Molecular Characterization of Virus Infecting Momordica charantia Linn and the Application of Trichoderma viride as Biocontrol Agent in Baccocco Cross River State, Nigeria

Momordica charantia Linn, commonly called bitter-melon or ampalaya, is a vigorous, tendril-bearing, frost tender, annual vine of the cucurbitacae family reported to play significant role in health and nutrition. Chlorotic spot symptoms were observed on this plant during a visit to some Gardens in Baccocco Cross River State, Nigeria in 2021. The aim of this study was to identify the virus infecting this plant and investigate the ability of Trichoderma viride to control the virus. Infected leaf samples of M. charantia were collected and maintained on young seedlings of cucumber through mechanical inoculation which was further used to test the ability of Trichoderma viride as biocontrol agent, the sample was further tested against RT-PCR. Result obtained from Gene sequence analysis revealed 87 % nucleotide sequence identity with Morroccan watermelon mosaic virus. This is the first report of MWMV infecting M. charantia in Nigeria. The result further showed that Trichoderma viride was very effective in the control of virus the pathogen.

First report of a secovirus associated with mountain celery chlorotic spot disease in Heilongjiang, China

Mountain celery (Heracleum moellendorffii Hance), an edible perennial herb of Northeast Asia, is sporadically cultivated as a vegetable crop or for medicinal purposes in Northeast China and Korea [1]. In July 2019, a small field of mountain celeries showing chlorotic spots was found in Wangkui, Heilongjiang, China. A small-RNA (sRNA) library was constructed with equal amounts of leaf tissues of a diseased mountain celery and a tomato sample showing mottling symptom from a nearby field using the TruSeq small RNA library preparation kit (Illumina). The library was sequenced by the HiSeq 4000 sequencer at Lianchuan Biotechnology Co., Ltd (Hangzhou, China). After trimming adaptor sequences and discarding low quality reads by Cutadapt [2], the remaining 6,949,946 reads of 17 to 27 nucleotides (nt) were de novo assembled as described [3]. The resulting 395 contigs were searched against the GenBank viral sequence database using the BLASTn and BLASTx algorithms. Twenty-three contigs showed high nt sequence similarities (89-100%) to the genomic sequence of tomato mosaic virus (ToMV). The deduced amino acid (aa) sequences of thirty contigs had 22-96% aa sequence identities to viruses in the family Secoviridae, e.g., surrounding non-legume associated secovirus (snLaSV) and lettuce secovirus 1 (LSV-1). No contig homologous to the genomic sequences of other plant viruses was identified. Total RNAs were extracted from the mountain celery and tomato separately and reverse transcribed into cDNAs by random hexamer plus Oligo-dT(18) using the Super® IV Reverse Transcriptase (Invitrogen, Shanghai, China). Polymerase chain reactions (PCR) showed that the secovirus was derived from the mountain celery, whereas the tomato was infected by ToMV. The genome of this secovirus was determined by reverse transcription (RT)-PCR and rapid amplification of cDNA ends (RACE). Amplicons were cloned and Sanger sequenced with at least three independent clones per amplicon. Sequences were assembled by the SeqMan Pro 7.1.0 in the Lasergene (DNASTAR, Madison, WI). The genome of this virus is composed of two RNAs of 6,616 and 5,356 nt (excluding the polyadenylic acid tails) (GenBank accession nos. MW143070 and MW143071, respectively). The thirty contigs assembled from sRNAs could be mapped to the genome. Pairwise sequence analyses showed that RNA1 and RNA2 and their encoded polyproteins shared the highest nt (82.7% and 82.2%) and aa (93.4% and 91.8%) sequence identities with the respective RNAs (GenBank accession nos. MN412739 and MN412740) and their encoded polyproteins of snLaSV [4]. In the phylogenetic trees, this virus sequence clustered with snLaSV and LSV-1 in a separate branch neighboring viruses of the subgenus Stramovirus or Satsumavirus in the genus Sadwavirus. These results suggest that this virus is an isolate of the unclassified snLaSV and was referred as snLaSV-CHN. RT-PCR with primers SecoR1-3700F and SecoR1-5100R confirmed the presence of snLaSV-CHN in other mountain celeries (11 of 23 tested) showing chlorotic spots symptoms but not in healthy ones from the same field. To the best of our knowledge, this is the first report of snLaSV infecting mountain celery in China and a more orthodox name, mountain celery chlorotic spot virus (MCCSV), is tentatively proposed. Our findings provide a better insight of the distribution and host range of this virus and further surveys are necessary to determine its incidence and damage in mountain celery. Funding: This study is financial supported by the Program for the Scientific Activities of Selected Returned Overseas Professionals in Heilongjiang Province (Grant No. 2018QD0002) and the China National Funds for Excellent Young Scientists (Grant No. 32022071). References Son, H. J. 2020. Food Sci Nutr. 9:514. Martin, M. 2011. EMBnet J. 17:10. Che, X., et al. 2020. Plant Dis. 104: 3085. Gaafar, Y. Z. A., et al. 2020. Front Microbiol. 11: 583242.

