Susceptible Host Plants Research Articles

Downy mildew effector HaRxL106 interacts with the transcription factor BIM1 altering plant growth, BR signaling and susceptibility to pathogens.

Hyaloperonospora arabidopsidis (Hpa) is an oomycete pathogen that causes downy mildew disease on Arabidopsis. This obligate biotroph manipulates the homeostasis of its host plant by secreting numerous effector proteins, among which are the RxLR effectors. Identifying the host targets of effectors and understanding how their manipulation facilitates colonization of plants are key to improve plant resistance to pathogens. Here we characterize the interaction between the RxLR effector HaRxL106 and BIM1, an Arabidopsis transcription factor (TF) involved in Brassinosteroid (BR) signaling. We report that HaRxL106 interacts with BIM1 in vitro and in planta. BIM1 is required by the effector to increase the host plant susceptibility to (hemi)biotrophic pathogens, and thus can be regarded as a susceptibility factor. Mechanistically, HaRxL106 requires BIM1 to induce the transcriptional activation of BR-responsive genes and cause alterations in plant growth patterns that phenocopy the shade avoidance syndrome. Our results support previous observations of antagonistic interactions between activation of BR signaling and suppression of plant immune responses and reveal that BIM1, a new player in this crosstalk, is manipulated by the pathogenic effector HaRxL106.

The phytopathogen Xanthomonas campestris senses and effluxes salicylic acid via a sensor HepR and an RND family efflux pump to promote virulence in host plants.

Salicylic acid (SA) plays an essential role in plant defense against biotrophic and semi-biotrophic pathogens. Following pathogen recognition, SA biosynthesis dramatically increases at the infection site of the host plant. The manner in which pathogens sense and tolerate the onslaught of SA stress to survive in the plant following infection remains to be understood. The objective of this work was to determine how the model phytopathogen Xanthomonas campestris pv. campestris (Xcc) senses and effluxes SA during infection inside host plants. First, RNA-Seq analysis identified an SA-responsive operon Xcc4167-Xcc4171, encoding a MarR family transcription factor HepR and an RND (resistance-nodulation-cell division) family efflux pump HepABCD in Xcc. Electrophoretic mobility shift assays and DNase I footprint analysis revealed that HepR negatively regulated hepABCD expression by specifically binding to an AT-rich region of the promoter of the hepRABCD operon, Phep. Second, isothermal titration calorimetry and further genetic analysis suggest that HepR is a novel SA sensor. SA binding released HepR from its cognate promoter Phep and then induced the expression of hepABCD. Third, the RND family efflux pump HepABCD was responsible for SA efflux. The hepRABCD cluster was also involved in the regulation of culture pH and quorum sensing signal diffusible signaling factor turnover. Finally, the hepRABCD cluster was transcribed during the XC1 infection of Chinese radish and was required for the full virulence of Xcc in Chinese radish and cabbage. These findings suggest that the ability of Xcc to co-opt the plant defense signal SA to activate the multidrug efflux pump may have evolved to ensure Xcc survival and virulence in susceptible host plants.

Susceptibility of Yellow Squash and Zucchini Cultivars to the Sweetpotato Whitefly, Bemisia tabaci Gennadius (MEAM1), in the Southeastern United States.

