Resistant Accessions Research Articles

Response of F1 arabica coffee genotypes descending from disease resistant Ethiopian accessions to coffee berry disease

Coffee is one of Tanzania’s primary agricultural export commodities but is seriously constrained by Colletotrichum kahawae which causes significant yield losses in Arabica coffee during high infection seasons. Using resistant varieties rather than chemical fungicides, which are costly and cause environmental pollution, is a more sustainable approach to controlling the disease. Several F1 hybrid genotypes developed from Ethiopian accessions of Arabica coffee of known Coffee berry disease (CBD) resistance were evaluated under CBD pressure to observe acquired resistance. Eight Arabica coffee genotypes were inoculated with three types of CBD pathogen isolates. Results revealed high resistance on two F1 genotypes (F90/64/4660 x KP423 and F89/64/4660 x KP423) with no infection to all C. kahawae isolates. Two Genotypes (F45/64/2049 x KP423 and F24/64/902 x KP423) revealed resistance moderately by scoring less than 50% infected berries, while F45/64/2061 x KP423 and F24/64/886 x KP423 demonstrated moderate susceptibility. The F1 genotypes with less infection are to be included in the breeding program to develop resistant varieties. Pathogenicity of three C. kahawae isolates obtained from different coffee growing areas in Tanzania was also observed for their effects on the tested genotypes. Isolate 2006/14 from Kibosho – Kombo was more aggressive in terms of infected berries, followed by isolate 2019/16 from Ugano-Mbinga. Isolates found to be more aggressive are potential for screening resistance to develop coffee berry disease varieties in Tanzania.

Evaluation of Septoria leaf spot (Septoria helianthi) alone and in combination with other foliar fungal spots on sunflower

Abstract In recent years, Septoria leaf spot has taken a strong place in the list of economically important diseases of sunflower. It may be a favorable factor for the development of other diseases on sunflower plants too. The aim of the research was to evaluate the frequency and degree of infection of sunflower plants with Septoria helianthi as well as possibility of simultaneous infection with this pathogen and other fungi which cause foliar spots, such as downy mildew, Alternaria leaf spot and Phoma black stem under conditions of stationary infectious nursery. The year 2021 turned out to be extremely favorable for the development of fungal leaf spots on sunflower. Assessment of fungal diseases of sunflower plants was performed in F2 families obtained after crossing ZL22A, ZL58A, ZL70A, ZL78A, and ZL169A lines of Zaporozhye breeding (Ukraine) with HAR7 line (originating from the USA). Each F2 family (sample) was obtained from self-pollination of one F1 plant with varying severity of Septoria disease. It was found that in the conditions of 2021, sunflower was quite affected by Septoria disease. The percentage of injured plants in F2 samples ranged from 41.0 to 100.0%. The severity of disease was different. Less resistant genotypes included plants with lesions on sunflower leaves of lower, middle, and upper tiers in approximately equal numbers, while more resistant genotypes had almost no plants with injured leaves of upper tiers. It was established that the development of Phoma disease occurred both on plants with Septoria leaf spot and on healthy plants. On average, among the plants infected with Phoma macdonaldii, the proportion of plants jointly affected by Phoma and Septoria diseases was 2/3. However, the frequency of simultaneous infection of plants with S. helianthi and P. macdonaldii in genotypes with different resistance to Septoria leaf spot differed significantly and ranged from 80% in less resistant to 40% in more resistant accessions. Most plants (about 90%) infected with Plasmopara halstedii were simultaneously infected with S. helianthi. That is, both of these pathogens can simultaneously develop on the same plant and lead to a decline in its basic physiological functions. The rate of simultaneous damage of sunflower by Alternaria and Septoria was quite low compared to plant damage by Alternaria alone and was less than 30%. This may mean that the pathogen of Alternaria leaf spot avoids plants with existing S. helianthi fungus.

