Dasheen mosaic virus (DsMV) is one of the major viruses affecting taro (Colocasia esculenta) production worldwide. Whole genome sequences were determined for two DsMV strains, Hawaii Strain I (KY242358) and Hawaii Strain II (KY242359), from taro in Hawaii. They represent the first full-length coding sequences of DsMV reported from the United States. Hawaii Strains I and II were 77 and 85% identical, respectively, with other completely sequenced DsMV isolates. Hawaii Strain I was most closely related to vanilla mosaic virus (VanMV) (KX505964.1), a strain of DsMV infecting vanilla in the southern Pacific Islands. Hawaii Strain II was most closely related to a taro DsMV isolate CTCRI-II-14 (KT026108.1) from India. Phylogenetic analysis of all available DsMV isolates based on amino acid sequences of their coat protein showed some correlation between host plant and genetic diversity. Analyses of DsMV genome sequences detected three recombinants from China and India among the six isolates with known complete genome sequences. The DsMV strain NC003537.1 from China is a recombinant of KJ786965.1 from India and Hawaii Strain II. Another DsMV strain KT026108.1 is a recombinant of Hawaii Strain II and NC003537.1 from China. The third DsMV strain KJ786965.1 from India is a recombinant of Hawaii Strain II and NC003537.1 from China. To our knowledge, this is the first report of recombination events in DsMV. Both Hawaii Strains I and II of DsMV were found widespread throughout the Hawaiian islands.

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Bacterial wilt caused by Ralstonia solanacearum is a destructive disease of many economically important crop species. A significant variation in wilt incidence and severity in eggplant and potato was observed among the growing areas surveyed. R. solanacearum isolates obtained both from eggplant and potato belong to biovar III, while isolates from eggplant belong to race 1 and isolates obtained from potato belong to race 3. Random amplified polymorphic DNA (RAPD) technique was used as a tool for assessing genetic variation and relationship among seven isolate groups of R. solanacearum viz., RsB-1, RsB-2, RsB-3, RsP-1, RsP-2, RsP-3 and RsP-4, consisting in a total of 28 isolates. Out of the RAPD markers used, amplification with four decamer primers produced 70 bands with sizes ranging from 100 to 1400 bp. Out of 70 bands, 68 bands (97.06%) were polymorphic and two bands (2.94%) were monomorphic amongst the seven R. solanacearum isolates group. The Unweighted Pair Group Method of Arithmetic Means (UPGMA) dendrogram constructed from Nei's genetic distance produced two main clusters of the seven isolates of R. solanacearum. The isolates RsB-1, RsB-2, RsB-3 and R-4 grouped in cluster І, while RsP-2, RsP-3 and RsP-4 grouped in cluster ІІ. The highest intra-variety similarity index (Si) was found in RsB-1 isolate (86.35%) and the lowest one in RsP-2 (56.59%). The results indicated that relatively higher and lower levels of genetic variation were found in RsP-3 and RsB-3, respectively. The coefficient of gene differentiation (G(st)) was 0.5487, reflecting the existence of a high level of genetic variations among seven isolates of R. solanacearum. Comparatively higher genetic distance (0.4293) and lower genetic identity (0.6510) were observed between RsB-2 and RsP-4 combinations. The lowest genetic distance (0.0357) and highest genetic identity (0.9650) were found in RsB-1 vs. RsB-2 pair. Thus, RAPD offers a potentially simple, rapid and reliable method to evaluate genetic diversity analysis in R. solanacearum.

