increasing here. [Con-clusion] Based on this study, watermelon production should be a prior consideration among the agricultural products in Guangxi. Related measures should be developed to optimize the regional distribution of watermelon in Guangxi and China to promote healthy competition in watermelon production.

Influence of Xenia Effect on the Fruit of Watermelon

[ Objective] To study the influence of xenia effect to the fruit of watermelon. [ Method ] Self-crossing and crossing by inbreeding of more generation female parent, male parent ：07-10-2-3-3（ tall spherical, golden yellow peel with thin lines, red flesh）, 07-32-2-3-5（ tall spherical, green peel with greenish thick lines, red flesh）, 07-33-1-2-3（tall spherical, green peel with greenish thin lines, red flesh） [ Result] It was found that Fo （07-10-2-3-3 × 07-32-2-3-5） and Fo （07-10-2-3-3 × 07-33-1-2-3） seed ripening was accelerated, and the sugar degree increased by 1.7 - 2.4%, and the flesh became crisp.[ Conclusion] The result demonstrates watermelon has xenia effect.

Morphological Diversity Analysis of Red-seed Watermelon (Citrullus lanatus ssp. vulgaris var. megalaspermus Lin et Chao) Germplasm Resources

[Objective] This study aimed to analyze the morphological diversity of red- seed watermelon （Citrullus lanatus ssp. vulgaris var. megalaspermus Lin et Chao） germplasm resources. [Method] Multiple cluster analysis and principal components analysis on the morphological traits of 51 red-seed watermelon germplasm resources were carried out. [Result] The coefficient of variations （CVs） of 39 morphological traits in 51 red-seed watermelon idioplasm resources ranged from 5.37% to 66.95%, with an average of 22.87%. The average of Shannon diversity information indices was 1.55. Among them, the Shannon diversity information index of seed length was the highest （2.16） and that of seed shell figure pattern was the lowest （0.32）. In ad- dition, the morphological diversity information indices of quantity characters were higher than that of quality characters. The principal components analysis revealed that the variance contribution rates of the first, second and third principal compo- nents were 19.49%, 15.32% and 9.55%, respectively. Cluster analysis divided the 51 materials into three broad branches based on the morphological traits. There was only one material in the fist branch and two in the second branch, and all the three materials were wild. The other 48 materials were divided into the third branch and all of them were cultivars. [Conclusion] This study provided a theoretical basis for the protection and utilization of red-seed watermelon resources.

Study on the Flowering,Fruiting and Seed Setting Characteristic of Wild Watermelon

[Objective] The flowering,fruiting and seed setting characteristic of wild watermelon were discussed in our paper.[Method] The flowering and fruiting habit of wild watermelon were observed,and the effect of different pollination methods（mixed pollination,single flower pollination and natural pollination）on fruit set percentage,weight per fruit,seeds per fruit and thousand-seed weight of wild watermelon were studied in our paper.[Result] Wild watermelon had few female flowers and low fruit set percentage;artificial pollination could not increase the fruit set percentage of wild watermelon obviously,but it could improve weight per fruit,seed yield and quality significantly,and mixed pollination was the best.[Conclusion] Our study could provide reference for the improvement of hybrid seed yield and quality of wild watermelon.

Genetic study on seed coat characteristics in multiploid watermelon

[ Objective] This study is to provide basis for the genetic improvement of triploid watermelon cultivars from seed coat characteristiscs by analyzing its genetic properties. [ Method ] Genetic effects of seed coat characteristics and their related characteristics in tdploid watermelon were analyzed by additive dominant genetic model based on 36 F1 hybrids which were crossed by six female parents of four ecotypes and six male parents of same ecotype according to North Carolina II crossing design. [ Result] The seed coat number characteristics was controlled by additive effects, dominant effects and error variance of genetic together. The additive effects of the length and width of abortive seed coat were significant, and the error variance was significant or highly significant. It was observed that there was a significant negative correlation of additive effects between the seed coat number and fringe soluble sugar. Also there was a significant negative correlation of dominant effects between lycopenes, dry matter and the seed coat number. However, there was a highly significant positive correlation in additive effects between the length and width of abortive seed coat. [ Conclusion ] The results provide guidance for genetic breeding of triploid watermelon cultivars.

Molecular Marker Assisted Selection for Fusarium Wilt Resistance Breeding in Watermelon(Citrullus lanatus)

Molecular identification on diploid and tetraploid watermelon breeding lines which were resistant to Fusarium wilt was carried out with the published dCAPS marker ＂4451_fon＂ which was closely linked with resistance gene of Fusarium wilt race 1. The results showed that all the diploid and tetraploid lines expressed as re- sistant genotype, which were defined as Fusarium wilt-resistant materials. The re- sults were consistent with that of artificial inoculation identification. Molecular identifi- cation results also indicated that the resistant lines were homozygote, and the Fusarium wilt-resistant gene would not separate or lose during the future self- crossed purification. Therefore, resistance selection would not be necessary in their progeny populations. The study results thought that dCAPS marker ＂4451_fon＂ could be applied on molecular marker assisted selection for Fusarium wilt resistance breeding in watermelon to increase breeding selection efficiency and accelerate breeding progress.

Application Effect of Cassava Starch Anaerobic Fermentation Liquid on Watermelon Production

In order to find out a new way for environment-friendly and resourcelized utilization of cassava starch processing wastewater, the cassava starch anaerobic fermentation liquid was applied in watermelon production, and its effects on the growth and development, yield and fruit quality of watermelon were investigated. The results showed that the cassava starch anaerobic fermentation liquid significant- ly promoted the vegetative and reproductive growth and improved the yield and fruit quality of watermelon. Compared with conventional fertilization, the application of cassava starch anaerobic fermentation both with COD concentration of 1 200 mg/L according to the amount of 150 t/hm2 promoted the growth of vines and leaves of watermelon plants, brought forward the flowering, fruiting and harvest of watermelon and significantly increased the fruit number, fruit weight, yield, fruit size, fruit shape index, soluble solid content, soluble sugar content, soluble protein content and Vita- min C content of watermelon. At the same time of improving the yield and quality of watermelon, cassava starch anaerobic fermentation liquid was turned into treasure as a liquid fertilizer. This study provides a new ideal for the yield and quality im- provement of watermelon and the wastewater treating of starch factories.

Purification of Antifungal Protein from Biocontrol Strain XG-1 against Fusarium Wilt of Watermelon

[Objective] This study aimed to isolate and purify the antifungal protein against Fusarium oxysporum f. sp niveum （FON） from Bacillus subtilis XG-I. [Method] The crude protein was obtained by using fractional precipitation with am- monium sulfate, then chromatography using both DEAE-Sepharose FF anion ex- change and Sephacryl S-100 gel filtration columns was adopted for further purifica- tion of the protein, followed by MALDI-TOF-MS analysis of the structure of the at- tained protein which was antagonistic to FON. [Result] The result from MALDI-TOF- MS analysis suggested that the antifungal protein extracted from strain XG-1 was highly homologous to the flagellin （gi114278900） deriving from B. subtilis, with a pro- tein score of 248 and a coverage rate of 63%. It was thus speculated that this an- tagonistic protein was a kind of flagellin with a molecular mass of 30.6 kD. [Conclusion] The results from this study provide theoretical basis for clarifying the mechanisms of the action of strain XG-1 as well as important references for the preven- tion and control of watermelon Fusarium wilt.