Aphelenchoides Besseyi Research Articles

High killing rate of nematode and promotion of rice growth by synthetic volatiles from Bacillus strains due to enhanced oxidative stress response.

The plant parasitic nematode Aphelenchoides besseyi is a major pest that poses serious threats to different vegetables and crop plants. In the present study, volatiles isolated from Bacillus spp. were utilized as green biocontrol agents to overcome nematodes. In in vitro experiment, Bacillus spp. GBSC56, SYST2, and FZB42 showed the strongest nematicidal activity with killing rates of 80.78%, 75.69%, and 60.45%, respectively, as compared with control. The selected synthetic volatile organic compounds (VOCs), namely albuterol, benzaldehyde (BDH), 1,2-benzisothiazol-3(2H)-one (1,2-HIT), dimethyl disulfide (DMDS), 2-undecanone (2-UD), and 1,3-propanediole (1,3-PD), exhibited strong nematicidal activity, with A. besseyi killing rate of 85.58%, 82.65%, 81.75%, 80.36%, 84.45%, and 82.36%, respectively, at 400 μg/mL. Microscopic analysis proved that the rapid mortality was due to the production of reactive oxygen species (ROS). Molecular docking attributed this ROS production to the nematicidal effect of synthetic VOCs on NADH DEHYDROGENASE SUBUNIT 2, which is known to play a critical role in the suppression of ROS in nematode models. In a greenhouse experiment, the Bacillus strains GBSC56, SYST2, and FZB42 and their synthetic VOCs significantly improved the physiological parameters in terms of growth promotion traits. In addition, selected genes related to growth promotion and defense genes showed a significant upregulation of their expression in rice seedlings treated with those synthetic VOCs. Overall, these findings revealed that the selected Bacillus strains and their synthetic VOCs possess high potential against A. besseyi. Moreover, this study also sheds new light on the mechanisms by which specific Bacillus nematicidal VOCs influence important genes involved in rice plant growth promotion and could effectively be used to suppress plant parasitic nematodes.

Discovery of quinazoline compound as a novel nematicidal scaffold

With the aim of discovering novel nematicidal scaffolds, the nematicidal activities of a series of quinazoline compounds were tested, with some compounds showing excellent results. Among them, the LC50 values of compound K11 against Bursaphelenchus xylophilus, Aphelenchoides besseyi, and Ditylenchus destructor were 7.33, 6.09, and 10.95 mg/L, respectively. In addition, the nematicidal activity of compound K11 against Meloidogyne incognita was 98.77% at 100 mg/L. Compound K11 not only increased the production of reactive oxygen species and the accumulation of lipofuscin and lipids in nematodes, but it also attenuated nematode pathogenicity by reducing the nematodes' antioxidant capacity. Transcriptomic analysis showed that compound K11 had significant effects on fatty acid degradation, metabolic pathways, and the differentially expressed genes related to redox processes in nematodes. Furthermore, the expression levels of the corresponding differentially expressed genes were verified using real-time quantitative polymerase chain reaction. Quinazoline can be used as a new nematicidal scaffold, and it is expected that more work will be done on the discovery of novel nematicides based on the lead compound K11 in the future.

Host-parasite relationship between Aphelenchoides besseyi and soybean

Summary Aphelenchoides besseyi is a concern to Brazilian agriculture, since the losses caused by the green stem and foliar retention syndrome in soybean, especially in hot and humid climates, could reach high levels. However, limited information is available regarding the host-parasite relationship. The objective of this study was to evaluate the capacity of A. besseyi to penetrate soybean roots and its movement in soybean tissues until reaching the top parts. Plants inoculated with 1000 A. besseyi were evaluated for root penetration from 1-28 days after inoculation (DAI), and post-penetration and movement inside tissues by staining them with acid fuchsin. Plant development, chronology of the symptoms and the number of pods were also evaluated at 60 DAI. Aphelenchoides besseyi was found in the cortex and xylem vessels of roots from 1 DAI. During the experimental period, the number of nematodes from roots to shoots increased more than 123, 330 and 430%, respectively, for roots, stems + petioles + inflorescences, and leaves, demonstrating the ascendent movement of A. besseyi. Necrotic lesions in young leaves and apical tissues were observed from 8 DAI; the typical symptom of ‘amachamiento’ was observed from 10 DAI, with enlargement of nodes and lesions in inflorescences and, at 30 DAI, stunted plants were detected. At 60 DAI, inoculated plants had lower numbers of pods and exhibited severe symptoms including abortion of flowers and tissue splitting and cortical lesions in a few pods and roots. These observations emphasise the importance of A. besseyi for Brazilian soybean production.