The sweetpotato whitefly, Bemisia tabaci (Gennadius) Middle East-Asia Minor 1 (MEAM1), causes significant losses to vegetable crops directly by sap-feeding, inducing plant physiological disorders, and elevating the build-up of sooty mold, and indirectly by transmitting plant viruses. In this study, we evaluated the susceptibility of 20 yellow squash and zucchini (Cucurbita pepo) cultivars to MEAM1, across three growing seasons in the southeastern United States. Weekly sampling of the numbers of MEAM1 adults, nymphs, and eggs were conducted from the fourth week after seed sowing and across 6 weeks during the summer and fall of 2021 and five weeks during the fall of 2022. In general, adult whitefly populations were high during the first week of sampling but decreased as the seasons progressed. The zucchini cultivar 'Black Beauty' harbored the most adults, while 'Green Eclipse Zucchini' was the least attractive zucchini cultivar to the adults in fall 2022. For yellow squash, 'Early Summer' (summer 2021) and 'Amberpic 8455' (summer 2021 and fall 2022) were the cultivars with the highest adult populations, while 'Lioness' (summer 2021) and 'Gourmet Gold Hybrid' (fall 2022) harbored the lowest adult counts. The whitefly egg counts across both vegetables trailed those of adults and peaked in the second week of sampling. The counts of nymphs increased as the seasons progressed, but there was a decline after the second week during fall 2021. For the yellow squash cultivars, 'Gourmet Gold Hybrid', (summer 2021 and fall 2022), 'Lioness', and 'Fortune' (summer 2021) recorded the highest yields. For zucchini, 'Golden Glory' (summer 2021) was the top performer. These results provide valuable information for whitefly management in yellow squash and zucchini based on host plant susceptibility and yield.

Viroids: infectious non coding RNAs

Viroids are the smallest non-coding infectious RNAs (between 246 and 401 nucleotides) known to be highly structured and replicate autonomously in the host plants. Although they do not encode any peptides, viroids induce visible symptoms in susceptible host plants. This article provides an overview of their physical and biological properties, the diseases they cause and their significance for the plants. The mechanisms underlying the expression of symptoms in host plants, their detection and various strategies employed for diseases prevention are also developed.

Identification of Phytophthora cinnamomi CRN effectors and their roles in manipulating cell death during Persea americana infection

The oomycete Phytophthora cinnamomi is a devastating plant pathogen with a notably broad host range. It is the causal agent of Phytophthora root rot (PRR), arguably the most economically important yield-limiting disease in Persea americana (avocado). Despite this, our understanding of the mechanisms P. cinnamomi employs to infect and successfully colonize avocado remains limited, particularly regarding the pathogen’s ability to maintain its biotrophic and necrotrophic lifestyles during infection. The pathogen utilises a large repertoire of effector proteins which function in facilitating and establishing disease in susceptible host plants. Crinkling and necrosis effectors (CRN/Crinklers) are suspected to manipulate cell death to aid in maintenance of the pathogens biotrophic and necrotrophic lifestyles during different stages of infection. The current study identified 25 P. cinnamomi CRN effectors from the GKB4 genome using an HMM profile and assigned putative function to them as either cell death inducers or suppressors. Function was assigned to 10 PcinCRNs by analysing their RNA-seq expression profiles, relatedness to other functionally characterised Phytophthora CRNs and tertiary protein predictions. The full-length coding sequences for these PcinCRNs were confirmed by Sanger sequencing, six of which were found to have two divergent alleles. The presence of alleles indicates that the proteins encoded may perform contradicting functions in cell death manipulation, or function in different host plant species. Overall, this study provides a foundation for future research on P. cinnamomi infection and cell death manipulation mechanisms.

Update on the Basic Understanding of Fusarium graminearum Virulence Factors in Common Wheat Research.

Wheat is one of the most important food crops, both in China and worldwide. Wheat production is facing extreme stresses posed by different diseases, including Fusarium head blight (FHB), which has recently become an increasingly serious concerns. FHB is one of the most significant and destructive diseases affecting wheat crops all over the world. Recent advancements in genomic tools provide a new avenue for the study of virulence factors in relation to the host plants. The current review focuses on recent progress in the study of different strains of Fusarium infection. The presence of genome-wide repeat-induced point (RIP) mutations causes genomic mutations, eventually leading to host plant susceptibility against Fusarium invasion. Furthermore, effector proteins disrupt the host plant resistance mechanism. In this study, we proposed systematic modification of the host genome using modern biological tools to facilitate plant resistance against foreign invasion. We also suggested a number of scientific strategies, such as gene cloning, developing more powerful functional markers, and using haplotype marker-assisted selection, to further improve FHB resistance and associated breeding methods.