Identification and characterization of resistance to soybean aphid in 22 highly resistant soybean accessions

Identification and characterization of resistance to soybean aphid in 22 highly resistant soybean accessions

Abstract 043: Prorenin Reduces Spontaneous Firing Rate In Cells Expressing Tyrosine Hydroxylase In The Hypothalamic Paraventricular Nucleus

The (pro)renin receptor (PRR) plays essential roles in cardiovascular and metabolic physiology. The tyrosine hydroxylase (TH) neurons in the paraventricular nucleus of the hypothalamus (PVN) have recently emerged as a key metabolic regulator that play functional roles in the regulation of the energy expenditure and metabolism. Using RNAScope in situ hybridization, we found that 95% of TH-containing neurons in the PVN (n=872 cells/3 mice) express the PRR. In this study, we aimed to examine the effects of PRR activation on the firing activity of the TH-containing neurons in the PVN (TH PVN ). We hypothesized that prorenin activation of the PRR increases firing activity of the TH PVN neuron. To test this hypothesis, we performed electrophysiological recordings in loose cell-attached voltage-clamp configuration in PVN slices from mice expressing TdTomato reporter for TH neurons (TH-cre-TdTomato mice). These experiments were carried out to isolate and record spontaneous firing rate (SFR). We abolished all the synaptic transmission by adding a GABA A receptor antagonist (picrotoxin, 50 μM), an antagonist of AMPA/kainate receptors (CNQX, 5 μM), and an NMDA receptor antagonist (D-APV, 50 μM) throughout the recording. The cells were discarded if the access resistance was >15 MΩ or fluctuated more than 15%. At the end of the experiments, tetrodotoxin (1 μM) was added to abolish and confirm neuronal activity. The SFR in TH PVN neurons was significantly decreased after application of prorenin (PR) (4.9 ± 0.87 and 3.2 ± 1.07 Hz, before and after PR, respectively; n = 10, p = 0.006, paired t -test) indicating that PR reduces spontaneous firing activity of the TH PVN neurons. To determine if this effect was due to the prorenin activation of the PRR, we recorded SFR in the presence of PRR antagonist (PRO20). There was no difference in the SFR (5.8 ± 1.58 Hz and 5.9 ± 1.7 Hz, n = 5, p = 0.903, paired t -test) in the TH PVN neurons between PRO20 and PRO20+PR group respectively suggesting that PRO20 blocks the effect of PR in reducing SFR in TH PVN neurons. Our results showed that the prorenin acts on the PRR to reduce the SFR of the TH PVN neurons. We conclude that PRR signaling in the TH PVN neurons might play a role in cardiovascular and metabolic regulation by the modulating the TH PVN neuronal plasticity.

Adult Genes Evaluation of Ethiopian Durum Accessions for Resistance to Stem Rust (Puccinia graminis f.sp. tritici)

The horizontal resistance is effective against broad range of pathogen races and even reduces the costs of fungicides for controlling.The objective of present study is based on the field assesment of adult resistance genes in Ethiopia durum wheat accessions for resistance to stem rust (Puccinia graminis f.sp. tritici). The 142 durum wheat accessions were obtained from the Ethiopian Biodiversity Institute and screening for stem rust in Debrezeit agricultural research experimental fields using alpha lattice design. The bulk of races (TTKSK (Ug99), TTTTF, TTRTF, JRCQC, TKTTF) inoculated during stem elongation stage. The disease assessment started the first symptom of seen in infector rows. In the field, durum accessions were examined utilizing for slow rust parameters. Accordingly, to that the 23 accessions were identified having low value of terminal rust resistance, low average coefficient of infection and low area under disease progress curve. The grain yield is negative and highly siginificant associated with slow rusting parameters. These accessions considered as having adult resistance genes with high partial resistance genes and important for further resistance breeding. Keywords: Accessions, Area under disease progress curve, Average cofficient of infection, Puccinia graminis f.sp. tritici, Terminal rust resistance DOI: 10.7176/JBAH/12-17-02 Publication date: September 30 th 2022

Identification and Characterization of Novel Sources of Resistance to Rust Caused by Uromyces pisi in Pisum spp.

