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FA insect pest activities in Korea, and Japan, threaten soybean production. Japan recorded a 90% reduction in soybean yield due to the infestation of the FA in 2000 (Nagano 2001) and its soybean pest occurrence was also identified in Korea (Kim 1991). It has a wide host range of about 540 plant species (Jandricic 2010) including, ornamentals (Blackman et al. 2000; Jandricic 2010), and common weeds (Capinera 2001). Furthermore, this aphid is considered a vector of about 45 plant viruses (Jandricic 2010; Miller 1997; Yovkova et al. 2013) causing further damage to plants. FA feeds on soybean plants by sucking out the sap from phloem tissues with its stylet and the release of toxic saliva that deforms both leaves and fruits (Sanchez et al. 2007). The feeding habit adversely affects soybean with leaf deformation, yellowing of leaf veins, sometimes necrosis, and plant wilting. A considerable amount of honeydew is excreted by FA which enhances mold growth on soybean leaves with a decrease in photosynthetic activities (Morkunas et al. 2011). The degree of damage depends on the FA density on the soybean.
To date, several soybean cultivars have been identified as resistant to FA. The first study on resistance in soybean to FA started in 2008 (Kim 2008), and two
FA also referred to as glasshouse potato aphid is a known as insect pest of different crops. It is believed to be a native of Europe (Blackman et al. 1984) but is now found worldwide especially in temperate and Mediterranean climatic regions as a crop pest hence, regarded as cosmopolitan (Essig 1942; Michelangelo 2019). It was originally described by studying its activities on its primary host which are common foxglove
FA is a shiny yellow, green, or yellowish-green insect pest (Capinera 2001) having on the abdomen dark-green patches around the base of their short cornicles (Fig. 1A). Aphid has long legs and antenna which are distinctively marked with black banding as shown in Figs. 1B and 1C (Stoetzel 1994). Adult oval body size is around 1.8 - 3.0 mm (Stoetzel 1994). In the process of feeding on the host plant by sucking its sap, plant vigor gradually diminishes in Figs. 1C, 1E and 1F. Under the lower temperatures, FA possesses a high reproductive rate ability which can support exceeding natural enemy suppression capacity (Alotaibi 2008). Therefore, biological control agents are incompetent under low temperatures in the management of FA (Bellefeuille 2021). FA has a complex but short lifecycle which enhances rapid population build-up. Aphid undergoes two forms of lifecycle (holocyclic and anholocyclic) on a host plant. Reproduction could be either sexual or asexual, even though asexual reproduction is most common. Eggs of FA survive winter season and wait till spring season before hatching into many nymphs. The nymphs immediately start to feed on plant sap and grow rapidly. FA has five nymphal instars (Capinera 2001) and undergoes molting four times before attaining the adult stage. At the end of each molt, the aphid leaves behind its shed skin on the host crop. The emerging adult aphid can actively reproduce for varying days depending on prevailing temperature while the females produce an average of 60 (25-81) nymphs (Capinera 2001). Adult aphids can either be winged (alatae) or wingless (apterae). Interaction between FAs and their environment is greatly affected by the effect of global warming (i.e., temperature) on its physiological function and life cycle (Hulle et al. 2010).
The development of FA is directly affected by prevailing temperature and host plant nutritional content (Seo et al. 2020). The mortality of nymphs was examined at various temperature and type of host plants (Kikuchi 2018; Kim 1991). The results showed that nymphs of FA showed 100% mortality at 30°C, and numbers of nymphs produced by adult females of FA was higher at 20°C than 28°C. Furthermore, nymphal stage duration showed significant difference based on the host plants, and temperature (Jandricic 2010). In temperate regions of the world, FA is found to survive in the winter season due to its adaptability at a lower developmental threshold (LDT). The aphid adapts underestimated LDT values between 3°C - 5°C on different crops (Jandricic 2010; Seo et al. 2020). For example, during the winter in Scotland, an anholocyclic form of FA could survive on weeds. A temperature range of 12.5 to 25°C supports high fecundity in the aphid, which could lead to outbreak (Kim 1991). In soybean, FAs exhibited the highest mean daily fecundity at 25°C and 20°C with cumulative
Plants have their unique immune system. It naturally has evolved resistance genes (
Table 1 . Identified soybean genes that confer resistance against FA.
