The bean weevil, Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae: Bruchinae), causes severe post-harvest losses in the common bean, Phaseolus vulgaris L. The control of this insect is still poor and involves the use of conventional insecticides. There is an increasing demand in the search for new active substances and products for pest control towards reduction of adverse effects on human health and the environment. The protection of grains with alternative products, such as essential oils, is a possible alternative to meet the needs described above. Therefore, this investigation evaluated the applications of basil, Ocimum basilicum, and citronella, Cymbopogon winterianus, essential oils for A. obtectus control. These essential oils significantly reduced the bean weight losses and the number of beans damaged by A. obtectus at higher doses than 60 or 120 μL/sample. The number of holes per bean did not differ between the doses of basil essential oil, not even at the dose of 60 μL, while it was higher at 120 μL, probably due to a lower capacity of movement of the insects treated with this dose and/or the oil’s direct or indirect effects on the insects. Basil and citronella oils exhibited similar patterns of insecticidal activity over the insect, both directly in adult insects or indirectly over bean seeds. These essential oils affected the development of A. obtectus since the greatest doses applied on beans decreased the emergence of the bean weevil. The results prove the insecticidal capacity of the tested essential oils and hence their potential as active substances against A. obtectus in environmentally low risk pest control strategies. Supplementary trials should be conducted under real storage conditions.

Trichoderma is a genus of fungi used for the biological control of plant diseases and a large number of its bio-formulates are available in the market. However, its efficacy under field conditions remains unclear, especially for the protection of grapevine plants against Grapevine Trunk Diseases (GTDs). These diseases are caused by a complex of fungal pathogens whose main point of entrance into the affected plants is through pruning wounds. In this research, different Trichoderma native strains have been evaluated according to their ability to grow at different temperatures and their capacity to colonize pruning wounds in adverse climatic conditions. Strains from section Trichoderma have adapted to cooler conditions. On the other hand, strains from clade Harzianum/Virens grow at higher temperatures. However, differences can also be found between strains inside the same clade/section. Native strains were able to colonize more than 70% of vine pruning wounds in winter conditions. The Trichoderma strain T154 showed a significantly higher re-isolation degree from vine plants and its concentration was optimized for spraying onto vine plants. In conclusion, Trichoderma native strains are better adapted to survive in a changing environment, and they could give better protection to grapevine plants in co-evolution with each specific vineyard.

The study of volatile organic compounds (VOCs) has expanded because of the growing need to search for new bioactive compounds that could be used as therapeutic alternatives. These small molecules serve as signals to establish interactions with other nearby organisms in the environment. In this work, we evaluated the antifungal effect of VOCs produced by different Streptomyces spp. This study was performed using VOC chamber devices that allow for the free exchange of VOCs without physical contact between microorganisms or the diffusible compounds they produce. Antifungal activity was tested against Escovopsis weberi, a fungal pathogen that affects ant nest stability, and the results showed that Streptomyces spp. CS014, CS057, CS131, CS147, CS159, CS207, and CS227 inhibit or reduce the fungal growth with their emitted VOCs. A GS-MS analysis of volatiles produced and captured by activated charcoal suggested that these Streptomyces strains synthesize several antifungal VOCs, many of them produced because of the presence of E. weberi, with the accumulation of various VOCs determining the growth inhibition effect.

Self-inhibitory processes are a common feature shared by different organisms. One of the main mechanisms involved in these interactions regarding microorganisms is the release of toxic diffusible substances into the environment. These metabolites can exert both antimicrobial effects against other organisms as well as self-inhibitory ones. The in vitro evaluation of these effects against other organisms has been widely used to identify potential biocontrol agents against phytopathogenic microorganisms. In the present study, we performed membrane assays to compare the self-inhibitory effects of soluble metabolites produced by several Trichoderma isolates and their antifungal activity against a phytopathogenic strain of Fusarium oxysporum. The results demonstrated that Trichoderma spp. present a high self-inhibitory activity in vitro, being affected in both their growth rate and the macroscopic structure of their colonies. These effects were highly similar to those exerted against F. oxysporum in the same conditions, showing no significant differences in most cases. Consequently, membrane assays may not be very informative by themselves to assess putative biocontrol capabilities. Therefore, different methods, or a combination of antifungal and self-inhibitory experiments, could be a better approach to evaluate the potential biocontrol activity of microbial strains in order to pre-select them for further in vivo trials.

The interest in the study of microbiological interactions mediated by volatile organic compounds (VOCs) has steadily increased in the last few years. Nevertheless, most assays still rely on the use of non-specific materials. We present a new tool, the volatile organic compound chamber (VOC chamber), specifically designed to perform these experiments. The novel devices were tested using four Trichoderma strains against Fusarium oxysporum and Rhizoctonia solani. We demonstrate that VOC chambers provide higher sensitivity and selectivity between treatments and higher homogeneity of results than the traditional method. VOC chambers are also able to test both vented and non-vented conditions. We prove that ventilation plays a very important role regarding volatile interactions, up to the point that some growth-inhibitory effects observed in closed environments switch to promoting ones when tested in vented conditions. This promoting activity seems to be related to the accumulation of squalene by T. harzianum. The VOC chambers proved to be an easy, homogeneous, flexible, and repeatable method, able to better select microorganisms with high biocontrol activity and to guide the future identification of new bioactive VOCs and their role in microbial interactions.

The field of plant-microbe interactions mediated by Biogenic Volatile Organic Compounds (BVOCs) still faces several limitations due to the lack of reliable equipment. We present a novel device designed to evaluate in vitro plant-microbe volatile interactions, the plant-microbe VOC Chamber. It was tested by evaluating the effects exerted on wheat development by volatiles from three Trichoderma harzianum strains, a wild type and two genetically modified strains; one expressing the tri5 gene, which leads to the synthesis and emission of the volatile trichodiene, and the other by silencing the erg1 gene, impairing ergosterol production. The wild type and the erg1-silenced strain enhanced fresh weight and length of the aerial part, but reduced root dry weight. Interestingly, no differences were found between them. Conversely, the tri5-transformant strain reduced root and aerial growth compared to the control and the other strains. No differences were observed regarding chlorophyll fluorescence quantum yield and leaf chlorophyll content, suggesting that the released BVOCs do not interfere with photosynthesis. The plant-microbe VOC Chamber proved to be a simple and reliable method to evaluate the in vitro effects of microbial BVOCs on plant development, perfect for the screening of microorganisms with interesting volatile traits.