Allelopathic Mechanism Of Chinese Chives Root Exudates On Regulating Resistance To Fusarium Wilt Of Bitter Gourd

Bitter melon(Momordica charantia L.)Fusarium wilt is a soil-borne disease caused by Fusarium oxysporum Schl.f.sp.momordicae in bitter gourd,which seriously harms the yield and quality of bitter gourd.Plant-derived fungicides are less harmful to the environment and human health,and have long been regarded as ideal substitutes for chemical fungicides.The intercropping rotation mode is one of the effective methods to reduce soil-borne diseases.Bulb vegetable(Allium),such as garlic,green garlic,and onions,are recognized as good previous crops,and their root exudates can effectively reduce the occurrence of soil-borne diseases by improving the soil micro-ecological environment,thereby alleviating continuous cropping obstacles.In this study,soil culture method was used to collect Chinese chives root exudates,and the allelopathic mechanism of Chinese chives root exudates in regulating Fusarium wilt was investigated by in vitro antibacterial test and bitter gourd-Chinese chives co-culture system.Gas chromatography high-throughput timeof-flight mass spectrometry(GC-TOF-MS)technique was used to identify the chemical composition of Chinese chives root exudates.The antibacterial experiment in vitro and adding exogenous chemical compound experiment verified its allelopathic effect on Fusarium wilt,and identified the main allelochemicals in the root exudates of Chinese chives.Multivariate statistical analysis and bioinformatics analysis methods were used to elucidate the allelopathic mechanism of Chinese chives root exudates regulating resistance to Fusarium wilt of bitter gourd.The main results were as follows:1.With the increase of root exudate concentration of Chinese chives,the inhibition rate of mycelia growth and spore germination decreased firstly and then increased,and the inhibition effect reached the maximum at 0.64 mg/g.The results showed that the root exudates of Chinese chives could significantly inhibit the mycelial growth and spore germination of Fusarium oxysporum Schl.f.sp.momordicae,and promoted the inhibition of Fusarium oxysporum Schl.f.sp.momordicae at low concentration,but inhibited the growth of Fusarium oxysporum Schl.f.sp.momordicae at high concentration.The composition of root exudates was identified by GC-TOF-MS,and a total of 473 peaks were identified,among which 29 peaks with similarity > 650 were mainly organic acids,amino acids,polysaccharides,alcohols and fatty acids.It was inferred that the main allelochemicals in root exudates of Chinese chives were L-pyroglutamic acid,benzoic acid and gallic acid.2.Through the co-cultivation test of bitter melon and Chinese chives,it is clear that intercropping Chinese chives has certain regulating effects on three varieties(strain)of bitter melon with different resistances,but the control effects are different.Among them,intercropping 20 Chinese chives has a significant effect on “Reke No.2”.The defense enzyme activities of different varieties of bitter gourd were different with the increase of the number of Chinese chives intercropping.The POD,PPO and SOD activities of “Reke No.1” showed a trend of promotion at low intercropping number and inhibition at high intercropping number.It could significantly increase the POD activity of “Reke No.2”,and intercropping 60 and 80 Chinse chives could significantly increase the POD and SOD activities of “No.176”.In conclusion,intercropping Chinese chives can significantly change the defense enzyme activities of bitter gourd,indicating that the root exudates of Chinese chives can improve the physiological resistance of bitter gourd and enhance the ability to resist Fusarium wilt stress,so as to reduce the occurrence of Fusarium wilt.Based on transcriptomic and metabolomic analysis,a joint analysis of the KEGG metabolic pathways shared by differentially expressed genes and differential metabolites was performed.The results showed that the beta-alanine metabolism pathway was most closely related to the response of bitter gourd to Fusarium wilt stress,and the MC07g0690 and MC08g2554 genes and metabolites uracil,pantothenic acid and L-aspartic acid in the leaves of bitter gourd were involved in this pathway and were significantly up-regulated.There is a positive regulatory relationship,and the differential expression modifies the response of