@article{adhikari_olukolu_paudel_pandey_halterman_louws_2024, title={Genotyping-by-Sequencing Reveals Population Differentiation and Linkage Disequilibrium in <i>Alternaria linariae</i> from Tomato}, volume={2}, ISSN={["1943-7684"]}, DOI={10.1094/PHYTO-07-23-0229-R}, abstractNote={Alternaria linariae (Neerg.) Simmons is an economically important foliar pathogen that causes early blight disease in tomatoes. Understanding genetic diversity, population genetic structure, and evolutionary potential is crucial to contemplating effective disease management strategies. We leveraged genotyping-by-sequencing (GBS) technology to compare genome-wide variation in 124 isolates of Alternaria spp. (A. alternata, A. linariae, and A. solani) for comparative genome analysis and to test the hypotheses of genetic differentiation and linkage disequilibrium (LD) in A. linariae collected from tomatoes in western North Carolina. We performed a pangenome-aware variant calling and filtering with GBSapp and identified 53,238 variants conserved across the reference genomes of three Alternaria spp. The highest marker density was observed on chromosome 1 (7 Mb). Both discriminant analysis of principal components (DAPC) and Bayesian model-based STRUCTURE analysis of A. linariae isolates revealed three subpopulations with minimal admixture. The genetic differentiation coefficient (FST) within A. linariae subpopulations were similar and high (0.86), indicating that alleles in the subpopulations are fixed and the genetic structure is likely due to restricted recombination. Analysis of molecular variance indicates higher variation among populations (89%) than within the population (11%). We found long-range LD between pairs of loci in A. linariae, supporting the hypothesis of low recombination expected for a fungal pathogen with limited asexual reproduction. Our findings provide evidence of a high level of population genetic differentiation in A. linariae, which reinforces the importance of developing tomato varieties with broad-spectrum resistance to various isolates of A. linariae.}, journal={PHYTOPATHOLOGY}, author={Adhikari, Tika B. and Olukolu, Bode A. and Paudel, Rajan and Pandey, Anju and Halterman, Dennis and Louws, Frank J.}, year={2024}, month={Feb} }
 @misc{meshram_adhikari_2024, title={Microbiome-Mediated Strategies to Manage Major Soil-Borne Diseases of Tomato}, volume={13}, ISSN={["2223-7747"]}, DOI={10.3390/plants13030364}, abstractNote={The tomato (Solanum lycopersicum L.) is consumed globally as a fresh vegetable due to its high nutritional value and antioxidant properties. However, soil-borne diseases can severely limit tomato production. These diseases, such as bacterial wilt (BW), Fusarium wilt (FW), Verticillium wilt (VW), and root-knot nematodes (RKN), can significantly reduce the yield and quality of tomatoes. Using agrochemicals to combat these diseases can lead to chemical residues, pesticide resistance, and environmental pollution. Unfortunately, resistant varieties are not yet available. Therefore, we must find alternative strategies to protect tomatoes from these soil-borne diseases. One of the most promising solutions is harnessing microbial communities that can suppress disease and promote plant growth and immunity. Recent omics technologies and next-generation sequencing advances can help us develop microbiome-based strategies to mitigate tomato soil-borne diseases. This review emphasizes the importance of interdisciplinary approaches to understanding the utilization of beneficial microbiomes to mitigate soil-borne diseases and improve crop productivity.}, number={3}, journal={PLANTS-BASEL}, author={Meshram, Shweta and Adhikari, Tika B.}, year={2024}, month={Feb} }
 @article{adhikari_siddique_louws_sim_panthee_2023, title={Molecular mapping of quantitative trait loci for resistance to early blight in tomatoes}, volume={14}, ISSN={1664-462X}, url={http://dx.doi.org/10.3389/fpls.2023.1135884}, DOI={10.3389/fpls.2023.1135884}, abstractNote={Early blight (EB), caused by Alternaria linariae (Neerg.) (syn. A. tomatophila) Simmons, is a disease that affects tomatoes (Solanum lycopersicum L.) throughout the world, with tremendous economic implications. The objective of the present study was to map the quantitative trait loci (QTL) associated with EB resistance in tomatoes. The F2 and F2:3 mapping populations consisting of 174 lines derived from NC 1CELBR (resistant) × Fla. 7775 (susceptible) were evaluated under natural conditions in the field in 2011 and in the greenhouse in 2015 by artificial inoculation. In all, 375 Kompetitive Allele Specific PCR (KASP) assays were used for genotyping parents and the F2 population. The broad-sense heritability estimate for phenotypic data was 28.3%, and 25.3% for 2011, and 2015 disease evaluations, respectively. QTL analysis revealed six QTLs associated with EB resistance on chromosomes 2, 8, and 11 (LOD 4.0 to 9.1), explaining phenotypic variation ranging from 3.8 to 21.0%. These results demonstrate that genetic control of EB resistance in NC 1CELBR is polygenic. This study may facilitate further fine mapping of the EB-resistant QTL and marker-assisted selection (MAS) to transfer EB resistance genes into elite tomato varieties, including broadening the genetic diversity of EB resistance in tomatoes.