Mmechanism Of Induced Disease-resistance By Salicylic Acid Against Exserohilum Turcicum

Inducing plants to improve their resistence by biological or chemical factors is one ofthe methods controlling plant disease. Researchs based on field and greenhouse testshowed that: salicylic acid (SA) and its functional analogs such as BTH and INA, couldavailably control various bacterial, fungal and virus disease in dicotyledon such as tobacco,tomato and cucumber. Besides, they showed well effects on controlling some mono-cotyledon diseases such as Powdery Mildew, Leaf Spot of Corn and Downy Mildew. Themain effect is that the mean rates of disease plants and the lesion aera in leaves are reduced.The further study revealed that induced disease-resistance is a process in which somemechanisms of disease resistance is activated in advance. For a certain plant disease, whichdefensive response for disease resistance is activated by SA or its analogs? How do theseresponses function in alleviating the occurrence and development of these sysptoms?Above-mentioned questions have not been researched systemiclly yet.So the resistance induced by SA against Exserohilum turcicum in susceptible maizecultivator and relative biochemical mechanisms were studied systemically in this paper.Here are the main results:The experiment indicated that more than 5mM SA had significant inhibition to sporegermination and mycelium growth of E. turcicum in vitro, and the higher SA concentrationthe stronger inhibition.The greenhouse tests indicated that: the lesion amount and lesion area on the leaf couldbe reduced in the maize seedlings (OH43, OH43Htl, Huangzao4, Huangzao4Htl) sprayedcontinuously for 6 days with 1, 10, 15, 20mM SA. The optimum concentration of SA was10mM, which had the effect of inhibition above 56ï¼…generally.The study on physiological mechanism of resistance to Northern Corn Leaf Blightshowed the infection speed of E. turcicum was slowed after the maize seedlings waspretreated by 10mM SA. Haustorium formation from papilla and the growth of haustoriunin the leaf cells were delayed compared with the water-control. The pretreatment of SAalso induced and promoted cell death in the infected cell as well as the adjacent.The activities of phenylalanine amonma lyase (PAL), chitinase andβ-1,3-glucanse wereenhanced significantly and the activity of CAT was decreased with SA treatment or treatment of E. turcicum inoculation after SA pretreatment, while, the activities of theseenzymes had little changes in the maize seedlings inoculated with E. turcicum only.The content of lignin, DAMBOA and the content of free and combined SA in the maizeleaves were increased with SA treatment or treatment of E. turcicum inoculation after SAinducing, contrastively, they changed barely in the maize leaves inoculated with E.turcicum only.The content of H₂JO₂ in the maize leaf were increased with treatment of E. turcicuminoculation after SA inducing, while it hadn't obvious changes in the maize seedlingsinoculated with E. turcicum only. But it had decreased in the leaves treated with SA.These results above showed that: in the compatible interaction system of maize and E.turcicum, many mechanisms for disease resistance were not activated, which made thepathogens readily infect the maize and lead to serious disease symptoms. Pretreated withSA activated inherent defensive mechanisms for disease in the maize seedlings, whichprevented the infection and spread of the pathogens and lighten the disease symptoms in acertain extent.