Prevalence and molecular characterization of viruses causing diseases in Bombyx mori L. (Lepidoptera: Bombycidae) from different climatic regions of India

Abstract

A number of viruses are known to cause the disease in mulberry silkworm, Bombyx mori L. and cause significant cocoon crop loss to the farmers. The study has been undertaken to assess the prevalence of silkworm viral diseases caused by B. Mori Nucleopolyhedrovirus (BmNPV), B. mori Infectious Flacherie Virus (BmIFV) and B. mori Densovirus1 (BmDNV1) through external symptoms and molecular characterization from different climatic regions of India. During the intensive exploratory surveys in 2017, silkworm larvae with typical symptoms of BmNPV, BmIFV and BmDNV1 were collected across seven provinces from North India [Kashmir (temperate), Jammu, Ghumarwin in Himachal Pradesh, Dehradun in Uttarakhand (subtropical) and South India [Karnataka, Andhra Pradesh and Tamil Nadu (tropical)]. Dissection of diseased specimens confirmed the presence of virus through anatomical changes viz, size, shape and colour of organs after disease attack. The viruses were isolated and identified through PCR amplification of highly conserved genes. The results reveal that BmNPV, BmIFV and BmDNV1 are evenly prevalent across India. The infection percentage of BmNPV, BmIFV and BmDNV1 in North India (11.41 ± 1.21, 7.81 ± 0.67 and 7.40 ± 0.61) was significantly higher than South India (1.61 ± 0.17, 1.52 ± 0.14 and 1.62 ± 0.14), respectively. The highest prevalence of these viruses was observed from subtropical followed by temperate and tropical climate. The knowledge of the prevalence of these viruses in India and their synergism with bacteria and influence of other possible factors is important for preventing cocoon crop losses caused by viral diseases in India.

Patterns in Genotype Composition of Indian Isolates of the Bombyx mori Nucleopolyhedrovirus and Bombyx mori Bidensovirus

“…Among the various diseases, grasserie caused by BmNPV is the most severe and contagious disease of B. mori that prevails in all rearing seasons and climatic regions, with varying prevalence [ 6 ]. In the seven BmNPV isolates from India described in this study, a certain homogeneity in the northern (BmNPV-Ka, BmNPV-Gh) and southern (BmNPV-An, BmNPV-My and BmNPV-Sa) samples of India was described on the basis of selected PCR markers.…”

“…The virus samples used in this study were isolated from naturally field-infected B. mori larvae collected from different climatic regions of India: the temperate region of Kashmir (Ka), the subtropical areas of Jammu (Ja), Ghumarwin in Himachal Pradesh (Gh) and Dehradun in Uttarakhand (De), as well as the tropical locations of Mysore in Karnataka (My), Anantapur in Andhra Pradesh (An) and Salem in Tamil Nadu (Sa) ( Figure 1 , Table 1 ) [ 6 ]. Although the prevalence of BmNPV was found throughout the sericulture practicing areas of India, the selected locations were hot spots, where a heavy incidence of BmNPV was observed or reported.…”

“…The pupating larvae produce cocoons from which silk thread can be harvested. The major constraints for increased cocoon yield in sericulture are the occurrence of diseases such as grasserie, flacherie, muscardine and pebrine caused by virus, bacteria, fungi and microsporidia infection, respectively [ 4 , 5 , 6 ]. Viruses are considered the most important pathogens in silk moth rearing, causing serious and significant economic damage, and thus posing a serious threat to global sericulture [ 7 ].…”

“…To date, only one isolate from India (BmNPV-India) was entirely sequenced and characterized, with a genome size of 126,879 bp and 138 ORFs [ 18 ]. Isolates of BmNPV were found as the most serious and dominant viral pathogen in almost all the sericultural practicing areas, with a maximum prevalence of 17.32% in Ghumarwin, Himachal Pradesh, and an overall average infection percentage of 7.19% in India during 2017 [ 6 ].…”

Studies on Natural and Experimental Nucleopolyhedrovirus Infection of the Silkworm, Bombyx mori (Race: PMCSR2(SL)) by PCR

“…The pupating larvae produce cocoons from which silk thread can be harvested. The major constraints for increased cocoon yield in sericulture are the occurrence of diseases such as grasserie, flacherie, muscardine, and pebrine caused by viruses, bacteria, fungi, and microsporidia infection, respectively (Khurad et al, 2004;Ravikumar et al, 2011;Gani et al, 2018b). Viruses are considered the most important pathogens in silk moth rearing, causing serious and significant economic damage and thus posing a serious threat to global sericulture (Kumar et al, 1990).…”