| Lotus(Nelumbo nucifera Gaertn.)belonging to Nymphaeaceae is a perennial aquatic herbaceous plant.According to its use,lotus is divided into lotus root,seed lotus and flower lotus.It is the largest aquatic vegetable cultivated in China with a long history.The products of lotus are rich in starch,proteins,vitamins,minerals and many other nutritional ingredients,which are deeply loved by domestic and foreign consumers.Asexual reproduction through rhizome is widely used in the production of lotus.The accumulation of diseases year by year is easy to lead to the degeneration of lotus root.At present,in terms of lotus,the diseases that have been reported are mainly the fungal diseases,including wilt rot and brown spot.And the relavant viruses that have been ever known are only lotus streak virus,Cucumber mosaic virus and Dasheen mosaic virus."Stiff lotus" is a common phenomenon wide distributed in the main producing area of lotus.Such lotus looks thin,stiff,with dark brown spots and streaks on the surface.In fact,these pots and streaks penetrate deeply below the epidermis.These symptoms seriously affect the quantity as well as quality of lotus.Previous studies have shown that "stiff lotus" may be caused by plant virus,but its symptoms are inconsistent with the above three viral symptoms.As a result,in this study,we detected and identified a kind of potyviruses,and studied its host range,distribution,genome structure,taxonomic status and genetic diversity.The main results are as follows:1.A kind of potyviruses was detected by high-throughput sequencing and RT-PCR.The 854 bp fragment was amplified,and BLAST showed that this virus shared a high similarity with Sweet potato latent virus(SPLV).And the virus can effectively infect the plants of Fabaceae,Chenopodiaceae,Cueurbitaceae and Solanaceae without obvious symptoms.The survey results showed that the detection rate of the potyviruses was 48.8%in 43 lotus samples collected in the main producing area of lotus in Jiangsu province,of which 12 samples were found to be“stiff lotus" with the detection rate up to 75%.It indicated that this virus was widely distributed in Jiangsu province.2.The whole genome sequence of lotus potyviruses is 10,081 nucleotide(nt),including a 143 nt 5' non-coding region,a 194 nt 3' non-coding region and a 9,741 nt open reading frame(ORF)encoding 3,247 amino acids.The nucleotide similarity between the virus and SPLV polyprotein was between 76.28%and 76.60%,the same as the standard of virus in Potyviridae of the latest International Committee on Taxonomy of Viruses(ICTV).There were four different sites for restriction enzyme cleavage between potyviruses and SPLV,and the lengths of PIPO encoded by them were quite different.In summary,the potyviruses found in lotus may be a new virus species,tentatively named Lotus latent virus,LLV.3.The phylogenetic analysis and genetic diversity analysis of the coat protein(CP)and first protein(P1)coding sequence of LLV showed that:LLV had a small genetic difference and could be divided into two groups:LLV-1 and LLV-2,among which most of the isolates were clustered in the LLV-2 group.Selective stress analysis revealed that LLV was under a strong negative selective pressure in the CP and P1 encoded proteins,which was similar to other reported potyviruses and might be related to the conserved functional domains of these two proteins. |
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