Search

A new virus in cotton (Gossypium hirsutum L.) required the need to graft plants to evaluate resistance. In searching the literature, several studies reported grafting, however the details surrounding the types of grafts, age, and acclimation environment are not described in detail. A graft is the union of rootstock and scion requiring good cambial tissue contact to be successful. Therefore, several different graft types, and the need for humidity was investigated. Initially, thirty plants were grown in the greenhouse. The first set of grafts were performed on fifteen plants between two graft types (T-graft and bottle shoot) and the need to be bagged for cambial humidity. The second set of fifteen were used to test the wedge, saddle-graft, whip-and-tongue, bottle shoot, and approach grafts on three plants each. The T-graft was chosen as the best for success as it provided the highest cambial contact. A set of twenty plants were grown to serve as rootstock for cotton leafroll dwarf virus (CLRDV) transmission. Two different infected CLRDV plants served as the scion for the virus which were grafted using the Tgraft. Three leaves below the graft node were used to test for the virus using PCR. Fourteen of 20 grafts had successful transmission of CLRDV, regardless of graft success. [ABSTRACT FROM AUTHOR]

Sicklepod (Senna obtusifolia L.) is a weed native to the American tropics which has become widespread in the southeastern United States, posing a significant challenge for row crop producers (McKinnon et al. 2012; Nice 1999). In August 2024, a foliar disease was observed on sicklepod throughout cotton (Gossypium hirsutum L.) plots in a nine-acre field at EV-Smith Plant Breeding Unit in Tallassee, Alabama (32.4967° N, 85.8905° W), U.S. The symptoms were round to irregular, 3 to 9 mm, brown to dark-brown lesions with alternating concentric rings, surrounded by a pale-yellow halo. The estimated disease incidence was 40%. Four symptomatic plants were sampled from different locations across the field for pathogen isolation. The leaves with lesions were surface sterilized by soaking in 1 % NaClO for 1 min, followed by 70 % ethanol for 1 min, and rinsed twice in sterile distilled water for 30 seconds. The lesions were excised and plated on V8 agar amended with 0.5 mL of lactic acid per 500 mL of medium. The plates were incubated at 22 °C under a 12-h light/dark cycle for ten days. Six fungal isolates with identical morphologies were obtained. During incubation, colonies developed gray aerial mycelium, turning dark gray to brown with age. The conidiophores were unbranched, erect or slightly curved, elongated, and brown, appearing singly or in clusters, with 3 to 14 pseudosepta. Conidia were obclavate to cylindrical to slightly curved, and multinucleate, containing 3 to 12 septa. Conidia were 50 to 193 µm in length and 5 to 14 µm in width. For molecular identification of pathogen, isolate SP1 was selected, and DNA was extracted from 100 mg of 10-day-old mycelium using the EZNA Fungal DNA Mini Kit (Omega Bio-tek, GA). Three regions, internal transcribed spacer (ITS; White et al. 1990), actin-encoding locus (act1; Carbine & Kohn, 1999), and hypervariable loci (ga4; Dixon et al. 2009) were used to confirm SP1 isolate. The sequences of ITS (PQ536090) and act1 (PQ876357) shared 100% identity, and 94.7% and 99.3% homology with ITS (ON316921) and act1 (MF320391), respectively. The ga4 sequence (PQ876356) shared 98% identity and 98.09% coverage with C. cassiicola (MH605239) in GenBank. For pathogenicity test, a conidial suspension of isolate SP1 (40,000 spores/mL) was sprayed onto sicklepod plants at the two-true-leaf stage in the greenhouse. Six plants were inoculated with the conidial suspension, while three additional plants were sprayed with sterile distilled water to serve as controls. Control and inoculated plants were transferred to a mist chamber constructed with PVC pipe (dimensions: 4 m × 4 m × 8 m) and enclosed with a transparent plastic sheet. The plants were arranged in a completely randomized design inside the chamber, and a mist system operated for 2 seconds every 10 minutes over three days to maintain humidity above 80%. Initial symptoms on the inoculated leaves were noted seven days post-inoculation, whereas no symptoms were observed on control plants. The experiment was repeated once, and the results were consistent. Based on morphology and sequence analyses, the fungal pathogen was reisolated from inoculated plants and identified as C. cassiicola, fulfilling Koch's postulates. To our knowledge, this is the first global report of C. cassiicola infecting sicklepod. The detection of this pathogen on a new host highlights its notable adaptability. With an extensive host range of over 400 species (Dixon et al. 2009), the pathogen poses a significant risk to a wide range of plant communities and crops, illustrating the importance of closely monitoring C. cassiicola in host and weed control.

