Calcium oxide, potassium phosphite and a Trichoderma enriched compost water suspension protect Capsicum annuum against Phytophthora capsici by priming the immune system.

Alessio Bellini,Lodovica Maria Gullino,Massimo Pugliese,Giovanna Roberta Meloni,Vladimiro Guarnaccia

doi:10.1002/ps.6401

Abstract

BACKGROUNDProper management of Phytophthora capsici in pepper cultivation is extremely important, since Phytophthora blight is the main disease of this crop worldwide. In the past, the main strategy adopted had been the use of fungicides, causing, in some cases, the development of P. capsici resistant strains. In this work three different treatments selected from previous studies (potassium phosphite, calcium oxide and a water suspension from Trichoderma sp. TW2 enriched compost) were tested to prove their ability to activate the systemic acquired resistance (SAR) in pepper against P. capsici; acibenzolar‐s‐methyl was used as positive control. Two independent growth chamber pot experiments were performed, spatially dividing the site of treatments application (as radical drench) and the site of inoculation (as agar plug on the third leaf).RESULTSLeaf lesions were measured, showing a significant reduction on all treated plants compared to the untreated control. To further confirm this hypothesis, the expression levels of three SAR key genes (CaPBR1, CaPO1 and CaDEF1) were evaluated though RT‐Real Time PCR at the three end‐point times: T0, T6 and T24. A significant increase of target genes expression at least in one end‐point time in each treated plant was observed. Eventually, statistical overaccumulation of salicylic acid was observed in the upper leaves at the same end‐point times, through HPLC‐MS/MS analysis.CONCLUSIONThis work confirmed the hypothesis that the three treatments tested have the ability to prime the plant immune system, leading pepper to an alert status able to confer a better defence against P. capsici. © 2021 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Highlights

Phytophthora capsici is a filamentous soilborne oomycete considered one of the most disruptive pathogens of some vegetable crops, representing the main problem on pepper (Capsicum annuum).[1]
The fact these molecules have a specific site of action together with some aspects of P. capsici biology, i.e., the sexual recombination through oospores production when two mating types are paired and the mutations in zoospores genome mediated by UV light since sporangia are hyaline,[4] led to the selection of some resistant strains
Average values of 3, 4, 4.6 and 4.8 mm were observed in compost water suspension, acibenzolar-s-methyl, potassium phosphite and calcium oxide treated plants, respectively, compared to an average value of 18 mm measured on the leaves of untreated plants

Summary

Introduction

Phytophthora capsici is a filamentous soilborne oomycete considered one of the most disruptive pathogens of some vegetable crops, representing the main problem on pepper (Capsicum annuum).[1]. Disease management is focused on several management tools including agronomical strategies, chemical fungicides and soil disinfestation.[3] A good control of the disease was guaranteed with the use of fungicides belonging to phenylamide class (PAF), in particular metalaxyl and its enantiomer mefenoxam. The fact these molecules have a specific site of action together with some aspects of P. capsici biology, i.e., the sexual recombination through oospores production when two mating types are paired and the mutations in zoospores genome mediated by UV light since sporangia are hyaline,[4] led to the selection of some resistant strains. Two independent growth chamber pot experiments were performed, spatially dividing the site of treatments application (as radical drench) and the site of inoculation (as agar plug on the third leaf)

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