Induction and suppression of the defense response mediated by two fungal derived molecules in strawberry plants

Strawberry plants and fruits are attacked by many pre- and postharvest pathogens affecting yields and profits, and the use of harmful agrochemicals is the common strategy used to control them. To avoid the negative impact caused by those chemicals, plant vaccination using defense elicitors becomes a new environmentally safe alternative. The protein AsES (34 kDa) obtained from the opportunistic pathogen Acremonium strictum proved to be successful on the control of Colletotrichum acutatum, and Botrytis cinerea, the etiological agents of the anthracnose and gray mold diseases in strawberry, respectively. Strawberry plants treated with AsES exhibit a biphasic intracellular oxidative burst (e.g., H₂O₂, O₂^.- and NO), calcium influx, stomata closure, salicylic acid accumulation, ethylene production, callose and lignin deposition, and the upregulation of several genes involved in the onset of the defense response. However, the success of the foliar application of AsES on plants can be seriously jeopardized if pathogens exerting a defense suppression effect are present in the crop area. In our lab we have demonstrated that a virulent isolate of the pathogen C. acutatum (M11) suppresses the defense response activated by AsES. Further studies showed that the isolate M11 produces a small molecule (<1 kDa) that is secreted to the medium causing the suppression of the oxidative burst, and most of the biochemical, physiological and molecular markers associated to the defense response mentioned above. This outcome casts a great deal of concern on the use of bioproduct to protect plants against diseases or as growth enhancement.