Pea rust is a major disease worldwide caused by Uromyces pisi in temperate climates. Only moderate levels of partial resistance against U. pisi have been identified so far in pea, urging for enlarging the levels of resistance available for breeding. Herein, we describe the responses to U. pisi of 320 Pisum spp. accessions, including cultivated pea and wild relatives, both under field and controlled conditions. Large variations for U. pisi infection response for most traits were observed between pea accessions under both field and controlled conditions, allowing the detection of genotypes with partial resistance. Simultaneous multi-trait indexes were applied to the datasets allowing the identification of partial resistance, particularly in accessions JI224, BGE004710, JI198, JI199, CGN10205, and CGN10206. Macroscopic observations were complemented with histological observations on the nine most resistant accessions and compared with three intermediates and three susceptible ones. This study confirmed that the reduced infection of resistant accessions was associated with smaller rust colonies due to a reduction in the number of haustoria and hyphal tips per colony. Additionally, a late acting hypersensitive response was identified for the first time in a pea accession (PI273209). These findings demonstrate that screening pea collections continues to be a necessary method in the search for complete resistance against U. pisi. In addition, the large phenotypic diversity contained in the studied collection will be useful for further association analysis and breeding perspectives.

Fine mapping of a recessive leaf rust resistance locus on chromosome 2BS in wheat accession CH1539.

The online version contains supplementary material available at 10.1007/s11032-022-01318-4.

Schottky-to-Ohmic switching in ferroelectric memristors based on semiconducting Hf0.93Y0.07O2 thin films

We demonstrate resistive switching and memristive behavior in devices consisting of ultrathin (4.5 nm) semiconducting, epitaxial ferroelectric Hf0.93Y0.07O2 (YHO) films on La0.7Sr0.3MnO3-buffered, Nb-doped SrTiO3 single crystal substrates with Au top electrodes. Unlike the tunneling-driven current–voltage characteristics of ferroelectric tunnel junctions which utilize ultrathin insulating (fully depleted) ferroelectric films, the semiconducting nature of our YHO films, i.e., the presence of free charge carriers introduced by Y doping, results in radically different current–voltage characteristics. Current–voltage measurements indicate a polarization-modulated transition from Schottky-barrier-controlled charge transport to Ohmic conduction in the YHO devices, which results in a large on/off ratio of up to 540. Moreover, voltage pulse train measurements reveal a broad range of accessible resistance states, which indicates the memristive behavior of the devices. Our results represent an important step toward the development of future nonvolatile memory and brain-inspired neuromorphic computing applications based on ultrathin semiconducting ferroelectric films.

There is no F in APC: Using physiological fluoride-free solutions for high throughput automated patch clamp experiments.

Fluoride has been used in the internal recording solution for manual and automated patch clamp experiments for decades because it helps to improve the seal resistance and promotes longer lasting recordings. In manual patch clamp, fluoride has been used to record voltage-gated Na (NaV) channels where seal resistance and access resistance are critical for good voltage control. In automated patch clamp, suction is applied from underneath the patch clamp chip to attract a cell to the hole and obtain a good seal. Since the patch clamp aperture cannot be moved to improve the seal like the patch clamp pipette in manual patch clamp, automated patch clamp manufacturers use internal fluoride to improve the success rate for obtaining GΩ seals. However, internal fluoride can affect voltage-dependence of activation and inactivation, as well as affecting internal second messenger systems and therefore, it is desirable to have the option to perform experiments using physiological, fluoride-free internal solution. We have developed an approach for high throughput fluoride-free recordings on a 384-well based automated patch clamp system with success rates >40% for GΩ seals. We demonstrate this method using hERG expressed in HEK cells, as well as NaV1.5, NaV1.7, and KCa3.1 expressed in CHO cells. We describe the advantages and disadvantages of using fluoride and provide examples of where fluoride can be used, where caution should be exerted and where fluoride-free solutions provide an advantage over fluoride-containing solutions.

