IntroductionAbelmoschusesculentus (family: Malvaceae) otherwise known as bhendi, okra or lady’s finger is previously included in the genus Hibiscus; however,now it is recognized as a distinct genus ‘Abelmoschus’ due to itscaducous nature of the calyx (Dhankhar et al., 2005). The word ‘Abelmoschus’is originated from the Arabian word “abul-l-mosk” meaning “source ofmusk,” denoting to the musky smell of theseeds. Bhendi is widely cultivatedin the temperature regions of Asia, Africa andSouthern Europe (Charrier, 1984). Thisplant is thought to be the native of South Africa and the first recordedreference was from Egyptians in 1216 A.D (Lamont, 1999). However, ten species of bhendi plants are present in India, of which A. esculentusis the only cultivated species (Dhankar et al.
2005). Bhendi is an allopolyploid with the lowest chromosomenumber in A. angulus (2n=56) and thehighest in A. caillei (2n=100), whichis an amphiployploid between A. esculentus (2n=13-140) and A. manihot(2n=60-68) (Siemonsma, 1982).
Developing countries like Asia and Africacontribute more than 99% of okra cultivation compared with other parts of theworld. Globally, bhendi cultivation is occupying an area of 1.83 million withthe annual yield of 9.62 million metric tons (MT). India contributes first inthe world with 6.5 million metric tons (72% of the total world production) of bhendiproduced from over 0.5 million hectare land (FAOSTAT, 2014).
Bhendi is a multipurpose crop withhuge economical importance. The green immature pod is a rich source of vitamins,iron, dietary fibers, amino acids (lysine and tryptophan), potassium, calcium,magnesium, and other mineral constituents (Hughes, 2009). Its seeds are a richsource of oil (30-40%) and proteins (15-20%) (Gemede et al. 2015). Its matureseed and stems are ample source of crude fibre and used in paper industry (Kochlar, 1986). The roots and stems are used forcleaning cane-juice during brown-sugar preparation (Shetty et al. 2013).
Besides,it has been found to possess various pharmacological and medicinal propertiesagainst high-cholesterol, diabetes and cancer (Jenkins et al. 2005; Sabitha etal. 2011). Despite its economicalimportance, Bhendi production is massively affected by several abiotic andbiotic factors and yield losses due to biotic factors are quite significant(Jellis 2009). The major biotic factors include various pathogens like fungi,bacteria, virus, mycoplasma, and nematode. The mostserious diseases caused by these pathogens are damping-off (Macrophominaphaseolina, Pythium aphanidermatum, and Rhizoctonia solani),vascular wilt (Fusarium oxysporum), Cercospora blight (Cercosporamalayensis), powdery mildew (Erysiphe cichoracearum, Oidiumabelmoschi), root and stem rot (Phytophthorapalmivora), rootknot nematode (Meloidogyne sp.), leaf spot (Alternaria sp., Cercospora malayensis), bhendi yellow vein mosaic disease(Bhendi yellow vein mosaic virus),and enation leaf curl disease (Enationleaf curl virus) (Abdel-Rehim et al.
1992, Tripathi, 1994; Sastry andSingh, 1974; Jose and Usha, 2003; Fajinmi and Fajinmi, 2006 & 2010; Singh,1996; Chandran et al. 2013; Sanwal et al. 2014). Amongthese, viruses are considered as a serious threat to bhendi production and itis observed that this crop is susceptible to at least 19 different plantviruses (Brunt et al.
1990, Swanson and Harrison 1993). Of these, bhendi yellow vein mosaic virus (BYVMV)and enation leaf curl virus ELCuV) belongs to the genus begomovirus (family:Geminiviridae) cause significant losses in bhendi production in terms of both yieldand quality. The infected plants are found to be associated with heavyinfestations of the whitefly Bemisiatabaci, the vector of begomoviruses. The loss in yield, due to YVMV and/or ELCuVin bhendi was found ranging from 30 to 100% depending on the age of the plantat the time of infection (Singh, 1996, Venkataravanappa etal. 2013). The descriptionof the family Geminiviridae to which bhendi yellow vein mosaic virus and enation leaf curl virus belongs aredetailed below:The family: GeminiviridaeThefamily Geminiviridae includesplant-infecting viruses with circular ssDNA genomes that are encapsidated in a twinnedicosahedral (or geminate) capsid (Zhanget al.
2001; Bottcher et al. 2004, Hanley-Bowdoin et al. 1999). This family contains more than 209 members ofplant-infecting geminiviruses (Fauquet and Stanley, 2005). Geminiviruses aredistributed globally and infect both monocotyledonous and dicotyledonousplants. They are often responsible for serious yield losses in economically importantcrops, including cassava, chickpea, cotton, bhendi, tomato, maize and legumes(Moffat, 1999; Legg and Fauquet, 2004; Briddon, 2003; Briddon and Markham,2000; Jose and Usha, 2000; Moriones and Navas-castillo, 2000; Varma andMalathi, 2003).
Symptoms of geminivirus infections include yellowing, stunting,mosaic, curling, foliar crinkling, and/or striations. Based on the genomeorganization, host range, insect vector, and sequence relationships, viruses inthe family Geminiviridae are dividedinto nine genera, viz., Becurtovirus, Begomovirus, Capulovirus, Curtovirus,Eragrovirus, Grablovirus, Mastrevirus, Topucovirus,and Turncurtovirus (Brown etal.
2012; Varsani et al. 2017). These genera are named from the abbreviationsof the type members Beet curly top Iran virus (BCTIV, Becurtovirus), Bean golden mosaicvirus (BGMV, Begomovirus), Euphorbia caput-medusae latentvirus (EcmLV, Capulovirus), Beet curly topvirus (BCTV, Curtovirus), Eragrostiscurvula streak virus (ECSV, Eragrovirus),Grapevine red blotchvirus (GRBV, Grablovirus), Maizestreak virus (MSV, Mastrevirus),Tomato pseudo curlytop virus (TPCTV, Topocuvirus), and Turnip curly topvirus (TCTV, Turncurtovirus).
They are transmitted byleafhoppers (mastreviruses, becurtoviruses and curtoviruses), treehoppers(topocuviruses, grabuloviruses) and whiteflies (begomoviruses) (Buck, 1999;Jeske, 2009; ICTV 2017 (10th report)).