Biological control, or biocontrol, is the exploitation of living agents (incl. viruses) to combat pestilential organisms (incl. pathogens, pests, and weeds) for diverse purposes to provide human benefits. Thus, during the last century the practices and concepts involved have evolved in separate streams associated with distinct scientific and taxonomic disciplines. In parallel developments, there have been increasing references to biological control in industrial contexts and legislation, resulting in conceptual and terminological disintegration. The aim of this paper is to provide a global conceptual and terminological platform that facilitates future development of the field. We review use of previously suggested terms in key fields (e.g., phytopathology, entomology, and weed science), eliminate redundant terminology, identify three principles that should underpin the concept, and then present a new framework for biological control, rooted in seminal publications. The three principles establish that (1) only living agents can mediate biological control, (2) biological control always targets a pest, directly or indirectly, and (3) all biocontrol methods can be classified in four main categories depending on whether resident agents are utilized, with or without targeted human intervention (conservation biological control and natural biological control, respectively) or agents are added for permanent or temporary establishment (classical biological control and augmentative biological control, respectively). Correct identification of what is, and is not, biological control can help efforts to understand and optimize biological pest control for human and environmental benefits. The new conceptual framework may contribute to more uniform and appropriate regulatory approaches to biological control, and more efficient authorization and application of biocontrol products.

Filamentous fungi produce small cysteine rich surface active amphiphilic hydrophobins on the outer surface of cell walls that mediate interactions between the fungus and the environment. The role of hydrophobins in surface hydrophobicity, sporulation, fruit body formation, recognition and adhesion to host surface and virulence have been reported. The aim of the present study was to characterize the biological function of hydrophobins in the fungal biocontrol agent Clonostachys rosea in order to understand their potential roles in biocontrol mechanisms.

Phytophthora infestans causes late blight disease on potato and tomato and is currently controlled by resistant cultivars or intensive fungicide spraying. Here, we investigated an alternative means for late blight control by spraying potato leaves with double-stranded RNAs (dsRNA) that target the P. infestans genes essential for infection. First, we showed that the sporangia of P. infestans expressing green fluorescent protein (GFP) can take up in vitro synthesized dsRNAs homologous to GFP directly from their surroundings, including leaves, which led to the reduced relative expression of GFP. We further demonstrate the potential of spray-induced gene silencing (SIGS) in controlling potato late blight disease by targeting developmentally important genes in P. infestans such as guanine-nucleotide binding protein β-subunit (PiGPB1), haustorial membrane protein (PiHmp1), cutinase (PiCut3), and endo-1,3(4)-β-glucanase (PiEndo3). Our results demonstrate that SIGS can potentially be used to mitigate potato late blight; however, the degree of disease control is dependent on the selection of the target genes. [ ] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Clonostachys rosea is a mycoparasitic fungus used for biological control of plant diseases. Its genome contains 31 genes putatively encoding for polyketide synthases (PKSs), 75% of which are arranged in biosynthetic gene clusters. Gene expression analysis during C. rosea interactions with the fungal plant pathogens Botrytis cinerea and Fusarium graminearum showed common and species-specific induction of PKS genes. Our data showed a culture media dependent correlation between PKS gene expression and degree of antagonism in C. rosea. The pks22 and pks29 genes were highly induced during fungal-fungal interactions but not during pigmentation, and gene deletion studies revealed that PKS29 was required for full antagonism against B. cinerea, and for biocontrol of fusarium foot rot on barley. Metabolite analysis revealed that Δpks29 strains has a 50% reduced production (P = 0.001) of an unknown polyketide with molecular formula C₁₅H₂₈O₃, while Δpks22 strains lost the ability to produce four previously unknown polyketides named Clonorosein A-D. Clonorosein A and B were purified, their structures determined, and showed strong antifungal activity against B. cinerea and F. graminearum. These results show that PKS22 is required for production of antifungal polyketide Clonorosein A-D, and demonstrate the role of PKS29 in antagonism and biocontrol of fungal plant diseases.

Lysin motif (LysM) modules are approximately 50 amino acids long and bind to peptidoglycan, chitin and its derivatives. Certain LysM proteins in plant pathogenic and entomopathogenic fungi are shown to scavenge chitin oligosaccharides and thereby dampen host defense reactions. Other LysM proteins can protect the fungal cell wall against hydrolytic enzymes. In this study, we investigated the biological function of LysM proteins in the mycoparasitic fungus Clonostachys rosea. The C. rosea genome contained three genes coding for LysM-containing proteins and gene expression analysis revealed that lysm1 and lysm2 were induced during mycoparasitic interaction with Fusarium graminearum and during colonization of wheat roots. Lysm1 was suppressed in germinating conidia, while lysm2 was induced during growth in chitin or peptidoglycan-containing medium. Deletion of lysm1 and lysm2 resulted in mutants with increased levels of conidiation and conidial germination, but reduced ability to control plant diseases caused by F. graminearum and Botrytis cinerea. The Δlysm2 strain showed a distinct, accelerated mycelial disintegration phenotype accompanied by reduced biomass production and hyphal protection against hydrolytic enzymes including chitinases, suggesting a role of LYSM2 in hyphal protection against chitinases. The Δlysm2 and Δlysm1Δlysm2 strains displayed reduced ability to colonize wheat roots, while only Δlysm1Δlysm2 failed to suppress expression of the wheat defense response genes PR1 and PR4. Based on our data, we propose a role of LYSM1 as a regulator of fungal development and of LYSM2 in cell wall protection against endogenous hydrolytic enzymes, while both are required to suppress plant defense responses. Our findings expand the understanding of the role of LysM proteins in fungal-fungal interactions and biocontrol.

Pectin is one of the major and most complex plant cell wall components that needs to be overcome by microorganisms as part of their strategies for plant invasion or nutrition. Microbial pectinolytic enzymes therefore play a significant role for plant-associated microorganisms and for the decomposition and recycling of plant organic matter. Recently, comparative studies revealed significant gene copy number expansion of the polysaccharide lyase 1 (PL1) pectin/pectate lyase gene family in the Clonostachys rosea genome, while only low numbers were found in Trichoderma species. Both of these fungal genera are widely known for their ability to parasitize and kill other fungi (mycoparasitism) and certain species are thus used for biocontrol of plant pathogenic fungi. In order to understand the role of the high number of pectin degrading enzymes in Clonostachys, we studied diversity and evolution of the PL1 gene family in C. rosea compared with other Sordariomycetes with varying nutritional life styles. Out of 17 members of C. rosea PL1, we could only detect two to be secreted at acidic pH. One of them, the pectate lyase pel12 gene was found to be strongly induced by pectin and, to a lower degree, by polygalacturonic acid. Heterologous expression of the PEL12 in a PL1-free background of T. reesei revealed direct enzymatic involvement of this protein in utilization of pectin at pH 5 without a requirement for Ca2+. The mutants showed increased utilization of pectin compounds, but did not increase biocontrol ability in detached leaf assay against the plant pathogen Botrytis cinerea compared to the wild type. In this study, we aimed to gain insight into diversity and evolution of the PL1 gene family in C. rosea and other Sordariomycete species in relation to their nutritional modes. We show that C. rosea PL1 expansion does not correlate with its mycoparasitic nutritional mode and resembles those of strong plant pathogenic fungi. We further investigated regulation, specificity and function of the C. rosea PEL12 and show that this enzyme is directly involved in degradation of pectin and pectin-related compounds, but not in C. rosea biocontrol.