Супресивен ефект на почвата към ризоктонийно кореново гниене, индуциран чрез имитирана монокултура на пшеница

Disease decline and induction of soil suppressiveness by continuous (5-6 years) monoculture with susceptible plant-host have been reported for various crop-pathogen systems. The present study achieves the goal of inducing suppressive effect in soil towards Rhizoctonia root rot (Rhizoctonia solani AG 4) through monoculture of winter wheat (Triticum aestivum L.). Twenty four high-quality wheat (c. Exotic) seeds were planted in plastic containers, each containing 1.1 L Alluvial-Meadow (sandy-clay) soil (Eutric Fluvisols, according to FAO classification). According to the treatment applied, the resulting plants were grown for 0-4 successive short cropping cycles, each lasting three months. Disease suppressiveness was measured in a bioassay in which the experimental units were rectangular, plastic containers (26 x 6 x 8 cm), with drainage holes in the bottom and detachable trays allowing for manual irrigation from the bottom of the container, 7 cm height of the column of tested soil in each container and a two-row crop of wheat (c. Exotic, 2 rows x 12 plants, 2 x 3 cm plant spacing). The spread of the disease was measured from a focus (point) source of inoculum of the pathogen – 20 inoculum grains from a pure culture developed on autoclaved (30 min at 121 °C) barley, introduced into the soil at the beginning of both rows after emergence of the plants. Immediately after termination of the soil suppressiveness test, the abundance of the major groups of soil microorganisms were determined in rhizosphere soil in each treatment by using the method of decimal dilutions and subsequent culturing on agar media. Separately, bacteria of the genus Pseudomonas were isolated from the rhizosphere soil on King’s medium. The antagonistic activity of 10 Pseudomonas spp. isolates from each treatment was tested against R. solani AG 4 in vitro by the double culture method. The monoculture of wheat imitated under controlled conditions resulted in a significant (P<0.05) reduction of the spread of Rhizoctonia root rot from the source of infection. Furthermore, statistically significant differences (P<0.05) were also found between the individual treatments with pre-cultivation of wheat: with the increase in the number of cultivation cycles from one to four, there was a significant reduction in disease spread – by 19.5%, 31.0%, 40.5% and 54.8%, respectively, as compared to the untreated control. Simultaneously, no substantial alterations were observed in the population densities of the monitored groups of microorganisms in the rhizosphere of the experimental plants, including ammonifying and spore-forming bacteria, microscopic fungi, Actinomycetes and bacteria, utilizing mineral N. With the increase in soil suppressiveness from the first to the fifth growing cycle of the crop, a significant increase in the average antagonistic activity of the isolated Pseudomonas spp. against R. solani AG 4 was observed. The thesis is argued that shattering rachis of the ripe ear in wild forms conditioned a continuous “natural” monoculture in which bread wheat and its predecessors grew and evolve during the prehistoric era. We speculate that this condition, along with the lack of genes for resistance to necrotrophic pathogens, have given rise to evolutionary stable defence mechanism and the latter based on mutualistic relationships between the host-plant and bacteria that naturally inhabit rhizosphere and exhibiting high antagonistic (antibiotic) activity against soil-borne plant pathogens. A manifestation of this mechanism is the increasing suppressive response of the soil and the disease decline during or after continuous wheat monoculture. The results obtained in this study are discussed in the light of the microbial eco-evolutionary dynamics in the plant rhizosphere. The progressively increasing pathogen-antagonistic activity of Pseudomonas spp. isolates is discussed as an example of “rapid microbial evolution”, accomplished by possible horizontal gene transfer within one or more successive cultivation cycles of the wheat crop.

Interaction of Meloidogyne incognita (Kofoid & White, 1919) Chitwood, 1949 Race 3 with Meloidogyne javanica (Treub, 1885) Chitwood, 1949 Race 3 in Tomato and Pepper

More than one species of root-knot nematodes can attack field vegetables and they can interact with each other. In this study, the interaction of Meloidogyne incognita race 3 and M. javanica race 3 on susceptible host plants (Falkon and Sena) were investigated in a growth chamber under controlled conditions. Experiments were arranged as a randomized plots design with four replications. The incidence of two Meloidogyne species in tomato and pepper hosts were determined by esterase phenotypes. No interaction was observed between the species after the mixed inoculation of 1000 J2 M. incognita race 3 and 1000 J2 M. javanica race 3 on the susceptible tomato plant (P≤0.05). Among mixed inoculation of the two species in the susceptible pepper, only the incidence of M. incognita race 3 was increased, while M. javanica race 3 was not detected in host plants.