HISTOPATHOLOGICAL PATTERNS OF LESIONS CAUSED BY TWO DICHORHAVIRUS

Different from most plant viruses, Brevipalpus mite-transmitted viruses (BTV) cause localized infection, not being able to systemically invade the infected plant. To broaden the specter of the histopathological changes in leaf tissues induced by BTV infection, we examined the tissue organization of leaf lesions caused by the infection of two additional representatives of dichorhaviruses, Clerodendrum chlorotic spot virus (ClCSV) and Coffee ringspot virus (CoRSV). In general, tissue alterations within the lesions followed the pattern noticed in CiLV-C and CiLV-N infection. In all analyzed lesions, necrotic cells form the central region that is surrounded by a chlorotic halo where hypertrophied cells commonly occur. Presence of reactive oxygen components were also a characteristic of the chlorotic halo. Though more cases of localized lesions on leaves infected by more BTV, remains to be analyzed, it seems that these lesions respond similarly upon infection by BTV, either Cile- or Dichorhavirus.

Distribution Pattern of Thrips (Thysanoptera: Thripidae) and Tomato Chlorotic Spot Virus in South Florida Tomato Fields

Tomato chlorotic spot virus (TCSV) is an orthotospovirus that causes a devastating disease in tomato (Lycopersicon esculentum Miller). TCSV emerged recently in South Florida. Studies were conducted in three commercial tomato fields in Miami-Dade County, Florida during the vegetable-growing seasons from October to April in 2015 through 2017. Each year, data were collected at 3, 6, and 9 wk after transplanting at various distances from the edges of each fields. Based on 3 yr total samples, three species of thrips were commonly observed melon thrips, Thrips palmi Karny (62.16 ± 0.79%), being the most abundant species followed by common blossom thrips, Frankliniella schultzei Trybom (21.55 ± 0.66%), and western flower thrips, Frankliniella occidentalis (Pergande) (16.26 ± 0.61%). Abundance of all thrips and TCSV infected plants was high at the edge of a tomato field 3 wk after transplanting with significantly fewer infected plants toward the center of the field. The distribution patterns of thrips and TCSV in various fields were mostly regular and aggregated across the sampling dates during the study period. Abundance of TCSV symptomatic plants and thrips species was high at the edge of the field and increased over time. The number of samples required to accurately determine population density of thrips was calculated by using three precision levels (0.10, 0.20, 0.30) at three predetermined densities of thrips (0.10, 0.20, and 0.40 per sample). This information will provide guidelines to growers, crop protection personnel, agricultural scouts, and researchers to develop a sustainable thrips and tospovirus management program.

Outbreaks of Tomato Chlorotic Spot Tospovirus in Commercial Tomato Fields and Effectiveness of Different Management Measures in South Florida

Tomato chlorotic spot tospovirus (TCSV) is an emerging tospovirus in south Florida. TCSV has caused significant damage to tomato production since its discovery in the United States in 2012. Effective measures for managing tomato chlorotic spot (TCS) disease have not been determined in commercial production fields except for planting resistant/tolerant tomato cultivars. In this study, the distribution of TCS in commercial tomato fields was investigated, and the two grower-implemented control measures, the use of resistant tomato cultivars and UV-reflective plastic mulch to repel TCSV vectors, were evaluated for any effect on the incidence of infection or disease when a severe outbreak occurred during the 2018 to 2019 season. A gradient TCS disease was found throughout the field planted with the susceptible cultivar ‘Sanibel’, suggesting a dispersal of the vectors from external sources and the influence of wind direction on disease distribution. Results from the surveys showed that the resistant/tolerant tomato cultivar ‘Red Bounty’ had significantly (P < 0.05) lower infection with TCSV compared with the susceptible cultivar Sanibel on the same type of plastic mulch in adjacent fields. UV-reflective plastic mulch significantly reduced TCS incidence in the susceptible tomato cultivar Sanibel compared with the standard white plastic mulch. This study provided first-hand support for recommendations to effectively manage TCS in tomato fields in south Florida.

Field Identification and Management of Greasy Spot Disease

Greasy spot is a disease that's frequently found in tropical and semitropical regions where citrus cultivars are grown. The disease is caused by Mycosphaerella citri. Symptoms appear as yellow to dark brown to black lesions occurring first on the underside of mature citrus leaves (Fig. 1). As the lesions develop on the underside of the leaves, they become darker and a corresponding chlorotic spot will appear on the upper leaf surface. These yellow (chlorotic) spots occur when infected cells fail to develop chlorophyll. Lesions are more yellowish and diffuse on lemons and grapefruit and more raised and darker on tangerines. Affected leaves fall prematurely from the tree during the fall and winter resulting in reduced tree vigor and yield. Greasy spot also infects the fruit of grapefruit trees producing rind blotch. This document is HS-1016, one of a series of the Horticultural Sciences Department, UF/IFAS Extension. Original publication date May 2005. HS-1016/HS263: Field Identification and Management of Greasy Spot Disease (ufl.edu)