Exogenous methyl jasmonate inhibits the spread/multiplication of Xanthomonas campestris pv. pelargonii in the leaves of Pelargonium x hortorum

Bacterial blight is the single most destructive disease of geraniums caused by Xanthomonas campestris pv. pelargonii (Xcp). In this study, we co-cultivated the cut ends of petioles from susceptible Pelargonium x hortorum plants with a virulent strain Xcp 514 and then examined the in vitro cultured leaves attached to the petioles for the early development of the bacterial blight. The blight spots are usually seen from 48-72 hours post co-cultivation. However, if exogenous methyl jasmonate (MeJA) is supplied following the co-cultivation, the leaves expressed few blight spots and the presence of the bacterium was not detected by Xcp-specific PCR. In contrast, Xcp 514 grew normally in a suspension culture supplemented with MeJA. Thus exogenous MeJA may inhibit the spread and/or multiplication of Xcp 514 in the leaf. This suggests that the genes responsive to jasmonate induction may play an important role in regulating the resistance of geraniums to Xcp.