Unstable Resistance Research Articles

Dynamic methylation and expression of alternative promoters for oestrogen receptor alpha in cell line models of fulvestrant resistance.

Oestrogen receptor alpha (ER; gene symbol ESR1) is the most important prognostic and treatment-predictive biomarker in breast cancer. Drugs targeting oestrogen and ER for endocrine therapy of breast cancer include aromatase inhibitors, the selective ER modulator tamoxifen and the selective ER degrader fulvestrant. Tumours can develop resistance to endocrine therapy through several mechanisms, which is often linked to altered expression of ER. To investigate the role of promoter methylation in the regulation of ESR1 expression, we used bisulfite sequencing to measure methylation at CpG sites in alternative ER promoter regions for six cell line models of fulvestrant resistance. Both CpG methylation and expression of alternative first exons changed dynamically, with striking differences between cell lines that had stable or unstable resistance upon fulvestrant withdrawal. Methylation at some CpG sites was strongly negatively correlated with expression of specific first exons. In a breast tumour cohort, higher relative expression of upstream alternative first exons was associated with worse prognosis in post-menopausal women with ER-positive tumours who received endocrine therapy.

Comparative Field Evaluation and Transcriptome Analysis Reveals that Chromosome Doubling Enhances Sheath Blight Resistance in Rice

Rice sheath blight, caused by Rhizoctonia solani Kihn (R. solani), poses a significant threat to rice production and quality. Autotetraploid rice, developed through chromosome doubling of diploid rice, holds great potential for enhancing biological and yield traits. However, its resistance to sheath blight in the field has remained unclear. In this study, the field resistance of 35 autotetraploid genotypes and corresponding diploids was evaluated across three environments from 2020 to 2021. The booting stage was optimal for inoculating period based on the inoculation and analysis of R. solani at five rice growth stages. We found autotetraploids generally exhibited lower disease scores than diploids, indicating enhanced resistance after chromosome doubling. Among the 35 genotypes, 16 (45.71%) displayed increased resistance, 2 (5.71%) showed decreased resistance, and 17 (48.57%) displayed unstable resistance in different sowing dates. All combinations of the genotype, environment and ploidy, including the genotype-environment-ploidy interaction, contributed significantly to field resistance. Chromosome doubling increased sheath blight resistance in most genotypes, but was also dependent on the genotype-environment interaction. To elucidate the enhanced resistance mechanism, RNA-seq revealed autotetraploid recruited more down-regulated differentially expressed genes (DEGs), additionally, more resistance-related DEGs, were down-regulated at 24 h post inoculation in autotetraploid versus diploid. The ubiquinone/terpenoid quinone and diterpenoid biosynthesis pathways may play key roles in ploidy-specific resistance mechanisms. In summary, our findings shed light on the understanding of sheath blight resistance mechanisms in autotetraploid rice.

Evaluating virulence features of Acinetobacter baumannii resistant to polymyxin B.

The increasing resistance to polymyxins in Acinetobacter baumannii has made it even more urgent to develop new treatments. Anti-virulence compounds have been researched as a new solution. Here, we evaluated the modification of virulence features of A. baumannii after acquiring resistance to polymyxin B. The results showed lineages attaining unstable resistance to polymyxin B, except for Ab7 (A. baumannii polymyxin B resistant lineage), which showed stable resistance without an associated fitness cost. Analysis of virulence by a murine sepsis model indicated diminished virulence in Ab7 (A. baumannii polymyxin B resistant lineage) compared with Ab0 (A. baumannii polymyxin B susceptible lineage). Similarly, downregulation of virulence genes was observed by qPCR at 1 and 3h of growth. However, an increase in bauE, abaI, and pgAB expression was observed after 6h of growth. Comparison analysis of Ab0, Ab7, and Pseudomonas aeruginosa suggested no biofilm formation by Ab7. In general, although a decrease in virulence was observed in Ab7 when compared with Ab0, some virulence feature that enables infection could be maintained. In light of this, virulence genes bauE, abaI, and pgAB showed a potential relevance in the maintenance of virulence in polymyxin B-resistant strains, making them promising anti-virulence targets.

