Study On The Resistance Induced By Salicylic Acid Against Phytophthora Capsici In Hot Pepper (Capsicum Annuum) And Relative Biochemical Mechanism

Pepper Phytophthora blight caused by Phytophthora capsici L. is the most destructive disease for reducing pepper yields in the world. Building up varietal resistance and induced resistance to the disease are of agricultural importance. In this paper, the disease resistance induced by SA and relative biochemical mechanism of the resistance against P. capsici were studied, by using 4 hot pepper lines with different resistant abilities and 1 P. capsici strain with middle pathogenicity. The following is major results:Higher constitutive lignin content, higher activity of PPO, POD and PAL in health hot pepper seedlings were correlated closely to varietal resistance to P. capsici.Content of lignin and activity of PPG, POD and PAL in 4 hot pepper seedlings tested were increased respectively in it's degree after inoculation with P. capsici, and these increments were more significant in the stems/roots of resistant lines than that in susceptible and high susceptible ones. The lignin content in the stems/roots had a significant positive correlation with disease resistance. However, the increments of PPO, POD and PAL activities in leaves of susceptible and high susceptible lines were ever higher than that in the resistant and tolerant lines, suggesting the enhancement of enzyme activities weren't in proportion to varietal resistance to P. capsici.The variation of lignin content and activities of PPO, POD and PAL in pepper seedlings existed spatial and temporal confinement. PAL activation appears rapid, while PPO activation, slow. Except PPO, the increment of lignin content and activity of PPO, POD and PAL at the infected part (stems/roots) were higher than that in the part far from inoculated site (leaves).SA could induce significantly the resistance of pepper seedlings to P. capsici, but CaCI2, KH2PO4 and VAM couldn't. SA at a relative low concentration from 0.15g/L to 0.3g/L had no antifungal activity in vitro against P. capsici. That means that the diseaseresistant enhancement of the plants treated with SA is due to the induction effect, but not the antifungal effect of SA. Between SA-treatment and challenge inoculation about 1 to 5 days internal was sufficient to induce the disease resistance of hot pepper, and the resistance could remain more than 20 days after SA-treatment.After SA-treatment, content of lignin, activity of PPO, POD, PAL and the disease-resistance of hot pepper were increased simultaneously, and the lignin content had a significant positive correlation with varietal resistance of pepper to P capsici. Since there existed a significant interaction of variance between plant host line and SA-treatment, the effect of induced resistance were ranged about 70% in tolerant pepper lines, 40% in resistant ones, and 18%~23% in susceptible and high susceptible ones.The lignin content and activity of PPO, POD and PAL in pepper seedlings by SA-treatment were much higher than that in untreated control after challenge inoculation with P capsici, and this kind of increment came more rapid and earlier in the resistant and tolerant pepper lines than in susceptible and high susceptible ones. After challenge inoculation, the lignin content was also significantly positively correlated with the disease resistance in SA-treated pepper plants, which suggested that the variation of lignin level, PPO, POD and PAL activities corresponded well with the induced resistance against P capsici in pepper plants by SA-treatment. Besides, after challenge inoculation, there appeared some new POD isoenzyme zymograms and/or disappeared some older ones.