Ulvan Reducing Infection of Conidia of Glomerella Leaf Spot Pathogen through Inhibiting Melanin Synthesis

Li Hongli; Yang Chunying; Li Tingting; Li Pingliang; Li Baohua; Lian Sen

doi:10.14083/j.issn.1001-4942.2025.03.020

Abstract：Apple Glomerella leaf spot is the main early defoliation disease in China at present.Ulvan is a polysaccharide from the cell wall of Ulva green algae,which has rich physiological activity to organisms and can improve the resistance of apple to Glomerella leaf spot.In this experiment,the mechanism of ulvan inhibi-ting the injection of Glomerella leaf spot was studied by indoor inoculation,spore germination and real-time quantitative PCR.The results showed that the average incidence rate of the leaves and fruits treated with ulvan before or after inoculation were 19.35％and 18.50％,respectively,while that of the control and treated with ulvan after 24 hours of inoculation were 36.50％and 46.83％,respectively.Treating with ulvan at early stage of pathogen invasion reduced the incidence of Glomerella leaf spot.Ulvan promoted the continuous elongation of conidial germinated tube,and could not form dark appressorium or effective infection pegs.Histological ob-servation showed that the appressorium treated with ulvan only partially formed infection pegs on the leaves,but did not further develop and pierce the host epidermal cells.The real-time quantitative PCR showed that the relative expression level of the melanin synthesis-related gene CfSCD at 6,12 and 24 hours of ulvan treatment reduced by 18.2％,31.3％and 47.6％,respectively,compared with the control.In conclusion,ulvan reduced the infection of conidia through promoting the growth of conidial germinated tubes,reducing the formation of appressorium and inhibiting the melanin synthesis.These results of this study proved the application direction of ulvan on controlling Glomerella leaf spot,and also could provide a technical way for green prevention and control of Glomerella leaf spot.