Virulent Populations Research Articles

Virulence Adaptation by Rice Planthoppers and Leafhoppers to Resistance Genes and Loci: A Review.

In recent decades, research on developing and deploying resistant rice has accelerated due to the availability of modern molecular tools and, in particular, advances in marker-assisted selection. However, progress in understanding virulence adaptation has been relatively slow. This review tracks patterns in virulence adaptation to resistance genes (particularly Bph1, bph2, Bph3, and bph4) and examines the nature of virulence based on selection experiments, responses by virulent populations to differential rice varieties (i.e., varieties with different resistance genes), and breeding experiments that interpret the genetic mechanisms underlying adaptation. The review proposes that varietal resistance is best regarded as a combination of minor and major resistance traits against which planthoppers develop partial or complete virulence through heritable improvements that are reversable or through evolutionary adaptation, respectively. Agronomic practices, deployment patterns, and herbivore population pressures determine the rates of adaptation, and there is growing evidence that pesticide detoxification mechanisms can accelerate virulence adaptation. Research to delay adaptation has mainly focused on gene pyramiding (i.e., including ≥ two major genes in a variety) and multilines (i.e., including ≥ two resistant varieties in a field or landscape); however, these strategies have not been adequately tested and, if not managed properly, could inadvertently accelerate adaptation compared to sequential deployment. Several research gaps remain and considerable improvements in research methods are required to better understand and manage virulence adaptation.

The response of the pepper with and without Me1 gene to Mi-1.2-virulent Meloidogyne incognita (Kofoid & White,1919) (Tylenchida: Meloidogynidae) isolates

Root-knot nematodes are important organisms that infect vegetables. Due to the intense use of Mi-1.2, virulent populations that break resistance have become widespread and have become an important factor limiting the use of this gene. Me1 resistance gene on pepper provides resistance against Meloidogyne arenaria (Neal, 1889) Chitwood, 1949 Meloidogyne incognita (Kofoid & White,1919) Chitwood, 1949 and Meloidogyne javanica (Treub, 1885) Chitwood, 1949 (Tylenchida: Meloidogynidae) species. However, there is limited information on the effectiveness of the Me1 gene against Mi-1.2 virulent populations. Therefore, it is important to know the reaction of pepper cultivars carrying the Me1 resistance gene against Mi-1.2 virulent populations. In this study, the response of resistant pepper cultivar MT-01 F1 (bearing Me1) and susceptible pepper cultivar Safran F1 against both Mi-1.2 natural virulent M. incognita isolates and Mi-1.2 selected virulent M. incognita isolate was investigated under controlled conditions. This study was conducted in Akdeniz University Faculty of Agriculture Department of Plant Protection Nematology Laboratory in 2021. All isolates caused many egg masses and galls on the resistant tomato cultivar Seval F1 as expected, and the susceptible pepper cultivar Safran F1. Five isolates were found to cause egg masses and gall formation, while the V3 isolate did not multiply on the resistant pepper cultivar MT-01 F1. The results showed that pepper cultivars carrying the Me1 gene exhibited different responses against Mi-1.2 virulent isolates.

Comparative Transcriptomic Analysis of Soybean Cyst Nematode Inbred Populations Non-adapted or Adapted on Soybean rhg1-a/Rhg4-Mediated Resistance.

Soybean cyst nematode (SCN, Heterodera glycines) is most effectively managed through planting resistant soybean cultivars, but the repeated use of the same resistance sources has led to a widespread emergence of virulent SCN populations that can overcome soybean resistance. Resistance to SCN HG type 0 (Race 3) in soybean cultivar Forrest is mediated by an epistatic interaction between the soybean resistance genes rhg1-a and Rhg4. We previously developed two SCN inbred populations by mass-selecting SCN HG type 0 (Race 3) on susceptible and resistant recombinant inbred lines, derived from a cross between Forrest and the SCN-susceptible cultivar Essex, which differ for Rhg4. To identify SCN genes potentially involved in overcoming rhg1-a/Rhg4-mediated resistance, we conducted RNA sequencing on early parasitic juveniles of these two SCN inbred populations infecting their respective hosts, only to discover a handful of differentially expressed genes (DEGs). However, in a comparison with early parasitic juveniles of an avirulent SCN inbred population infecting a resistant host, we discovered 59 and 171 DEGs uniquely up- or downregulated in virulent parasitic juveniles adapted on the resistant host. Interestingly, the proteins coded by these 59 DEGs included vitamin B-associated proteins (reduced folate carrier, biotin synthase, and thiamine transporter) and nematode effectors known to play roles in plant defense suppression, suggesting that virulent SCN may exert a heightened transcriptional response to cope with enhanced plant defenses and an altered nutritional status of a resistant soybean host. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Identification and Characterization of a Virulent Meloidogyne incognita Population Breaking Tomato Mi-1-Mediated Resistance in Indiana