Current status of Botryosphaeriaceae species in Italy: Impacts on agricultural crops and forest ecosystems

Many fungi belonging to Botryosphaeriaceae are well-known as causal agents of diseases in economically and ecologically important agricultural crops and forest trees. In Italy, the high diffusion of Botryosphaeriaceae infections observed over the last decade, has shown the importance of this group of fungi, which are becoming limiting factors for plant production in agricultural systems, nurseries and natural and urban landscapes. Global warming and stress factors such as occasional extreme climatic events can affect the susceptibility of host plants, as well as fungus behaviour, increasing the risk of future infections. Available reports of Botryosphaeriaceae in Italy have been examined, focusing on wood and fruit pathogens, resulting in a list of ten genera and 57 species. Diplodia is the most widespread genus in Italy with 76 records on 44 hosts, while at species level, Neofusicoccum parvum, Botryosphaeria dothidea and Diplodia seriata show the widest host ranges and many records. The ability of the pathogens to remain latent on asymptomatic plants, and uncontrolled trade of plant materials among countries, facilitate the dissemination and potential introduction of new Botryosphaeriaceae species. Preventive detection and adequate control strategies are always needed to limit the potential damage caused by Botryosphaeriaceae. This review had particular emphasis on host-pathogen associations, disease symptoms, geographic distribution, metabolite production, and accurate pathogen identification.

Adapting Plant Protection Strategies to Meet the Challenges Posed by Climate Change on Plant Diseases: A review

Climate change poses a significant challenge to global agriculture, with profound implications for plant disease dynamics and plant protection strategies. This review aims to synthesize current research on the impact of climate change on plant diseases, particularly focusing on how these changes affect pathogen life cycles, host resistance, and disease distribution. Emphasizing the Indian context, this paper explores the adaptation of plant protection strategies in response to these challenges, including the integration of traditional methods and advanced scientific approaches. It provides a comprehensive overview of the key aspects of climate change relevant to agriculture, including changes in temperature, precipitation patterns, and atmospheric CO2 levels. It delves into the direct and indirect impacts of these climatic changes on plant diseases, highlighting how altered environmental conditions influence pathogen virulence and the susceptibility of host plants. This section also discusses the shifted patterns in pest and disease distribution due to climate change, with a focus on the Indian agricultural scenario. Then it examines the current challenges in plant protection, assessing the limitations of traditional methods like chemical, biological, and cultural control in the context of a changing climate. It identifies critical areas such as increased disease incidence, pathogen resistance development, and the necessity for sustainable and adaptable plant protection strategies. Further it explores various adaptive strategies, including Integrated Disease Management (IDM), advances in breeding for disease resistance, biotechnological approaches, and climate-smart agricultural practices. It outlines how IDM principles and practices are being adapted to new climate scenarios, the role of genetic engineering and traditional breeding in developing disease-resistant varieties, the development of biopesticides and biocontrol agents, and the application of climate forecasts in disease management. Case studies and practical applications from different regions of India provide real-world examples of effective adaptation strategies, drawing lessons and best practices. The review concludes by identifying research gaps, advocating for multidisciplinary collaborations between plant pathology, climatology, and agronomy, and emphasizing the critical role of policy in supporting adaptive strategies. This comprehensive synthesis and analysis aim to contribute to the broader understanding of plant protection in the era of climate change and guide future research and policy-making in this vital field.

Microbial diversity in soils suppressive to Fusarium diseases.

