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The current investigation assessed the effectiveness of 30 citrus germplasms in combating citrus canker pathogenesis in Assam, North‐East India. Significant differences were observed among the examined citrus germplasms in terms of per cent disease severity and disease reduction against Xanthomonas citri pv. citri. Among the 30 different germplasms, eight germplasms, namely, Jora tenga (14.67%), Bonjora (15.58%), Holong tenga (15.75%), Latipes (17.34%), Patijora (17.75%), Birajora (18.50%), Cleopatra mandarin (20.00%) and Ada jamir (20.18%), exhibited highest disease resistance potential. The study recorded that the germplasm Latipes, which are resistant, had the highest total phenol content (21.26 mg/g dry weight), while the susceptible one, Grapefruit (7.85 mg/g dry weight), had the lowest total phenol content. Jora tenga exhibited the highest flavonoid content, measuring at 6.48 mg/g dry weight, whereas White pummelo had the lowest flavonoid content, measuring at 1.88 mg/g dry weight. Similarly, the highest alkaloid percentage was recorded in resistant germplasm, Adajamir (10.52%), while the lowest was in susceptible germplasm, Volkameriana (2.30%). The levels of total phenol, alkaloid and flavonoid contents exhibited a significant negative correlation with the per cent disease severity of citrus canker disease in both Pearson correlation and Spearmen correlation analysis. The current research on bioprospecting of citrus germplasms in relation to citrus canker pathogenesis has the potential to offer valuable insights into mitigating the transmission of bacterial pathogens and eliminating sources of infection by employing resistant cultivars and implementing approved doses of plant protection formulations. [ABSTRACT FROM AUTHOR]

Citrus is affected by many diseases, and hence, the movement of citrus propagative materials is highly regulated in the USA. Currently used regulatory pathogen detection methods include biological and laboratory-based technologies, which are time-consuming, expensive, and have many limitations. There is an urgent need to develop alternate, rapid, economical, and reliable testing methods for safe germplasm exchange. Citrus huanglongbing (HLB) has devastated citrus industries leading to an increased need for germplasm exchanges between citrus growing regions for evaluating many potentially valuable hybrids for both HLB resistance and multilocational performance. In the present study, Next-Generation Sequencing (NGS) methods were used to sequence the transcriptomes of 21 test samples, including 15 well-characterized pathogen-positive plants. A workflow was designed in the CLC Genomics Workbench software, v 21.0.5 for bioinformatics analysis of the sequence data for the detection of pathogens. NGS was rapid and found to be a valuable technique for the detection of viral and bacterial pathogens, and for the discovery of new citrus viruses, complementary to the existing array of biological and laboratory assays. Using NGS methods, we detected beet western yellows virus, a newly reported citrus virus, and a variant of the citrus yellow vein-associated virus associated with the "fatal yellows" disease. [ABSTRACT FROM AUTHOR]

Huanglongbing (HLB), associated with the proteobacterium 'Candidatus Liberibacter asiaticus'(CLa), is a destructive disease in citrus. Resistance/tolerance has been identified in some citrus species, wild relatives, and transgenic citrus genotypes. The objectives of this study were to: (1) evaluate the response of the citrus germplasm collection from Puerto Rico (namely 'Rico') to HLB, (2) determine the most appropriate rootstock-genotype combination, and (3) quantify the presence of the bacterium in the plant tissue by quantitative polymerase chain reaction (qPCR). Seventeen genotypes were grafted onto 'HRS 812' and 'Swingle' citrumelo rootstocks. The plants were inoculated with HLB infected buds and evaluated at 12 months after inoculation in a greenhouse in Adjuntas, Puerto Rico. The genotypes 'Lares' and 'Padilla' had significantly higher incidence (>65.0%) and severity (3.2–4.3) compared to 'Mexican Lime' and 'Tahiti Lime' that had lower scores (<18.0%, 1.1–1.3) using both rootstocks. In contrast, the genotypes 'Fronton', 'PR-Sel-1', and 'Rico 7–376' grafted on HRS 812; and 'Pietri 334' grafted on Swingle citrumelo had lower HLB incidence (<10%) and severity (<1.5). Significantly higher mean cycle threshold (Ct) values were only observed for the genotypes Fronton (37.0), Tahiti Lime (36.5), and Pietri 334 (36.2) compared to Padilla (34.7 and 32.7 when HRS 812 and Swingle citrumelo was used as rootstock, respectively). Citrus genotypes having lower HLB scores were identified, however, their reaction varied according to the rootstock used. [ABSTRACT FROM AUTHOR]

Seventy four percent of the budwood tree sources samples from the Greek national citrus germplasm foundation collection were positive for one or more viroids. Citrus exocortis viroid (CEVd) and Hop stunt viroid (HSVd), the two potentially damaging viroids for the Greek citriculture, especially after transitioning to Citrus tristeza virus resistant/tolerant rootstocks and scions, were detected along with Citrus bark cracking viroid, Citrus bent leaf viroid (CBLVd), and Citrus dwarfing viroid (CDVd). All samples tested negative for Citrus viroid V (CVd-V), CVd-VI and CVd-I-LSS (CBLVd variant). An HSVd isolate related to the non-cachexia variant contained two critical cachexia-related nucleotide changes, while two more isolates were unique among the previously reported HSVds. Unusual CDVd isolates with altered RNA secondary structure were identified in trees additionally co-infected with CEVd and HSVd. Budwood sources that had previously undergone therapy tested negative for all targeted viroids, suggesting that budwood sources in Greece can be protected against graft-transmissible pathogens, even under severe inoculum pressure. Therapied and tested citrus propagative material requires a comprehensive program not available currently in Greece, involving regulators, scientists, and the private sector, for the establishment and successful operation of a national citrus germplasm collection. [ABSTRACT FROM AUTHOR]

In the past decade Colletotrichum gloeosporioides, C. karstii, and Alternaria alternata represent emerging fungal pathogens on citrus in the Mediterranean basin. Selection of tolerant Citrus germplasm offers evaluable long-term solution and should be considered as promising alternative to limit synthetic fungicide application to manage Alternaria and Colletotrichum infections in Citrus groves. In this study, the high variability of pre-harvest disease symptoms among 37 Citrus accessions was investigated in Italy in the most representative Sicilian production districts covering 1500 ha and including 20 homogeneous areas over an eleven-year survey period (2010–2020). Early fruit drop, brown spot, and anthracnose on fruit and leaves, pre-harvest fruit drop, and twig blight and defoliation associated to Alternaria and Colletotrichum spp. were identified on oranges, mandarins, and lemons. Comprehensively, first extensive data obtained herein on field susceptibility within "Tarocco" blood orange group to above disease symptoms clearly indicate as "Tarocco Nucellare 57-1E-1," "Tarocco Tapi," "Tarocco Sant'Alfio," and "Tarocco Catania" accessions should be preferred to remaining Tarocco ones. A broad degree of tolerance or susceptibility was also observed within other Citrus group as it happens for tolerant lemon "Femminello Zagara Bianca," thus demonstrating a putative resource for further studies to employ in a breeding program for genetic improvement of Citrus. [ABSTRACT FROM AUTHOR]