High-tunnel production is increasing rapidly in the US due to its effectiveness in extending production seasons. Tomato is considered one of the most profitable crops grown in high tunnels. The elevated soil temperature and constant soil moisture in high tunnels lead to the buildup of root-knot nematodes (RKNs). Growing RKN-resistant tomato cultivars or grafting onto RKN-resistant tomato rootstocks is considered effective in managing RKNs. However, all of the RKN-resistant tomato cultivars or rootstocks carry the same resistance gene, Mi-1. This lack of diversity in resistance has led to the emergence of virulent RKN populations breaking tomato Mi-1 resistance. Here, we identified and characterized a virulent population of Meloidogyne incognita from a high tunnel in Indiana. The M. incognita population was confirmed as being able to infect and reproduce on two resistant tomato cultivars, Better Boy and Early Girl, carrying the Mi-1 gene, under a controlled environment at 24 °C. To our knowledge, this is the first report of a virulent M. incognita population breaking Mi-1 resistance in Indiana. Virulent M. incognita populations overcoming Mi-1 resistance were previously reported in California and Georgia in the US. This work emphasizes the importance of regularly monitoring RKN population virulence to sustainably manage the pest.

Fortifying nematode resistance through susceptibility gene inactivation

The predominant genetic defense mechanism against soybean cyst nematode (SCN) in 95% of the North America market is under threat by virulent SCN populations. Usovsky et al. identified GmSNAP02 as an SCN susceptibility gene through fine-mapping of unique bi-parental populations. Loss-of-function of GmSNAP02 confers enhanced resistance to more virulent SCN.

Combined miRNA and mRNA sequencing reveals the defensive strategies of resistant YHY15 rice against differentially virulent brown planthoppers.

The brown planthopper (BPH) poses a significant threat to rice production in Asia. The use of resistant rice varieties has been effective in managing this pest. However, the adaptability of BPH to resistant rice varieties has led to the emergence of virulent populations, such as biotype Y BPH. YHY15 rice, which carries the BPH resistance gene Bph15, exhibits notable resistance to biotype 1 BPH but is susceptible to biotype Y BPH. Limited information exists regarding how resistant rice plants defend against BPH populations with varying levels of virulence. In this study, we integrated miRNA and mRNA expression profiling analyses to study the differential responses of YHY15 rice to both avirulent (biotype 1) and virulent (biotype Y) BPH. YHY15 rice demonstrated a rapid response to biotype Y BPH infestation, with significant transcriptional changes occurring within 6 hours. The biotype Y-responsive genes were notably enriched in photosynthetic processes. Accordingly, biotype Y BPH infestation induced more intense transcriptional responses, affecting miRNA expression, defenserelated metabolic pathways, phytohormone signaling, and multiple transcription factors. Additionally, callose deposition was enhanced in biotype Y BPH-infested rice seedlings. These findings provide comprehensive insights into the defense mechanisms of resistant rice plants against virulent BPH, and may potentially guide the development of insect-resistant rice varieties.

