Study On The Chemistry Between Valsa Mali Var. Mali And Its Host

Plant secondary metabolites are usually the functional substances to provide plants with defense against diseases and pests,but the adaptation of pathogenic fungi to plant chemical defense system in the process of infecting host plants is one of the reasons for serious diseases.At present,there are few reports on this adaptation mechanism.Valsa mali var.mali(Vmm)mainly hosts Malus plants.The infection of this pathogenic fungus can cause the canker of Malus stems and the decay of fruit,and even cause the death of trees in serious cases.In order to explore the toxicity of Valsa mali var.mali and reveal the adaptive mechanism of Vmm to the chemical defense system of plants.In this paper,Vmm-30 and its host plants Malus pumila Mill.and M.sieversii were used as research materials.Through infection induction guided chemical separation,combined with phytochemical and spectral structure identification methods,as well as biological activity methods,the toxic substances of Vmm-30 and its utilization mechanism of host primary and secondary metabolites were studied.Malus pumila Mill.and M.sieversii were analyzed the chemical substances in the roots,leaves and stems by High Performance Liquid Chromatography(HPLC-DAD),it is found that phlorizin(1)is the most important secondary metabolite in all parts of Malus,the content in Malus pumila Mill.and M.sieversii stems are high as 8.24 ±0.17-9.46 ± 1.22 mg/g DW,and phlorizin is defense substance of Malus.In order to explore the chemical response of plants infected by pathogenic fungi,the chemical substances of stems infected by Vmm-30 were systematically analyzed.It was found that the content of phlorizin in branches decreased significantly after infection by Vmm-30.After the mixed culture of phlorizin and non-nutritional suspension,the analysis of HPLC-DAD and Ultra Performance High Liquid Chromatography(UPLC-MS / MS)showed that Vmm-30 could degrade phlorizin into phloretin(2),phloroglucinol(3),3-(4-hydroxyphenyl)propionic acid(4),4-hydroxy-cinnamic acid(5),3-hydroxy-cinnamic acid(6),4’-hydroxyacetophenone(7),trans-cinnamic acid(8),4-hydroxyphenylacetic acid(9),4-hydroxybenzoic acid(10)and 3,4-dihydroxybenzoic acid(11).Quantitative analysis showed that the content of downstream degradation products increased in the infected stems.In this paper,the effects of phlorizin and its degradation products on the germination of Vmm-30 spores were studied by co-culture with Vmm-30 nonnutritional suspension.Compared with the control,the concentration of pathogen spores increased significantly within 120-168 hours of co-culture solution with phlorizin.In the co-culture of the degradation products of phlorizin,phloroglucinol(3),4-hydroxyphenylpropionic acid(4),4-hydroxyphenylacetic acid(9),4-hydroxybenzoic acid(10)and 3,4-dihydroxybenzoic acid(11)can promote the increase of spore concentration of pathogenic fungi,and significantly increase in24-36 hours.The time was significantly shorter than phlorizin.Microscopic observation showed that the germination of spores was observed during the period when the spore concentration increased.This study showed that phlorizin and its degradation products could promote the spores of Vmm-30 germination.The chemical substances in the fermentation broth of Vmm-30 were further separated,and the substances with phytotoxic activity were found through activity screening.Compound W-C-3(5-methylmellein)could significantly inhibit the growth of Amaranthus tricolor L.seeds at the concentration of 50 μg/m L(p< 0.05);Compound W-C-1(4-methoxybenzoic acid)can cause reddish brown spots on Malus leaves at the concentration of 100 μg/m L.This study enriched the chemical diversity of Vmm-30 and revealed that the toxic substances of the pathogen itself were also one of the reasons for the successful invasion of the host plant.Due to the preferential parasitism of Valsa mali var.mali to Malus plants,starting from the chemical defense system of host plants for the first time,this study found that the process of Valsa mali var.mali invading the host is not only completed by a simple invasion mechanism,but also a diverse and complex process.In the process of infecting the host,the pathogen uses the defense substances of the host plant,degrading the main secondary metabolite phlorizin to benefit its own growth,so as to break the defense system of the plant.Moreover,the metabolites obtained from degradation are used to promote the germination of their own spores,so that the conidia can colonize faster and multiply in the host,so as to speed up the infection to the host.Then,the pathogen can also produce some toxic substances,resulting in the pathological changes of the host plant.In this paper,the degradation products of phlorizin by Valsa mali var.mali were systematically studied,and the degradation pathway of phlorizin by Vmm-30 was clarified;It was found for the first time that Vmm-30 could promote the germination of its own conidia by using the degradation products of phlorizin.By studying the relationship between Valsa mali var.mali and the secondary metabolites of the host,this paper expounds the chemical mechanism of the pathogen invading the host,explains how the Valsa Mali var.Mali breaks through the chemical defense line of the plant,reveals the reason why the Valsa Mali var.Mali can successfully infect Malus plants from the perspective of chemical defense substances,and provides a theoretical basis for the occurrence and prevention of Valsa mali var.mali.