Design Guideline for a Cantilever-Type MEMS Switch with High Contact Force

Micromechanical switches are of significant interest for advanced radio frequency and microwave systems, but their practical implementation is limited by low reliability. Electrodes of a microscopic size develop weak contact force that leads to high and unstable contact resistance. The force is typically increased by using a sophisticated switch design with extended lateral dimensions, although a simple and compact cantilever is more preferable. The paper describes for the first time a comprehensive approach to enhance the force of an electrostatically actuated switch. The strategy is applied to a miniature device based on a 50 µm long cantilever. The contact force is increased from 10 to 112 µN, making the switch strong enough to achieve low and stable contact resistance. The restoring force is also enhanced in order to ensure reliable de-actuation. The growth of forces is accompanied by a reduction in the pull-in voltage. Connecting several cantilevers in parallel and manipulating the number and position of contact bumps additionally improves the force and mechanical stability of the switch. An optimal design contains a triple cantilever with two bumps. It provides 50% higher force per contact compared to the single-cantilever switch at the same pull-in voltage and keeps the advantages of a miniature device. The proposed design strategy may be used for building reliable MEMS switches.

MEMS SWITCH BASED ON CANTILEVER WITH INCREASED CONTACT FORCE

MEMS switches are of significant interest for promising radio-electronic systems, but have not yet found widespread use due to the low reliability of microcontacts. The switch develops low contact force, which results in high and unstable contact resistance. The force is usually increased by using electrodes with complex shapes and large areas, but a simple and compact configuration is preferable. This work presents a key based on a 50 µm long cantilever. For the first time, a method for selecting the vertical dimensions of a product is described, increasing the clamping force to values ​​​​in excess of 100 μN, necessary for reliable operation of the contacts. Test samples were manufactured and tested, and the performance characteristics were compared with the calculation results.

FRACTURE SAFETY OF LIQUEFIED NATURAL GAS TANK IN CRYOGENIC CONDITIONS

High-manganese austenitic steel has been developed as a new cryogenic steel for application in liquified natural gas (LNG) storage and fuel tanks, with improved fracture toughness and safety at cryogenic temperatures. Generally, the fracture toughness decreases at lower temperatures; therefore, cryogenic steel requires a high fracture toughness to prevent unstable fractures. This study conducted unstable ductile fracture tests with 30-mm-thick high-manganese austenitic steel and evaluated its applicability to LNG storage and fuel tanks. The ductile fracture resistance in the weld joints was evaluated, including the weld metal and heat-affected zone. The unstable fracture resistance was evaluated for different LNG tank types. It was found that high-manganese austenitic steel has excellent unstable fracture characteristics and good material performance as a cryogenic steel; therefore, it can be applied in LNG storage and fuel tanks.

The evolution of infectious transmission promotes the persistence of mcr-1 plasmids.

Conjugative plasmids play a vital role in bacterial evolution and promote the spread of antibiotic resistance. They usually cause fitness costs that diminish the growth rates of the host bacteria. Compensatory mutations are known as an effective evolutionary solution to reduce the fitness cost and improve plasmid persistence. However, whether the plasmid transmission by conjugation is sufficient to improve plasmid persistence is debated since it is an inherently costly process. Here, we experimentally evolved an unstable and costly mcr-1 plasmid pHNSHP24 under laboratory conditions and assessed the effects of plasmid cost and transmission on the plasmid maintenance by the plasmid population dynamics model and a plasmid invasion experiment designed to measure the plasmid's ability to invade a plasmid-free bacterial population. The persistence of pHNSHP24 improved after 36 days evolution due to the plasmid-borne mutation A51G in the 5'UTR of gene traJ. This mutation largely increased the infectious transmission of the evolved plasmid, presumably by impairing the inhibitory effect of FinP on the expression of traJ. We showed that increased conjugation rate of the evolved plasmid could compensate for the plasmid loss. Furthermore, we determined that the evolved high transmissibility had little effect on the mcr-1-deficient ancestral plasmid, implying that high conjugation transfer is vital for maintaining the mcr-1-bearing plasmid. Altogether, our findings emphasized that, besides compensatory evolution that reduces fitness costs, the evolution of infectious transmission can improve the persistence of antibiotic-resistant plasmids, indicating that inhibition of the conjugation process could be useful to combat the spread of antibiotic-resistant plasmids. IMPORTANCE Conjugative plasmids play a key role in the spread of antibiotic resistance, and they are well-adapted to the host bacteria. However, the evolutionary adaptation of plasmid-bacteria associations is not well understood. In this study, we experimentally evolved an unstable colistin resistance (mcr-1) plasmid under laboratory conditions and found that increased conjugation rate was crucial for the persistence of this plasmid. Interestingly, the evolved conjugation was caused by a single-base mutation, which could rescue the unstable plasmid from extinction in bacterial populations. Our findings imply that inhibition of the conjugation process could be necessary for combating the persistence of antibiotic-resistance plasmids.

