Studies On Induced Resistance Of Citrus Canker

Eight microbes and four abiotic elicitors were used for induction of host resistance against citrus canker. In greenhouse tests, Colletotrichum gloeosporioides showed 35% efficacy for the induced resistance after 15 d of challenge inoculation, and 75% lesion inhibition rate against the disease was observed in the 5thd after challenge inoculation. Xanthomonas oryaze pv. oryaze and Xanthomonas axonopodis pv. manihotis showed 27% efficacy for the induced resistance after 25 d of challenge inoculation, and average 34% lesion inhibition rate against the disease was observed in 25d after challenge inoculation. Inoculations by the microbes could protect adjacent host leaves from the infection by X. axonopodis pv. citri for at least 25 d. Abiotic elicitors showed the highest efficacy for the induced resistance in the 5th d after challenge inoculation, and highest lesion inhibition rate was recorded in the 15th d after challenge inoculation. Pinpricking was an effective method for the inoculations by zoetic inducers. Spray was an effective method for the inoculations by abiotic elicitors. The most effective induced resistance was obtained in the 30-day-old navel orange leaves, under the challenge inoculation after 72 h induced inoculation. Studies on the activities of peroxidase(POD), polyphenoloxidase(PPO) and phenylalanine Ammonialyase (PAL) in navel orange leaves after induced inoculations by Colletotrichum gloeosporioides, Xanthomonas oryaze pv. oryaze, and induced treatments by 200mg/L salicylic acid and 50 μg/mL chitosan-25G were carried out. The experimental results indicated that the activities of POD and PPO after induced inoculation were all higher than that of the control, and activities of PAL in zoetic inducer inoculations were all lower than that of the control, and activities of PAL in abiotic elicitros treatments were all higher than that of control. The dissection of diseased tissue showed that the induced inoculations resulted in more suberization in the lesions than that of the control.