Intercropping with guava (Psidium guajava L.) can assist with the management of Asian citrus psyllid (ACP, Diaphorina citri Kuwayama), the insect vector of the huanglongbing pathogen, in citrus orchards. Sulfur volatiles have a repellent activity and physiological effects, as well as being important components of guava volatiles. In this study, we tested whether the sulfur volatiles emitted by guava plants play a role in plant–plant communications and trigger anti-herbivore activities against ACP in sweet orange plants (Citrus sinensis L. Osbeck). Real-time determination using a proton-transfer-reaction mass spectrometer (PTR-MS) showed that guava plants continuously release methanethiol, dimethyl sulfide (DMS), and dimethyl disulfide (DMDS), and the contents increased rapidly after mechanical damage. The exposure of orange plants to DMDS resulted in the suppression of the developmental performance of ACP. The differential elevation of salicylic acid (SA) levels; the expression of phenylalanine ammonia lyase (PAL), salicylate-O-methyl transferase (SMT), and pathogenesis-related (PR1) genes; the activities of defense-related enzymes PAL, polyphenol oxidase (PPO), and peroxidase (POD); and the total polyphenol content were observed in DMDS-exposed orange plants. The emission of volatiles including myrcene, nonanal, decanal, and methyl salicylate (MeSA) was increased. In addition, phenylpropanoid and flavonoid biosynthesis, and aromatic amino acid (such as phenylalanine, tyrosine, and tryptophan) metabolic pathways were induced. Altogether, our results indicated that DMDS from guava plants can activate defense responses in eavesdropping orange plants and boost their herbivore resistance to ACP, which suggests the possibility of using DMDS as a novel approach for the management of ACP in citrus orchards.

Metarhizium anisopliae, an entomopathogenic fungus, has been widely used for the control of agricultural and forestry pests. However, sporulation degeneration occurs frequently during the process of successive culture, and we currently lack a clear understanding of the underlying mechanisms. In this study, the metabolic profiles of M. anisopliae were comparatively analyzed based on the metabolomics approach of gas chromatography–mass spectrometry (GC–MS). A total of 74 metabolites were detected in both normal and degenerate strains, with 40 differential metabolites contributing significantly to the model. Principal component analysis (PCA) and potential structure discriminant analysis (PLS-DA) showed a clear distinction between the sporulation of normal strains and degenerate strains. Specifically, 23 metabolites were down-regulated and 17 metabolites were up-regulated in degenerate strains compared to normal strains. The KEGG enrichment analysis identified 47 significant pathways. Among them, the alanine, aspartate and glutamate metabolic pathways and the glycine, serine and threonine metabolism had the most significant effects on sporulation, which revealed that significant changes occur in the metabolic phenotypes of strains during sporulation and degeneration processes. Furthermore, our subsequent experiments have substantiated that the addition of amino acids could improve M. anisopliae’s spore production. Our study shows that metabolites, especially amino acids, which are significantly up-regulated or down-regulated during the sporulation and degeneration of M. anisopliae, may be involved in the sporulation process of M. anisopliae, and amino acid metabolism (especially glutamate, aspartate, serine, glycine, arginine and leucine) may be an important part of the sporulation mechanism of M. anisopliae. This study provides a foundation and technical support for rejuvenation and production improvement strategies for M. anisopliae.

Fusarium concentricum Nirenberg & O’ Donnell (Ascomycota: Hypocreales) is a fungal species known to infect plants, but never reported as entomopathogenic. Polychrosis cunninhamiacola Liu et Pei (Lepidoptera: Tortricidae: Olethreutinae) is a major and widespread insect pest causing economic losses to cultivated Chinese fir Cunninghamia lanceolata (Lamb.) Hook. It is routinely controlled by extensive use of chemical insecticides, which is perceived as environmentally unsustainable. During March and April of 2019–2020, muscardine cadavers of larvae and pupae of P. cunninhamiacola infected with growing fungus were collected in a fir forest in northern Guangdong Province, China. Conidia were isolated and cultured on PDA medium, from which the fungal strain was identified as F. concentricum FCPC-L01 by morphology and by sequence alignment match with Tef-1α gene. Pathogenicity bioassays at the conidial concentration 1 × 10⁷ revealed P. cunninhamiacola adults and Danaus chrysippus (L.) (Lepidoptera: Nymphalidae) larvae are sensitive to the fungal infection, but not the fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae). We believe results indicate this fungal strain might be applicable against specific target insect pests. As this is the first record of a natural infection caused by F. concentricum in insects, we propose host specificity tests should be done to evaluate its potential as a biocontrol agent.

The weevil Curculio chinensis Chevrolat (Coleoptera: Curculionidae) is a major cause of economic losses to growers of Camellia oleifera in China, as females lay their eggs in developing fruits and the hatching larvae feed on their seed, aborting fruit growth. Olfactory cues play a key role in the host location of this weevil. The present study focused on identifying volatiles from different parts of the host plant Ca. oleifera, namely, the leaves, fruit peel, and seeds, and testing the antennal and behavioral responses of adult Cu. chinensis to those same volatiles. Methods relied on gas chromatography, electroantennograms, and Y-tube bioassays. The results included a total of twenty-five volatiles emitted by the three plant parts, among which eight elicited antennal responses in Cu. chinensis adults of both sexes. The behavioral bioassays indicated that 3-hexenal, trans-2-hexen-1-ol, methyl salicylate, geraniol, and phenethyl alcohol were attractive to Cu. chinensis, while trans-2-hexenal and 2-ethyl-1-hexanol were repellent. Tests with different concentrations indicated that the behavioral response could be dose-dependent. Future studies should focus on field tests with blends of the attractant compounds in order to develop novel, improved control methods for field applications.

The Pseudomonas strain T1-3-2^T isolated from the cone of Cunninghamia laceolata exhibited growth-promoting and antifungal activity. Strain T1-3-2^T was characterized by a polyphasic taxonomy and complete genome sequencing analysis to explore its taxonomic position and biocontrol potentials fully. The results revealed that strain T1-3-2^T shares a high degree of similarity with Pseudomonas eucalypticola and is distinct from any known Pseudomonas species. The G + C content was 61.65%, and the difference was greater than 1 compared to “P. eucalypticola”. Additionally, values of the average nucleotide identity blast (ANIb), average nucleotide identity MUMmer (ANIm), and DNA-DNA hybridization (DDH) between T1-3-2^T and its closest known related species, “P. eucalypticola”, were below the thresholds necessary for species delineation. Furthermore, the T1-3-2^T strain exhibited the distinctions with the multiple polar flagella and the specific quinone system with MK8 compared with that of “P. eucalypticola”. Collectively, these findings affirm the designation of strain T1-3-2^T as a new Pseudomonas species, proposed to be named Pseudomonas silvicola, with T1-3-2^T as the type strain. Genomic analyses revealed strain T1-3-2^T contains three circular DNA contigs, including a 7,613,303 bp chromosome and two plasmids (952,764 bp and 84,880 bp). Bioinformatics analyses further offered potential insight into the molecular mechanisms whereby this strain can promote plant growth and control disease, revealing encoded genes related to antibiotic and secondary metabolite production, the uptake and biosynthesis of siderophores, and pyoverdine biosynthesis. These genomic data offer a valuable foundation for future efforts to apply the T1-3-2^T strain in research contexts.