Abstract
Litchi (Litchi chinensis Sonn.) is a commercially important fruit but its production and quality are restricted by litchi downy blight, caused by the oomycete pathogen Peronophythora litchii Chen. Volatile substances produced by a biocontrol antinomycetes Streptomyces fimicarius BWL-H1 could inhibited P. litchii growth and development both in vitro and in detached litchi leaf and fruit infection assay. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) analyses indicated that volatile organic compounds (VOCs) from BWL-H1 resulted in severe damage to the endomembrane system and cell wall of P. litchii cells in vitro and abnormal morphology of appressoria, as well as deformed new hyphae in infection process. VOCs could suppress mycelial growth, sporulation, while with no obvious effect on sporangia germination. Based on gas chromatography-mass spectrophotometric analyses, 32 VOCs were identified from S. fimicarius BWL-H1, the most abundant of which was phenylethyl alcohol. Eight VOCs, including phenylethyl alcohol, ethyl phenylacetate, methyl anthranilate, α-copaene, caryophyllene, humulene, methyl salicylate and 4-ethylphenol, that are commercially available, were purchased and their bioactivity was tested individually. Except for humulene, the other seven tested volatile compounds shown strong inhibitory activity against mycelial growth, sporulation, sporangia germination and germ-tube growth of P. litchii. Especially, 4-ethylphenol showed the highest inhibitory effect on sporulation at a very low concentration of 2 µL/L. Overall, our results provided a better understanding of the mode of action of volatiles from BWL-H1 on P. litchii, and showed that volatiles from BWL-H1 have the potential for control of postharvest litchi downy blight.
Highlights
Litchi (Litchi chinensis Sonn.) is one of the most popular and important subtropical fruits due to its taste, appearance, and economic value [1]
The effect of volatiles produced by wheat seed culture of S. fimicarius BWL-H1 was tested in a sealed Petri dish chamber, and the result showed that radial mycelial growth of P. litchii was greatly suppressed by the volatiles in a dose-dependent manner
No mycelial growth was observed in the presence of volatiles produced by 40 g/L BWL-H1 cultures (Figure 1A–J), whereas autoclaved wheat seed displayed no observable effects on radial mycelial growth
Summary
Litchi (Litchi chinensis Sonn.) is one of the most popular and important subtropical fruits due to its taste, appearance, and economic value [1]. Litchi downy blight, caused by Peronophythora litchii. P. litchii can infect litchi plants at a broad range of growth. P. litchii infects litchi leaves or fruits through oospores, which subsequently develop into sporangia and release zoospores in the litchi orchard. The oomycete infection initially causes withering and watery brown spots on the infection sites of tender leaf or fruit, or panicle rot, and produces downy white sporangiophores during late infection, which leads to major pre- and postharvest decay of the fruit and results in considerable economic losses [2,3]. A wide range of chemical fungicides have been tested and evaluated to control this disease [4], but considering of the unavoidable emergence of fungicide resistance as well as toxicological risks and environmental pollution [5], alternative means to control litchi downy blight are urgently required
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