Full length articleGenetic diversity and geographic distribution of Bemisia tabaci species complex in Nepal
Introduction
Bemisia tabaci is an important pest of major vegetable and ornamental crops (De Barro et al., 2000, Cahill et al., 1996). It is a polyphagous pest and can cause damage in numerous plants via different mechanisms. For instance, it can cause direct damage through piercing and sucking sap from plant foliage, thus weakening plant growth and causing chlorosis as well as wilting of leaves. It can also cause indirect damage by producing and accumulating honeydew, which facilitates mold growth on foliage, thereby reducing photosynthetic rate and plant yield. In addition, B. tabaci transmit plant viruses belonging to the families Begomovirus, Carlavirus, Crinivirus, Ipomovirus, and Torradovirus. Since the last few decades, infestation of B. tabaci results in severe economic losses in tropical and subtropical regions (Jones, 2003, Navas-Castillo and Fiallo-Olivé, E., Sánchez-Campos, S., , 2011).
The distribution of B. tabaci is worldwide and highly diversed in genetic characteristics. It has been recognized as a complex of cryptic species that are morphologically indistinguishable from each other but genetically diverse (Dinsdale et al., 2010, Alemandri et al., 2012, Firdaus et al., 2013, Hadjistylli et al., 2016). Therefore, to identify the B. tabaci cryptic species, different molecular methods, including analysis of 16S rDNA, mitochondrial cytochrome oxidase 1 (COI), and ribosomal internal transcribed spacer 1 sequences, have been used to distinguish them over the past two decades (Frohlich et al., 1999, De Barro et al., 2000). The most widely used method is analysis of COI nucleotide sequence (Dinsdale et al., 2010, De Barro et al., 2011).
Within the complex, each cryptic species has their own genetic characteristicis such as different host palnt preference, pesticide resistance, and plant virus transmission ability (Horowitz et al., 2005, Jiu et al., 2007, Liu et al., 2007, Brown, 2010, Crowder et al., 2010, Gorman et al., 2010). Geographic distribution of B. tabaci can altered due to differences in cropping pattern, host plants, and other environmental conditions (Brown, 2010). Several studies have reported that at least 44 distinct cryptic species of B. tabaci are globally distributed (Boykin et al., 2012, Alemandri et al., 2012, Chowda-Reddy et al., 2012, De Barro et al., 2011, Dinsdale et al., 2010, Esterhuizen et al., 2013, Firdaus et al., 2013, Hu et al., 2018). Recently new cryptic species such as Asia II 13 and Spain 1 were also reported (Kanakala and Ghanim, 2019). At least 11 cryptic species (Asia I, Asia I India, Asia II 1, Asia II 5, Asia II 7, Asia II 8, Asia II 10, Asia II 11, Asia II 13, China 3, and MEAM1) have been already reported from South Asian countries including India, Pakistan, and Bangladesh which are located near to Nepal (Ellango et al., 2015, Prasanna et al., 2015, Kumar et al., 2016, Masood et al., 2017, Islam et al., 2018, Khatun et al., 2018, Kanakala and Ghanim, 2019). However, there has been no study on its genetic diversity and geographic distribution of B. tabaci species complex in Nepal.
The present study primarily aimed to identify the cryptic species of B. tabaci through analysis of COI nucleotide sequences based on their phylogenetic relationship and geographical distribution in Nepal.
Section snippets
B. tabaci samples
Adult B. tabaci individuals were collected from various host plants consisting of vegetables, fruits, and ornamental plants across 23 districts from east to west Nepal during the summer of 2017 and 2019 (Table 1). Samples were collected using an aspirator and were preserved in 95% ethanol and stored at −20 °C for molecular analysis. Approximately 10–100 adults were collected for each sample.
Genomic DNA extraction and polymerase chain reaction
Total genomic DNA was extracted from individual whitefly using a PureLink Genomic DNA Mini Kit
Identification of cryptic species of B. tabaci in Nepal
All over, the partial sequence (817 bp) of COI gene were amplified from 76 B. tabaci samples collected from 23 districts in Nepal. These sequences were submitted to the Genbank with the accession numbers MH990376–MH990395 and MN840088–MN840143 (Table 1; Fig. 1). Among them, three cryptic species—Asia I, Asia II 1, and Asia II 5—were identified using the maximum-likelihood phylogram of previously known sequences from the Genbank database (Fig. 2). The COI sequence variation among all the samples
Discussion
This is the first report on B. tabaci cryptic species in Nepal. From mitochondrial COI-based nucleotide sequence and pairwise sequence divergence analyses, we found three cryptic species, Asia I, Asia II 1, and Asia II 5, with nucleotide sequence variation of 0.12%–15.56%. However, invasive cryptic species, MEAM1 and MED were not detected in Nepal even the MEAM1 was already reported from the neighboring countries, India (Ellango et al., 2015) and Pakistan (Ahmed et al., 2011).
All these three
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the research grant (Z-1543086-2017-21-01) from Animal and Plant Quarantine Agency, Korea.
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