Transcriptome-wide identification and transcriptional profiling reveal remarkable expression modulation of redox genes in Zingiber zerumbet against Pythium myriotylum

Using a transcriptome-based bioinformatics approach coupled with custom gene expression microarray we studied the expression of redox genes in a resistant accession of Zingiber zerumbet (L.) in response to the oomycete pathogen Pythium myriotylum Drechsler. Expression of 97 genes comprising of 11 RBOHs, two CATs, three AOXs, four SODs, five APXs, two FERs, three PrxRs, five GPXs, eight GSTs, 15 GRXs, 16 POXs, and 23 TRXs was examined at 18 h, 36 h and 48 h post-inoculation with P. myriotylum. Microarray data revealed significant (p ≤ 0.05) modulation of 41 genes belonging to 10 gene families. The RT-qPCR analysis and enzyme activity assays of selected redox candidates corroborated the microarray data. The genes encoding extracellular ROS generators RBOHD, RBOHB and POX57 were significantly induced. Among the ROS scavengers, while the gene encoding chloroplast localized Cu–Zn SOD and peroxisomal CAT2 were significantly upregulated, the gene producing chloroplast localized APX6 and APXT and mitochondrial AOX1a and AOX1b were significantly declined. Similarly, the expression of certain members belonging to the cellular redox regulators GST, GRX, and TRX were also modulated. The results highlight the involvement of a large-scale transcriptional reprogramming of redox machinery in Z. zerumbet in mounting host defence against P. myriotylum.

Antioxidant enzymes associated with resistance to Fusarium oxysporum f. sp. melonis race 1.2 in melon

Fusarium wilt of melon, Cucumis melo L. (Cucurbitaceae) caused by Fusarium oxysporum f. sp. melonis (FOM), induces severe symptoms, thus dramatically limiting the yield in melons globally. Incorporating genetic resistance in cultivated crops is considered the most efficient and sustainable solution to control root rot diseases. However, resistance to FOM in melon is quantitative in nature, and the mechanism is poorly understood, and the information about melon-FOM race interactions is still limited. This study explored the changes in the eight antioxidant enzyme activities; catalase (CAT), chitinase (CHI), β-1,3-glucanase (GLU), peroxidase (POX), phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), superoxide dismutase (SOD), and as well as total phenol contents (TPCs) in roots of two resistant ‘Shante-F1’ and ‘Khatooni’ and two susceptible ‘Shante-T’ and ‘Shahabadi’ melon accessions, over the time courses of 7, 14 and 21 days (dpi) following inoculation with an isolate of FOM race-1.2.The results revealed that the up-regulated of this set of defense-related enzymes was a key factor against FOM race-1.2 infection, with levels being elevated up to 3-fold in the resistant accessions. In addition, biomass growth parameters (BMPs), roots and shoots (fresh and dry weights, heights, diameters and roots volume) following inoculation displayed almost similar trends observed for the enzyme activity in resistant melon accessions in comparison to susceptible ones. Thus, studying the physiological metabolic pathways of the related enzymes appears to be an important biochemical marker for breeding programs aiming to elucidate the FOM race 1.2 resistance mechanisms in melon. A better insight in melon defense responses can help to establish biochemical characteristics for the selection of resistant melon sources and provide a theoretical basis for disease control and breeding of melon plants with higher levels of resistance to FOM race 1.2 isolates.

Evaluation of the early defoliation trait and identification of resistance genes through a comprehensive transcriptome analysis in pears