Fusarium species are cosmopolitan soil phytopathogens from the division Ascomycota, which produce mycotoxins and cause significant economic losses of crop plants. However, soils suppressive to Fusarium diseases are known to occur, and recent knowledge on microbial diversity in these soils has shed new lights on phytoprotection effects. In this review, we synthesize current knowledge on soils suppressive to Fusarium diseases and the role of their rhizosphere microbiota in phytoprotection. This is an important issue, as disease does not develop significantly in suppressive soils even though pathogenic Fusarium and susceptible host plant are present, and weather conditions are suitable for disease. Soils suppressive to Fusarium diseases are documented in different regions of the world. They contain biocontrol microorganisms, which act by inducing plants' resistance to the pathogen, competing with or inhibiting the pathogen, or parasitizing the pathogen. In particular, some of the Bacillus, Pseudomonas, Paenibacillus and Streptomyces species are involved in plant protection from Fusarium diseases. Besides specific bacterial populations involved in disease suppression, next-generation sequencing and ecological networks have largely contributed to the understanding of microbial communities in soils suppressive or not to Fusarium diseases, revealing different microbial community patterns and differences for a notable number of taxa, according to the Fusarium pathosystem, the host plant and the origin of the soil. Agricultural practices can significantly influence soil suppressiveness to Fusarium diseases by influencing soil microbiota ecology. Research on microbial modes of action and diversity in suppressive soils should help guide the development of effective farming practices for Fusarium disease management in sustainable agriculture.

Industrial-scale composting process as a successful method for inactivation of potato cyst nematodes (Globodera spp. Skarbilovich) and sugar beet cyst nematode (Heterodera schachtiiSchmidt)

Cyst producing nematodes are persistent soil-borne organisms causing severe damage to cultivated plants. Persistence of the economically relevant cyst nematode species Globodera pallida, G. rostochiensis and Heterodera schachtii was investigated at different stages during a large-scale industrial composting process to evaluate its efficiency to prevent spread of these nematodes into natural and agricultural habitats. Using reference cyst nematodes incorporated into organic waste from households and the processing industry, the effect of anaerobic fermentation and aerobic composting processes were investigated. Treated cysts were analysed for viability and reproductive potential by performing hatching tests and bioassays on susceptible host plants. The investigated composting plant showed temperatures between 40 and 72 °C at aerobic composting conditions depending on the sample position (bottom, middle, top) within the pile. We found no viable juveniles or reproductive potential of Globodera spp. (Loof and Bakker 1992) and less than 5 per cent reproduction of H. schachtii. Additionally to temperature conditions, we presume that competition of the microbial community and their released biodigestants like fatty acids also play a major role in successful treatment of these severe pest organisms.

The Impact of the Soil Survival of the Pathogen of Fusarium Wilt on Soil Nutrient Cycling Mediated by Microorganisms.

Fusarium wilt of Momordica charantia in the greenhouse is one of the most severe crop diseases in Shandong Province, P.R. China. This study aimed to investigate the mechanisms of accumulation and long-term survival of the pathogen in naturally pathogenic soils. Soil physicochemical properties were tested after applying a highly virulent strain of Fusarium wilt to M. charantia in an artificial disease nursery. The functional structure of soil microorganisms was analyzed through amplicon sequencing. The highly virulent strain SG-15 of F. oxysporum f. sp. momordicae was found to cause Fusarium wilt in M. charantia in Shandong Province. The strain SG-15 could not infect 14 non-host crops, including Solanum melongena and Lycopersicon esculentum, but it had varying degrees of pathogenicity towards 11 M. charantia varieties. In the artificial disease nursery for Fusarium wilt of M. charantia, the F. oxysporum was distributed in the soil to a depth of 0-40 cm and was mainly distributed in crop residues at 0-10 cm depth. During crop growth, F. oxysporum primarily grows and reproduces in susceptible host plants, rather than disease-resistant hosts and non-host crops. The colonization of the pathogen of Fusarium wilt significantly changed the soil physicochemical properties, the functional structure of soil microorganisms and the circulation of soil elements such as carbon, nitrogen, phosphorus and sulfur. Soil pH value, organic matter content, available iron content, available manganese content, FDA hydrolase activity and polyphenol oxidase activity were significantly correlated with the relative abundance of Fusarium wilt pathogens in the soil. In general, this study suggests that susceptible host plants facilitate the accumulation of Fusarium wilt pathogens in the soil. These pathogens can mediate the decomposition process of plant residues, particularly those of diseased plants, and indirectly or directly affect soil's chemical properties.