Immersion corrosion of material extrusion steel 316 L: Influence of immersion time and surface roughness

This work investigates the influence of surface roughness on the immersion corrosion of Steel 316 L fabricated via the material extrusion (ME) additive manufacturing (AM) method. For that purpose, a metal-polymer filament was used to produce ME specimens via fused filament fabrication. An experimental investigation was performed on both ME and wrought Steel 316 L specimens which were immersion-tested in a NaCl corrosive solution for three different exposure times. The specimens were also separated into to two groups according to their surface roughness. The corrosion-tested ME Steel 316 L presented an austenitic microstructure with twins and polygonal grains. Approximately ten percent of the phase volume was found to be in ferrite form, which is a known factor promoting corrosion in steel alloys. Moreover, substantial porosity was observed, manifested in the form of inclusions and irregular/spherical defects, which are typically caused by the ME fabrication process. The ME Steel 316 L has exhibited an unstable corrosion resistance, unlike the wrought material. The varying corrosion performance of the ME Steel 316 L amy be attributed to a weaker passivation ability, relative to its wrought counterpart, owe to the combined effect of δ–ferrite in the microstructure and macroscopic porosity. n statistical evaluation of the results, via ANOVA, suggested that the exposure time can be an influential factor for the ME Steel 316 L corrosion resistance. Surface roughness may also have an effect, however less significant. This study has identified, for the first time, the transitional character of the corrosion behaviour of ME Steel 316 L at lower exposure times. These new findings for the ME Steel 316 L and the results from the present analysis can inform the community seeking to use this AM alloy within corrosive environments.

Negative Impact of Unstable Spiromesifen Resistance on Fitness of Tetranychus urticae (Acari: Tetranychidae).

Two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is a phytophagous haplodiploid mite and its control is largely based on the use of pesticides. But, the short life cycle and high reproductive rate allow them to develop resistance to many pesticides. To design a strategy for resistance management, a fitness cost study was conducted on different populations of T. urticae, i.e., spiromesifen selected (SPIRO-SEL), unselected (Unsel), and reciprocal crosses. After twelve rounds of selections, T. urticae developed high spiromesifen resistance (71.7-fold) compared to the Unsel strain. Results showed a fitness cost for SPIRO-SEL, Cross1 (Unsel ♀ × SPIRO-SEL ♂), and Cross2 (SPIRO-SEL ♀ × Unsel ♂) with a relative fitness values of 0.63, 0.86, and 0.70, respectively. There was a significant increase in the incubation period, quiescent larvae, and egg to adult male and female developmental period of the SPIRO-SEL compared with Unsel strain. Moreover, resistance to spiromesifen was unstable with a decline in resistance value of - 0.05. The presence of unstable spiromesifen resistance associated with fitness costs suggests that intermittent withdrawal of its usage could potentially preserve its effectiveness for management of T. urticae.

Unstable fipronil resistance associated with fitness costs in fipronil-selected Aedes aegypti L.