Early defoliation, which usually occurs during summer in pear trees, is gradually becoming a major problem that poses a serious threat to the pear industry in southern China. However, there is no system for evaluating the responses of different cultivars to early defoliation, and our knowledge of the potential molecular regulation of the genes underlying this phenomenon is still limited. In this study, we conducted field investigations of 155 pear accessions to assess their resistance or susceptibility to early defoliation. A total of 126 accessions were found to be susceptible to early defoliation, and only 29 accessions were resistant. Among them, 19 resistant accessions belong to the sand pear species (Pyrus pyrifolia). To identify the resistance genes related to early defoliation, the healthy and diseased samples of two sand pear accessions, namely, the resistant early defoliation accession ‘Whasan’ and the susceptible early defoliation accession ‘Cuiguan’, were used to perform RNA sequencing. Compared with ‘Cuiguan’, a total of 444 genes were uniquely differentially expressed in ‘Whasan’. Combined with GO and KEGG enrichment analyses, we found that early defoliation was closely related to the stress response. Furthermore, a weighted gene co-expression network analysis revealed a high correlation of WRKY and ethylene responsive factor (ERF) transcription factors with early defoliation resistance. This study provides useful resistant germplasm resources and new insights into potentially essential genes that respond to early defoliation in pears, which may facilitate a better understanding of the resistance mechanism and molecular breeding of resistant pear cultivars.

Identification and Characterization of Potato Zebra Chip Resistance Among Wild Solanum Species

Potato zebra chip (ZC) disease, associated with the uncultured phloem-limited bacterium, Candidatus Liberibacter solanacearum (CLso), is transmitted by the potato psyllid Bactericera cockerelli. Potato ZC disease poses a significant threat to potato production worldwide. Current management practices mainly rely on the control of the psyllid to limit the spread of CLso. The present study investigated new sources of ZC resistance among wild Solanum species. A taxonomically diverse collection of tuber-bearing Solanum species was screened; one ZC-resistant accession and three ZC-tolerant accessions were identified among the 52 screened accessions. Further characterization of the resistant accession showed that the resistance was primarily associated with antibiosis effects due to differences in leaf trichome density and morphology of the wild accession, which could limit the psyllid feeding and oviposition. This germplasm offers a good resource for further understanding ZC and psyllid resistance mechanisms, contributing to potato breeding efforts to develop ZC resistance cultivars. Alternatively, it could be used as a potential trap crop to manage psyllid and control ZC disease.

Screening and evaluation for antibiosis resistance of the spring wheat accessions to the grain aphid, Sitobion miscanthi (Takahashi) (Hemiptera: Aphididae)

Resistant cultivar deployment is an effective method for cereal aphid management. Under greenhouse conditions, preliminary antibiosis resistance screening was conducted on 114 Ethiopian and 22 Chinese spring wheat accessions. After performing a bioassay to determine antibiosis resistance, aphid feeding behaviour and phenolic acid content analyses were performed on the aphid resistant wheat accessions by electrical penetration graph (EPG) and high performance liquid chromatography (HPLC), respectively. Among the wheat accessions, two high resistances, 27 moderate-resistances, and 35 low-resistances to Sitobion miscanthi were identified. The antibiosis resistance test showed prolonged pre-adult and pre-reproductive periods, shorter reproductive periods, lower fecundity, an intrinsic rate (rm) of increase, and a finite rate (λ) of increase of S. miscanthi on Lunxuan 145, Wane, Lunxuan 6, 204511, Lunxuan 103 and 5215 than those on the aphid-susceptible accession Beijing 837. The changes for the parameters of aphid feeding behaviour, including spending a longer time in the penetration and phloem salivation phases and less time in the phloem sap-feeding phase on the resistant wheat accessions, indicated that the aphid resistance may occur during the phloem phase and may be due to difficulties in the mechanical probing of the mesophyll cells. Additionally, the HPLC analysis showed higher contents of: 1) ferulic acid in Lunxuan 145, Lunxuan 103 and Lunxuan 6; 2) p-coumaric acid in Lunxuan145; 3) vanillic acid in Lunxuan 145, Wane and Lunxuan 6; 4) syringic acid in Lunxuan 103; and 5) caffeic acid in 5215. The contents of some phenolic acids within wheat leaves, such as p-courmaric acid and vanillic acid showed significant positive correlation with the duration of aphid development, but negative correlation with the aphid fecundity. The concentrations of these acids may be the causes of antibiosis resistance to S. miscanthi. The identification of grain aphid-resistant wheat accessions in our study will be helpful in future breeding program for pest control.