Antifeedant and insecticidal effects of alfalfa saponins in the management of the Japanese beetle Popillia japonica

AbstractPopillia japonica is a quarantine pest of priority interest for the EU, given its potentially important economic, social and environmental impacts. Alternative strategies to chemical methods are essential to limit its spread in newly infested areas with favourable climatic and environmental conditions. Saponins are biologically active molecules widely distributed in plants, displaying a well‐known repellent activity combined with a mortality effect against insects. In this context, saponins were extracted from alfalfa Medicago sativa, where medicagenic and zanhic acid glycosides and Soyasaponin I were the most abundant compounds and used in the laboratory and semi‐field experiments for treating leaves of susceptible host plants for P. japonica. Under laboratory conditions, a food deterrence effect and a significant mortality rate were observed using Corylus avellana leaves treated at increasing saponin concentrations, ranging from 1% to 5% w/v. Semi‐field condition experiment supported the food deterrence effect, as a significant food preference was observed for untreated plants of Vitis vinifera compared to treated plants. The promising results obtained suggest that alfalfa saponins could represent a potential eco‐friendly approach for Japanese beetle control.

Chitin synthases containing myosin motor-like domain are required for cell wall integrity and virulence of vascular wilt pathogen Verticillium dahliae

Verticillium wilt (VW) of cotton poses a serious threat to the quality and yield of cotton. Verticillium dahliae is the primary causal agent of cotton VW. Moreover, V. dahliae can infect more than 200 species of dicotyledonous plants. The fungal cell wall plays a crucial role in its growth, development and pathogenicity. However, the mechanism of cell wall synthesis in V. dahliae and its role in pathogenesis remains unclear. In this study, we identified two chitin synthase (CHS) genes VdChs5 and VdChs7 containing myosin motor-like domain (MMD) and characterized their role in virulence of V. dahliae. The results showed that the functions of VdChs5 and VdChs7 were largely redundant, and target deletion of both VdChs5 and VdChs7 in V. dahliae did not affect vegetative growth, but reduced conidial production. ΔVdChs5Chs7 deletion mutant failed to colonize and proliferate in cotton vascular tissue, and exhibited significantly reduced virulence on cotton, suggesting that VdChs5 and VdChs7 are necessary for pathogenesis. In addition, the thickness of the cell wall in ΔVdChs5Chs7 showed significantly decreased, and ΔVdChs5Chs7 mutant exhibited hypersensitivity to cell wall perturbing agents and reactive oxygen species (ROS), indicating that VdChs5 and VdChs7 play key roles in cell wall integrity. Further, host-induced gene silencing (HIGS) silenced transcripts of VdChs5 and VdChs7 in susceptible cotton (Gossypium hirsutum L. acc. TM-1) enhanced resistance to cotton VW. Taken together, our data demonstrated that VdChs5 and VdChs7 play pivotal roles in proliferation, cell wall integrity, and pathogenicity, and provided a novel strategy to improve Verticillium wilt resistance in cotton and other susceptible host plants.

Evaluation of Host Plant Susceptibility Indices and Screening of Sugarcane Promising Lines for Resistance Potential Against Whitefly, Aleurolobus barodensis (Maskell) in Sindh, Pakistan.