Mosquitoes are very serious household and medically important pests transmitting many diseases of humans and animals. Among mosquitoes, Aedes aegypti L., is an active transmitter of dengue and lumpy skin disease virus, horrible and terrifying diseases, causing human and animal death throughout the world. Fipronil is a new chemistry insecticide used to control agriculture and medically important insect pests. It affects the GABA receptors in the nervous system and consequently causes the death of the pests. A laboratory experiment was conducted to investigate the onset of fipronil resistance and associated fitness costs in Ae. Aegypti. Moreover, the stability of fipronil resistance was evaluated after five generations of rearing without selection pressure. The population of Ae. Aegypti was exposed continuously for 12 generations to fipronil under controlled conditions. The fipronil selected population (Fipro-Sel Pop) had a 317 and 115.7-fold level of resistance compared to a susceptible and field population, respectively. Relative fitness for Fipro-Sel Pop was 0.57, with a significant disadvantage in larval duration, developmental time, percent hatchability, intrinsic rate of natural increase (rm), net reproductive rate (Ro), number of larvae in the next generation, and mean relative growth rate (MRGR) when compared to the Unselected population (Un-Sel Pop). However, the relative fitness value of Cross1 (Un-Sel Pop ♂ × Fipro-Sel Pop ♀) and Cross2 (Fipro-Sel Pop ♂ × Un-Sel Pop ♀) was 1.69 and 1.12, respectively. It is evident from the results that fipronil resistance comes with a fitness disadvantage, and it is unstable in the Fipro-Sel Pop of Ae. Aegypti. Therefore, the alternation of fipronil with other chemicals or suspension of fipronil usage for some time could improve its efficacy by delaying resistance development in Ae. Aegypti. Further research should be performed to investigate the field applicability of our findings.

One-Step Patterned Contact-Resistance-Free Stretchable Strain Sensors With High Linearity and Repeatability for Body-Motion Detection

AbstractMost of the resistive-type stretchable strain sensors exhibit large sensing ranges and high sensitivity but suboptimal repeatability and linearity because of the contact-resistance mechanism. To achieve high repeatability and linearity, several sensors with contact-resistance-free structures are proposed. However, due to the different geometric layouts of the conductive materials and the insulating substrates, the patterning of these sensors requires multiple processes including photolithography and etching, which may cause high costs and are not suitable for consumer wearable applications. Here, we report a design for stretchable strain sensors based on a one-step patterned contact-resistance-free structure, i.e., the independent-sensing-and-stretchable-function structure (ISSFS). The stretchability mainly comes from the overall large deformation of the wide curved segments (the stretchable parts), while the resistance variation is mainly attributed to the tensile strain of the narrow straight segments (the sensing parts). High linearity (R2 = 0.999) and repeatability (repeatability error = 1.44%) are achieved because neither unstable contact resistance nor nonlinear constitutive and geometric behaviors occur during the sensing process. The conductive materials and the insulating substrates do not need to have different geometric layouts; thus, they can be patterned by only one-step laser cutting. The proposed sensors show great potential in body-motion detection for wearable devices.

Effect of autosomally inherited, incompletely dominant, and unstable spinosad resistance on physiology of Tribolium castaneum (Coleoptera: Tenebrionidae): Realized heritability and cross-resistance

The red flour beetle, Tribolium castaneum (Herbst) is one of the most destructive pests of stored commodities like cereals and grains in different tropical and sub tropic areas of the world. It causes qualitative and quantitative losses of stored products. Spinosad is recommended internationally to reduce pest infestations in storage structures. In this study, a population of T. castaneum collected from flour mills was selected with spinosad (Spin-Sel) and developed a resistant ratio of 122-fold after 12 generations. Spinosad resistance in Spin-Sel was unstable and decreased from 122 to 92-fold in the absence of selection pressure. Very low cross resistance to chlorpyrifos (8-fold), profenofos (3-fold), and cypermethrin (5-fold) in the Spin-Sel population as compared to the Unselected was observed. The toxicity data of heterozygotes revealed that spinosad resistance was autosomal and incompletely dominant. The realized heritability (h2) value was 0.07 for the first half selected generations and 0.17 for the latter half generations. The overall h2 value was 0.17. This study provides useful information that might clarify the nature of spinosad resistance in T. castaneum and help to formulate management strategies to delay the onset of resistance.