Botryosphaeria stem blight is a fungal disease of blueberry caused by members of the Botryosphaeriaceae family, which can lead to rapid wilting of leaves and stems, often resulting in significant yield loss and even plant death. Botryosphaeria stem blight is a major disease in Alabama, however, information on the distribution and causal pathogens for stem blight in Alabama is limited. This study surveyed blueberry farms in Alabama and nearby parts of Georgia and Mississippi to reveal the occurrence, species identities, and virulence of causal pathogens for Botryosphaeria stem blight. As part of this work, a total of 45 symptomatic blueberry samples were collected between 2021 and 2023. Phylogenetic analysis based on DNA sequences of the ITS, β-tubulin, and EF1-α genomic regions revealed that Botryosphaeriaceae (34%) was the most common family associated with disease samples, followed by Sporocadaceae (21%), Diaporthaceae (13%), Pleosporaceae (9%), and other families. Within Botryosphaeriaceae, Neofusicoccum and Lasiodiplodia were the most common genera identified. Virulence testing on the blueberry cultivar 'Vernon' using an attached-stem assay showed that isolates of Neofusicoccum kwambonambiense, Neofusicoccum sp., Lasiodiplodia sp., N. parvum, and N. ribis caused the longest lesion length four weeks after inoculation, compared to isolates of other genera and species. Results of this study provide the latest information on the distribution, pathogenicity, and virulence of blueberry stem blight pathogens in Alabama and nearby states. Aggressive isolates identified in this study may be useful for screening blueberry cultivars for stem blight tolerance.

This strategic plan summarizes the major accomplishments achieved in the last quinquennial by the soybean [Glycine max (L.) Merr.] genetics and genomics research community and outlines key priorities for the next 5 years (2024-2028). This work is the result of deliberations among over 50 soybean researchers during a 2-day workshop in St Louis, MO, USA, at the end of 2022. The plan is divided into seven traditional areas/disciplines: Breeding, Biotic Interactions, Physiology and Abiotic Stress, Functional Genomics, Biotechnology, Genomic Resources and Datasets, and Computational Resources. One additional section was added, Training the Next Generation of Soybean Researchers, when it was identified as a pressing issue during the workshop. This installment of the soybean genomics strategic plan provides a snapshot of recent progress while looking at future goals that will improve resources and enable innovation among the community of basic and applied soybean researchers. We hope that this work will inform our community and increase support for soybean research., (© 2024 The Author(s). The Plant Genome published by Wiley Periodicals LLC on behalf of Crop Science Society of America.)

Cercospora leaf blight (CLB), caused by Cercospora cf. flagellaris , C. kikuchii , and C. cf. sigesbeckiae , is a significant soybean [ Glycine max (L.) Merr.] disease in regions with hot and humid conditions causing yield loss in the United States and Canada. There is limited information regarding resistant soybean cultivars, and there have been marginal efforts to identify the genomic regions underlying resistance to CLB. A Genome-Wide Association Study was conducted using a diverse panel of 460 soybean accessions from maturity groups III to VII to identify the genomic regions associated to the CLB disease. These accessions were evaluated for CLB in different regions of the southeastern United States over 3 years. In total, the study identified 99 Single Nucleotide Polymorphism (SNPs) associated with the disease severity and 85 SNPs associated with disease incidence. Across multiple environments, 47 disease severity SNPs and 23 incidence SNPs were common. Candidate genes within 10 kb of these SNPs were involved in biotic and abiotic stress pathways. This information will contribute to the development of resistant soybean germplasm. Further research is warranted to study the effect of pyramiding desirable genomic regions and investigate the role of identified genes in soybean CLB resistance., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Patel, Allen, Buckley, Chen, Clubb, Mozzoni, Orazaly, Florez, Moseley, Rupe, Shrestha, Price, Ward and Koebernick.)