S/N | Soybean Cultivar | Origin | Description | Reference |
---|---|---|---|---|
1 | IT 104704 | Korea | Strong antibiosis effect against aphid | (Koh et al. 2020) |
2 | IT 188399 | Korea | Strong antibiosis effect against aphid | (Koh et al. 2020; Lee et al. 2008) |
3 | PI 230977 | Has strong aphid resistance | (Koh et al. 2018; Koh et al. 2020) | |
4 | PI 366121 | Japan | Showed antixenosis and antibiosis resistance against aphid | (Kim et al. 2021; Koh et al. 2018; Koh et al. 2020; Lee 2015) |
5 | PI 548502 | Japan | A high degree of aphid antibiosis resistance | (Ohnishi et al. 2012; Takahashi et al. 2002) |
6 | Tohoku149 | Japan | Has strong aphid resistance | (Sato et al. 2013; Sato et al. 2014) |
Host plant resistance is the heritable trait a plant species possess that enhances a decrease in insect pest population and activities on such plants (Dogimont et al. 2010). There are three categories of host plant resistance, antibiosis, antixenosis, and tolerance. Antibiosis could suppress the growth and development of insect pest. Antixenosis is a non-preference reaction of insect pest to host plants, caused by the morphological or chemical factors of host plant, which affect the insect pest behavior (Kamphuis et al. 2013; Smith 2005; Smith et al. 2012). In soybean, FA resistance responses are antixenosis and antibiosis (Koh et al. 2018; Lee 2015). Host plant aphid resistance is a promising control strategy with the advantage of cost-effectiveness, environmental safety, and compatibility with other control strategies.
In the case of SA, several resistant soybean cultivars were identified with different resistance to
The identified FA resistant cultivars were Adams and wild soybean
Table 2 . Identified soybean genes that confer resistance against FA.
Gene | Chromosome | Soybean Cultivar | Form of Resistance | FA Biotype | References |
---|---|---|---|---|---|
3 | PI 548502 | Antibiosis resistance | Japanese | (Kamiya 2008; Ohnishi et al. 2012) | |
7 | PI 366121 | Antixenosis and Antibiosis resistance | Korea | (Kim et al. 2021; Lee 2015) |
Most of the identified resistant cultivars are yet to be genetically and molecularly characterized. Soybean wild germplasms possess independently evolving genotypes within a geographical location with the prospect of improving soybean genetics against FA. Identifying wild soybean relatives with FA resistance trait is ongoing with the view of transferring the trait to soybean cultivar. Presently, characterized soybean germplasm includes Plant Introduction PI 366121 and Glycine soja wild soybean (Table 1 and Table 2) which showed resistance to FA, The PI has been successfully crossed with Williams 82, a susceptible soybean cultivar to FA (Kim et al. 2021; Lee 2015).
The
In fine-mapping Raso1 on chromosome 3 at a 63-kb interval between markers Gm03-11 and Gm03-12 of the Williams 82 genome sequence, three candidate genes, which are
Resistance gene
Mapping of the
Aphids are generally known for their peculiar ability to swiftly adapt to new varieties of plants that earlier express resistance. This complicated condition was regarded as an “arms race” between aphids and plants (Botha 2013). The challenges from soybean aphid resistance development in overcoming soybean resistance, therefore, suggested the stacking of various
With the possibility of FA overcoming resistance in the few identified resistant soybean cultivars, there is a need to identify more soybean genetic resources with inherent resistance. This involves the screening of large-scale soybean germplasm which will be assayed for their performance after infestation by FA. Then molecular and genetic characterization of the identified resistant variety for novel resistance gene is carried out. The process involves crossing, making genetic populations (F2, recombinant inbred line (RIL)), genotyping, phenotyping, and QTL analysis. Little attention is given to genetic and molecular information on soybean resistance to FA when compared to soybean resistance to SA.
The discovery of new resistant genes against FA can be followed by combining its effect with the already reported resistance gene for sustaining and durable host plant resistance. A good understanding of the molecular mechanisms that support enhanced resistance in pyramiding genes would facilitate more directed approaches for crop improvement. Further studies using proteome and transcriptome analysis on the identified
In genome sequencing research, unlike soybean aphids and pea aphids (464.3 Mbp and 302.9 Mbp), genomic information of the FA has not yet been revealed (Giordano et al. 2020; International Aphid Genomics 2010; Nouhaud et al. 2018; Wenger et al. 2020). Therefore, the study of whole-genome sequence assembly of FA is needed to understand FA adaptation to soybean, diversity of FA, and biotype evolution. Genetically characterizing FA biotypes will explain the mechanisms of FA virulence on resistant soybean cultivars and hence, explore the use of host plant resistance to achieve optimum soybean production.
In conclusion, the response of a few identified soybean cultivars and wild relatives to the aphid showed resistance to FA. The inheritance of the resistance gene and mechanism of action is not fully understood due to its complexity. Commercial production of soybean varieties with inherent resistance to FA has not been carried out due to the possible emergence of virulent FA biotypes that break down the dominant
This research was funded by the National Research Foundation of Korea (Project No. RS-2023-00246459).
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