Abstract:

Medicago sativa is an important forage， but the infection with alfalfa virus disease seriously affects the yield and nutritional quality of alfalfa. In this study， the virus pathogens of alfalfa samples， which exhibited mosaic， wrinkled， and curled leaves， collected from Botanical Garden of Shanxi Agricultural University were identified by small RNA deep sequencing technology and RT-PCR/PCR methods. It was found that the diseased leaf samples were co-infected by alfalfa mosaic virus （AMV）， pea streak virus （PeSV）， alfalfa dwarf virus （ADV） and alfalfa leaf curl virus （ALCV）. The whole genome sequence of ALCV isolate SXTG （OP748371） was obtained by PCR amplification. Sequence analysis showed that the complete sequence of ALCV isolate SXTG shared the highest similarity with the ALCV isolate Colonia Dora （MG792026）， namely 97.34%. Sequence alignment analysis of the AMV CP gene （OP748369） nucleoside sequence and its encoded amino acid sequences showed that the AMV isolate SX had the highest similarity with the AMV isolate ACat （MW835977）， with nucleotide and amino acid similarities of 99.24% and 99.54%， respectively. Similarly， the amplified ADV CP gene sequence was uploaded to GenBank， the registration number OP957285 was obtained and the isolate was named ADV Shanxi Taigu alfalfa isolate （SXJZ）. Sequence analysis showed that the isolate SXJZ had the closest genetic relationship with ADV isolate N1 （MZ221810）， with an amino acid sequence similarity of 99.43%. Further sequence alignment analysis of the amino acid （OQ108501） encoded by PeSV CP gene showed that the similarity of the amino acid encoded by the coat protein of the Shanxi alfalfa isolate （SXJZ） and other PeSV isolates was 100%. This is the first time that the compound infection of ALCV， ADV， AMV and PeSV has been detected in alfalfa plants in Shanxi Province. These results will help to understand the molecular evolution of the virus disease infecting alfalfa and provide a theoretical basis for the prevention and control of the virus disease.

Key words: Medicago sativa, alfalfa mosaic virus, alfalfa leaf curl virus, alfalfa dwarf virus, pea streak virus, sequence analysis