Organic mulch can suppress litchi downy blight through modification of soil microbial community structure and functional potentials.

BACKGROUND: Organic mulch is an important management practice in agricultural production to improve soil quality, control crop pests and diseases and increase the biodiversity of soil microecosystem. However, the information about soil microbial diversity and composition in litchi plantation response to organic mulch and its attribution to litchi downy blight severity was limited. This study aimed to investigate the effect of organic mulch on litchi downy blight, and evaluate the biodiversity and antimicrobial potential of soil microbial community of litchi plantation soils under organic mulch. RESULTS: Organic mulch could significantly suppress the disease incidence in the litchi plantation, and with a reduction of 37.74% to 85.66%. As a result of high-throughput 16S rRNA and ITS rDNA gene illumine sequencing, significantly higher bacterial and fungal community diversity indexes were found in organic mulch soils, the relative abundance of norank f norank o Vicinamibacterales, norank f Vicinamibacteraceae, norank f Xanthobacteraceae, Unclassified c sordariomycetes, Aspergillus and Thermomyces were significant more than that in control soils. Isolation and analysis of antagonistic microorganism showed that 29 antagonistic bacteria strains and 37 antagonistic fungi strains were unique for mulching soils. CONCLUSIONS: Thus, we believe that organic mulch has a positive regulatory effect on the litchi downy blight and the soil microbial communities, and so, is more suitable for litchi plantation.

Genome Sequence Data of Peronophythora litchii, an Oomycete Pathogen Causing Litchi Downy Blight.

Peronophythora litchii is an oomycete pathogen that exclusively infects litchi, with infection stages affecting a broad range of tissues. In this study, we obtained a near chromosome-level genome assembly of P. litchii ZL2018 from China using Oxford Nanopore Technologies long-read sequencing and Illumina short-read sequencing. The genome assembly was 64.15 Mb in size and consisted of 81 contigs with an N50 of 1.43 Mb and a maximum length of 4.74 Mb. Excluding 34.67% of repeat sequences, 14,857 protein-coding genes were identified, among which 14,447 genes were annotated. We also predicted 306 candidate RxLR effectors in the assembly. The high-quality genome assembly and annotation resources reported in this study will provide new insight into the infection mechanisms of P. litchii.[Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. 2021.

Antifungal Activity of Natural Volatile Organic Compounds against Litchi Downy Blight Pathogen Peronophythora litchii.

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.

6-Pentyl-2H-pyran-2-one from Trichoderma erinaceum Is Fungicidal against Litchi Downy Blight Pathogen Peronophythora litchii and Preservation of Litchi.

The postharvest losses of litchi caused by litchi downy blight are considerably high. We identified a natural antifungal volatile pyrone, 6-pentyl-2H-pyran-2-one (6PP), synthesized by Trichoderma erinaceum LS019-2 and investigated as biocontrol for litchi downy blight and preservation. 6PP significantly inhibited the growth and sporangial germination of Peronophythora litchii, the causal agent of litchi downy blight, and caused severe cellular and intracellular destructions, as evidenced by electron microscopic analysis. Furthermore, in the treatment, the fruit kept better color, higher weight, and antioxidant activity, so it can maintain freshness and prolong shelf life. Metabolome analysis confirmed the decline of lipids and the accumulation of organic acids in litchi fruits in response to 6PP treatment. These effects from 6PP could alleviate disease effects and prolong the shelf life of litchi fruits. These findings suggested that 6PP could be a useful natural product to control downy blight disease and a new preservative of litchi fruits.

Biocontrol Using Bacillus amyloliquefaciens PP19 Against Litchi Downy Blight Caused by Peronophythora litchii.

Bacillus amyloliquefaciens has been widely used in the agriculture, food, and medicine industries. Isolate PP19 was obtained from the litchi fruit carposphere and showed biocontrol efficacy against litchi downy blight (LDB) whether applied preharvest or postharvest. To further understand the underlying regulatory mechanisms, the genome of PP19 was sequenced and analyzed. The genome comprised a 3,847,565 bp circular chromosome containing 3990 protein-coding genes and 121 RNA genes. It has the smallest genome among 36 sequenced strains of B. amyloliquefaciens except for RD7-7. In whole genome phylogenetic analysis, PP19 was clustered into a group with known industrial applications, indicating that it may also produce high-yield metabolites that have yet to be identified. A large chromosome structural variation and large numbers of single nucleotide polymorphisms (SNPs) between PP19 (industrial strain) and UMAF6639 (plant-associated strain) were detected through comparative analysis, which may shed light on their functional differences. Preharvest treatment with PP19 enhanced resistance to LDB, by decreasing the plant H2O2 content and increasing the SOD activity. This is the first report of an industrial strain of B. amyloliquefaciens showing a plant-associated function and with major potential for the biocontrol of LDB.

Dataset on collecting volatile compounds produced by three bacteria and testing their efficacy against the pathogen Peronophythora litchii.

This data article provides supporting information to a related research article "Identification of volatile organic compounds for the biocontrol of postharvest litchi fruit pathogen Peronophythora litchii" (Zheng et al., 2019) [1]. The litchi downy blight (LDB) caused by Peronophythora litchii is a major postharvest disease that can severely damage litchi trees and harvested litchi fruit. This data article describes the analysis of volatile compounds (VOCs) in three bacterial biological control agents (BCAs) of LDB (Bacillus amyloliquefaciens PP19, Bacillus pumilus PI26, and Exiguobacterium acetylicum SI17) via gas chromatography/mass spectrometry (GC-MS). Volatile compounds produced by the three BCAs were captured at five culture time of 24, 36, 48, 60 and 72 h by a solid-phase micro extraction method. The chemical compositions were identified and their retention times as well as relative peak areas were analyzed. Compounds commonly produced at more than one time points were then subjected to in vitro (on petri dish) and in vivo (litchi fruit and leaves) evaluations for their antagonistic activities against the pathogen Peronophythora litchii.