The Effect of Unstable Resistance Training with Blood Flow Restriction on Short-Term Memory, Strength and Dynamic Balance in Older Adults

Abstract Introduction. The aim of the present study was to investigate the effect of unstable resistance training with blood flow restriction (URT with BFR) on short-term memory, strength and dynamic balance in older adults. Material and Methods. A total of 27 male older adults (age= 62 ± 1.5 years) were randomly divided into two experimental groups: URT with BFR, URT without BFR, and a control group. The training program for the experimental groups consisted of bodyweight Scott exercise (three sessions a week for four weeks). The first two weeks included three sets, each set consisted of 15 repetitions at 60-second intervals. The second two weeks included four sets, with each set consisting of 15 repetitions and the use of weight constituting 5% of each person’s body weight (mean = 3.5 ± 1.5kg). To restrict blood flow, an 8-cm wide elastic band was used at 72 ± 9 mm Hg arterial pressure. All subjects performed Wechsler memory, 30-sec chair stand test, and timed up and go test (TUG) before and after the intervention. Data analysis was carried out using analysis of covariance (ANCOVA) and Bonferroni post hoc test. Results. The results showed that URT with BFR was significantly superior to other groups in the variables of strength (p = 0.001), dynamic balance (p = 0.0001) and short-term memory (p = 0.04). Conclusions. These findings suggest that URT with BFR can be a useful training method for older adults.

Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae) Fitness and Resistance Stability to Diamide and Pyrethroid Insecticides in the United States.

Simple SummarySpodoptera exigua is a polyphagous pest, commonly known as beet armyworm. This pest is distributed worldwide and causes yield reduction in a variety of crops. Chemical control using synthetic insecticides is the primary strategy to manage beet armyworm. In the United States, beet armyworm resistance to both chlorantraniliprole and bifenthrin insecticides was first reported in 2020. Here we examined beet armyworm fitness and stability of resistance to chlorantraniliprole and pyrethroid insecticides, since knowledge of the stability of resistance is a crucial aspect when recommending rotation of insecticides with different mode of action. Our results have indicated no decrease in bifenthrin resistance for at least a three-year period (i.e., 27 generations) when insecticide exposure was suspended. However, susceptibility to chlorantraniliprole dropped approximately 160-fold through this three-year period. Our results indicate that beet armyworm resistance to bifenthrin is stable, but unstable to chlorantraniliprole. Unstable resistance can be successfully managed at field level by switching off the selection pressure with replacement of the insecticide other than a pyrethroid.In the United States, beet armyworm resistance to both chlorantraniliprole and bifenthrin insecticides was first reported in 2020. Here we examined beet armyworm fitness and stability of resistance to chlorantraniliprole and pyrethroid insecticides since knowledge of the stability of resistance is a crucial aspect when recommending rotation of insecticides with different mode of action. Concentration-mortality bioassays were performed with field and laboratory susceptible populations. The F2, F13, and F27 generations of the field-derived population, maintained in the laboratory without insecticide, were exposed to commercial formulations of bifenthrin and chlorantraniliprole using the leaf-dip bioassay method (IRAC n. 007). Insects from F27 had the fitness components (survival, body weight, development time) documented and compared by LSM in each insecticide concentration tested. The resistance ratio to chlorantraniliprole reached 629, 80, 15-fold at F2, F13, and F27, respectively. These results contrast with an over 1000-fold resistance ratio to bifenthrin in all generations. The field-derived population had fitness reduced by chlorantraniliprole, but not by bifenthrin. In summary, the resistance of beet armyworm to bifenthrin was stable with no shift in fitness. In contrast, resistance to chlorantraniliprole was not stable through the generations kept in the laboratory without selection pressure, likely due to fitness cost.

Molecular Identification and Caspofungin Susceptibility Profile in Comparison to Oregano Antifungal Effects on Oral Candida Isolates

