Occurrence and molecular characterization of Potato spindle tuber viroid(PSTVd) isolates from potato plants in North China

China is the largest potato producing country worldwide,with this crop representing the fourth largest staple food crop in China.However,the steady presence of Potato spindle tuber viroid（PSTVd） over the past five decades has a significant economic impact on potato production.To determine why PSTVd control measures have been ineffective in China,more than 1 000 seed potatoes collected between 2009 and 2014 were subjected to PSTVd detection at the Supervision and Testing Center for Virus-free Seed Potatoes Quality,Ministry of Agriculture,China.A high PSTVd infection rate（6.5%） was detected among these commercial seed potatoes.Some breeding lines of potato collected from 2012 to 2015 were also tested for PSTVd infection,revealing a high rate of PSTVd contamination in these potato propagation materials.Furthermore,comparison of the full-length sequences of 71 different Chinese PSTVd isolates revealed a total of 74 predominant PSTVd variants,which represented 42 different sequence variants of PSTVd.Comparative sequence analysis revealed 30 novel PSTVd sequence variants specific to China.Comprehensive phylogenetic analysis uncovered a close relationship between the Chinese PSTVd sequence variants and those isolated from Russia.It is worth noting that three intermediate strains and six mild strains were identified among these variants.These results have important implications for explaining the ineffective control of PSTVd in China and thus could serve as a basic reference for designing more effective measures to eliminate PSTVd from China in the future.

Analysis of fig tree virus type and distribution in China

The common fig（Ficus carica L.）was one of the earliest horticultural crops to be domesticated.A number of different viruses can infect fig trees including Fig mosaic virus（FMV）that has been detected in several commercial fig trees in Xinjiang,China.However,the distribution of FMV and other fig-infecting viruses in China remains unknown.In the present study,a sample from an ancient fig tree growing in Xinjiang was investigated by electron microscopy（EM）followed by PCR/RT-PCR,and FMV,Fig badnavirus 1（FBV-1）and Fig leaf mottle-associated virus 1（FLMaV-1）were detected.Fig leaf samples（252）from commercial orchards across China were subjected to PCR/RT-PCR,and FMV,FBV-1 and Fig fleck-associated virus（FFka V）were relatively abundant（44.4,48.4 and 44%,respectively）,while FLMaV-1 and Fig mild mottle-associated virus（FMMa V）were much scarcer（5.6 and 0.4%,respectively）,and FLMaV-2,Fig cryptic virus（FCV）,and Fig latent virus（FLV）were not detected.The presence of disease-causing viruses in fig trees presents a significant challenge for fig producers in China.This study may help to promote actions aimed at controlling fig viruses,especially FMV.

Effect of strawberry vein banding virus and strawberry mottle virus co-infection on the growth and development of strawberry

Strawberry mottle virus(SMoV)and strawberry vein banding virus(SVBV)cause diseases on strawberry plants,but the effect of coinfection of SMoV and SVBV on the growth,development,and defense system of strawberry(Fragaria×ananassa Duchesne)remains unknown.We investigated the effect of SMoV and SVBV coinfection on strawberry cultivar‘Benihope’.The results showed that stem diameter,leaf size,leaf number,relative chlorophyll content,total chlorophyll content,photosynthetic parameters,and stomatal aperture of SMoV and SVBV co-infected strawberry(VIS)plants were in a weaker level than uninfected control plants,indicating that viruses inhibited the growth and photosynthesis of strawberry plants.Furthermore,the initiation of flowering and fruiting stages of VIS plants were delayed by about three weeks compared with the controls,and the fruiting period was shortened,demonstrating that the reproduction of VIS plants was inhibited.Fruit quality was damaged in VIS plants due to a significant increase in fruit firmness and titratable acidity and decrease in total soluble solid content than control fruits.More dead cells and H_(2)O_(2) accumulated along the veins of VIS leaves,and the content of abscisic acid and catalase activity significantly increased,whereas anthocyanin content was lower than that of control plants.The results demonstrate that SVBV and SMoV coinfection inhibits the growth and development of‘Benihope’strawberry plants,and the plants respond to viruses by regulating stomatal aperture,the accumulation of ABA and antioxidants.To our knowledge,this study contributes information to understand how both viruses impair the strawberry growth and development for the first time.

Complete nucleotide sequences of two isolates of Cherry virus A from sweet cherry in China

Cherry virus A（CVA） is a member of the genusCapilovirus, in the familyBetalfexiviridae. The infection rate of CVA was high in sweet cherry in China. We determined the complete nucleotide sequences of two isolates of CVA from Tai’an, Shan-dong Province, China using high ifdelity PCR enzymes and speciifc primer pairs for amplifying long fragments in RT-PCR and RACE. The ful-length sequences from isolates ChTA11 and ChTA12 are both 7382 nucleotide （nt） long, excluding the poly（A） tail, encode two open reading frames （ORFs） and have similar genome organization to the two isolates in Gen-Bank. The complete nucleotide sequence of ChTA11 is 98.2 and 81.2% nt identity to the isolates from Germany and India in GenBank, respectively, and the ChTA12 isolate is 98.2 and 81.0% similar. Analysis of the nucleotide and amino acid sequences showed that the domain of unknown function （DUF1717） is more variable compared with other domains. This is the ifrst report of the complete nucleotide sequences of CVA isolates infecting sweet cherry in China.

The genome of herpes simplex virus type 1 is prone to form short repeat sequences

Herein, we report a very high content of simple sequence repeats (SSRs) covering 66.12% of the herpes simplex virus type 1 (HSV-1) genome when a low threshold is adopted to define SSRs, indicating that repeat sequence is a very important character of the HSV-1 genome. The repeats with two iterations account for 68.33% of the total repeats. In reality, the genome of HSV-1 is prone to form shorter repeat sequences. For mono-, di- and trinucleotide repeats, the repeat numbers decreased with the increase of repeats iterations, implicating that the formation tendency of SSRs might be from low iterations to high iterations. The high iterations SSRs might have subjected to strong selected pressure and survived to perform different functions. The analysis suggested that the repeats formation may be an essential evolutionary driving force for the HSV-1 genome, and the results might be helpful for studying the genome structure, repeats genesis and genome evolution of HSV-1.