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Papaya ringspot virus (PRSV) is the major constraint to papaya (Carica papaya) production in Bangladesh. Disease symptoms occurred in 90 to 100% of the plants surveyed. Full-length genomes of PRSV strains from severely infected papaya plants were determined using the Illumina NextSeq 500 platform, followed by Sanger DNA sequencing of viral genomes obtained by reverse-transcription PCR(RT-PCR). The genome sequences of two distinct PRSV strains, PRSV BD-1 (10,300 bp) and PRSV BD-2 (10,325 bp) were 74 and 83% identical to each other, respectively, at the nucleotide and amino acid levels. PRSV BD-1 and PRSV BD-2 were 74 to 75% and 79 to 88% identical, respectively, to other full-length PRSV sequences at the nucleotide level. Based on phylogenetic analysis, PRSV BD-2 was most closely related to PRSV-Meghalaya (MF356497) from papaya in India. PRSV BD-1 formed a branch distinct from the other PRSV sequences based on nucleotide and amino acid sequence comparisons. Comparisons of the genome sequences of these two strains with other sequenced PRSV genomes indicated two putative recombination events in PRSV BD-2. One recombinant event contained a 2,766-nucleotide fragment highly identical to PRSV-Meghalaya (MF356497). The other recombinant event contained a 5,105-nucleotide fragment highly identical to PRSV-China (KY933061). The occurrence rates of PRSV BD-1 and PRSV BD-2 in the sampled areas of Bangladesh were approximately 19 and 69%, respectively. Plants infected with both strains (11%) exhibited more severe symptoms than plants infected with either strain alone. The full-length genome sequences of these new PRSV strains and their distribution provide important information regarding the dynamics of papaya ringspot virus infections in papaya in Bangladesh.

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In this study, we describe the further genomic characterization of several pineapple mealybug wilt-associated virus (PMWaV) members of the genus Ampelovirus, family Closteroviridae, using high-throughput sequencing (HTS). PMWaV-2 is a necessary factor in the complex etiology of mealybug wilt disease of pineapple (MWP). The complete PMWaV-1 genome was described previously, but the genomes of PMWaV-2, PMWaV-3, and putative PMWaV-4 and PMWaV-5 species lack complete characterization. To further study MWP etiology through genomic characterization of PMWaVs, a cDNA library from total RNA of pineapple plants was generated and underwent HTS. A PMWaV-4 genome of 12,932 nucleotides was assembled from the HTS data. Proteins from the PMWaV-4 genome shared high amino acid similarity to those of PMWaV-1. The RNA-dependent RNA polymerase (RdRp), heat shock protein 70 homolog (HSP70h), and coat protein (CP) proteins of PMWaV-4 shared 88, 87, and 85% amino acid identity, respectively, to those of PMWaV-1 (AF414119) indicating PMWaV-4 is a distinct strain of PMWaV-1 but not a distinct ampelovirus species. Therefore, we suggest that PMWaV-4 be designated PMWaV-1 strain 4 (MN539275). Further, we used HTS to obtain a new isolate of PMWaV-1 (MN539276) and supplemented the available sequences of the genomes of PMWaV-2 (MN539272 and MN539273) and PMWaV-3 (MN539274) in their 5′-terminal regions.

Effect of seed treatment on seedling health of chili (BARI Morich 1) was studied at Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh. BAU Bio-fungicide (3% of seed weight), chitosan (1% solution), thiovit (0.3% of seed weight), compressed moist heat (54ºC for 15 minutes), neem leaf extract (1:1 w/v), garlic clove extract (1:3 w/v), ginger extract (1:2 w/v) and allamonda leaf extract (1:1 w/v) were employed as seed treating agents. The treated seeds were placed on moistened blotter paper. Data were recorded on percent germination, production of percent healthy seedling and seedling vigour of chili. The results of seed health testing showed that, five different seed borne fungi viz. Colletotrichum capsici, Curvularia lunata, Rhizopus stolonifer, Aspergillus flavus and Fusarium moniliforme were found to be associated with the tested chili seed samples. Among these fungi, Curvularia lunata was the most prevalent one which was followed by Rhizopus stolonifer, Colletotrichum capsici, Fusarium moniliforme and Aspergillus flavus. All the seed treating agents were found to be effective compared to control in controlling seed borne fungi for the blotter method. The highest percentage of germination (93.33%) was recorded when the seeds of BARI Morich 1 were treated with BAU Bio-fungicide, whereas the lowest percentage of germination (61.33%) was recorded in case of untreated seeds. The highest percentage of healthy seedling (95.33%) was recorded when the seeds were treated with BAU Bio-fungicide and allamonda leaf extracts, whereas the lowest percentage of healthy seedling (59.00%) was recorded in case of untreated seeds. The highest vigour index (681.59) was recorded when the seeds were treated with neem leaf extracts, whereas the lowest vigour index (214.66) was recorded in case of untreated seeds.