Whole-Genome Resequencing Deciphers New Insight Into Genetic Diversity and Signatures of Resistance in Cultivated Cotton Gossypium hirsutum.

Cotton is an important crop that produces fiber and cottonseed oil for the textile and oil industry. However, cotton leaf curl virus disease (CLCuD) stress is limiting its yield in several Asian countries. In this study, we have sequenced Mac7 accession, a Gossypium hirsutum resistance source against several biotic stresses. By aligning with the Gossypium hirsutum (AD1) 'TM-1' genome, a total of 4.7 and 1.2 million SNPs and InDels were identified in the Mac7 genome. The gene ontology and metabolic pathway enrichment indicated SNPs and InDels role in nucleotide bindings, secondary metabolite synthesis, and plant-pathogen interaction pathways. Furthermore, the RNA-seq data in different tissues and qPCR expression profiling under CLCuD provided individual gene roles in resistant and susceptible accessions. Interestingly, the differential NLR genes demonstrated higher expression in resistant plants rather than in susceptible plants expression. The current resequencing results may provide primary data to identify DNA resistance markers which will be helpful in marker-assisted breeding for development of Mac7-derived resistance lines.

Resistance of Palmer amaranth (Amaranthus palmeri) to S-metolachlor in the midsouthern United States

AbstractPalmer amaranth (Amaranthus palmeri S. Watson) is one of the most problematic weeds in many cropping systems in the midsouthern United States because of its multiple weedy traits and its propensity to evolve resistance to many herbicides with different mechanisms of action. In Arkansas, A. palmeri has evolved metabolic resistance to S-metolachlor, compromising the effectiveness of an important weed management tool. Greenhouse studies were conducted to evaluate the differential response of A. palmeri accessions from three states (Arkansas, Mississippi, and Tennessee) to (1) assess the occurrence of resistance to S-metolachlor among A. palmeri populations, (2) evaluate the resistance level in selected accessions and their resistant progeny, (3) and determine the susceptibility of most resistant accessions to other soil-applied herbicides. Seeds were collected from 168 crop fields between 2017 and 2019. One hundred seeds per accession were planted in silt loam soil without herbicide for >20 yr and sprayed with the labeled rate of S-metolachlor (1,120 g ai ha−1). Six accessions (four from Arkansas and two from Mississippi) were classified resistant to S-metolachlor. The effective doses (LD50) to control the parent accessions ranged between 73 and 443 g ha−1, and those of F1 progeny of survivors were 73 to 577 g ha−1. The resistance level was generally greater among progeny of surviving plants than among resistant field populations. The resistant field populations required 2.2 to 7.0 times more S-metolachlor to reduce seedling emergence 50%, while the F1 of survivors needed up to 9.2 times more herbicide to reduce emergence 50% compared with the susceptible standard.

Pathogenicity of Colletotrichum coccodes causing anthracnose disease and its effect on growth and yield of sweet potato [Ipomoea batatas (L.) Lam

The disease causing ability of Colletotrichum coccodes and the effect of anthracnose on growth and yield of sweet potato accessions were evaluated in a two-year field trial. Field layout was a randomized complete block design with 16 sweet potato accessions replicated thrice. Young leaves of sweet potato accessions were sprayed with an inoculum concentration of 2.1 × 107 in a two-split application in the field with growth, yield, and disease indices recorded. Pathogenicity of C. coccodes was significantly highest among four accessions; OW4, SE10, SE12 and SPK-004 with abundant necrosis on leaves and stems of inoculated plants. Disease incidence varied between 2.48% - 52.83%, and 2.77% - 50.73%, during the 2018 and 2019 planting seasons respectively, with host response ranging from being susceptible to resistant. Accessions OW5 and OS15 had significantly lower disease incidence and severity than other treatments (p = 0.031 and 0.28 respectively) and also produced the highest yield ranging between 15.84 - 17.29, and 14.88 - 15.72 t/ha-1, in 2018 and 2019, respectively. This study has shown that anthracnose causes significant reduction in expected yield in sweet potato cultivation and also identified two resistant sweet potato accessions that can be useful sources in breeding for resistance to the disease.