The whiteflies are polyphagous, host, and feed on the sap of sugarcane leaves may cause a loss in yield production. This study was designed to screen out the fifteen sugarcane genotypes to recognize their comparative resistance/susceptibility during 2014-15 and 2015-16. The whitefly attack was first found in June, rapidly increased in August, and reached its maximum population in October. After that, the population gradually declined from November to December. The highest 1.80 per cm2 leaf-1 population of whitefly (nymph + puparia) was recorded on YT-53, followed by 1.56 per cm2 leaf-1 in S-2007-AUS-384, which showed moderate susceptibility. The genotypes Hoth-127, NARC-1, and CP-TJ-349, exhibited less susceptible responses with an average range of 1.01-1.50 per cm2 leaf-1. The other genotypes, i.e., CP-TJ-349, Hoth-326, Th-910, S-2005-CSSG-33, S-2007-AUS-384, Hoth-2109, LAM-76/TJ-803, Th-1201, S-2009-CPSG-06, S-1996-NSG-197, NARC-2, and Th-1210 showed resistance response with an average range of 0.01-1.00 per cm2 leaf-1. The maximum Host Plant Susceptibility Indices (HPSIs) during 2015 (16% and 15%), 2016 (13% and 14%), and cumulative (16% and 14%) were recorded in YT-53 and S-2007-AUS-384, respectively. Based on the cumulative result of HPSIs, these genotypes keep in the moderately susceptible category. Similarly, the genotypes Hoth-127, NARC-1, and CP-TJ-349 showed intermediate HPSIs (12, 11, and 9% respectively, found to be less susceptible. While the genotypes, i.e., Hoth-326, Th-910, S-2005-CSSG-33, LAM-76/TJ-803, Hoth-2109, Th-1201, S-1996-NSG-197, S-2009-CPSG-06, NARC-2, and Th-1210 were recorded minimum HPSIs in the range of 1-8% possibly found to be resistant.

Two salivary proteins Sm10 and SmC002 from grain aphid Sitobion miscanthi modulate wheat defense and enhance aphid performance.

The grain aphid Sitobion miscanthi is a serious pest of wheat that causes severe economic damage by sucking phloem sap and transmitting plant viruses. Here, two putative salivary effector homologs from S. miscanthi (Sm10 and SmC002) were selected based on sequence similarity to other characterized aphid candidate effectors. These effectors were then delivered into wheat cells separately via the type III secretion system of Pseudomonas fluorescens to elucidate their functions in the regulation of plant defenses and host fitness. The results showed that the delivery of either Sm10 or SmC002 into wheat plants significantly suppressed callose deposition and affected the transcript levels of callose synthase genes. The expression levels of salicylic acid (SA)-associated defense genes were upregulated significantly in wheat leaves carrying either Sm10 or SmC002. Moreover, LC-MS/MS analysis revealed that wheat SA levels significantly increased after the delivery of the two effectors. The results of aphid bioassays conducted on the wheat plants carrying Sm10 or SmC002 showed significant increases in the survival and fecundity of S. miscanthi. This study demonstrated that the Sm10 and SmC002 salivary effectors of S. miscanthi enhanced host plant susceptibility and benefited S. miscanthi performance by regulating wheat defense signaling pathways.

Feeding Behavior Comparison of Bean Bugs, Riptortus pedestris and Halyomorpha halys on Different Soybean Cultivars

Riptortus pedestris (Fabricius) and Halyomorpha halys (Stål) are the major pests that feed on soybean pods, seeds, and fruits. Higher populations and damage occur during the soybean maturity stages (podding to harvest). To compare the feeding behavior of R. pedestris and H. halys, we used the six most cultivated cultivars (Daepung-2ho, Daechan, Pungsannamul, Daewon, Seonpung, and Seoritae) in Korea using the electropenetrography (EPG) technique. Both R. pedestris and H. halys, the NP (non-penetration), a non-probing waveform, was the shortest in the Pungsannamul (298 and 268 min) and the longest in the Daepung-2ho (334 and 339 min), respectively. The feeding waveforms Pb (phloem feeding: E1-Salivation and E2-Sap feeding) and G (xylem feeding) were the longest in Pungsannamul and the shortest in Daepung-2ho. In addition, as a result of investigating the damage rate by planting six cultivars of beans in the field, as expected, the proportions of damage types B and C were highest in Pungsannamul and lowest in Daepung-2ho. These results reveal that both bug species ingest xylem sap from leaflets and stems using a salivary sheath strategy to acquire water and nutrients from soybean pods/seeds with cell-rupture tactics. This study provides perceptive information to understand the feeding behavior, field occurrence, and damage patterns of R. pedestris and H. halys, which may have key implications for the management of hemipteran pests by determining the specificity and susceptibility of host plants.

