G. P. Wang

Genome Sequence of the Edible Cultivated Mushroom Lentinula edodes (Shiitake) Reveals Insights into Lignocellulose Degradation.

Lentinula edodes, one of the most popular, edible mushroom species with a high content of proteins and polysaccharides as well as unique aroma, is widely cultivated in many Asian countries, especially in China, Japan and Korea. As a white rot fungus with lignocellulose degradation ability, L. edodes has the potential for application in the utilization of agriculture straw resources. Here, we report its 41.8-Mb genome, encoding 14,889 predicted genes. Through a phylogenetic analysis with model species of fungi, the evolutionary divergence time of L. edodes and Gymnopus luxurians was estimated to be 39 MYA. The carbohydrate-active enzyme genes in L. edodes were compared with those of the other 25 fungal species, and 101 lignocellulolytic enzymes were identified in L. edodes, similar to other white rot fungi. Transcriptome analysis showed that the expression of genes encoding two cellulases and 16 transcription factor was up-regulated when mycelia were cultivated for 120 minutes in cellulose medium versus glucose medium. Our results will foster a better understanding of the molecular mechanism of lignocellulose degradation and provide the basis for partial replacement of wood sawdust with agricultural wastes in L. edodes cultivation.

First Report of Colletotrichum fructicola Causing Bitter Rot of Pear (Pyrus bretschneideri) in China

Pyrus bretschneideri cv. Dangshansuli is the most important commercial Asiatic pear cultivar worldwide. In recent years, a fruit rot disease of unknown etiology have caused considerable fresh market losses in the Dangshansuli production operations in Dangshan county, Anhui Province, China. Fresh market losses typically range from 60 to 90% and in 2008 were estimated at US

First Report of Cherry necrotic rusty mottle virus on Stone Fruit Trees in China

150 million. Symptomatic mature Dangshansuli pears were collected from an orchard in Dangshan County in February 2008. A thin section (about 1 mm3) of symptomatic tissue was sterilized in a bleach and placed on potato dextrose agar (PDA) medium for isolation. From all fruit, a single fungus was recovered displaying gray-white dense aerial mycelium. Identical fungi were isolated from six additional symptomatic Dangshansuli pears collected from other orchards in the county. Pathogenicity tests using one isolate (DS-0) were conducted in triplicate by placing 4 mm diameter discs from 7-day-old PDA plates onto the mature Dangshansuli pear fruit that were incubated in an incubator at 25°C with a 12-h photoperiod for 30 days. An equal number of noncolonized PDA inoculations were included as a control. Isolate DS-0 caused symptoms similar to those in the field within 7 days and complete collapse of cortical tissues within 30 days. No symptoms were observed on control fruit. Round brownish lesions with a diameter of about 3 cm on inoculated fruit was populated by sunken, rotiform acervuli on which numerous, colorless, oblong single cell shape conidia with width/length of 6 × 20 μm were produced. A comparison of morphology and sequence analysis of the ribosomal internal transcribed spacer (ITS) regions in pre- and post-inoculation cultures from inoculated fruit confirmed the presence DS-0. To further characterize DS-0, aliquots of extracted genomic DNA from the fungus were subjected to PCR amplification and sequencing of seven gene regions from the ITS, actin (ACT), β-tubulin 2 (TUB2), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), manganese-superoxide dismutase (SOD2), chitin synthase (CHS-1), and calmodulin (CAL), using the primers listed by Weir et al (4), except for the primer pair of ITS1 (5-TCCGTAGGTGAACCTGCGG-3) and ITS4 (5-TCCTCCGCTTATTGATATGC-3) for ITS amplification, and SODglo2-R (5-TAGTACGCGTGCTCGGACAT-3) and SODglo2-R (5-TAGTACGCGTGCTCGGACAT-3) for TBU2 amplification. Two or three clones of PCR products of each gene were sequenced and compared (GenBank Accession Nos. KC410780 to KC410786) to published data at http://www.cbs.knaw.nl/colletotrichum . The result indicated that DS-0 shared the highest similarity of 99.91% with Colletotrichum fructicola, corroborating numerous reports of Colletotrichum spp. causing bitter rot of pear on P. pyrifolia (1,2,3,4). C. fructicola was only recently reported as causing bitter rot of P. pyrifolia (4) and to our knowledge, this is the first report of C. fructicola causing bitter rot of P. bretschneideri, which will help producers select the best management practices for this devastating disease. References: (1) P. F. Cannon et al. Stud. Mycol. 73:181, 2012. (2) N. Tashiro et al. J. Gen. Plant Pathol. 78:221, 2012. (3) G. K. Wan et al. Mycobiology 35:238, 2007. (4) B. S. Weir et al. Stud. Mycol. 73:115, 2012.