Fabrication of a dual pH-responsive and photothermal microcapsule pesticide delivery system for controlled release of pesticides.

The development of stimulus-responsive and photothermally controlled-release microcapsule pesticide delivery systems is a promising solution to enhance the effective utilization and minimize the excessive use of pesticides in agriculture. In this study, an AVM@CS@TA-Fe microcapsule pesticide delivery system was developed using avermectin as the model drug, chitosan and tannic acid as the wall materials, and tannic acid-Fe complex layer as the photothermal agent. The optical microscope, scanning electron microscope, transmission electron microscope, and Fourier-transform infrared spectroscope were used to characterize the prepared microcapsule. The slow-release, UV-shielding, photothermal performance, and nematicidal activity of the microcapsule were systematically investigated. The results showed that the system exhibited excellent pH-responsive and photothermal-sensitive performances. In addition, the UV-shielding performance of the delivery system was improved. The photothermal conversion efficiency (η) of the system under the irradiation of near-infrared (NIR) light was determined to be 14.18%. Moreover, the nematicidal activities of the system against pine wood nematode and Aphelenchoides besseyi were greatly increased under the irradiation of light-emitting diode (LED) simulated sunlight. The release of the pesticide-active substances in such a pesticide delivery system could be effectively regulated with the irradiation of NIR light or LED-simulated sunlight. Thus, the developed pesticide delivery system may have broad application prospects in modern agriculture fields. © 2022 Society of Chemical Industry.

Density-related establishment and reproduction of Aphelenchoides besseyi (Nematoda: Aphelenchoididae) populations on Oryza sativa

Density-related establishment and reproduction of Aphelenchoides besseyi (Nematoda: Aphelenchoididae) populations on Oryza sativa

Nutrient Omission and Aphelenchoides besseyi Interaction in Soybean Plants

ABSTRACT The phytonematode Aphelenchoides besseyi gained prominence in Brazil following its identification as the etiological agent of leaf and green stem retention in soybean plants. Thus, this study evaluated the effects of nutrient omission on the phytotechnical characteristics of soybean in the presence and absence of A. besseyi. The experiments were carried out in a completely randomized 2 × 11 factorial arrangement, with 11 treatments: control (no nutrients), complete nutrition, and individual -N, -P, -K, -S, -B, -Cu, -Fe, -Mn, and -Zn omission were applied to inoculated and uninoculated plants, and six replicates. The presence of A. besseyi adversely affected the growth characteristics, except when -P, -S, -B, -Mn, and -Zn were omitted. The nematode reduced the root length in treatments omitting -K, -S, -B, -Cu, -Fe, -Mn, and -Zn and root fresh weight when -N, -P, -K, and -Cu were omitted. In the absence of the pathogen, N assimilation did not differ significantly between the treatments; however, it was negatively influenced by the presence of the pathogen in the control and complete nutrition treatment. The leaf area index values were the lowest in inoculated plants with no nutrition, with complete nutrition, and with -N, -P, -K, and -Cu omissions. The micro- and macronutrients concentration and the shoot dry weight (SDW) were high in the presence of the nematode, except in treatments where -N, -S, and -Mn were omitted. The nutritional status does not affect infection by the nematode A. besseyi, but the application of nutrients is necessary for soybean development.