Host-specific co-evolution likely driven by diet in Buchnera aphidicola

BackgroundRussian wheat aphid (Diuraphis noxia Kurd.) is a severe pest to wheat, and even though resistance varieties are available to curb this pest, they are becoming obsolete with the development of new virulent aphid populations. Unlike many other aphids, D noxia only harbours a single endosymbiont, Buchnera aphidicola. Considering the importance of Buchnera, this study aimed to elucidate commonalities and dissimilarities between various hosts, to better understand its distinctiveness within its symbiotic relationship with D. noxia. To do so, the genome of the D. noxia’s Buchnera was assembled and compared to those of other aphid species that feed on diverse host species.ResultsThe overall importance of several features such as gene length and percentage GC content was found to be critical for the maintenance of Buchnera genes when compared to their closest free-living relative, Escherichia coli. Buchnera protein coding genes were found to have percentage GC contents that tended towards a mean of ~ 26% which had strong correlation to their identity to their E. coli homologs. Several SNPs were identified between different aphid populations and multiple isolates of Buchnera were confirmed in single aphids.ConclusionsEstablishing the strong correlation of percentage GC content of protein coding genes and gene identity will allow for identifying which genes will be lost in the continually shrinking Buchnera genome. This is also the first report of a parthenogenically reproducing aphid that hosts multiple Buchnera strains in a single aphid, raising questions regarding the benefits of maintaining multiple strains. We also found preliminary evidence for post-transcriptional regulation of Buchnera genes in the form of polyadenylation.

Defense Regulatory Network Associated with circRNA in Rice in Response to Brown Planthopper Infestation

The brown planthopper (BPH), Nilaparvata lugens (Stål), a rice-specific pest, has risen to the top of the list of significant pathogens and insects in recent years. Host plant-mediated resistance is an efficient strategy for BPH control. Nonetheless, BPH resistance in rice cultivars has succumbed to the emergence of distinct virulent BPH populations. Circular RNAs (circRNAs) play a pivotal role in regulating plant–environment interactions; however, the mechanisms underlying their insect-resistant functions remain largely unexplored. In this study, we conducted an extensive genome-wide analysis using high-throughput sequencing to explore the response of rice circRNAs to BPH infestations. We identified a total of 186 circRNAs in IR56 rice across two distinct virulence groups: IR-IR56-BPH (referring to IR rice infested by IR56-BPH) and IR-TN1-BPH, along with a control group (IR-CK) without BPH infestation. Among them, 39 circRNAs were upregulated, and 43 circRNAs were downregulated in the comparison between IR-IR56-BPH and IR-CK. Furthermore, in comparison with IR-CK, 42 circRNAs exhibited upregulation in IR-TN1-BPH, while 42 circRNAs showed downregulation. The Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that the targets of differentially expressed circRNAs were considerably enriched in a multitude of biological processes closely linked to the response to BPH infestations. Furthermore, we assessed a total of 20 randomly selected circRNAs along with their corresponding expression levels. Moreover, we validated the regulatory impact of circRNAs on miRNAs and mRNAs. These findings have led us to construct a conceptual model that circRNA is associated with the defense regulatory network in rice, which is likely facilitated by the mediation of their parental genes and competing endogenous RNA (ceRNA) networks. This model contributes to the understanding of several extensively studied processes in rice-BPH interactions.

Comparative histopathology of virulent and avirulent Meloidogyne javanica populations on susceptible and resistant tomato plants.

The Mi-1.2 gene confers resistance to a wide range of Meloidogyne species, being the most important resistance factor employed in tomato breeding so far. However, many aspects related to the interaction of Mi-1.2-carrying tomato cultivars and virulent/avirulent Meloidogyne populations have not yet been clarified. Herein, comparative histopathological analyses were carried after inoculation of the homozygous (Mi-1.2/Mi-1.2) tomato rootstock 'Guardião' and the susceptible cultivar 'Santa Clara' (mi-1.2/mi-1.2) with virulent and avirulent populations of M. javanica. In the susceptible control, it was possible to visualize second stage juveniles (J2) of avirulent population and feeding sites from 2 to 30 days after infection (DAI) with females reaching maturity at 24-34 DAI. In the resistant rootstock, the Mi-1.2 gene-mediated resistance was related mainly to early defense responses (pre-infection and hypersensitive reaction), which led to an immunity-like phenotype that completely prevented the reproduction of the avirulent Meloidogyne population. On the other hand, J2s of the virulent M. javanica population were able to penetrate roots much more than the avirulent population, migrated and developed normally, showing intense and similar pattern of penetration from 4 to 34 DAI in the root tissues of both resistant and susceptible tomato genotypes. The total numbers of J2, J3, J4, and females counted in 'Santa Clara' for the virulent population of M. javanica were higher than in 'Guardião'.