First Report of Cherry green ring mottle virus on Cherry and Peach Grown in China

During the growing seasons of 2010 through 2012, leaf tissues from 206 stone fruit trees, including one flowering cherry, three sour cherry, six nectarine (Prunus persica L. var. nucipersica Schneider), 14 apricot, 24 plum (P. domestica L.), 41 sweet cherry, and 117 peach [P. persica (L.) Batsch] trees, grown in six provinces of China, were randomly collected and tested for the CNRMV infection by RT-PCR. Out of those sampled trees, 37 showed shot holes and vein yellowing symptoms. Total RNA was extracted from leaves using the CTAB protocol reported by Li et al. (2). The primer pair CGRMV1/CGRMV2 (1) was used to amplify a fragment of 949 bp from CNRMV genome, which includes the CP gene (804 bp). PCR products with the expected size were detected in one sweet cherry, one apricot, one peach, one plum, and two sour cherry plants. However, no correlation between PCR data and symptom expression could be found. PCR products were cloned into the vector pMD18-T (TaKaRa, Dalian, China). Three independent clones from each isolate were sequenced by Genscript Corp., Nanjing, China, and sequences were deposited in the GenBank under accession nos. JX491635, JX491636, JX491637, JX648205, and JX648206. Results of sequence analysis showed that sequences of the five CNRMV isolates shared the highest nt (99.0 to 99.6%) and aa (98.9 to 100%) similarities with a cherry isolate from Germany (GenBank Accession No. AF237816). The sequence of one isolate from a peach tree (JX648205) was divergent and shared only 84.7 to 86.1% nt and 94.4 to 95.1% aa similarities with those cp sequences. Clones intra each isolate shared more than 99% nt similarities. To confirm CNRMV infection, seedlings of peach GF 305 were graft-inoculated with bud-woods from a peach and a sweet cherry tree, which was positive to CNRMV and also two other viruses: Cherry green ring mottle virus (CGRMV) and Plum bark necrosis stem pitting-associated virus (PBNSPaV), as tested by RT-PCR. Grafted seedlings were kept in an insectproof greenhouse and observed for symptom development. In May of the following year, some newly developed leaves of inoculated seedlings showed vein yellowing, ringspot, and shot hole symptoms. Results of Protein A sandwich (PAS)-ELISA using an antiserum raised against the recombinant CP of a CNRMV isolate (unpublished) and RT-PCR confirmed CNRMV infection in inoculated trees. In addition to CNRMV, tested seedlings were also found to be infected with CGRMV and PBNSPaV by RT-PCR. To our knowledge, this is the first report on the occurrence of CNRMV on stone fruit trees in China, and also the first record of the CNRMV infection in peach and plum plants. Given the economic importance of its hosts and the visible symptoms of the viral disease, it is important to prevent the virus spread by using virus-tested propagation materials. References: (1) R. Li and R. Mock. J. Virol. Methods 129:162, 2005. (2) R. Li et al. J. Virol. Methods 154:48, 2008.

Biological and Molecular Characteristics of a Novel Partitivirus Infecting the Edible Fungus Lentinula edodes

