Effects Of Forsythia Suspensa Extract On Tomato Crown And Stem Rot Resistance And Plant Growth

Tomato is one of the most important vegetable crops and widely cultivated in China due to its high economic and nutritional value.Crown and stem rot spread quickly with the flow of water,and causes severe disease on tomato with almost 100% loss of the total yield.Currently crown and stem rot threats the tomato production in facilitates of northern China,and its causal agent is Fusarium solani(F.solani)which has many races with diverse resistance against fungicide.The conventional method to control the crown and stem rot is to apply different types of fungicides,while excessive application leads to the evolution of pathogen with higher resistance to fungicides,residues of fungicide in tomatoes and destruction of soil environment.Herbal medicines contain many active compounds which can either inhibit pathogen growth or stimulate plant defense against pathogen infection.Therefore,in this study we investigated the effects of Forsythia suspensa(F.suspensa)extract and its active compound forsythiaside A on the inhibition of F.solani growth on the medium or in tomato plants and the promotion of tomato plant growth under normal growth conditions without the fungal infection.Our results are as follows:1)We first isolated the fungal pathogen from tomato plant with severe symptoms of crown and stem rot.Morphological analyses of colonies and spores indicated that the fungal pathogen belongs to Fusarium.Analyses of internal transcribed spacer(ITS)and elongation factor 1-alpha(EF-1α)sequences from the fungal pathogen revealed that it was a new isolate of F.solani strain.Re-inoculation with this isolate on tomato plants resulted in the same disease symptoms of crown and stem rot confirming the pathogenicity of the fungal pathogen.2)We established three inoculation methods with the new isolate of F.solani including inoculating seedlings grown on the medium,inoculating soil-grown seedlings at the junction between stem and root,and inoculating soil-grown seedlings by mixing fungal pathogens in the soil.We compared the infection efficiency of three method by analyzing the disease incidence,length of disease spot and time for the occurrence of disease symptom.The first method had 100% disease incidence and required 4 days for the symptom occurrence.The second method had 84% disease incidence and required 10 days for the symptom occurrence.The third method had 71% disease incidence and required 21 days for the symptom occurrence.The method of inoculating soil-grown seedlings at the junction between stem and root is the simplest,followed by inoculating soil-grown seedlings by mixing fungal pathogens in the soil,and inoculating seedlings grown on the medium is the most complicated.3)We investigated the inhibitory effects of F.suspensa extract on the fungal growth on the medium.Concentrated solution of 100 g/L(w/v)F.suspensa extract by 2.5-,5.0-,7.5-or10-fold all effectively inhibited fungal growth,in which 7.5-fold concentrated solution had the best effect.4)We treated F.solani isolate inoculated tomato seedling with F.suspensa extract and its active compound forsythiaside A through the irrigation,both of which significantly reduced the disease symptoms.Forsythiaside A had better effects than F.suspensa extract.5)We sprayed F.suspensa extract at the concentration of 2,4,6,8 and 10 g/L on tomato leaves,and noticed that low concentration could promote plant growth and 6 g/L had the best effects,while 8 and 10 g/L had inhibitory effects.6)We compared the effects of three application methods with 6 g/L F.suspensa extract on tomato growth including spray,irrigation,and spray plus irrigation.The spray method could promote the leaf photosynthesis,the irrigation method could enhance the underground tissue growth,while the spray plus irrigation method led to the growth inhibition.7)We also investigated the effects of forsythiaside A on tomato growth using spray,irrigation,and spray plus irrigation method.All three methods could promote tomato plant growth including aboveground and underground tissues,and the irrigation method had the best effects.