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Abstract
Rice sheath blight, a fungal disease caused by Rhizoctonia solani, seriously threatens rice production. Some of the volatile organic compounds (VOCs) produced by microbes are inhibitory to the growth of the plant pathogen, and hence may have the potential as environmentally friendly antifungal substances. However, information on the inhibitory effect of VOCs released by rice rhizosphere bacteria on R. solani is scarce. In this study, bacteria from the rice rhizosphere capable of inhibiting the growth of R. solani via releasing VOCs were screened using a double Petri dish assay. Headspace solid phase microextraction and gas chromatography mass spectrometry (GC/MS) were used to identify and quantify the VOCs. The contributions of VOCs to the inhibition of the growth of R. solani were estimated by constructing a random forest model, and were verified using pure compounds. Nine strains (i.e., Pseudomonas sp. No. 3, Enterobacter sp. No. 26, Enterobacter sp. No. 34, Pseudomonas sp. No. 35, Ralstonia sp. No. 50, Bacillus sp. No. 62, Arthrobacter sp. No. 146, Brevibacillus sp. No. 2–18, and Paenisporosarcina sp. No. 2–60) showed various inhibition on R. solani growth via VOCs. The inhibitory effect ranged from 7.84% to 100%, with Ralstonia sp. No. 50 completely inhibiting the growth of R. solani. Five VOCs (i.e., benzoic acid ethyl ester, 3-methyl-butanoic acid, 2-ethyl-1-hexanol, 3-methyl-1-butanol, and 6-methyl-5-hepten-2-one) identified by random forest model were confirmed to be toxic to R. solani when applied as a pure chemical compound. In particular, benzoic acid ethyl ester, 3-methyl-butanoic acid, and 2-ethyl-1-hexanol were lethal to R. solani. In summary, the rice rhizosphere bacteria (Ralstonia sp. No. 50) and VOCs (benzoic acid ethyl ester, 3-methyl-butanoic acid, and 2-ethyl-1-hexanol) showed potential to be used as new resources for biological control of rice sheath blight.
Highlights
They all inhibited the growth of R. solani by releasing volatile organic compounds (VOCs), with the inhibition ranging from 7.84% to 100%
In this study we found that nine bacterial strains isolated from the rice rhizosphere inhibited the growth of R. solani without direct contact, indicating that these bacteria released VOCs that were inhibitory to the growth of R. solani
There are many related reports in the literature on bacteria that could inhibit the growth of pathogens by releasing VOCs [21,22], no report can be found on the VOCs released by rice rhizosphere bacteria that can inhibit the growth of R. solani
Summary
Rice is an important staple food crop globally. Rice sheath blight caused by Rhizoctonia solani is one of the most economically important rice diseases worldwide, causing devastating crop losses and representing a serious threat to global food security [1,2]. Rice sheath blight is mainly controlled by fungicides [3]. A range of alternate control measures such as fertilization, soil amendments, and agricultural management have been recommended. These alternative measures are time-consuming and laborious, which is not effective [7,8,9]. It is imperative to search for new active agents against rice sheath blight
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