The Effect of Polyphenols on Pomegranate Fruit Susceptibility to Pilidiella granati Provides Insights into Disease Tolerance Mechanisms

Abstract

Pilidiella granati, also known as Coniella granati, is the etiological agent of pomegranate fruit dry rot. This fungal pathogen is also well-known as responsible for both plant collar rot and leaf spot. Because of its aggressiveness and the worldwide diffusion of pomegranate crops, the selection of cultivars less susceptible to this pathogen might represent an interesting preventive control measure. In the present investigation, the role of polyphenols in the susceptibility to P. granati of the two royalties-free pomegranate cultivars Wonderful and Mollar de Elche was compared. Pomegranate fruit were artificially inoculated and lesion diameters were monitored. Furthermore, pathogen DNA was quantified at 12–72 h post-inoculation within fruit rind by a real time PCR assay setup herein, and host total RNA was used in expression assays of genes involved in host-pathogen interaction. Similarly, protein extracts were employed to assess the specific activity of enzymes implicated in defense mechanisms. Pomegranate phenolic compounds were evaluated by HPLC-ESI-MS and MS2. All these data highlighted ‘Wonderful’ as less susceptible to P. granati than ‘Mollar de Elche’. In the first cultivar, the fungal growth seemed controlled by the activation of the phenylpropanoid pathway, the production of ROS, and the alteration of fungal cell wall. Furthermore, antifungal compounds seemed to accumulate in ‘Wonderful’ fruit following inoculation. These data suggest that pomegranate polyphenols have a protective effect against P. granati infection and their content might represent a relevant parameter in the selection of the most suitable cultivars to reduce the economic losses caused by this pathogen.

Antifungal Activity and DNA Topoisomerase Inhibition of Hydrolysable Tannins from Punica granatum L.

“…In a previous study [ 5 ], a putative protective effect of pomegranate polyphenols against C. granati was observed. To deeper investigate the activity of these compounds against some of the most devastating pomegranate phytopathogens belonging to Alternaria, Botrytis, Colletotrichum , and Coniella genera, a simple, rapid and reliable spectrophotometric method was used.…”

“…C. granati and B. cinerea proved to be the most and the least sensitive fungus to treatments, respectively. This was reasonably due to the different ability of the tested phytopathogens to hydrolyze polyphenols [ 5 ]. The higher susceptibility of C. granati was probably due to its metabolism, since it has been demonstrated that other species of the genus possess enzymes involved in phenolic compound degradation, such as tannases and aryl sulfotransferase [ 9 ].…”

“…To assess the ability of C. albicans to lysate pomegranate hydrolysable tannins by its enzymatic activity as a response to the pathogen attack, in analogy to what has been previously described for the phytopathogen C. granati [ 5 ], a method based on ultra high-performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC-HRMS) was developed and applied for the analysis of polyphenols in lysates from C. albicans cultures. Quantitative data related to the amount of pomegranate polyphenols detected in cell lysates from C. albicans cultures belonging to two representative strains (one classified and one clinically isolated) treated with punicalagin and punicalin are shown in Table S2 .…”

“…In a recent study, pomegranate cultivars with different susceptibility to the fungal etiological agent of fruit dry rot Coniella granati , also known as Pilidiella granati , were tested for their phenolic profile. The HPLC analyses of the extracts indicated the presence of characteristic peaks in the fungal inoculated samples, corresponding to phenolic compounds derived from the degradation of punicalagin, which is the main ellagitannin present in this fruit [ 5 ]. Since C. granati is fairly able to enzymatically lysate this class of compounds, it is reasonable that the phenolic production is a response to the pathogen attack, i.e., the fungus hydrolyses them in a positive feedback mechanism that ends up in a minor susceptibility of some varieties [ 5 ].…”

“…The HPLC analyses of the extracts indicated the presence of characteristic peaks in the fungal inoculated samples, corresponding to phenolic compounds derived from the degradation of punicalagin, which is the main ellagitannin present in this fruit [ 5 ]. Since C. granati is fairly able to enzymatically lysate this class of compounds, it is reasonable that the phenolic production is a response to the pathogen attack, i.e., the fungus hydrolyses them in a positive feedback mechanism that ends up in a minor susceptibility of some varieties [ 5 ]. This finding supports also the hypothesis that pomegranate polyphenols might play a role in the different susceptibility of pomegranate cultivars to C. granati , their content being a putative marker in selecting programs of new resistant germplasm [ 5 ].…”