Background: Candida species have an unstable resistance to common antifungal drugs. The treatment of oral candidiasis requires the identification of new anti-Candida agents with no side effects like medicinal plants. Objectives: The present study aims to investigate the antifungal effects of caspofungin and oregano essential oil on oral Candida species isolated from cancer patients. Methods: Seventy-three Candida species were identified and isolated by conventional and microbiological tests from cancer patients (n = 100) suspected of oral candidiasis. The minimum inhibitory concentrations (MICs) of the oregano essential oil and caspofungin were determined by microdilution assay and evaluated according to the Clinical and Laboratory Standards Institute (CLSI-2017). The gene regions of samples were studied using the polymerase chain reaction (PCR) method. Results: Candida glabrata (35, 47.9%) was the predominant species. Most of the Candida strains were isolated from patients with stomach cancer (35, 47.9%). The highest resistance to caspofungin was reported for C. albicans (5.5%). Also, FKS mutant isolates were associated with resistance to caspofungin. MIC90 value for oregano essential oil against C. albicans was 4096 µL/mL, which was equal to MIC90 value against C. glabrata. There was a significant difference between the MICs of caspofungin and oregano essential oil, that inhibits the growth of Candida isolates. Conclusions: The results of this study showed that the caspofungin has high antifungal effect on Candida species, specially non-albicans Candida. As the findings indicated, the oregano had good anti-Candida potent. Therefore, we could hope to treat fungal diseases by producing an appropriate herbal medicine.

Vulnerability studies of okra genotypes to bhendi yellow vein mosaic virus (BYVMV)

India is the leading okra producer globally, but its production suffers due to losses caused by Bhendi yellow vein mosaic virus (BYVMV) disease which is transmitted by whitefly. Due to its unstable resistance nature and limited availability of sources for resistance in cultivated types, the crop improvement programme of okra has not taken a fast pace. In this study, sixty-four distinct genotypes of okra were screened for their resistance to BYVMV under natural epiphytotic conditions of Delhi. It was found that the disease incidence (DI), coefficient of infection (CI), vulnerability index (VI), and adult whitefly count (AWC) varied significantly amongst the different okra genotypes. The highest mean DI was recorded in Pusa Sawani (86.5%) and DI was 0% in the genotypes Pusa Bhindi-5 (DOV-66), DOV-89 and DOV-92. The coefficient of infection (CI) was highest in Pusa Sawani (70.39%). Maximum VI was recorded in Pusa Sawani (83%) and 0% VI in the wild genotypes IC-141040, IC-90560 and cultivated Pusa Bhindi-5, DOV-81 and DOV-92. Similarly, AWC was maximum in Pusa Sawani (30.4) and the lowest number in DOV-26 (1.2). The number of whiteflies peaked at 80 days after sowing and subsequently decreased. Pusa Sawani was the most susceptible genotype and Pusa Bhindi-5 and DOV-92 were the most resistant genotypes based on this study. The resistant genotypes Pusa Bhindi-5 and DOV-92 can be used for the transfer of BYVMV resistance in other susceptible lines or varieties and also for hybrid development in future okra improvement programmes.

Contact-Resistance-Free Stretchable Strain Sensors with High Repeatability and Linearity.

Most of the existing stretchable strain sensors are based on the contact-resistance mechanism, where the stretchability and resistance variation depend on the change of the contact relationship of the conductive microstructures. These sensors usually exhibit large sensing ranges and gauge factors but unsatisfactory repeatability and linearity of the electrical responses because the contact is unstable. Here, we report a completely different design for stretchable strain sensors based on a contact-resistance-free structure, i.e., the off-axis serpentine sandwich structure (OASSS), with the mechanism of the stretch-bending-stretch transformation (SBST). Neither unstable contact resistance nor nonlinear constitutive and geometric behaviors occur for the OASSS while the sensor undergoes a large applied strain (50%), which guarantees high repeatability (repeatability error = 1.58%) and linearity (goodness-of-fit >0.999). Owing to such performances, the present sensors are not only applied to monitoring human activities and medical surgery but also to the ground tests of Tianwen-1, China's first Mars exploration mission.

A rapidly reversible mutation generates subclonal genetic diversity and unstable drug resistance

Most genetic changes have negligible reversion rates. As most mutations that confer resistance to an adverse condition (e.g., drug treatment) also confer a growth defect in its absence, it is challenging for cells to genetically adapt to transient environmental changes. Here, we identify a set of rapidly reversible drug-resistance mutations in Schizosaccharomyces pombe that are caused by microhomology-mediated tandem duplication (MTD) and reversion back to the wild-type sequence. Using 10,000× coverage whole-genome sequencing, we identify nearly 6,000 subclonal MTDs in a single clonal population and determine, using machine learning, how MTD frequency is encoded in the genome. We find that sequences with the highest-predicted MTD rates tend to generate insertions that maintain the correct reading frame, suggesting that MTD formation has shaped the evolution of coding sequences. Our study reveals a common mechanism of reversible genetic variation that is beneficial for adaptation to environmental fluctuations and facilitates evolutionary divergence.

