Fungal communities associated with Heterodera glycines and their potential in biological control: a current update

Biological control of predatory fungi inhabiting activated sludge in wastewater treatment

The unfavorable phenomenon of activated sludge bulking that occurs in sewage treatment plants (WWTPs) is caused by the over-proliferation of filamentous bacteria that should be limited by the Lecane rotifers that feed on them; however, predatory, rotiferovorous fungi that often inhabit WWTPs pose a real threat to these organisms. To solve this problem, we investigated the interaction of the fungus Clonostachys rosea, which is a known Biological Control Agent (BCA) and the predacious Zoophagus sp. in simplified laboratory culture conditions. The presence of C. rosea in the cultures reduced the number of active traps, thus translating into a much smaller number of rotifers being caught. The mycelium of C. rosea was labeled with a red fluorescent protein (RFP). The life cycle of C. rosea that were attacking Zoophagus sp. (hunting for rotifers) is described. C. rosea spores germinate into single-celled forms and penetrate the interior of the Zoophagus mycelium where they feed on the cytoplasm. Then is the mycelium produced abundantly and forms conidiophores. This type of life strategy has not been known before. The obtained results demonstrated the potential of C. rosea as a BCA that can be used to protect rotifers in the event of an infection of activated sludge by the predatory fungi that threaten the rotifer population.

Biochar application alters soil metabolites and nitrogen cycle-related microorganisms in a soybean continuous cropping system

Biochar application is a promising practice to enhance soil fertility. However, it is unclear how field-aged biochar affects the soil metabolites and microbial communities in soybean fields. Here, the rhizosphere soil performance after amending with biochar addition rates at 0 (CK), 20 (B20), 40 (B40), and 60 t ha-1 (B60) was examined via a five-year in-situ field experiment based on a soybean continuous cropping system. Untargeted metabolomics and metagenomics analysis techniques were applied to study the regulatory mechanism of biochar on soybean growth from metabolomics and N cycle microbiology perspectives. We found that the contents of soil total N (TN), available N (Ava N), NH4+-N, and NO3--N were significantly increased with biochar addition amounts by 20.0-65.7 %, 3.6-10.7 %, 29.5-57.1 %, and 24.4-46.7 %, respectively. The B20, B40, and B60 triggered 259 (236 were up-regulated and 23 were down-regulated), 236 (220 were up-regulated and 16 were down-regulated), and 299 (264 were up-regulated and 35 were down-regulated) differential metabolites, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis and topology analysis demonstrated that differential metabolites were highly enriched in seven metabolic pathways such as Oxidative phosphorylation and Benzoxazinoid biosynthesis. Moreover, ten differential metabolites were up-regulated in all three treatments with biochar. Biochar treatments decreased the Nitrospira abundance in soybean rhizosphere soil while increasing Bradyrhizobium abundance significantly in B60. Mantel test revealed that as the biochar addition rate grows, the correlation between Nitrospira and soil properties other than NO3--N became stronger. In conclusion, the co-application of biochar with fertilizers is a feasible and effective way to improve soil N supply, even though biochar has undergone field aging. This work offers new insights into the variations in soil metabolites and microbial communities associated with N metabolism processes under biochar addition in soybean continuous cropping soils.

Comparative Effectiveness of Filamentous Fungi in Biocontrol of Meloidogyne javanica and Activated Defense Mechanisms on Tomato

The nematicidal potential of five filamentous fungi as biological control agents (BCAs) against the root-knot nematode (RKN), Meloidogyne javanica, infecting tomato was assessed in vitro and in pot experiments. The five promising native taxa, namely Trichoderma longibrachiatum, T. harzainum, T. asperellum, Lecanicillium spp., and Metacordyceps chlamydosporia, were selected to compare their effectiveness against both chemical (Mocap, 10% ethoprophos) and biological (abamectin) nematicides on M. javanica reproduction indices and plant growth parameters. The stimulation of defense mechanisms was assessed by monitoring changes in the enzymatic activities of the polyphenol oxidase (PPO), peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT), lipid peroxidation (MDA), phenols, and proteins content of tomato roots. The laboratory assays revealed that T. longibrachiatum, M. chlamydoporia, and Lecanicillium spp. seemed to be the most effective under laboratory conditions, with more than 60% of juvenile mortality. The egg infection rate was above 62%, and the egg hatching rate was below 32%. The direct parasitism by the five taxa was confirmed by scanning electron microscope observation. The results of this study found a similar parasitism mechanism for T. longibrachiatum, T. harzianum, and M. chlamydosporia, where their hyphae and spores adhered to the M. javanica juveniles cuticle layer and formed trapping rings around them. The pot experiment results showed that T. harzianum and Lecanicillium spp. enhanced the plant growth parameters. Trichoderma longibrachiatum, abamectin, and the ethoprophos-based nematicides effectively decreased the reproduction rates of the nematode. The Trichoderma species and M. chlamydosporia significantly reduced the gall index and female fecundity of RKN. The treatment with BCAs and chemical nematicides involved a significant increase in the antioxidant activities of nematode-infected plants. The ethoprophos and fungal treatments decreased the MDA and total phenols content compared with the nematode-infested seedlings. This paper analyzes the advancements made towards the effective and efficient biocontrol of M. javanica using different fungal taxa, especially T. longibrachiatum and M. chlamydosporia, and the implications of these advancements for sustainable agriculture and food security.

Management of potato cyst nematodes with special focus on biological control and trap cropping strategies

Potato cyst nematodes (PCNs; Globodera spp.) are one of the most difficult pests of potato to manage worldwide. Indiscriminate use of pesticides and their hazardous effects discourage the use of many chemicals for the management of PCNs. As a result, biological control agents and trap crops have received more attention from growers as safer ways to manage PCNs. The biological control agents such as Pochonia chlamydosporia, Purpureocillium lilacinum, Trichoderma spp., Pseudomonas fluorescens, Bacillus spp., Pasteuria spp., and others are recognized as potential candidates for the management of PCNs. Moreover recently, the use of trap crop Solanum sisymbriifolium also showed promise by drastically reducing soil populations of PCNs. Integration of these management strategies along with other practices including identification, conservation, and multiplication of native antagonists, will facilitate efficient management of the PCNs in potato cropping system. Some of the promising research approaches that are being used against PCNs are addressed in this review. © 2022 Society of Chemical Industry.

Exploring Soybean Resistance to Soybean Cyst Nematode

Resistance to the soybean cyst nematode (SCN) is a topic incorporating multiple mechanisms and multiple types of science. It is also a topic of substantial agricultural importance, as SCN is estimated to cause more yield damage than any other pathogen of soybean, one of the world's main food crops. Both soybean and SCN have experienced jumps in experimental tractability in the past decade, and significant advances have been made. The rhg1-b locus, deployed on millions of farm acres, has been durable and will remain important, but local SCN populations are gradually evolving to overcome rhg1-b. Multiple other SCN resistance quantitative trait loci (QTL) of proven value are now in play with soybean breeders. QTL causal gene discovery and mechanistic insights into SCN resistance are contributing to both basic and applied disciplines. Additional understanding of SCN and other cyst nematodes will also grow in importance and lead to novel disease control strategies.