Natural Biostimulants Elicit Plant Immune System in an Integrated Management Strategy of the Postharvest Green Mold of Orange Fruits Incited by Penicillium digitatum

Abstract

This study was aimed at testing the integrated use of a natural biostimulant based on seaweed (Ascophyllum nodosum) and plant (alfalfa and sugarcane) extracts and reduced dosages of the conventional synthetic fungicide Imazalil (IMZ) to manage postharvest rots of orange fruits. The following aspects were investigated: (i) the effectiveness of postharvest treatment with natural biostimulant alone or in mixture with IMZ at a reduced dose against green mold caused by Penicillium digitatum; (ii) the differential expression of defense genes in orange fruits treated with the natural biostimulant both alone and in combination with a reduced dose of IMZ; (iii) the persistence of the inhibitory activity of both biostimulant and the mixture biostimulant/IMZ against green mold; and (iv) the residue level of fungicide in citrus peel when applied alone or in combination with the biostimulant. Treatments with the chemical plant resistance-inducer potassium phosphite, alone or with a reduced dose of IMZ, were included for comparison. The mixture of natural biostimulant and IMZ at a low dose consistently reduced the incidence and severity of fruit green mold and induced a significant increase of the expression level of β-1,3-glucanase-, peroxidase (PEROX)-, and phenylalanine ammonia-lyase (PAL)-encoding genes in fruit peel, suggesting that the natural biostimulant elicits a long-lasting resistance of citrus fruits to infections by P. digitatum. Interestingly, the residual concentration of IMZ in fruits treated with the biostimulant/fungicide mixture was significantly lower than that of IMZ in fruits treated only with the fungicide at the same dose and by far below the threshold values set by the European Union. This study laid the foundations for (i) conceiving a practical and more eco-friendly alternative to the conventional postharvest management of green mold of citrus fruits, based almost exclusively on the use of synthetic fungicide IMZ, alone or mixed with potassium phosphite and (ii) providing a better insight into the mechanisms of disease resistance induction by biostimulants.

Co-Infections by Fusarium circinatum and Phytophthora spp. on Pinus radiata: Complex Phenotypic and Molecular Interactions

“…The complex interactions of plant-multiple microorganisms represent a major topic of modern Plant Pathology [52,53]. Indeed, several studies started to investigate the mechanisms by which microorganisms interact with each other and affect the phenotypic and genetic response of plants as a consequence of their pathogenetic activity [52][53][54][55].…”

“…The complex interactions of plant-multiple microorganisms represent a major topic of modern Plant Pathology [52,53]. Indeed, several studies started to investigate the mechanisms by which microorganisms interact with each other and affect the phenotypic and genetic response of plants as a consequence of their pathogenetic activity [52][53][54][55]. In order to try to elucidate how simultaneous infections by different plant pathogens can affect the progression of a specific plant disease traditionally imputed to a single pathogen, this study addressed the plant-microorganism interaction in the pine pitch canker pathosystem (Pinus radiata-Fusarium circinatum) under the additional influence of two aggressive Phytophthora species that cause stem cankers of pines.…”

“…This kind of resistance is correlated with the synthesis of pathogenesis-related (PR) proteins, which, in turn, is mediated by the up-regulation of genes encoding enzymes involved in the biosynthesis of salicylic acid (SA) [68]. Plant cellular respiration is also usually stimulated by pathogenic infections [45,[50][51][52]. In such a kind of oxygen stress condition, it has been observed that plants respond by the synthesis of pyruvate decarboxylase (PDC), which then converts the pyruvate into acetaldehyde and CO 2 and makes possible the production of energy [46].…”

Inhibitory Activity of Shrimp Waste Extracts on Fungal and Oomycete Plant Pathogens

“…Moreover, the restricted number of active ingredients which are allowed for post-harvest treatments increases the risk of selection of fungicide resistant plant pathogens, with the consequent dramatic reduction of the efficacy of synthetic fungicides [7]. For these reasons, during past years, their application has been strictly limited by several governmental institutions worldwide [8,9].…”

“…In order to satisfy the growing request for high-quality and, at the same time, safe and eco-friendly products, throughout the past two decades, the research field strongly focused on the investigation of the potentialities of alternative means to synthetic fungicides to control plant diseases; these include antagonistic microorganisms or derivatives thereof, natural biostimulants [7,9,10], as well as natural antimicrobial compounds [11,12].…”