Effectivity of the Consortium of Rhizobacteria and Endophytic Bacteria to Controls the White Tip Disease of Rice Caused by Seed-Borne Nematode Aphelenchoides besseyi

<p>Aphelenchoides besseyi is a seed-borne nematode that causes white-tip disease in rice. Yield losses due to this nematode infection reach 30-50% in various countries. This research aimed to investigate the effectiveness of a consortium of rhizobacteria and endophytic bacteria in controlling the white tip disease while promoting the growth of rice seeds infected by A. besseyi. The experiments conducted were a bacterial compatibility test, in vitro test to examine the nematicidal activity of bacterial consortium, and an in vivo test to investigate the effectiveness of bacterial consortium to suppress disease occurrence and promote the growth of rice. The research was conducted at the Plant Protection Laboratory, Faculty of Agriculture, University of Jember from July 2020 to December 2020. The experiments used a randomized block design with five concentration levels of bacterial suspension of 20%, 40%, 60%, 80%, and 100%. The results showed that the endophytic bacterial consortium effectively controlled the growth of A. besseyi up to 80% compared to control. Furthermore, the percentage of white tip symptoms in the control plant reached 83%. In comparison, it was observed lower in a range from 74.5% to 25% in plants treated with a suspension of endophytic bacterial consortium. The control plant’s symptom length reached 3.94 cm, while the average symptom length in the treated plant ranged from 3.41 cm to 1.50 cm. The application of endophytic bacteria was also found to accelerate plant growth by increasing plant height and root length of the rice plant. The effectiveness of a consortium of rhizobacteria and endophytic bacteria to control white tip disease while increasing plant growth of rice in Indonesia is first reported in this manuscript.</p>

Aphelenchoides besseyi Ab-FAR-1 Interacts with Arabidopsis thaliana AtADF3 to Interfere with Actin Cytoskeleton, and Promotes Nematode Parasitism and Pathogenicity.

Fatty acid and retinol binding proteins (FAR) are unique proteins found in nematodes and are considered potential targets for controlling these parasites. However, their functions in nematode parasitism and pathogenicity and interaction with hosts are still unclear. In this study, we investigated the specific roles of rice white tip nematodes (RWTNs), Aphelenchoides besseyi, and a protein, Ab-FAR-1, to elucidate the parasitic and pathogenic processes of nematodes. The results showed that the expression level of Ab-far-1 was significantly up-regulated after A. besseyi infection of the plant. The immunofluorescence and subcellular localisation showed that Ab-FAR-1 was secreted into plant tissues mainly through the body wall of nematodes and might act in the nucleus and cytoplasm of plant cells. The pathogenicity of RWTNs was enhanced in Arabidopsis thaliana overexpressing Ab-FAR-1 and inhibited in Ab-far-1 RNAi A. thaliana. Yeast two-hybrid, Co-IP, BiFC, and nematode inoculation experiments showed that Ab-FAR-1 could interact with the A. thaliana actin-depolymerizing factor protein AtADF3, and the A. thaliana adf3 mutant was more susceptible to nematodes. An in vitro actin filament depolymerisation assay demonstrated that Ab-FAR-1 could inhibit AtADF3-mediated depolymerisation of actin filaments, and the turnover process of cellular actin filaments was also affected in A. thaliana overexpressing Ab-FAR-1. In addition, flg22-mediated host defence responses were suppressed in A. thaliana overexpressing Ab-FAR-1 and adf3 mutants. Therefore, this study confirmed that RWTNs can affect the turnover of actin filament remodelling mediated by AtADF3 through Ab-FAR-1 secretion and thus inhibit plant PAMP-triggered immunity (PTI), promoting the parasitism and pathogenicity of nematodes.

The Fight against Plant-Parasitic Nematodes: Current Status of Bacterial and Fungal Biocontrol Agents.