Substitution mapping and characterization of brown planthopper resistance genes from traditional rice cultivar 'Rathu Heenati' (Oryza sativa L.).

The brown planthopper (BPH; Nilaparvata lugens Stål) is a devastating pest that causes severe rice yield losses in Asia. Introducing multiple BPH resistance genes into rice cultivars is an effective and sustainable way to mitigate yield losses. A traditional rice cultivar, 'Rathu Heenati', has durable BPH resistance due to multiple resistance genes (including BPH3 and BPH17) and quantitative trait loci (QTLs). However, these genes have not been used in Japanese rice breeding owing to limited genetic information. To identify markers tightly linked to BPH3 and BPH17 introgressed into the 'Sagabiyori' (susceptible) genetic background, we performed substitution mapping. BPH3 was delimited between RM3132 and RM589 on chromosome 6, and BPH17 between RM16493 and RM16531 on chromosome 4. We also performed QTL analysis to identify additional BPH resistance genes from 'Rathu Heenati' and detected a QTL, denoted as qBPH3.1, on chromosome 3. The effect of pyramiding BPH3 and BPH17 was significantly greater against virulent BPH populations than that of either gene alone. The combination of BPH3, BPH17 and qBPH3.1 from 'Rathu Heenati' might be facilitated to improve commercial Japanese cultivars with more robust BPH resistance.

Genomic analysis of Enterococcus faecium from non-clinical settings: antimicrobial resistance, virulence, and clonal population in livestock and the urban environment.

Enterococci are commensals of the gastrointestinal tract of humans and animals that evolved into opportunistic pathogens with high antimicrobial resistance and virulence. Multidrug-resistant Enterococcus is a major cause of hospital-acquired infections worldwide. For this reason, the characterization of non-clinical reservoirs of Enterococci and their epidemiological link to resistant hospital isolates is crucial for controlling their spread. A total of 295 samples collected from livestock (pigs and cows, n = 135) and environment (public buses, passengers hands, and urban environments, n = 160) were screened for Enterococcus spp. E. faecium antimicrobial resistance profiles, virulence potential, and clonal population were further characterized. Enterococci were detected in 90.5% (n = 267) of the samples, with a higher prevalence in livestock (100%) than the environment (82.5%, p < 0.0001), but none of the isolates exhibited vancomycin resistance. E. faecalis was the most prevalent species (51.7%), predominantly found in livestock (62.2%), while E. faecium was more common in the environment. Of the 59 E. faecium isolates, 78% showed resistance to ≥3 antibiotic classes and contained associated resistance genes, namely tetracyclines (tetM and tetL), beta-lactams (mutations in pbp5), and high-level resistance to aminoglycosides (ant(6)-Ia and aac(6')-aph(2″)). A wide array of virulence factors was detected among E. faecium, associated with adherence, biofilm formation, and adaptation to host response, while hospital-associated virulence markers, such as IS16, were less frequent, probably due to the non-clinical nature of the isolates. Clonal population analysis revealed a diverse E. faecium population. Although no direct epidemiological link could be traced between our isolates and specific clinical isolates, infection-associated genetic backgrounds were identified in non-clinical isolates: one isolate from pigs belonged to CC17 (ST32), while four isolates belonged to CC94, including one recovered from pigs (ST296), one from cows (ST2206), one from the urban environment (ST1205), and other from buses (ST800). This study underscores a high prevalence of clinically relevant Enterococcus species among healthy livestock and the environment. Despite the absence of vancomycin resistance and limited hospital infection-associated clonal lineages, the presence of E. faecium with significant virulence potential and resistance to critical antibiotics in human and veterinary medicine highlights the need for continuing surveillance of non-clinical reservoirs.

Seasonal Dynamics of Various Scab-Causing Streptomyces Genotypes Among Potato Fields on Prince Edward Island.