Nucleotide-binding leucine-rich repeat network underlies nonhost resistance of pepper against the Irish potato famine pathogen Phytophthora infestans.

Nonhost resistance (NHR) is a robust plant immune response against non-adapted pathogens. A number of nucleotide-binding leucine-rich repeat (NLR) proteins that recognize non-adapted pathogens have been identified, although the underlying molecular mechanisms driving robustness of NHR are still unknown. Here, we screened 57 effectors of the potato late blight pathogen Phytophthora infestans in nonhost pepper (Capsicum annuum) to identify avirulence effector candidates. Selected effectors were tested against 436 genome-wide cloned pepper NLRs, and we identified multiple functional NLRs that recognize P. infestans effectors and confer disease resistance in the Nicotiana benthamiana as a surrogate system. The identified NLRs were homologous to known NLRs derived from wild potatoes that recognize P. infestans effectors such as Avr2, Avrblb1, Avrblb2, and Avrvnt1. The identified CaRpi-blb2 is a homologue of Rpi-blb2, recognizes Avrblb2 family effectors, exhibits feature of lineage-specifically evolved gene in microsynteny and phylogenetic analyses, and requires pepper-specific NRC (NLR required for cell death)-type helper NLR for proper function. Moreover, CaRpi-blb2-mediated hypersensitive response and blight resistance were more tolerant to suppression by the PITG_15 278 than those mediated by Rpi-blb2. Combined results indicate that pepper has stacked multiple NLRs recognizing effectors of non-adapted P. infestans, and these NLRs could be more tolerant to pathogen-mediated immune suppression than NLRs derived from the host plants. Our study suggests that NLRs derived from nonhost plants have potential as untapped resources to develop crops with durable resistance against fast-evolving pathogens by stacking the network of nonhost NLRs into susceptible host plants.

Antixenosis by a resistant Musa cultivar to stem borer Odoiporus longicollis attack and expression of microsomal α-amylase by the pest

Banana pseudo-stem weevil (BPW) Odoiporus longicollis Olivier is a serious pest of Musa cultivars which completes its lifecycle as an internal parasite in the pseudo-stem of susceptible host plants. The larval stage of BPW is destructive and difficult to control as larvae are endophytic. Plantains (bananas), resistant to infestation by BPW, exhibited antixenosis against the larvae. Experimental maintenance of the larvae for 4 days in the live pseudo-stem of the resistant plantain resulted in the disruption of carbohydrate metabolism and imbalance of protein-free amino acid turnover. The pseudo-stem possesses three larvicides: stigmasterol-3-O-glucoside (SOG), sulfoquinovosyl diacylglycerol (SQDG), and betulinic acid (BA). Larvicides cause significant elevation in hemolymph protein and reduction in total free amino acids. Larvae treated with larvicides showed elevated activities of hexokinase, trehalase, and lactic acid dehydrogenase, which resulted in significant decrease of glucose and trehalose but sharp increase of lactic acid. Also, inhibition in the activity of glycogen phosphorylase caused significant increase of fat body glycogen in affected larvae. At LD20 concentration, toxicities by SOG, SQDG, and BA were similar but antixenosis by the resistant host plant was more severe due to the simultaneous action of three larvicides present in the resistant, live pseudo-stem. Disruption of carbohydrate metabolism and imbalance of protein-amino acid turnover due to toxicity by larvicides resulted in slow death of the larvae. The larval body responded against toxicity through the induction of the amy gene, which resulted in increased synthesis of α-amylase. The protein was sequenced as ID AHN 92452.2 with 496 amino acids, and the gene has 1491 nucleotides. Defense mechanisms by the larvae are not sufficient to resist antixenosis by the host plant. SOG, SQDG, and BA can be used synergistically as a larvicide for the control of BPW.