Resistance genes expression pattern analysis of Serendipita indica-root colonized sour orange plants in challenging with citrus bacterial blast (Pseudomonas viridiflava)

Citrus bacterial blast disease is one of the prevalent diseases in most citrus-growing regions in the world. Plants use a wide range of mechanisms to defend against pathogens, and the plant-pathogen interaction induces the expression of genes involved in the plant resistance. Furthermore, symbiotic association between plant and mycorrhizal fungi could effectively promote growth and protect the plant against adverse environmental conditions. In the present study, Serendipita indica-root colonized sour orange seedlings were infected by Pseudomonas viridiflava and the expression patterns of PR1, PR2, PR3, PR4, PR5, PAL, POX, and LOX genes in the early stages of citrus blast disease were investigated using the qRT-PCR at different sampling times. According to the results, the response of defense genes to bacterial infection was time dependent. In the S. indica-colonized sour orange plants, the highest level of PR1, PR4, PAL, POX, PR3, and PR5 genes expression was observed at 48 h after infection, but the expression of PR2 and LOX genes was increased at 72 h after infection compared to the control plants. It seems that S. indica can induce systemic effects and prepare the host plant to increase the expression of defense genes more rapidly once it receives a signal for the presence of the pathogen.