Potato common scab is an important bacterial plant disease caused by numerous Streptomyces species and strains. A better understanding of the genetic diversity and population dynamics of these microorganisms in the field is crucial to develop effective control methods. Our research group previously studied the genetic diversity of scab-causing Streptomyces spp. in Prince Edward Island, one of Canada's most important potato-growing provinces. Fourteen distinct Streptomyces genotypes were identified and displayed contrasting aggressiveness toward potato tubers. To better understand the distribution and occurrence of these genotypes over time under field conditions, the population dynamics were studied in nine commercial potato fields throughout a growing season. A comparative genomic-driven approach was used to design genotype-specific primers and probes, allowing us to quantify, using quantitative polymerase chain reaction, the abundance of each of the 14 genotypes in field soil. Thirteen of the previously identified genotypes were detected in at least one soil sample, with various frequencies and population sizes across the different fields under study. Interestingly, weakly virulent genotypes dominated, independent of time or location. Among them, three genotypes accounted for more than 80% of the genotypes' combined population. Although the highly virulent genotypes were detected in lower relative abundance than the weakly virulent ones, an increase in the highly virulent genotypes' population size was observed over the growing season in most fields. The results will ultimately be useful for the development of targeted common scab control strategies.

The Outlook of Tomatoes with extended Shelf Life in Nigeria and the Ensuing Safety Measures and Regulated Introduction by Nigerian Regulatory Authorities

Tomato (Solanum lycopersicum) is widely consumed worldwide. The primary chance to influence tomatoes' edibility and market value lies in regulating the synthesis and function of the plant hormone ethylene responsible for ripening. The usage of harmless substances on tomato surfaces, a reduction in storage temperature, the implementation of modified atmosphere packaging, or a combination of these approaches have been associated with increasing tomatoes’ shelf life. As crop plants containing a genetically modified trait through molecular techniques continue their transition from the laboratory to the field, the National Biotechnology Development Agency (NABDA) has been reported to be developing genetically modified (GM) tomatoes by deactivating polygalacturonase (PG) gene that is responsible for polygalacturonase which is the enzyme that aids fruit softening and subsequently increases the shelf life of the tomatoes to be released in the Nigerian market. This article looks at tomatoes (S. lycopersicum) and the methods used in increasing their shelf life with more focus on the genetically modified tomatoes and the needed regulations by the Nigerian regulatory bodies before its commercialization in the country. Environmental and health hazards that require careful consideration in the course of embarking on the genetical modification and introduction of the hybrid tomatoes into the Nigeria markets encompass potential biodiversity loss, adverse impacts on natural food chains, and the potential rise of more virulent pathogen populations. Nevertheless, it is crucial to emphasize that the biotechnological processes and products must be accompanied by effective regulations to mitigate these concerns, National Biosafety Management Agency is believed to be engaged with these needs.

Transcriptome-wide N6-methyladenosine (m6A) profiling of compatible and incompatible responses reveals a nonhost resistance–specific m6A modification involved in soybean–soybean cyst nematode interaction

Soybean cyst nematode (SCN, Heterodera glycines) is a devastating pathogen that infects soybean (Glycine max L. Merrill) and disrupts soybean production worldwide. SCN infection upregulates or downregulates the expression of multiple genes in soybean. However, the regulatory mechanisms that underlie these changes in gene expression remain largely unexplored. N6-methyladenosine (m6A) methylation, one of the most prevalent mRNA modifications, contributes to transcriptional reprogramming during plant responses to pathogen infection. Nevertheless, the role of m6A methylation in establishing compatible and incompatible soybean responses to SCN has not previously been studied. Here, we performed transcriptome-wide m6A profiling of soybean roots infected with virulent and avirulent populations of SCN. Compared with the compatible response, the incompatible response was associated with higher global m6A methylation levels, as well as more differentially modified m6A peaks (DMPs) and differentially expressed genes (DEGs). A total of 133 and 194 genes showed significant differences in both expression and m6A methylation levels in compatible and incompatible interactions; the most significantly enriched gene ontology terms associated with these genes were plant–pathogen interaction (compatible) and folate biosynthesis (incompatible). Our findings demonstrate that the m6A methylation profiles of compatible and incompatible soybean responses are distinct and provide new insights into the regulatory mechanism underlying soybean response to SCN at the post-transcriptional modification level, which will be valuable for improving the SCN resistance breeding.

Patterns of asexual reproduction of the soybean aphid, Aphis glycines (Matsumura), with and without the secondary symbionts Wolbachia and Arsenophonus, on susceptible and resistant soybean genotypes.