}, journal={Frontiers in Plant Science}, publisher={Frontiers Media SA}, author={Adhikari, Tika B. and Siddique, Muhammad Irfan and Louws, Frank J. and Sim, Sung-Chur and Panthee, Dilip R.}, year={2023}, month={May} }
 @article{oh_ingram_shekasteband_adhikari_louws_dean_2023, title={Tissues and mechanisms associated with Verticillium wilt resistance in tomato using bi-grafted near-isogenic lines}, volume={5}, ISSN={["1460-2431"]}, url={https://doi.org/10.1093/jxb/erad182}, DOI={10.1093/jxb/erad182}, abstractNote={Abstract Host resistance is the primary means to control Verticillium dahliae, a soil-borne pathogen causing major losses on a broad range of plants, including tomato. The tissues and mechanisms responsible for resistance remain obscure. In the field, resistant tomato used as rootstocks does not confer resistance. Here, we created bi-grafted plants with near-isogenic lines (NILs) exhibiting (Ve1) or lacking (ve1) resistance to V. dahliae race 1. Ten days after inoculation, scion and rootstock tissues were subjected to differential gene expression and co-expression network analyses. Symptoms only developed in susceptible scions regardless of the rootstock. Infection caused more dramatic alteration of tomato gene expression in susceptible compared with resistant tissues, including pathogen receptor, signaling pathway, pathogenesis-related protein, and cell wall modification genes. Differences were observed between scions and rootstocks, primarily related to physiological processes in these tissues. Gene expression in scions was influenced by the rootstock genotype. A few genes were associated with the Ve1 genotype, which was independent of infection or tissue type. Several were physically clustered, some near the Ve1 locus on chromosome 9. Transcripts mapped to V. dahliae were dominated by secreted candidate effector proteins. These findings advance knowledge of molecular mechanisms underlying the tomato–V. dahliae interaction.}, journal={JOURNAL OF EXPERIMENTAL BOTANY}, author={Oh, Yeonyee and Ingram, Thomas and Shekasteband, Reza and Adhikari, Tika and Louws, Frank J. and Dean, Ralph A.}, editor={Höfte, MonicaEditor}, year={2023}, month={May} }
 @article{adhikari_aryal_redpath_broeck_ashrafi_philbrick_jacobs_sozzani_louws_2022, title={RNA-Seq and Gene Regulatory Network Analyses Uncover Candidate Genes in the Early Defense to Two Hemibiotrophic Colletorichum spp. in Strawberry}, volume={12}, ISSN={["1664-8021"]}, DOI={10.3389/fgene.2021.805771}, abstractNote={Two hemibiotrophic pathogens, Colletotrichum acutatum (Ca) and C. gloeosporioides (Cg), cause anthracnose fruit rot and anthracnose crown rot in strawberry (Fragaria × ananassa Duchesne), respectively. Both Ca and Cg can initially infect through a brief biotrophic phase, which is associated with the production of intracellular primary hyphae that can infect host cells without causing cell death and establishing hemibiotrophic infection (HBI) or quiescent (latent infections) in leaf tissues. The Ca and Cg HBI in nurseries and subsequent distribution of asymptomatic infected transplants to fruit production fields is the major source of anthracnose epidemics in North Carolina. In the absence of complete resistance, strawberry varieties with good fruit quality showing rate-reducing resistance have frequently been used as a source of resistance to Ca and Cg. However, the molecular mechanisms underlying the rate-reducing resistance or susceptibility to Ca and Cg are still unknown. We performed comparative transcriptome analyses to examine how rate-reducing resistant genotype NCS 10-147 and susceptible genotype ‘Chandler’ respond to Ca and Cg and identify molecular events between 0 and 48 h after the pathogen-inoculated and mock-inoculated leaf tissues. Although plant response to both Ca and Cg at the same timepoint was not similar, more genes in the resistant interaction were upregulated at 24 hpi with Ca compared with those at 48 hpi. In contrast, a few genes were upregulated in the resistant interaction at 48 hpi with Cg. Resistance response to both Ca and Cg was associated with upregulation of MLP-like protein 44, LRR receptor-like serine/threonine-protein kinase, and auxin signaling pathway, whereas susceptibility was linked to modulation of the phenylpropanoid pathway. Gene regulatory network inference analysis revealed candidate transcription factors (TFs) such as GATA5 and MYB-10, and their downstream targets were upregulated in resistant interactions. Our results provide valuable insights into transcriptional changes during resistant and susceptible interactions, which can further facilitate assessing candidate genes necessary for resistance to two hemibiotrophic Colletotrichum spp. in strawberry.