Plant-parasitic nematodes (PPNs) are among the most notorious and underrated threats to food security and plant health worldwide, compromising crop yields and causing billions of dollars of losses annually. Chemical control strategies rely heavily on synthetic chemical nematicides to reduce PPN population densities, but their use is being progressively restricted due to environmental and human health concerns, so alternative control methods are urgently needed. Here, we review the potential of bacterial and fungal agents to suppress the most important PPNs, namely Aphelenchoides besseyi, Bursaphelenchus xylophilus, Ditylenchus dipsaci, Globodera spp., Heterodera spp., Meloidogyne spp., Nacobbus aberrans, Pratylenchus spp., Radopholus similis, Rotylenchulus reniformis, and Xiphinema index.

First record of Aphelenchoides besseyi on foxtail millet (Setaria italica) in Henan Province of China.

Aphelenchoides besseyi is one of the important plant-parasitic nematodes on rice, reducing approximate 10-20% of the rice yield annually (Jones et al. 2013). Foxtail millet (Setaria italica) has been a major cereal crop in Northern China, especially in the semi-arid areas of this region, for thousands of years. In August of 2019 and 2020, a survey of nematodes on autumn grain crops was performed each year. One foxtail millet field (N34° 58' 027″ and E113° 39' 059″) in Yuanyang County of Henan Province caught our attention. Some upper leaves showed chlorosis without or with necrotic tips, and flag leaves presented crinkling and distortion, stalks were colored, earheads were vertical, glumes were brown or light black and open, and grains became thin. A total of ten samples were collected, and the nematodes were isolated from the spike pieces by shallow plate method and counted under a stereomicroscope. The average number of nematodes per earhead of foxtail millet counted up to 1738.75 ± 107.72. Morphologically, females were slender with a short stylet, an oval metacorpus with a distinct valve, a labial region slightly wider than the first body annulus and a conoid tail with a terminus bearing a star-shaped mucro with four pointed processes. The females were characterized as follows (mean ± SD; n=20): body length (L) = 668.92 ± 12.73 µm (647.38 to 689.70 µm); maximum body width (W) = 14.35 ± 1.11 µm (12.12 to 16.88 µm); L/W = 46.83 ± 2.94 (40.44 to 50.03); tail length = 38.93 ± 3.48 µm (33.41 to 45.92 µm); L/tail length = 17.31 ± 1.44 (14.47 to 19.62); and stylet length (ST) = 11.57 ± 0.57 µm (10.77 to 12.34 µm). The males had three pairs of ventrosubmedian papillae with the first one adanal, spicula curved with a slight basal process, terminus bearing four mucrones arranged variably, and the whole worm was in 'J' shape. The males could be described as follows (mean ± SD, n = 20): L = 606.66 ± 10.70 µm (586.49 to 626.37 µm); W = 13.95 ± 0.60 µm (12.71 to 14.94 µm); L/W = 43.55 ± 1.69 (40.73 to 46.43); tail length = 35.54 ± 1.93 µm (31.41 to 38.18 µm); L/tail length = 17.07 ± 0.79 (16.05 to 18.67); ST = 11.53 ± 0.56 µm (1061 to 12.76 µm). All the key morphometrics were consistent with those of A. besseyi reported from Brazil (Favoreto et al. 2018) and China (Lin et al. 2004; Ou et al. 2014). The amplifications of rDNA internal transcribed spacer (ITS) fragments generated a PCR fragment of 830 bp from a single nematode, using the primers set TW81 (5'-GTTTCCGTAGGTGAACCTGC-3') and AB28 (5'-ATATGCTTAAGTTCAGCGGGT-3') (Joyce et al. 1994). Five independent PCR experiments were conducted, and all the PCR products were purified and sequenced. Nucleotide sequence of ITS-rDNA was deposited in GenBank with Accession Number OK090549.1. The obtained ITS region sequence was more than 99% identical to those of A. besseyi reported from China (MW216945.1) and India (JF826518.1, JF826519.1 and JF826517.1). These ITS sequence results further supported that the isolated nematodes were A. besseyi. Subsequently, the species-specific primers of A. besseyi (BSF, 5'-TCGATGAAGAACGCAGTGAATT-3' and BSR, 5'-AGATCAAAAGCCAATCGAATCAT-3') were used for confirmation by PCR (Cui et al. 2010). An expected PCR fragment of 312 bp was obtained, which was consistent with those of A. besseyi reported previously. The pathogenicity of identified A. besseyi was confirmed by infection of foxtail millet (Setaria italica cv. 'Yugu33'). Foxtail millet budding seeds were sown in the pots contained 150 mL of sterile soil mixture. In two weeks, 10 seedlings were inoculated with 100 A. besseyi each, and 4 plants were non-inoculated as the control. The foxtail millet seedlings were grown in a plant-growth chamber at 25/30°C under 12 h dark/12 h light. On the average, 73.3 and 138.2 of A. besseyi were isolated from each plant at 15 and 40 days post inoculation, respectively. Both the morphological and molecular characteristics were identical with those nematodes obtained from the original samples. All the upper leaves of the inoculated plants showed chlorosis and necrosis, symptoms that were similar to those observed in the field, and neither symptom developed on the non-inoculated control plants, nor were nematodes re-isolated from the control plants. To the best of our knowledge, this is the first record of A. besseyi on foxtail millet in Henan Province of North China. Henan is one of the most important grain-producing areas in China, and A. besseyi is an important domestic quarantine nematode, which may become a severe threat to cereal production in Henan Province. Our findings will be very beneficial for A. besseyi management and further research on foxtail millet in Henan Province of North China.