Cercospora leaf blight (CLB) of soybean, caused by Cercospora cf. flagellaris , C. kikuchii , and C. cf. sigesbeckiae , is an economically important disease in the southern United States. Cultivar resistance to CLB is inconsistent; therefore, fungicides in the quinone outside inhibitor (QoI) class have been relied on to manage the disease. Approximately 620 isolates from plants exhibiting CLB were collected between 2018 and 2021 from 19 locations in eight southern states. A novel polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay based on two genes, calmodulin and histone h3 , was developed to differentiate between the dominant species of Cercospora , C. cf. flagellaris , and C. cf. sigesbeckiae . A multilocus phylogenetic analysis of actin, calmodulin, histone h3, ITS rDNA, and transcription elongation factor 1-α was used to confirm PCR-RFLP results and identify remaining isolates. Approximately 80% of the isolates collected were identified as C. cf. flagellaris , while 15% classified as C. cf. sigesbeckiae , 2% as C. kikuchii , and 3% as previously unreported Cercospora species associated with CLB in the United States. PCR-RFLP of cytochrome b ( cytb ) identified QoI-resistance conferred by the G143A substitution. Approximately 64 to 83% of isolates were determined to be QoI-resistant, and all contained the G143A substitution. Results of discriminatory dose assays using azoxystrobin (1 ppm) were 100% consistent with PCR-RFLP results. To our knowledge, this constitutes the first report of QoI resistance in CLB pathogen populations from Alabama, Arkansas, Kentucky, Mississippi, Missouri, Tennessee, and Texas. In areas where high frequencies of resistance have been identified, QoI fungicides should be avoided, and fungicide products with alternative modes-of-action should be utilized in the absence of CLB-resistant soybean cultivars., Competing Interests: The author(s) declare no conflict of interest.

Target spot caused by Corynespora cassiicola is a problematic disease in tropical and subtropical soybean ( Glycine max ) growing regions. Although resistant soybean genotypes have been identified, the genetic mechanisms underlying target spot resistance has not yet been studied. To address this knowledge gap, this is the first genome-wide association study (GWAS) conducted using the SoySNP50K array on a panel of 246 soybean accessions, aiming to unravel the genetic architecture of resistance. The results revealed significant associations of 14 and 33 loci with resistance to LIM01 and SSTA C. cassiicola isolates, respectively, with six loci demonstrating consistent associations across both isolates. To identify potential candidate genes within GWAS-identified loci, dynamic transcriptome profiling was conducted through RNA-Seq analysis. The analysis involved comparing gene expression patterns between resistant and susceptible genotypes, utilizing leaf tissue collected at different time points after inoculation. Integrating results of GWAS and RNA-Seq analyses identified 238 differentially expressed genes within a 200 kb region encompassing significant quantitative trait loci (QTLs) for disease severity ratings. These genes were involved in defense response to pathogen, innate immune response, chitinase activity, histone H3-K9 methylation, salicylic acid mediated signaling pathway, kinase activity, and biosynthesis of flavonoid, jasmonic acid, phenylpropanoid, and wax. In addition, when combining results from this study with previous GWAS research, 11 colocalized regions associated with disease resistance were identified for biotic and abiotic stress. This finding provides valuable insight into the genetic resources that can be harnessed for future breeding programs aiming to enhance soybean resistance against target spot and other diseases simultaneously., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Patel, Patel, Bowen and Koebernick.)

Target spot is caused by Corynespora cassiicola , which heavily affects soybean production areas that are hot and humid. Resistant soybean genotypes have been identified; however, the molecular mechanisms governing resistance to infection are unknown. Comparative transcriptomic profiling using two known resistant genotypes and two susceptible genotypes was performed under infected and control conditions to understand the regulatory network operating between soybean and C. cassiicola . RNA-Seq analysis identified a total of 2571 differentially expressed genes (DEGs) which were shared by all four genotypes. These DEGs are related to secondary metabolites, immune response, defense response, phenylpropanoid, and flavonoid/isoflavonoid pathways in all four genotypes after C. cassiicola infection. In the two resistant genotypes, additional upregulated DEGs were identified affiliated with the defense network: flavonoids, jasmonic acid, salicylic acid, and brassinosteroids. Further analysis led to the identification of differentially expressed transcription factors, immune receptors, and defense genes with a leucine-rich repeat domain, dirigent proteins, and cysteine (C)-rich receptor-like kinases. These results will provide insight into molecular mechanisms of soybean resistance to C. cassiicola infection and valuable resources to potentially pyramid quantitative resistance loci for improving soybean germplasm., Competing Interests: The authors declare no conflict of interest.

