Apple scab control and activation of plant defence responses using potassium phosphite and chitosan

摘要

In this study, the effects of two elicitors (potassium phosphite and chitosan) on apple scab (Venturia inaequalis) and their ability to modulate plant defences were assessed. Potassium phosphite and chitosan were sprayed on apple seedlings 7 days before fungus inoculation, and disease intensity was evaluated 14 days after inoculation. Samples of leaves treated with phosphite or chitosan that proved to be susceptible and moderately susceptible to disease were then collected for analysis of their metabolic profile by attenuated total reflectance-Fourier transform infrared spectroscopy. The activity of the plant defence enzymes and the phenolic compound content were also determined by spectrophotometry and high performance liquid chromatography, respectively. The effect of product application on the germination of V. inaequalis was also evaluated. Moderately susceptible leaves presented higher peroxidase activity, regardless of the application of a product. Although it reduced spore germination by 45 %, chitosan did not affect the intensity of the disease. On the other hand, potassium phosphite (2 mu L mL(-1)) reduced significantly the severity of scab by up to 62 % and it promoted the accumulation of salicylic acid, protocatechuic acid, and epicatechin in susceptible leaves, especially after the challenge with V. inaequalis. The salt did not exhibit antimicrobial activity. The resistance induced by potassium phosphite could thus play a significant role in scab control.