Toxicity of Bacillus thuringiensis Strains Derived from the Novel Crystal Protein Cry31Aa with High Nematicidal Activity against Rice Parasitic Nematode Aphelenchoides besseyi.

The plant parasitic nematode, Aphelenchoides besseyi, is a serious pest causing severe damage to various crop plants and vegetables. The Bacillus thuringiensis (Bt) strains, GBAC46 and NMTD81, and the biological strain, FZB42, showed higher nematicidal activity against A. besseyi, by up to 88.80, 82.65, and 75.87%, respectively, in a 96-well plate experiment. We screened the whole genomes of the selected strains by protein-nucleic acid alignment. It was found that the Bt strain GBAC46 showed three novel crystal proteins, namely, Cry31Aa, Cry73Aa, and Cry40ORF, which likely provide for the safe control of nematodes. The Cry31Aa protein was composed of 802 amino acids with a molecular weight of 90.257 kDa and contained a conserved delta-endotoxin insecticidal domain. The Cry31Aa exhibited significant nematicidal activity against A. besseyi with a lethal concentration (LC50) value of 131.80 μg/mL. Furthermore, the results of in vitro experiments (i.e., rhodamine and propidium iodide (PI) experiments) revealed that the Cry31Aa protein was taken up by A. besseyi, which caused damage to the nematode’s intestinal cell membrane, indicating that the Cry31Aa produced a pore-formation toxin. In pot experiments, the selected strains GBAC46, NMTD81, and FZB42 significantly reduced the lesions on leaves by up to 33.56%, 45.66, and 30.34% and also enhanced physiological growth parameters such as root length (65.10, 50.65, and 55.60%), shoot length (68.10, 55.60, and 59.45%), and plant fresh weight (60.71, 56.45, and 55.65%), respectively. The number of nematodes obtained from the plants treated with the selected strains (i.e., GBAC46, NMTD81, and FZB42) and A. besseyi was significantly reduced, with 0.56, 0.83., 1.11, and 5.04 seedling mL−1 nematodes were achieved, respectively. Moreover, the qRT-PCR analysis showed that the defense-related genes were upregulated, and the activity of hydrogen peroxide (H2O2) increased while malondialdehyde (MDA) decreased in rice leaves compared to the control. Therefore, it was concluded that the Bt strains GBAC46 and NMTD81 can promote rice growth, induce high expression of rice defense-related genes, and activate systemic resistance in rice. More importantly, the application of the novel Cry31Aa protein has high potential for the efficient and safe prevention and green control of plant parasitic nematodes.

Design, Synthesis, and Biological Activity of Novel Chalcone Derivatives Containing an 1,2,4-Oxadiazole Moiety.