Plant breeding is used to develop crops with host resistance to aphids, however, virulent biotypes often develop that overcome host resistance genes. We tested whether the symbionts, Arsenophonus (A) and Wolbachia (W), affect virulence and fecundity in soybean aphid biotypes Bt1 and Bt3 cultured on whole plants and detached leaves of three resistant, Rag1, Rag2 and Rag1 + 2, and one susceptible, W82, soybean genotypes. Whole plants and individual aphid experiments of A. glycines with and without Arsenophonus and Wolbachia did not show differences in overall fecundity. Differences were observed in peak fecundity, first day of deposition, and day of maximum nymph deposition of individual aphids on detached leaves. Bt3 had higher fecundity than Bt1 on detached leaves of all plant genotypes regardless of bacterial profile. Symbionts did not affect peak fecundity of Bt1 but increased it in Bt3 (A+W+) and all Bt3 strains began to deposit nymphs earlier than the Bt1 (A+W-). Arsenophonus in Bt1 delayed the first day of nymph deposition in comparison to aposymbiotic Bt1 except when reared on Rag1 + 2. For the Bt1 and Bt3 strains, symbionts did not result in a significant difference in the day they deposited the maximum number of nymphs nor was there a difference in survival or variability in number of nymphs deposited. Variability of number of aphids deposited was higher in aphids feeding on resistant plant genotypes. The impact of Arsenophonus on soybean aphid patterns of fecundity was dependent on the aphid biotype and plant genotype. Wolbachia alone had no detectable impact but may have contributed to the increased fecundity of Bt3 (A+W+). An individual based model, using data from the detached leaves experiment and with intraspecific competition removed, found patterns similar to those observed in the greenhouse and growth chamber experiments including a significant interaction between soybean genotype and aphid strain. Combining individual data with the individual based model of population growth isolated the impact of fecundity and host resistance from intraspecific competition and host health. Changes to patterns of fecundity, influenced by the composition and concentration of symbionts, may contribute to competitive interactions among aphid genotypes and influence selection on virulent aphid populations.

Emergence of COVID-19 Variants: An Update.

Severe acute respiratory disease virus-2 (SARS CoV-2) is one of the deadliest global threats faced by mankind to date. Despite the colossal efforts, the viral pandemic swept across all boundaries. Besides the virulence and susceptible population, the low proofreading capacity and error-prone mechanism of RNA-dependent RNA polymerase (RdRp) have contributed to new variants and reinfections. The World Health Organization has officially categorized these variants as variants of concern or variants of interest. This nomenclature is not merely to suffice the surveillance but also to have effective treatment and vaccine options in place. Coronavirus disease 2019 (COVID-19) variants have the propensity to render the available treatment strategies futile owing to the mutations they acquire. The futility of treatment strategies can be attributed either to the ineffectiveness or the shortage of supply given the skyrocketing increase in the number of cases. Presently, the Omicron variant is the most widespread one and is known to escape the protection, be it immune-derived, vaccination-derived, or hybrid. WHO has recommended modification in vaccine development policies and few companies have introduced Omicron-adapted vaccine jabs. Keeping in view the unending tale of COVID-19 variants and the huge data available on the same, this review focuses on providing insight into the emergence and ongoing dynamics of these new COVID-19 variants.

Identification and characterization of a virulent population of Meloidogyne graminicola

Identification and characterization of a virulent population of Meloidogyne graminicola

Crop rotation with Meloidogyne-resistant germplasm is useful to manage and revert the (a)virulent populations of Mi1.2 gene and reduce yield losses.

