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Biocontrol of Penicillium digitatum on Postharvest Citrus Fruits by Pseudomonas fluorescens 时间:2018-11-15 12:00 来源:未知作者:admin 点击: 次 Abstract:The effectiveness of the bacteria antagonist Pseudomonas fluorescens to control green mold caused by Penicillium digitatum on oranges (Citrus sinensis Osbeck, cv. Jincheng) and the possible modes of action were evaluated. Whether in vitro or in vivo, treatments with cell-free autoclaved cultures or culture filtrate had limited capacity to suppress P. digitatum, while P. digitatum was significantly inhibited by bacterial fluid (P. fluorescens in the nutrient broth liquid medium) and bacterial suspension (P. fluorescens in sterile distilled water) with living cells. There was a positive relationship between the concentration of P. fluorescens in bacterial suspension and its biological efficacy. In addition, P. fluorescens was effective when applied preventatively but not when applied curatively. In the inoculated wounds, the population of P. fluorescens was an approximately 28- and 34-fold increase after being incubated at 20°C for 8 d and at 4°C for 16 d, respectively, and P. digitatum could effectively stimulate the growth and reproduction of P. fluorescens. Moreover, P. fluorescens was able to inhibit spore germination and germ tube elongation of P. digitatum as well as induce resistance on citrus peel by increasing the chitinase (CHI) activity and advancing the activities peaks of β-1,3-glucanase (GLU), peroxidase (POD), and phenylalanine ammonia lyase (PAL). All of these results support the potential application of P. fluorescens against green mold on postharvest citrus.
1. Introduction
Citrus fruits are important commercial fruits and widely distributed in the world. It is estimated that the global citrus production in 2017 was up to around 50 million metric tons [1]. Besides good sensorial characteristics, citrus contain high levels of antioxidant compounds, including vitamin C, flavanones, and anthocyanins [2, 3]. However, citrus fruits are exposed to many postharvest diseases during transportation and storage, among which green mold, caused by Penicillium digitatum, is one of the most devastating diseases, causing significant economic and resource losses in the world [4–6]. In addition, P. digitatum can cause an allergic response by producing countless air-borne spores [3, 7]. Traditionally, application of synthetic fungicides such as thiabendazole and imazalil was the main method to control green mold [8, 9], while resulted in pathogen resistance [10]. Public pressure to reduce fungicide use and to obtain healthy and safe fruits has driven research for development of no-chemical approaches to control postharvest diseases [3, 6, 11]. Among the different means, the use of antagonistic microorganisms for biological control of fruits decay appears to be an excellent option [12–14].
The biological control of major postharvest pathogens for citrus was reported by all kinds of microbial antagonists such as Bacillus subtilis [15, 16], Pseudomonas spp. [17], Debaryomyces hansenii [18], Kloeckera apiculate [13], Candida membranifaciens [6], and so forth. Pseudomonas fluorescens, a Gram-negative bacterium that is a common and abundant inhabitant in the soil and plant surfaces [19], has the capacity to inhibit or suppress a variety of pathogenic fungi [20, 21]. As an effective biocontrol agent, P. fluorescens has been studied extensively for plant disease in the rhizosphere for producing antibiotics such as phenazine-1-carboxylicacid (PCA) and 2,4-diacetylphloroglucinol (DAPG) [22, 23], producing volatile compounds [24, 25], excreting siderophore to compete with iron [26], competing for nutrients and space sites [27] and inducing systemic resistance [28, 29]. However, there are few researches or reports on its potential as a biocontrol agent in postharvest disease of fruits, especially for citrus fruits.