To discover a lead compound for agricultural use, 34 novel chalcone derivatives containing an 1,2,4-oxadiazole moiety were designed and synthesized. Their nematocidal activities against Bursaphelenchus xylophilus, Aphelenchoides besseyi, and Ditylenchus dipsaci and their antiviral activities against tobacco mosaic virus (TMV), pepper mild mottle virus (PMMoV), and tomato spotted wilt virus (TSWV) were evaluated. Biological assay results indicate that compounds A13 and A14 showed good nematocidal activities against B. xylophilus, A. besseyi, and D. dipsaci, with LC50 values of 35.5, 44.7, and 30.2 μg/ml and 31.8, 47.4, and 36.5 μg/ml, respectively, which are better than tioxazafen, fosthiazate, and abamectin. Furthermore, compound A16 demonstrated excellent protective activity against TMV, PMMoV, and TSWV, with EC50 values of 210.4, 156.2, and 178.2 μg/ml, respectively, which are superior to ningnanmycin (242.6, 218.4, and 180.5 μg/ml).

CRISPR/Cas12a Coupled With Recombinase Polymerase Amplification for Sensitive and Specific Detection of Aphelenchoides besseyi.

Aphelenchoides besseyi (A. besseyi), a seed-borne parasitic nematode, is the causal agent of rice white tip disease (RWTD), which may result in a drastic loss of rice yield. Seed treatments are currently considered to be the most effective means of preventing the spread of RWTD. Therefore, the rapid, highly specific, and accurate detection of A. besseyi from rice seeds is crucial for the surveillance, prevention, and control of RWTD. Here, we describe a novel detection assay that combines recombinase polymerase amplification (RPA) and CRISPR/Cas12a to detect A. besseyi (termed RPA-Cas12a-Ab), with a low limit of detection (LOD) of 1 copy/μl of plasmid or 1:107 diluted DNA extracted from individual nematodes. To improve the user-friendliness, lateral flow strip assay (LFA) was adopted to visualize the detection result. The LOD of the RPA-Cas12a-Ab LFA assay was 1,000 copies/μl plasmid or 1:10 diluted DNA extracted from individual nematodes. The assay developed in this study was able to identify A. besseyi in 45 min with high accuracy and sensitivity without cross reaction with three closely related non-A. besseyi species. Thus, RPA-Cas12a-Ab is a rapid, sensitive, and specific detection system that requires no sophisticated equipment and shows promise for on-site surveillance of A. besseyi.

Feeding Selectivity of Aphelenchoides besseyi and A. pseudogoodeyi on Fungi Associated with Florida Strawberry.

Aphelenchoides besseyi and A. pseudogoodeyi are foliar nematodes associated with commercial strawberry production in Florida, United States. The reproductive and feeding habits of these two nematode species were assessed on Florida isolates of the fungi Botrytis cinerea, Colletotrichum gloeosporioides, Macrophomina phaseolina, and Neopestalotiopsis rosae, which are pathogenic to strawberry, and nonpathogenic isolates of Fusarium oxysporum and Monilinia fructicola grown on potato dextrose agar in Petri dishes. Each culture was inoculated with six specimens of mixed life stages of A. besseyi or A. pseudogoodeyi and incubated at 24°C under axenic and nonaxenic conditions 23 and 31 days after inoculation, respectively. A. besseyi reproduction rates were greater on strawberry-pathogenic isolates of B. cinerea, C. gloeosporioides, and N. rosae than on the nonpathogenic isolates of F. oxysporum and M. fructicola. In contrast, reproductive rates of A. pseudogoodeyi did not vary among fungi cultures. For both nematode species, M. phaseolina was a poor host because it did not produce mycelium on the media used. Our findings indicate that A. besseyi is more selective in its fungal-feeding preference than A. pseudogoodeyi. Additionally, A. pseudogoodeyi eggs and juveniles were significantly more numerous than adults. Yet, for A. besseyi, adult stages were more abundant. Fungi aid in the maintenance of soil-dwelling populations of these two nematode species. Removing fungus-infected strawberry plant residues is both a desirable and effective management practice to limit A. besseyi in central Florida commercial strawberry fields.