Genome-wide association study reveals candidate genes for gummy stem blight resistance in cucumber

Gummy stem blight (GSB), caused by Didymella bryoniae, is a serious fungal disease that leads to decline in cucumber yield and quality. The molecular mechanism of GSB resistance in cucumber remains unclear. Here, we investigated the GSB resistance of cucumber core germplasms from four geographic groups at the seedling and adult stages. A total of 9 SNPs related to GSB resistance at the seedling stage and 26 SNPs at the adult stage were identified, of which some are co-localized to previously mapped Quantitative trait loci (QTLs) for GSB resistance (gsb3.2/gsb3.3, gsb5.1, and gsb-s6.2). Based on haplotype analysis and expression levels after inoculation, four candidate genes were identified within the region identified by both Genome-wide association study (GWAS) and previous identified QTL mapping, including Csa3G129470 for gsb3.2/gsb3.3, Csa5G606820 and Csa5G606850 for gsb5.1, and Csa6G079730 for gsb-s6.2. The novel GSB resistant accessions, significant SNPs, and candidate genes facilitate the breeding of GSB resistant cucumber cultivars and provide a novel idea for understanding GSB resistance mechanism in cucumber.

Selective sublimation of GaN and regrowth of AlGaN to co-integrate enhancement mode and depletion mode high electron mobility transistors

In the present study, the selective sublimation of the p-GaN cap layer of Al(Ga)N/GaN HEMTs is developed to replace the commonly used dry etching with no risk of damage in the barrier layer in order to fabricate enhanced mode transistors. Thanks to this approach, enhancement-mode transistors are fabricated with a threshold voltage between 0 V and +1.5 V depending on the barrier layer aluminum molar fraction and thickness. Furthermore, we show the benefit of the combination of selective sublimation with the regrowth of AlGaN to reduce access resistance in these transistors which can be co-integrated with depletion-mode devices fabricated in the same process in areas where p-GaN has been totally evaporated.

Novel Impedance Measures as Biomarker for Intracochlear Fibrosis

Measurement of the complex electrical impedance of the electrode contacts can provide new insights into the factors playing a role in the preservation of residual hearing with cochlear implants (CIs). However, unraveling the contributions related to the different phenomena from impedance data necessitates more advanced measurement and analysis techniques. The present study explores a new impedance measurement option recently included into the cochlear-implant programming software and aims to contribute to a more solid basis for the clinical use of impedance measures as a biomarker for fibrous tissue formation. Twenty adult CI-recipients were followed from surgery until 1 year after implantation by means of Electrode Voltage Telemetry (EVT), also called Electric Field Imaging or TransImpedance-Matrix measurement, and a 4-point technique for probing the voltage between adjacent electrode contacts. The data were compared to the electrode location derived from computed tomography, and to the device usage log. Using our impedance model for electrical stimulation of the cochlea, the polarization impedance related the electrode–tissue interface was determined, and the bulk impedance (access resistance) was split into a near-field and a far-field component. On average, the polarization impedance increased abruptly after surgery, indicating a strong passivation of the electrode contacts before cochlear-implant initiation. Its initial rise resolved almost completely soon after device switchon (2–4 weeks). The gradual increase of the access resistance mainly happened during the first 40 days on a time scale very similar to that observed in a guinea-pig study correlating impedance changes to fibrous tissue growth. The higher increase towards the round window is consistent with the higher amount of tissue observed in histological animal studies close to the electrode entry point. While the initial changes were due to the near-field resistance, the far-field resistance began to rise only after one month for half of the study group, once the near-field component had reached its critical value. This suggests indeed fibrosis initiating near the electrode contacts and spreading thereafter farther away. The near-field resistance positively correlated to device usage. EVT data allow for a further decomposition of the impedance at a cochlear-implant electrode, yielding a more detailed description of the postoperative intracochlear phenomena, such as fibrosis.