Exogenous treatment with salicylic acid attenuates occurrence of citrus canker in susceptible navel orange (Citrus sinensis Osbeck).
Citrus canker caused by Xanthomonas axonopodis pv. citri (Xac) is a devastating bacterial disease threatening the citrus industry. Salicylic acid (SA) plays a key role in plant defense response to biotic stress, but information is scarce concerning the application of SA to enhancing Xac resistance. In the present research attempts were made to investigate how exogenous application of SA influenced canker disease outbreak in navel orange (Citrus sinensis). Exogenously applied SA at 0.25 mM significantly enhanced the endogenous free and bound SA, particularly the latter. Upon exposure to Xac, lower disease incidence rate and smaller lesion sites were observed in the samples pre-treated with SA, accompanied by repression of bacterial growth at the lesion sites. Concurrent with the augmented disease resistance, SA-treated leaves had higher H₂O₂ level and smaller stomata apertures before or after Xac infection when compared with their counterparts pre-treated with water (control). SA treatment elevated the activities of phenylalanine ammonia-lyase and β-1,3-glucanase, but only the latter was higher in the SA-treated samples after Xac infection. In addition, mRNA levels of two pathogenesis-related genes, CsCHI and CsPR4A, were higher in the SA-treated samples relative to the control. Taken together, our results strongly suggest that the exogenously applied SA has evoked a cascade of physiological and molecular events that function singly or in concert to confer resistance to Xac invasion.
Key Laboratory of Horticultural Plant Biology of Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan 430070, China.
Yin
Y
Wang
Ji-Hong
JH
Liu
D000890:Anti-Infective Agents / Q000494:pharmacology; D032084:Citrus sinensis / Q000235:genetics / Q000378:metabolism* / Q000382:microbiology*; D060467:Disease Resistance / Q000187:drug effects* / Q000502:physiology; D017343:Genes, Plant / Q000187:drug effects / Q000235:genetics; D006861:Hydrogen Peroxide / Q000378:metabolism; D010650:Phenylalanine Ammonia-Lyase / Q000378:metabolism; D010935:Plant Diseases / Q000382:microbiology / Q000628:therapy*; D010940:Plant Proteins / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D020156:Salicylic Acid / Q000378:metabolism / Q000494:pharmacology*; D053532:Xanthomonas axonopodis / Q000187:drug effects* / Q000472:pathogenicity*
D000890:Anti-Infective Agents; D010940:Plant Proteins; D012333:RNA, Messenger; C053376:pathogenesis-related proteins, plant; D006861:Hydrogen Peroxide; D010650:Phenylalanine Ammonia-Lyase; D020156:Salicylic Acid