Using Chemical Ecology to Enhance Weed Biological Control

In agricultural systems, chemical ecology and the use of semiochemicals have become critical components of integrated pest management. The categories of semiochemicals that have been used include sex pheromones, aggregation pheromones, and plant volatile compounds used as attractants as well as repellents. In contrast, semiochemicals are rarely utilized for management of insects used in weed biological control. Here, we advocate for the benefit of chemical ecology principles in the implementation of weed biocontrol by describing successful utilization of semiochemicals for release, monitoring and manipulation of weed biocontrol agent populations. The potential for more widespread adoption and successful implementation of semiochemicals justifies multidisciplinary collaborations and increased research on how semiochemicals and chemical ecology can enhance weed biocontrol programs.

Response of soil bacterial community to bioorganic fertilizer application as a weed management strategy in rice paddy

Background: The growth of weed is common problem in rice cropping, leading to the application of herbicidal substances to suppress weed growth. Weed biocontrol through novel bioorganic fertilizer (BIO) has been established in rice cultivation, however, its main herbicidal components and influence on soil bacterial community are unknown.Results: We identified three herbicidal components, hexadecanoic, isovaleric, and 2-methylbutyric acids, in BIO extract. We conducted 16S rRNA sequencing to identify changes in soil bacterial community in response to BIO treatments and performed a RDA analysis with soil chemical properties and weed-control effect. The OTU, Chao1 and Shannon indices did not differ substantially among the BIO treatments, and the bacterial diversity was not significantly affected by BIO. As result from PCA analysis, we discovered that soil bacterial community was not significantly influenced by BIO. We identified six dominant phyla (Proteobacteria, Acidobacteria, Chloroflexi, Nitrospirae, and Verrucomicrobia) in BIO-treated paddies. The five most abundant genera were Anaeromyxobacter, Candidatus Nitrosotalea, Clostridum sensustricto1, Haliangium and Candidatus Nitrotoga. From the RDA analysis, the highest correlations were obtained for soil pH, total K, and Pseudomonas. The weed-control effect mostly correlated with the abundance of Candidatus Koribacter, Clostridium sebsustricto 9, and Nonomuraea. Rice yield had a distinct relationship with Nonomuraea, Nitrospira, and Candidatus Koribacter.Conclusions: With the changes in soil pH and total K, BIO could impact bacterial communities and weed control, and in turn affect rice yield. This foundation can be helpful that application BIO is a “not harmful” and feasibility weed biocontrol strategy.

Transcriptome analysis identified the mechanism of synergy between sethoxydim herbicide and a mycoherbicide on green foxtail

Certain synthetic herbicides can act synergistically with specific bioherbicides. In this study, a sethoxydim herbicide at 0.1× label rate improved biocontrol of herbicide-sensitive green foxtail (Setaria viridis, GFT) by Pyricularia setariae (a fungal bioherbicide agent), but did not change the efficacy on a herbicide-resistant GFT biotype. Reference transcriptomes were constructed for both GFT biotypes via de novo assembly of RNA-seq data. GFT plants treated with herbicide alone, fungus alone and herbicide + fungus were compared for weed-control efficacy and differences in transcriptomes. On herbicide-sensitive GFT, sethoxydim at the reduced rate induced ABA-activated signaling pathways and a bZIP transcription factor 60 (TF bZIP60), while improved the efficacy of biocontrol. The herbicide treatment did not increase these activities or improve biocontrol efficacy on herbicide-resistant plants. An exogenous application of ABA to herbicide-sensitive plants also enhanced bZIP60 expression and improved biocontrol efficacy, which supported the results of transcriptome analysis that identified the involvement of ABA and bZIP60 in impaired plant defense against P. setariae. It is novel to use transcriptome analysis to decipher the molecular basis for synergy between a synthetic herbicide and a bioherbicide agent. A better understanding of the mechanism underlining the synergy may facilitate the development of weed biocontrol.

Predation on weed seeds and seedlings by Pheretima guillelmi and its potential for weed biocontrol

The soil weed seedbank is the source of future weed infestations. Seed predation can result in a large number of seed losses, thus contributing to weed biocontrol. Earthworms are important predators of seeds and seedlings and affect seeds and seedling survival after gut passage. A study was conducted to assess the ability of Pheretima guillelmi (Kinberg) to ingest and digest the seeds and seedlings of 15 main farmland weed species. Pheretima guillelmi ingested the seeds and seedlings of each weed species tested. The percentages of seeds and seedlings ingested were 96.7% to 100% and 21.7% to 94.2%, respectively. Pheretima guillelmi showed greater ingestion of seeds than seedlings for each species and digested the seeds and seedlings of each weed species tested to varying extents. The percentages of seeds and seedlings digested were less than 15% irrespective of the weed species. Passage through the gut of P. guillelmi affected the survival of seeds and seedlings. The germination of large crabgrass [Digitaria sanguinalis (L.) Scop.], green foxtail [Setaria viridis (L.) P. Beauv.], goosegrass [Eleusine indica (L.) Gaertn.], Chinese sprangletop [Leptochloa chinensis (L.) Nees], Malabar sprangletop [Leptochloa fusca (L.) Kunth], redroot pigweed (Amaranthus retroflexus L.), common purslane (Portulaca oleracea L.), barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], and ricefield flatsedge (Cyperus iria L.) seeds egested by P. guillelmi decreased by 46%, 49%, 47%, 25%, 38%, 26%, 32%, 13%, and 15%, respectively, compared with their respective controls. In contrast to seed ingestion, ingestion of seedlings by P. guillelmi was fatal to individuals of all weed species; no seedlings survived passage through the gut. Our results indicate that predation of weed seeds and seedlings by P. guillelmi probably depletes the soil weed seedbank and that the introduction of P. guillelmi into fields is a potential strategy for weed biocontrol in farmland.