Objective The effect of exogenous methyl jasmonate on resistance to bacterial leaf stripe (BLS) was studied, which would provide a theoretical basis for the prevention and control of BLS in rice.

Method With rice BLS-resistant and susceptible near isogenic lines (K9 and G9) as materials, 0.1 mmol/L methyl jasmonate (MeJA) were sprayed on BLS-resistant and susceptible near isogenic lines (K9 and G9) plants respectively at tillering stage, and water spraying was used as control (CK). The inoculation with Xanthomonas oryzae pv. Oryzicola (Xoc) were conducted at 0, 12, 24, 48, 72 h after MeJA treatment, then the symptoms of BLS were investigated. In K9 and G9 plants sprayed with MeJA for 48 h then inoculated with Xoc, the expression changes of hormone-pathway related genes were further analyzed at 0, 6, 12, 24 and 48 h after inoculation.

Result In K9 plants, the lesion lengths of leaves inoculated at 0, 24, 48, 72h after being sprayed with MeJA were significantly shorter than those in CK; in G9 plants, the lesion lengths of leaves inoculated at 0 h and 12 h after being sprayed with MeJA were significantly longer than those in CK, while inoculated at 72 h after being sprayed with MeJA were significantly shorter than those in CK. Compared with the CK, relative expression levels of jasmonate-pathway related genes LOX2 and AOS2, and pathogenesis-related gene PR10 were upregulated, while relative expression levels of alicylic acid-pathway related genes PAD4 and PAL, ethylene-pathway related genes EIN2 and ERF70, and pathogenesis-related gene PR1a were downregulated in K9 plants inoculated at 48h after being sprayed with MeJA; relative expression levels of jasmonate-pathway related genes LOX2 and AOS2, salicylic acid-pathway related genes PAD4 and PAL and pathogenesis-related genes PR1a and PR10 were upregulated, while relative expression level of ethylene-pathway related gene EIN2 was downregulated in G9 plants inoculated at 48h after being sprayed with MeJA.

Conclusion Exogenous MeJA affects the BLS-resistance in rice resistant and susceptible near isogenic lines. The resistance responses of resistant and susceptible near isogenic lines to Xoc are different at different inoculation time points after MeJA treatment. Exogenous MeJA involves in the defense response to Xoc infection by inducing the expression changes of jasmonate, salicylic acid and ethylene pathway-related genes and pathogenesis-related genes.