Interactions between cranberries and fungi: the proposed function of organic acids in virulence suppression of fruit rot fungi.

Mariusz Tadych,Jennifer Johnson-Cicalese,Nicholi Vorsa,James F White,Yifei Wang,Marshall S Bergen,James J Polashock

doi:10.3389/fmicb.2015.00835

Abstract

Cranberry fruit are a rich source of bioactive compounds that may function as constitutive or inducible barriers against rot-inducing fungi. The content and composition of these compounds change as the season progresses. Several necrotrophic fungi cause cranberry fruit rot disease complex. These fungi remain mostly asymptomatic until the fruit begins to mature in late August. Temporal fluctuations and quantitative differences in selected organic acid profiles between fruit of six cranberry genotypes during the growing season were observed. The concentration of benzoic acid in fruit increased while quinic acid decreased throughout fruit development. In general, more rot-resistant genotypes (RR) showed higher levels of benzoic acid early in fruit development and more gradual decline in quinic acid levels than that observed in the more rot-susceptible genotypes. We evaluated antifungal activities of selected cranberry constituents and found that most bioactive compounds either had no effects or stimulated growth or reactive oxygen species (ROS) secretion of four tested cranberry fruit rot fungi, while benzoic acid and quinic acid reduced growth and suppressed secretion of ROS by these fungi. We propose that variation in the levels of ROS suppressive compounds, such as benzoic and quinic acids, may influence virulence by the fruit rot fungi. Selection for crops that maintain high levels of virulence suppressive compounds could yield new disease resistant varieties. This could represent a new strategy for control of disease caused by necrotrophic pathogens that exhibit a latent or endophytic phase.

Highlights

Many pathogens possess a latent phase where they grow within tissues of hosts without causing harm or resulting in expression of disease symptoms (Luo and Michailides, 2001; Sauer et al, 2002; Vega et al, 2010; O’Connell et al, 2012; Tadych et al, 2012; Delaye et al, 2013)
Cranberry Fruit Our results showed that the levels of benzoic acid (BA), quinic acid (QA), and citric acid (CA) in developing cranberry fruit were significantly different depending on a cranberry genotype and a fruit development stage (Table 2)
Our data show that levels of QA in cranberries of the six tested genotypes decreased throughout fruit development (Table 2) and the rot-resistant genotypes (RR) showed a more gradual decline in QA levels during the first 2 weeks of our study than that observed in the more rot-susceptible genotypes (Figure 3D)

Summary

Introduction

Many pathogens possess a latent phase where they grow within tissues of hosts without causing harm or resulting in expression of disease symptoms (Luo and Michailides, 2001; Sauer et al, 2002; Vega et al, 2010; O’Connell et al, 2012; Tadych et al, 2012; Delaye et al, 2013). It is only after this period of latent development that disease expression may become evident. Müll (Oudemans et al, 1998; Polashock et al, 2009; Tadych et al, 2012)

Methods

Results

Conclusion