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.

Litchi downy blight (LDB) caused by Peronophythora litchii destroys 20–30% of litchi fruit every year and causes significant economic losses. Some Exiguobacterium strains exhibit considerable promise in both agricultural and industrial sectors. E. acetylicum SI17, isolated from the litchi fruit carposphere, demonstrated significant biocontrol activity against LDB through pre-harvest treatment. To elucidate its underlying regulatory mechanisms, the genome of SI17 was sequenced and analyzed, revealing a circular chromosome spanning 3,157,929 bp and containing 3541 protein-coding genes and 101 RNA genes. Notably, 94 genes were implicated in the production of secondary metabolites. Among the 29 Exiguobacterium strains so far sequenced, SI17 possessed the largest genome. In the phylogenomic analysis encompassing the entire genome, SI17 was clustered into Group I. Treating litchi fruit with SI17 before harvesting resulted in a decrease in H₂O₂ content in the fruit peel and an increase in superoxide dismutase activity, thus enhancing resistance to LDB. Interestingly, SI17 did not display plate antagonism against Peronophythora litchii SC18. It can be inferred that SI17 generates secondary metabolites, which enhance litchi’s resistance to LDB. This study represents the first documentation of an Exiguobacterium strain exhibiting a role in litchi plant disease and showcasing significant potential for the biological control of LDB.

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.

As a non-pathogenic oomycete, Pythium oligandrum possesses unique advantages, particularly in the context of being a biological control agent. With the increasing awareness of consumer consciousness, people are paying more attention to the use of environmentally friendly strategies in plant disease prevention and control. Pythium oligandrum is a type of biocontrol oomycete that can be developed as a biological control agent, and it does not have adverse effects on humans in the prevention and control of plant diseases. Consequently, there is increasing scientific interest in the beneficial plant–microbe interactions mediated by P. oligandrum. Currently, the main points of focus regarding the beneficial role of P. oligandrum in plant interactions are as follows: (i) P. oligandrum can activate plant defense responses and cause plants to produce resistance, thus protecting them from disease attacks; (ii) it is a strong mycoparasite that can coil around various oomycetes and fungi, directly killing pathogenic microorganisms; (iii) in addition, it can also promote plant growth. In this paper, we will discuss the aforementioned three main features in detail.

Potato production is severely threatened by the oomycete Phytophthora infestans, the fungus Alternaria solani, and the bacterium Ralstonia solanacearum; however, strategies capable of simultaneously managing these three pathogen classes remain relatively scarce. In this study, we designed a series of signal peptide (SP)-fused recombinant constructs containing four functional modules with distinct antimicrobial and immune-inducing properties: GAFP1-2×FYVE, an oomycete-inhibiting antimicrobial protein; BbAFP1-ErBD, a fungal-suppressive protein fragment; the pathogen-associated molecular pattern (PAMP) csp22 derived from R. solanacearum, which elicits effective anti-bacterial immunity; and the microbe-associated molecular pattern (MAMP) PpEli2 identified from Pythium periplocum, which triggers broad-spectrum plant defense responses. Through systematic evaluation of six module order rearrangements, we identified SP-cBG as the optimal multi-domain combination. Further optimization via the introduction of a rigid alpha-helical linker (HL4) yielded SP-cBG-HL4, which tended to show superior resistance against all three pathogens, as reflected in smaller lesion diameters and decreased bacterial titers. qRT-PCR analyses revealed that SP-cBG-HL4 significantly upregulated PTI (CYP71D20, PTI5), SA (PR1, PR2), and JA/ET (PR3, PR4) defense marker genes. Collectively, these findings show that modular domain assembly combined with linker-mediated modular combinatorial optimization represents a powerful engineering strategy for achieving broad-spectrum disease resistance, offering a promising approach to simultaneously control oomycete, fungal, and bacterial pathogens of plants.