Identification And Molecular Characterization Of Fig Viruses In China

The common fig(Ficus carica) belonging to the family Moraceae the genus Ficus is a perennial wooden plant. It is considered to be one of the earliest domesticated fruit trees. Viral diseases are important threat to fig production. The most common of these disease is Fig mosaic disease(FMD) which occurs in almost all the fig-planted regions in the world. FMD w as frequently found in Xinjiang China in recent years. However, the distribution of FMD and presence of fig viruses in China are still unclear. In this study, a survey was performed to identity the occurrence and distribution of FMD and detect related fig viruses using electron microscopy(EMS), next generation sequencing, PCR/RT-PCR. Molecular characters of some viruses occurred in China were determined. The main results obtained in this study were shown as following:1. The survey of FMD was carried out in Xinjiang Uygur Autonomous Region( Atushi, Kashgar, Aksu, Urumqi and Hotan), Jiangsu province(Suqian and Yangzhou), and Beijing. FMD was mainly found in Atushi and Kashgar of Xinjiang but not found in Jiangsu and Beijing. More than 86% of the trees in these two regions showed typical symptoms of FMD, indicating that FMD is common only in Xinjiang.2. A total of 252 fig leaf samples were collected during the survey of FMD. Viral detection of these samples showed existence of five different fig viruses: Fig mosaic virus(FMV), Fig badnavirus 1(FBV-1), Fig fleck-associated virus(FFkaV), Fig leaf mottle-associated virus 1(FLMa V-1), and Fig mild mottle-associated virus(FMMaV). FLMa V-1 and FMMaV were detected only in few samples. In contrast, FMV and FFka V were detected in more than 40% of all the collected samples. The positive samples for these two viruses were mainly collected from Xinjiang. Moreover, FBV-1 was detected with the highest rate and was able to be found in almost all fig production areas. In a word, FBV-1, FMV, and FFkaV were three main fig viruses in China.3. FMV, FFkaV, and FLMa V may be associated with FMD in China. FMV could be found in almost all diseased fig leaf sample, indicating a strong relationship of this virus with FMD. It is important to note that FFkaV and FLMa V were present in diseased fig leaf samples with relative high detection rate, which suggests that complexity of the symptoms of FMD may be associated with mixed infection of FFkaV and FLMaV with FMV.4. New strains of FBV-1, FFkaV and FLMa V-1 and related novel virus may exist in Chinese fig samples. i) The gene of RT/RNase H was amplif ied from Chinese fig samples using the degenerate primers of the genus Badnavirus. The obtained sequence of this viral gene only showed 74% of sequence similar ity with this gene of FBV-1. The sequence similar ity is lower than the standard for defining a new species in genus Badnavirus. This indicated that the Chinese isolate of F BV-1 may be a new species. ii) The complete genome of a Chinese FFkaV isolate contained 6723 nucleotides and encoded three open reading frames(ORFs). Unlike the reported FFkaV isolated, the Chinese FFkaV isolate contained ORF3 and a longer 5 terminal noncoding region. The distinctive genomic organization of the Chinese FFkaV isolate implied existence of a novel viral species. iii) A Chinese FLMa V isolate showed low sequence similarity with those reported isolates of this virus, indicating that the Chinese FLMaV isolate may be a new strain or a novel virus belong to the family Closteroviridae.This study performed a survey of fig mosaic disease in several major fig producing areas in China and revealed the occurrence of different fig viruses, some of which may be associated with fig mosaic disease. The distribution of these different fig viruses was also observed. In addition, possible economic loss was evaluated based on the presence and distribution of the fig mosic disease. The results of this study supply basic data for understanding the epidemic and spread of fig mos ic disease in China, which has signif icant implication for controling this disease and ensuring healthy development of fig industry in China.