Establish An Efficient Disease Assay And Screen Tomato Resistant To Gray Leaf Spot

Tomato(Solanum lycopersicum)is an important economic crop in the world.The tomato genome sequencing and annotation has been completed.Also,tomato has resourceful genetic materials,which make it a classic model plant for studying pathogen-plant interaction.However,tomato is susceptible to many diseases that seriously decrease the quality and yield of tomato.Tomato gray leaf spot disease is caused by fungal species of Stemphylium.It occurs more and more frequent in tomato recently.Tomato gray leaf spot develops on tomato leaves very fast and make it very difficult to control.The studies on tomato grey leaf spot is few,since it hasn't been considered as a major disease of tomato.Currently the lack of resistant tomato to grey leaf spot has caused huge economic losses.One of the major reasons is that tomato breeders don't have a reliable and efficient disease assay that could be easily used to screen disease resistant tomato.Therefore,it is extremely urgent to establish an efficient disease assay to screen tomato resistant to gray leaf spot.In this study,we established a highly efficient artificial infection system of gray leaf spot.The results show that this system is an efficient experimental system for screening resistant tomato and studying the mechanism of tomato resistance.First,we collected tomato infected by gray leaf spot disease from various places.We then isolated,identified and purified the pathogen.After purification of the pathogen,we obtained a large number of conidia of the pathogen.Genome sequencing suggests that the pathogen is Stemphylium lycopersici.We thus built up an optimal experimental system to infect Stemphylium lycopersici on tomato.Second,using the disease assay we screened and identified tomato that are resistant to gray leaf spot.The results showed that this assay is a highly efficient system and could be used for large scale tomato screening.Finally,we used the disease assay and investigate the mechanism of tomato resistant to gray leaf spot.We found that disease resistant tomato can inhibit the growth of Stemphylium lycopersici.In addition,we observed the early stage of pathogen-host interaction at cellular level by tissue sections analysis.Gene expression analysis by qPCR showed that infection of Stemphylium lycopersici highly induce gene expression of pathogen-related genes.In gray leaf spot resistant tomato the expression level of defensive genes are higher than that of susceptible tomato.It suggests that this disease assay is also highly efficient to study the molecular basis of tomato resistant to gray leaf spot.