Aphelenchoides besseyi Parasitizing Cowpea (Vigna unguiculata) in Brazil.

Several species of nematodes are known to cause losses to cowpea (Vigna unguiculata) throughout the world. In Brazil, Aphelenchoides besseyi was described as causing damage on soybean, cotton, and common bean, but no report was found about the parasitism of this nematode in cowpea. This study aimed to verify the host reaction of cowpea cultivars to A. besseyi. The experiment was conducted under greenhouse conditions, using two A. besseyi populations as inocula, obtained from symptomatic soybean and cotton plants collected in naturally infested fields. Cultivars Imponente, Aracê, Guariba, Tumucumaque, Nova Era, and Tracuateua were inoculated with 500 A. besseyi of each population, separately, into soil, and after 30 days from the inoculation nematodes were extracted from shoot systems. Both populations were able to parasitize all the cowpea cultivars. Independently of the cultivar, cowpea plants exhibited symptoms of leaf deformation similar to those described for soybean, cotton, and common bean and, in addition, severe brooming was observed, with the interior of the stems being porous and necrotic. To our knowledge, this is the first report of parasitism by A. besseyi of cowpea in Brazil, under greenhouse conditions, increasing the list of hosts of this nematode.

Experimental modelling for phenotyping soybean host reaction to Aphelenchoides besseyi

Summary The nematode causing the green stem and foliar retention syndrome of soybean, Aphelenchoides besseyi, is a concern to Brazilian growers, especially in warm and humid climates, where losses can reach 60% of the yields. Management options have not yet been studied properly, but apparently genetic variability is found in soybean genotypes in the resistance to this nematode. However, the correct phenotyping of soybean genotypes is compromised by the scarcity of studies of this pathosystem. Therefore, the objective of this study was to evaluate the inoculum densities of A. besseyi and the plant ages at inoculation to obtain the correct phenotyping of soybean genotypes. Experiments were conducted under glasshouse conditions with the soybean ‘Elite’, using a completely randomised design and a factorial scheme (five nematode population densities: 150, 300, 600, 1200 and 2400 nematodes plant−1, and three plant ages at inoculation: 7, 12 and 17 days after planting). Evaluations were performed 35 days after inoculation, extracting nematodes from soil, roots and shoot parts of plants to obtain the final population of the nematodes of each replicate. The inoculum of 150-300 A. besseyi specimens per plant is the most suitable to assess the reaction of soybean genotypes to this nematode as it resulted in the greatest reproduction factors. Population densities higher than 1500 nematodes per plant could lead to misclassification of the host reaction because of the inconsistent reproduction factors obtained.

Soybean development under different Aphelenchoides besseyi and Meloidogyne incognita populations

The green stem Aphelenchoides besseyi and gall Meloidogyne incognita phytonematodes cause soybean yield losses. Thus, the objective of this study was to evaluate the effects of different populations of A. besseyi and M. incognita on soybeans. The experiment had 10 treatment groups [T1: control, T2: A. besseyi (500), T3: M. incognita (2,000), T4: A. besseyi (250) + M. incognita (2,000), T5: A. besseyi (500) + M. incognita (2,000), T6: A. besseyi (250) + M. incognita (4000), T7: A. besseyi (500) + M. incognita (4,000) individuals, T8: A. besseyi (250) + M. incognita (8,000), T9: A. besseyi (500) + M. incognita (5,000), and T10: A. besseyi (1,000) + M. incognita (8,000) individuals] with six replicates. Inoculations were done on day 10 after soybean germination, and evaluations were conducted after 60 d. Plant height, shoot fresh weight, root fresh weight, number of pods (NP), pod fresh weight, number of grains (NG), grain yield (GY), amount of A. besseyi in the shoot, and M. incognita in the roots were analyzed. The 500 A. besseyi + 8,000 M. incognita treatment reduced all variables and led to considerable damage to soybean development. In addition, GY, NG, and NP were reduced in the different nematode population density groups, influencing soybean agronomic characteristics.

