Soybean cyst nematodes: a destructive threat to soybean production in China

Soybean cyst nematode (SCN), Heterodera glycines, is one of the most important pests in soybean production worldwide. In China, 11 different races of SCN, including a newly identified race ‘X12’ with super-virulence, have been surveyed and found to be distributed in 22 provinces. Among them, races 1, 3 and 4 are dominant in the two principal soybean-producing areas, Northeast China and Huanghuaihai Valley, causing over 120 million dollars of annual yield loss. Rapid and reliable PCR-based approaches have been developed for the molecular diagnosis of SCN. High-throughput methods for the identification of soybean resistance against SCN are also developed with specific single nucleotide polymorphism markers by using Kompetitive Allele Specific PCR technology. Over 10,000 soybean germplasm sources were evaluated for their SCN resistance, and 28 SCN-resistant soybean accessions were selected to construct an applied core collection, which has been used for soybean breeding in China. Recently, the genome sequences of SCN and soybean are publically available, and two major SCN-resistant genes (rhg1 and Rhg4) have been identified in soybean, which greatly facilitate the researches on SCN virulence and soybean resistance, and also soybean resistance breeding against SCN. However, the management of SCN still faces many bottlenecks, for instance, the single resistance genes in soybean cultivars can be easily overcome by new SCN races; the identified resistance genes are inadequate to meet the practical breeding needs; and our understanding of the mechanisms of SCN virulence and soybean resistance to SCN are limited. SCN is a destructive threat to soybean production throughout the world including China. In this review, the major progress on soybean SCN is summarized, mainly focusing on the recent research progress in SCN, soybean resistance to SCN and integrated management of SCN in China, and aiming at a better understanding of the current SCN research status and prospects for future work.

Combining targeted metabolite analyses and transcriptomics to reveal the specific chemical composition and associated genes in the incompatible soybean variety PI437654 infected with soybean cyst nematode HG1.2.3.5.7

Background Soybean cyst nematode, Heterodera glycines, is one of the most devastating pathogens of soybean and causes severe annual yield losses worldwide. Different soybean varieties exhibit different responses to H. glycines infection at various levels, such as the genomic, transcriptional, proteomic and metabolomic levels. However, there have not yet been any reports of the differential responses of incompatible and compatible soybean varieties infected with H. glycines based on combined metabolomic and transcriptomic analyses. Results In this study, the incompatible soybean variety PI437654 and three compatible soybean varieties, Williams 82, Zhonghuang 13 and Hefeng 47, were used to clarify the differences in metabolites and transcriptomics before and after the infection with HG1.2.3.5.7. A local metabolite-calibrated database was used to identify potentially differential metabolites, and the differences in metabolites and metabolic pathways were compared between the incompatible and compatible soybean varieties after inoculation with HG1.2.3.5.7. In total, 37 differential metabolites and 20 KEGG metabolic pathways were identified, which were divided into three categories: metabolites/pathways overlapped in the incompatible and compatible soybeans, and metabolites/pathways specific to either the incompatible or compatible soybean varieties. Twelve differential metabolites were found to be involved in predicted KEGG metabolite pathways. Moreover, 14 specific differential metabolites (such as significantly up-regulated nicotine and down-regulated D-aspartic acid) and their associated KEGG pathways (such as the tropane, piperidine and pyridine alkaloid biosynthesis, alanine, aspartate and glutamate metabolism, sphingolipid metabolism and arginine biosynthesis) were significantly altered and abundantly enriched in the incompatible soybean variety PI437654, and likely played pivotal roles in defending against HG1.2.3.5.7 infection. Three key metabolites (N-acetyltranexamic acid, nicotine and D,L-tryptophan) found to be significantly up-regulated in the incompatible soybean variety PI437654 infected by HG1.2.3.5.7 were classified into two types and used for combined analyses with the transcriptomic expression profiling. Associated genes were predicted, along with the likely corresponding biological processes, cellular components, molecular functions and pathways. Conclusions Our results not only identified potential novel metabolites and associated genes involved in the incompatible response of PI437654 to soybean cyst nematode HG1.2.3.5.7, but also provided new insights into the interactions between soybeans and soybean cyst nematodes.

Status of soybean cyst nematodes and integrated management in China.

This chapter focuses on the host range, geographical distribution, economic importance, damage symptoms and biology and life cycle of the soyabean cyst nematode Heterodera glycines in China. Some information on their interactions with other nematodes and pathogens, efficacy and optimization of some recommended integrated nematode management systems and future outlook and research requirements for nematode management strategies are also presented.

In Vitro Screening of a Culturable Soybean Cyst Nematode Cyst Mycobiome for Potential Biological Control Agents and Biopesticides

Fungal biological control of soybean cyst nematodes (SCN) is an important component of integrated pest management for soybean. However, very few fungal biological control agents are available in the market. In this study, we have screened fungi previously isolated from SCN cysts over 3 years from a long-term crop rotation field experiment for their ability to antagonize SCN using (i) parasitism, (ii) egg hatch inhibition, and (iii) J2 mortality. We evaluated egg parasitism using an in-vitro egg parasitism bioassays and scored parasitism using the egg parasitic index (EPI) and fluorescent microscopy. The ability of these fungi to produce metabolites causing egg hatch inhibition and J2 mortality was assessed in bioassays using filter-sterilized culture filtrates. We identified 10 high-performing isolates each for egg parasitism and toxicity toward SCN eggs and J2s and repeated the tests after storage for 1 year of cryopreservation at −80°C to validate the durability of biocontrol potential of the chosen 20 isolates. Although the parasitic ability changed slightly for the majority of strains after cryopreservation, they still scored 5/10 on EPI scales. There were no differences in the ability of fungi to produce antinemic metabolites after cryopreservation. [Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Molecular Basis of Soybean Resistance to Soybean Aphids and Soybean Cyst Nematodes

Soybean aphid (SBA; Aphis glycines Matsumura) and soybean cyst nematode (SCN; Heterodera glycines Ichninohe) are major pests of the soybean (Glycine max [L.] Merr.). Substantial progress has been made in identifying the genetic basis of limiting these pests in both model and non-model plant systems. Classical linkage mapping and genome-wide association studies (GWAS) have identified major and minor quantitative trait loci (QTLs) in soybean. Studies on interactions of SBA and SCN effectors with host proteins have identified molecular cues in various signaling pathways, including those involved in plant disease resistance and phytohormone regulations. In this paper, we review the molecular basis of soybean resistance to SBA and SCN, and we provide a synthesis of recent studies of soybean QTLs/genes that could mitigate the effects of virulent SBA and SCN populations. We also review relevant studies of aphid–nematode interactions, particularly in the soybean–SBA–SCN system.