bitter gourd to Fusarium wilt stress.It is speculated that the root exudates of Chinese chives can induce the up-regulation of MC07g0690 and MC08g2554 genes in the leaves of bitter gourd,thereby affecting the beta-alanine metabolism pathway and making it susceptible to Fusarium wilt.The metabolite levels of uracil,pantothenic acid and L-aspartic acid were increased in the infected leaves of bitter gourd,which improved the resistance of bitter gourd to Fusarium wilt and was beneficial to resist the infection of Fusarium wilt.3.Through the co-cultivation test of bitter gourd and Chinese chives,it was clear that intercropping of Chinese chives improves the soil micro-ecological environment of bitter gourd.Among them,intercropping 20 and 40 Chinese chives significantly improved the activity of soil acid phosphatase and sucrase of “Reke No.1”.Intercropping 40 Chinese chives could significantly increase the soil urease and catalase activities of “Reke No.2”,and intercropping 60 Chinese chives could significantly increase the activities of soil invertase and acid phosphatase,intercropping 80 Chinese chives reduced the activity of sucrase in “No.176” soils.It indicated that intercropping Chinese chives could change soil micro-ecological environment by increasing soil enzyme activity,thereby improving the ability of bitter gourd to resist pathogenic bacteria infection.Based on a combination of high-throughput sequencing technology and bioinformatics method.It was found that Chinese chives root exudates could increase the diversity of bitter melon rhizosphere soil microbial community,and the effect on fungi was greater than that on bacteria,Chinese chives can directional enrichment of beneficial microbial groups through root exudates,such as Mortierella,Pseudomonas and Bacillus,resulting in changes in the rhizosphere microbial community structure,this in turn increases the resistance of bitter gourd to Fusarium wilt.The results showed that when bitter gourd was infected by Fusarium wilt,the root exudates of Chinese chives could change the rhizosphere microbial community structure of bitter gourd,thereby causing changes in the functional abundance of the microbial community,increasing the resistance of bitter gourd to Fusarium wilt.4.Through the antibacterial test of the possible main allelochemicals L-pyroglutamic acid,benzoic acid and gallic acid,it was found that the three allelochemicals have significant allelopathic inhibitory effects on Fusarium oxysporum Schl.f.sp.momordicae.With the increase of allelochemicals concentration,the inhibitory effect on Fusarium oxysporum Schl.f.sp.momordicae showed an increasing trend,and 5 mmol/L treatment had the best antibacterial effect,and the allelopathy was benzoic acid > L-pyroglutamic acid > gallic acid.The pot experiment was carried out by exogenous addition method with the best antibacterial allelochemicals L-pyroglutamic acid and benzoic acid.The results showed that Lpyroglutamic acid and benzoic acid had obvious regulating effect on Fusarium wilt of bitter gourd,and benzoic acid was higher than L-pyroglutamic acid.Two allelochemicals can increase the chlorophyll content,defense enzyme activity and soil enzyme activity of bitter gourd.It was indicated that benzoic acid and L-pyroglutamic acid can change the soil microenvironment by increasing the physiological resistance of bitter gourd.Thus,the bitter gourd can resist to the infestation of Fusarium wilt.The allelopathy of leaf physiological and biochemical indicators and soil enzyme activities were comprehensively evaluated,and 5mmol/L treatment has the best effect.The optimal disease-resistant concentration confirmed that the root exudates of Chinese chives could regulate the resistance of bitter gourd to Fusarium wilt.In summary,this research studied the allelopathic mechanism of Chinese chives root exudates regulating resistance to Fusarium wilt of bitter gourd,and revealed that Chinese chives root exudates inhibited Fusarium oxysporum Schl.f.sp.momordicae by regulating the growth physiological resistance and improving the rhizosphere soil micro-ecological environment of bitter gourd.Therefore,the systemic resistance of bitter gourd is improved to cope with the stress caused by the invasion of Fusarium oxysporum Schl.f.sp.momordicae,and the ability of bitter gourd to resist Fusarium wilt is enhanced,thereby reducing the occurrence of Fusarium wilt.