The new effector AbSCP1 of foliar nematode (Aphelenchoides besseyi) is required for parasitism rice

Plant parasitic nematodes secrete effector proteins to parasitize hosts successfully. Of these proteins, serine carboxypeptidases have critical roles in pathogenicity. This study investigated the role of new effector AbSCP1 in Aphelenchoides besseyi pathogenicity. In situ hybridization and qRT-PCR analyses indicated that AbSCP1 was exclusively expressed in the esophageal glands and upregulated in juveniles. Subcellular localization assays indicated that the protein was expressed in the nucleus. The ability to hydrolyze C-terminal amino acid residues was proven for AbSCP1. Moreover, RNAi significantly reduced the expression of AbSCP1 and RNAi-treated nematodes’ reproductive potential. Pathogenicity assays on rice showed that RNAi-treated nematodes were less pathogenic than the untreated control groups. These results suggest the important role of AbSCP1 in the A. besseyi infection process.

Sex ratio of Aphelenchoides besseyi within Oryza sativa seeds with relation to reproduction of rehydrated adult females

AbstractThe white‐tip nematode, Aphelenchoides besseyi, is a seedborne ectoparasite of rice, Oryza sativa. It enters dehydrated quiescence within maturing seeds. Soaking dry seeds in water causes the quiescent nematodes to revive and the rehydrated nematodes emerge from the seeds. Two field nematode populations in Japan exhibited female‐biased sex ratios of living and dead adults in seeds (the proportion of females [female ratio] = 0.816, 0.803) and no influence of the number of adults in a seed on the female ratio. Single rehydrated female adults recovered from seeds reproduced without males whereas single juveniles did not do so. Most rehydrated female adults had sperms in the spermatheca. If all females mate with males in a seed before dehydration, the expected number of mated females, E(n), is given by the product of the female ratio, the number of adults in a seed (n) and the probability that both sexes occur in a seed. The E(n) value peaked at an n‐specific female ratio (fopt). When the female ratio was invariable (ffix), the expected number of mated females per seed, , peaked at an ffix value (optimum ffix value) of 0.794 and 0.788 for the two populations, where g(n) expressed the proportion of seeds harbouring n adults (n ≥ 2). The overall fit of actual numbers of recovered females to the expectations obtained from the optimum ffix value was better than that to the expectations from the n‐specific fopt values. The optimum ffix values were close to the actual female ratios.

The ACE genes in Aphelenchoides besseyi isolates and their expression correlation to the fenamiphos treatment

Aphelenchoides besseyi could cause great yield losses of rice and many economically important crops. Acetylcholinesterase (AChE) inhibitors were commonly used to manage plant-parasitic nematodes. However, nematodes resistant to AChE inhibitors have been increasingly reported due to the extensive use of these chemicals. The current study was aimed to establish the correlation between fenamiphos (an AChE-inhibitor) sensitivities and acetylcholinesterase genes (ace) by analyzing two isolates of A. besseyi (designated Rl and HSF), which displayed differential sensitivities to fenamiphos. The concentrations of fenamiphos that led to the death of 50% (LD50) of Rl and HSF were 572.2 ppm and 129.4 ppm, respectively. Three ace genes were cloned from A. besseyi and sequenced. Sequence searching and phylogenic analyses revealed that AChEs of R1 and HSF shared strong similarities with those of various vertebrate and invertebrate species. Molecular docking analysis indicated that AChEs-HSF had much higher affinities to fenamiphos than AChEs-R1. Quantitative reverse transcriptase-PCR analyses revealed that expression of three ace genes were downregulated in HSF but were upregulated in Rl after exposure to 100 ppm fenamiphos for 12 h. The results indicated that the expression of the ace genes was modulated in response to fenamiphos in different nematode strains. An increased expression of the ace genes might contribute to fenamiphos-insensitivity as seen in the Rl isolate.