Cotton leafroll dwarf virus (CLRDV) is a yield-limiting, aphid-transmitted virus that was identified in cotton, Gossypium hirsutum L., in the United States of America in 2017. CLRDV is currently classified in the genus Polerovirus, family Solemoviridae. Although 8 species of aphids (Hemiptera: Aphididae) are reported to infest cotton, Aphis gossypii Glover is the only known vector of CLRDV to this crop. Aphis gossypii transmits CLRDV in a persistent and nonpropagative manner, but acquisition and retention times have only been partially characterized in Brazil. The main objectives of this study were to characterize the acquisition access period, the inoculation access period, and retention times for a U.S. strain of CLRDV and A. gossypii population. A sub-objective was to test the vector competence of Myzus persicae Sulzer and Aphis craccivora Koch. In our study, A. gossypii apterous and alate morphs were able to acquire CLRDV in 30 min and 24 h, inoculate CLRDV in 45 and 15 min, and retain CLRDV for 15 and 23 days, respectively. Neither M. persicae nor A. craccivora acquired or transmitted CLRDV to cotton., (© The Author(s) 2023. Published by Oxford University Press on behalf of Entomological Society of America.)

Cotton (Gossypium hirsutum L.) is used as a non-host of tomato yellow leaf curl virus (TYLCV) (family Geminiviridae, genus Begomovirus) in many studies (Ghanim and Czosnek 2000; Legarrea et al. 2015; Zeidan and Czosnek 1991), but only one reports methods used to determine host-status (Sinisterra et al. 2005), and there is one contradictory report from China stating cotton is a host of TYLCV (Li et al. 2014). In October 2018, cotton was screened for the presence of begomoviruses in Elmore, Escambia and Macon Counties, AL, where infestations of its whitefly vector (Bemisia tabaci Genn.) occurred in August. DNA was extracted from fully expanded leaves from the upper 1/3 of the canopy using a DNeasy® Plant Mini Kit (QIAGEN, Hilden, Germany) and amplified with primers V324/C889 targeting a 575 bp coat protein fragment of begomoviruses (Brown et al. 2001). Five out of 200 cotton samples tested positive, and sequences recovered from three samples revealed 98-99% identity to TYLCV isolates in NCBI (Accession Nos. MT947801-03); sequences from the other two samples were of low quality and inconclusive. These samples were not available for additional tests, therefore, we proceeded to confirm host status using a monopartite clone of TYLCV-Israel (Reyes et al. 2013) reported in the US (Polston et al. 1999). All experiments were conducted in growth chambers with 16:8 light:dark cycle at 25.0℃ and 50% RH. Cotton seedlings (DeltaPine 1646 B2XF) at the 2-3 true leaf stage and tomatoes (Solanum lycopersicum L., var. 'Florida Lanai') at the 4 true leaf stage were agroinoculated at the stem tissue between the apical meristem and the first node (Reyes et al. 2013). Tomato served as a positive control; tomato and cotton mock inoculated with an empty vector were negative controls. A hole-punch was used to collect 4 leaf discs along midveins of the three, uppermost fully expanded leaves. DNA was extracted 28 days after inoculation as described above. A 390 bp segment of the intergenic region of TYLCV-A was amplified using primers PTYIRc287/PTYIRv21 (Nakhla et al., 1993). PCR results from agroinoculated plants confirmed (2/18) cotton plants, (5/5) tomatoes and (0/10) mock inoculated controls were infected with TYLCV. Whitefly transmission to cotton was confirmed using a leaf-disc bioassay for rapid testing (Czosnek et al. 1993). Bemisia tabaci MEAM-1 reared on eggplant (non-host of TYLCV) were placed on agroinoculated TYLCV-infected tomato/span> plants for a 96-h acquisition access period. Cohorts of 10 viruliferous B. tabaci were aspirated into 30mL cups each containing a 2.5cm healthy cotton leaf disc set in plant agar. After a 48-h inoculation access period, adults and their eggs were removed from the leaf discs. Leaf discs were held another 96-h before they were tested for TYLCV using the methods described above. TYLCV-infection was confirmed in (9/20) cotton leaf discs, demonstrating the viral load delivered by whiteflies was high enough to initiate local infection in cotton. No obvious begomovirus symptoms were observed on cotton plants in the field or laboratory. Field collection of samples was prompted by symptoms attributed to cotton leafroll dwarf virus (Avelar et al. 2017). TYLCV infection of cotton does not appear to be of economic importance. Additional information is needed to determine the frequency of infection in the field, specificity of TYLCV isolate x cotton genotype interactions leading to successful infection, and underlying causes of conflicting host-status reports in previously published studies.