| Muskmelon is an important cash fruit crop worldwide.However,its production and quality is threatened by Fusarium oxysporum f.sp.melonis and autotoxicity in the continuous monocropping system,and phenolics(benzoic acid,ferulic acid and cinnamic acid)is accounted for the continuous cropping problem.Crop rotation,is reported to be an ideal allelopathic approach to solve soil-borne sickness,improve the utilization rate of soil nutrients and microbial diversity.However,the accumulation of pathogens in soil and the deterioration of soil physic-biochemical properties are commonly exist,which duing to the neglect of the allelopathic performance of crops.This study aimed to develop a practical and sustainable method to control Fusarium wilt of muskmelon using allelopathic crops,the root exudates of 14 crop plants were tested for their ability to suppress the growth of F.oxysporum f.sp.melonis and promote the seed germination and seedling growth of muskmelon;the allelochemaicals of the crops and its allelopathic effects on F.oxysporum and muskmelon were examined;also the mechanism of action of allelochemicals and the effects of allelochemicals on rhizosphere microbial constructure were explored.1.The allelopathic effect of root exudates from 14 test crops on F.oxysporum and muskmelonThe allelopathic effect of root exudates from 14 test crops on F.oxysporum and muskmelon was examined,and the results showed that the root exudates of fennel,onion,rape,crown daisy and lettuce inhibited the growth of F.oxysporum,stimulated the seed germination and seedling growth of muskmelon.The higher the concentration of the root exudates,greater was the inhibition of spore germination and mycelial at 0.01-0.1g-mL-1 concentration.When the concentration of root exudates from 5-crops lower than 0.05 g-mL-1,the seed germination and seedling growth were promoted significantly;and the magnitude of enhacement was decreased above 0.05 g·mL-1 concentration.The maximum stimulation was with root exudates of rape at 0.05 g·mL-1 concentration and the seed germination(%),germination potential and germination index was 86.52%.80.22%and 26.32,respectively;and enhanced the root and shoot growth of muskmelon.And onion and rape root exudates were more stimulatory than lettuce and crown daisy.2.Determination and bioassay of phenolic acids in fennel,onion and rape root exudatesPhenolics in fennel,onion and rape root exudates were detected by HPLC and the benzyl benzoate,dibutyl phthalate and p-tolyl benzoate were identified in all the 3-plants root exudates with high concentration.These phenolics were demonstrated that suppressed the spore germination and mycelial growth of F.oxysporum at test concentration,and the magnitude of inhibition increased with the increasing phenolic acid concentration.Seed and seedling treatment with p-tolyl benzoate promoted the muskmelon seed germination at 0.1 mmol·L-1 concentration,benzyl benzoate and dibutyl phthalate stimulated the germination of muskmelon seeds and the growth of muskmelon seedlings significantly even at 0.25 mmol·L-1 concentration.3.The allelopathic mechanism of root euxdates from 3-crops and allelochemicals on F.oxysporumThe cell wall-degrading enzymes(pectinase?cellulase??-glucosidase)activity,the intracellular protective enzyme(SOD?POD?CAT)activity,fusaric acid of F.oxysporum with treatment of root exudates from fennel,onion and rape and 3-phenolics(benzyl benzoate,dibutyl phthalate and ?-tolyl benzoate)respectively were tested,and the results indicated that were all lower than the control distinctively.4.The effect of allelopathic compounds on the expression of pathogenic and defense gene of F.oxysporumThe relative expression quantity of Fochs V,FUBT,SOD and POD gene of F.oxysporum wras detected by Real-time PCR Detection System.The result of quantitative PCR analysis showed that root exudates of fennel,dibutyl phthalate and benzyl benzoate inhibited Fochs V,FUBT,SOD and POD gene significantly.The minimum relative quantity expression of 4 genes of F.oxysporum were found in the treatment of fennel root exudates at 0.1g·mL-1 concentration,lower than that of dibutyl phthalate and benzyl benzoate.5.The effect of allelopathic crops and phenolics on rhizosphere microbial community structureIn this research,we studied the content,structure and abundance of rhizosphere microbial community by Illumina MiSeq pyrosequencing,aimed to explore the effect of different cultivation,muskmelon replant(M),fennel/muskmelon rotation(F)and treatment with benzyl benzoate(P),on rhizosphere microbial community.The results indicated that Proteobacteria and Ascomycota were predominant in all treatments.Compared with the control,the abundance of Fusarium in M was increased evidently,however,that of F and P were decreased.Moreover,the community richness of bacteria decreased,and the biodiversity had no notable changes,while the community richness and biodiversity of fungi increased in M.The community richness and biodiversity of fungi were increased in F and P,while that of fungi reduced.6.The effect of crop rotation and Trichodera spp.on alleviating continous cropping obstacle of muskmelonPot experiments indicated that root exudates from fennel,onion and rape reduced the Fusarium wilt of muskmelon.Phenolics in rhizosphere soil of muskmelon replant were detected by HPLC and p-hydroxybenzoic acid,ferulic acid,cinnamic acid and benzoic acid were identified with high concentration.Compared with phenolics in muskmelon replant,these 4-autotoxic compounds decreased by 14.33%,44.0%,78.20%and 55.65%in fennel/muskmelon rotation and decreased by 19.51%,29.32%,36.10%and 51.05%in treatment with benzyl benzoate;fennel/muskmelon rotation and benzyl benzoate treatments,in company with Trichodera spp.(Trichoderma harzianum and Trichoderma viride),the degradation increased significantly.This result revealed that fennel/muskmelon rotation,benzyl benzoate and Trichodera spp,exhibited the degration ability of autotoxic compounds. |
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