}, journal={FRONTIERS IN GENETICS}, author={Adhikari, Tika B. and Aryal, Rishi and Redpath, Lauren E. and Broeck, Lisa and Ashrafi, Hamid and Philbrick, Ashley N. and Jacobs, Raymond L. and Sozzani, Rosangela and Louws, Frank J.}, year={2022}, month={Mar} }
 @article{ingram_oh_adhikari_louws_dean_2020, title={Comparative Genome Analyses of 18 Verticillium dahliae Tomato Isolates Reveals Phylogenetic and Race Specific Signatures}, volume={11}, ISSN={["1664-302X"]}, DOI={10.3389/fmicb.2020.573755}, abstractNote={Host resistance is one of the few strategies available to combat the soil borne pathogenic fungus Verticillium dahliae. Understanding pathogen diversity in populations is key to successfully deploying host resistance. In this study the genomes of 18 V. dahliae isolates of races 1 (n = 2), 2 (n = 4), and 3 (n = 12) from Japan, California, and North Carolina were sequenced and mapped to the reference genome of JR2 (from tomato). The genomes were analyzed for phylogenetic and pathogen specific signatures to classify specific strains or genes for future research. Four highly clonal lineages/groups were discovered, including a lineage unique to North Carolina isolates, which had the rare MAT1-1 mating type. No evidence for recombination between isolates of different mating types was observed, even in isolates of different mating types discovered in the same field. By mapping these 18 isolates genomes to the JR2 reference genome, 193 unique candidate effectors were found using SignalP and EffectorP. Within these effectors, 144 highly conserved effectors, 42 mutable effectors (truncated or present in some isolates but absent in others), and 7 effectors present in highly variable regions of the chromosomes were discovered. Of the 144 core effectors, 21 were highly conserved in V. alfalfae and V. longisporum, 7 of which have no known function. Within the non-core effectors 30 contained large numbers of non-synonymous mutations, while 15 of them contained indels, frameshift mutations, or were present on highly variable regions of the chromosome. Two of these highly variable region effectors (HVREs) were only present in race 2 isolates, but not in race 3 isolates. The race 1 effector Ave1 was also present in a highly variable region. These data may suggest that these highly variable regions are enriched in race determinant genes, consistent with the two-speed genome hypothesis.}, journal={FRONTIERS IN MICROBIOLOGY}, author={Ingram, Thomas W. and Oh, Yeonyee and Adhikari, Tika B. and Louws, Frank J. and Dean, Ralph A.}, year={2020}, month={Nov} }
 @misc{philbrick_adhikari_louws_gorny_2020, title={Meloidogyne enterolobii, a Major Threat to Tomato Production: Current Status and Future Prospects for Its Management}, volume={11}, ISSN={["1664-462X"]}, DOI={10.3389/fpls.2020.606395}, abstractNote={The guava root-knot nematode, Meloidogyne enterolobii (Syn. M. mayaguensis), is an emerging pathogen to many crops in the world. This nematode can cause chlorosis, stunting, and reduce yields associated with the induction of many root galls on host plants. Recently, this pathogen has been considered as a global threat for tomato (Solanum lycopersicum L.) production due to the lack of known resistance in commercially accepted varieties and the aggressiveness of M. enterolobii. Both conventional morphological and molecular approaches have been used to identify M. enterolobii, an important first step in an integrated management. To combat root-knot nematodes, integrated disease management strategies such as crop rotation, field sanitation, biocontrol agents, fumigants, and resistant cultivars have been developed and successfully used in the past. However, the resistance in tomato varieties mediated by known Mi-genes does not control M. enterolobii. Here, we review the current knowledge on geographic distribution, host range, population biology, control measures, and proposed future strategies to improve M. enterolobii control in tomato.}, journal={FRONTIERS IN PLANT SCIENCE}, author={Philbrick, Ashley N. and Adhikari, Tika B. and Louws, Frank J. and Gorny, Adrienne M.}, year={2020}, month={Nov} }