A rotation sequence of ungrafted and grafted tomato-melon-pepper-watermelon on resistant rootstocks 'Brigeor', Cucumis metuliferus, 'Oscos' and Citrullus amarus, respectively, was carried out in a plastic greenhouse, ending with a susceptible or resistant tomato crop. The rotation was conducted in plots infested by an avirulent (Avi) or a partially virulent (Vi) Meloidogyne incognita population to the Mi1.2 gene. At the beginning of the study, the reproduction index (RI, relative reproduction in the resistant respect susceptible tomato) of Avi and Vi populations was 1.3% and 21.6%, respectively. Soil nematode density at transplanting (Pi) and at the end (Pf) of each crop, disease severity and crop yield were determined. Moreover, the putative virulence selection and fitness cost were determined at the end of each crop in pot tests. In addition, a histopathological study was carried out 15 days after nematode inoculation in pot test. The volume and number of nuclei per giant cell (GC) and the number of GC, their volume and the number of nuclei per feeding site in susceptible watermelon and pepper were compared with C. amarus and resistant pepper. At the beginning of the study, the Pi of Avi and Vi plots did not differ between susceptible and resistant germplasm. At the end of the rotation, the Pf of Avi was 1.2 the Pi in susceptible and 0.06 in resistant, the cumulative yield of grafted crops was 1.82 times higher than that of the ungrafted susceptible ones, and the RI in resistant tomato less than 10% irrespective of the rotation sequence. Concerning the Vi, Pf was below the detection level at the end of the rotation in resistant and 3 times Pi in the susceptible. The cumulative yield of grafted crops was 2.83 times higher than that of the ungrafted and the RI in resistant tomato was 7.6%, losing the population's virulence. In the histopathological study, no differences in number of GC per feeding site were observed in watermelon compared to C. amarus, but they were more voluminous and contained higher number of nuclei per GC and per feeding site. Regarding pepper, Avi population did not penetrate resistant rootstock.

Development and characterization of near-isogenic lines for brown planthopper resistance genes in the genetic background of japonica rice 'Sagabiyori'.

The brown planthopper (BPH: Nilaparvata lugens Stål) is one of the most destructive insects in rice production. The use of host plant resistance has potential to reduce damage caused by BPH. The heat tolerance japonica rice 'Sagabiyori', with superior grain quality and high soluble starch in the stem, is highly susceptible to damage by BPH. Here, to enhance its BPH resistance, we developed seven near-isogenic lines (NILs) carrying BPH2, BPH17-ptb, BPH32, BPH3, BPH17, BPH20, and BPH21 through marker-assisted selection and evaluated resistance to two BPH populations. Most lines were more resistant to the Hadano-1966 BPH population than Sagabiyori but were less effective against the highly virulent Koshi-2013 population. Nevertheless, in antixenosis tests, Koshi-2013 settled less on all NILs than on Sagabiyori. In addition, adult mortality and the percentage of fresh weight loss of lines carrying BPH17 and BPH3 indicated that these lines have higher resistance to Koshi-2013 than Sagabiyori. Current study revealed that BPH resistance of Sagabiyori became stronger by transferring BPH3 and BPH17 genes. Thus, BPH3 and BPH17 might be valuable for breeding programs to enhance BPH resistance of high grain quality rice varieties with heat tolerance.

Development of pyramided lines carrying brown planthopper resistance genes in the genetic background of Indica Group rice (Oryza sativa L.) variety 'IR64'.

The development of resistant rice (Oryza sativa L.) varieties is a key strategy for the eco-friendly control of brown planthopper (BPH: Nilaparvata lugens Stål). However, BPH outbreaks occur frequently owing to the evolution of virulent strains in the field and the rapid breakdown of monogenic resistance to BPH. Therefore, to enhance BPH resistance and gauge the effectiveness of gene pyramiding against strongly virulent BPH, we developed pyramided lines (PYLs) in the genetic background of 'IR64' carrying BPH resistance genes. We developed six IR64-PYLs (BPH3 + BPH17, BPH32 + BPH17, BPH32 + BPH20, BPH3 + BPH17-ptb, BPH20 + BPH3, and BPH17-ptb + BPH32) through marker-assisted selection. To assess the resistance of the IR64-PYLs, we conducted antibiosis test, honeydew test, and modified seedbox screening test (MSST) using strongly virulent BPH populations. The level of BPH resistance increased in all six IR64-PYLs compared to both 'IR64' and the corresponding NILs in MSST. Among them, IR64-BPH3 + BPH17 and IR64-BPH32 + BPH17 exhibited the highest resistance to BPH. However, the resistance level of most IR64-PYLs was not significantly higher than that of the corresponding NILs in antibiosis test. Thus, these PYLs could serve as a valuable resource for breeding programs aimed at improving resistance to virulent strains of BPH and enhancing their durability.