Stability and fitness cost associated with spirotetramat resistance in Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae)

Dusky cotton bug, Oxycarenus hyalinipennis Costa (Hemiptera: Lygaeidae) is an important pest of cotton and causing economic losses to this crop. It also remains active round the year, infesting a number of host plants. Spirotetramat is a systemic insecticide and is effective against many sucking insect pests. A field collected population of O. hyalinipennis was reared in the laboratory under continuous spirotetramat selection pressure for 21 generations for the development of resistance to spirotetramat. The Spiro-Sel population was further reared for seven generations without insecticide exposure to assess the stability of spirotetramat resistance. Leaf dip method was used for the bioassays and selection. In this study, the impact of spirotetramat resistance on its stability and life history traits of Spiro-Sel, C1 (15 Spiro-Sel♀ × 15 UNSEL ♂) and C2 (15 Spiro-Sel♂ × 15 UNSEL ♀) O. hyalinipennis was assessed. Spiro-Sel (G21 ) population developed 2333-fold and 20.83-fold resistance compared with the susceptible and unselected (UNSEL) populations, respectively. Resistance to spirotetramat was unstable after seven generations (G28 ) when reared without exposure to any insecticide. A significant reduction in overall nymphal survival, fecundity, egg hatching and net reproductive rate of Spiro-Sel population was observed when compared with UNSEL population. Intrinsic rate of natural increase, biotic potential and mean relative growth rate were also lower in Spiro-Sel population compared to UNSEL population. The Spiro-Sel, C1 and C2 population had a relative fitness of 0.44, 0.51 and 0.44, respectively. Results of our study suggested that fitness cost is involved in the development of spirotetramat resistance. Unstable resistance and high fitness cost may provide great benefits to limit the evolution of resistance to spirotetramat in O. hyalinipennis. © 2021 Society of Chemical Industry.

Discovery of the REN11 Locus From Vitis aestivalis for Stable Resistance to Grapevine Powdery Mildew in a Family Segregating for Several Unstable and Tissue-Specific Quantitative Resistance Loci.

Race-specific resistance loci, whether having qualitative or quantitative effects, present plant-breeding challenges for phenotypic selection and deciding which loci to select or stack with other resistance loci for improved durability. Previously, resistance to grapevine powdery mildew (GPM, caused by Erysiphe necator) was predicted to be conferred by at least three race-specific loci in the mapping family B37-28 × C56-11 segregating for GPM resistance from Vitis aestivalis. In this study, 9 years of vineyard GPM disease severity ratings plus a greenhouse and laboratory assays were genetically mapped, using a rhAmpSeq core genome marker platform with 2,000 local haplotype markers. A new qualitative resistance locus, named REN11, on the chromosome (Chr) 15 was found to be effective in nearly all (11 of 12) vineyard environments on leaves, rachis, berries, and most of the time (7 of 12) stems. REN11 was independently validated in a pseudo-testcross with the grandparent source of resistance, “Tamiami.” Five other loci significantly predicted GPM severity on leaves in only one or two environments, which could indicate race-specific resistance or their roles in different timepoints in epidemic progress. Loci on Chr 8 and 9 reproducibly predicted disease severity on stems but not on other tissues and had additive effects with REN11 on the stems. The rhAmpSeq local haplotype sequences published in this study for REN11 and Chr 8 and 9 stem quantitative trait locus (QTL) can be used directly for marker-assisted selection or converted to SNP assays. In screening for REN11 in a diversity panel of 20,651 vines representing the diversity of Vitis, this rhAmpSeq haplotype had a false positive rate of 0.034% or less. The effects of the other foliar resistance loci detected in this study seem too unstable for genetic improvement regardless of quantitative effect size, whether due to race specificity or other environmental variables.