Cherry green ring mottle virus (CGRMV; a member of the genus Foveavirus in the family Flexiviridae) has a single-stranded, positive-sense RNA genome of approximately 8.4 kb (4). The viral infection on several Prunus spp. has been mainly reported in Japan, New Zealand, and some countries in Africa, Europe, and North America (3). The virus can cause leaf yellowing on sour and tart cherry. Sweet cherry plants are symptomless hosts of the virus. During the growing season of 2010, leaf samples were collected randomly from one ornamental cherry (Prunus serrulata L.) and 26 sweet cherry (P. avium (L.) L.) plants grown in Shangdong and Henan provinces in northern China and 64 peach (P. persica L. Batsch) plants grown in Hubei Province in central China and tested for the presence of CGRMV by reverse transcription (RT)-PCR. Total RNA was extracted from leaves using the CTAB protocol reported by Li et al (2). Primer set, CGRMV1/CGRMV2 (1), was used for the amplification of a 949-bp fragment, which contains the complete CP gene of 807 bp. PCR products with the expected size were identified in one ornamental cherry, seven sweet cherry, and eight peach plants. Although some of sampled plants showed leaf chlorosis, we did not find the specific association between the symptom and CGRMV infection. The obtained PCR products were cloned into the vector pMD18-T (TaKaRa, Dalian, China). Three independent clones from each isolate were sequenced by Genscript Corp., Nanjing, China. Results showed that CP sequences from the Chinese CGRMV isolates shared 87.7 to 99.8% nucleotide and 93.3 to 100% deduced amino acid similarities, and clones intra each isolate shared more than 99% nt similarities. The CP gene sequences of two representative isolates from cherry (YT-Ch-1) and peach (Pe-HB-18) were submitted to GenBank with Accession Nos. HQ539656 and JF810672, respectively. The neighbor-joining phylogenetic trees generated with nucleotide and amino acid sequences of CP genes by Clustal X v1.8 revealed that all Chinese CGRMV isolates fell into two well-resolved clades. Most of the Chinese CGRMV isolates (12 of 16 isolates, including the isolate YT-Ch-1) were grouped in a large clade represented by isolate ITA5 (GenBank Accession No. AF533159). Four isolates from peach (including the isolate Pe-HB-18) clustered into another clade represented by isolate ITA6 (GenBank Accession No. AF533160). In July 2010, peach GF305 seedlings were inoculated by side grafting with budwoods from two CGRMV positive cherry plants. In May 2011, some newly developed leaves from all inoculated plants showed vein yellowing. The CGRMV infection in these inoculated peach GF305 plants was detected by RT-PCR and protein A sandwich-ELISA using antiserum raised against the recombinant CP of CGRMV isolate YT-Ch-1 (unpublished data). These results further confirmed the CGRMV infection on field cherry plants as detected by RT-PCR. To our knowledge, this is the first record of the presence of CGRMV in ornamental and sweet cherry and peach plants in China, which provides valuable information for further evaluating the sanitary status of the virus in sweet cherry and peach orchards in China. References: (1) R. Li and R. Mock. J. Virol. Methods 129:162, 2005. (2) R. Li et al. J. Virol. Methods 154:48, 2008. (3) K. G. Parker et al. USDA. Agric. Handb. No. 437:193, 1976. (4) Y. Zhang et al. J. Gen. Virol. 79:2275, 1998.

First report of Plum bark necrosis stem pitting-associated virus in stone fruit trees in China.

A new partitivirus named Lentinula edodes partitivirus 1 (LePV1) was isolated from a diseased L. edodes strain with severe degeneration of the mycelium and imperfect browning in bag cultures. The nucleotide sequences of LePV1 dsRNA-1 and dsRNA-2 were determined; they were 2,382 bp and 2,245 bp in length, and each contained a single ORF encoding RNA-dependent RNA polymerase (RdRp) and coat protein (CP), respectively. The purified virus preparation contained isometric particles 34 nm in diameter encapsidating these dsRNAs. Phylogenetic analyses showed LePV1 to be a new member of Betapartitivirus, with the RdRp sequence most closely related to Grapevine partitivirus. RT-PCR analysis showed that 27 of the 56 Chinese L. edodes core collection strains carry LePV1, with the virus being more common in wild strains than cultivated strains. In addition, qPCR analysis suggested that coinfection with L. edodes mycovirus HKB (LeV-HKB) could increase replication of the RdRp gene of LePV1. This study may be essential for the development of more accurate disease diagnostics and the formulation of control strategies for viral diseases in L. edodes.

First report of Cucumber mosaic virus in taro plants in China.

Plum bark necrosis and stem pitting disease was first observed on a Black Beaut plum (Prunus salicina Lindl.) in the United States in 1986 and later is several other countries. Plum bark necrosis stem pitting-associated virus (PBNSPaV; genus Ampelovirus, family Closteroviridae), the putative causal agent of the disease, infects many stone fruit species and causes decline, gummosis, flattening of scaffold branches, and stem necrotic pits in some diseased trees (1,3). An investigation of the incidence of PBNSPaV on stone fruit trees in China was conducted during 2009 and 2010. Leaf samples were collected from 47 trees, including peach (P. persica L. Batsch), nectarine (P. persica L. var. nucipersica Schneider), plum (P. domestica L.), ornamental plum (P. cerasifera Ehrb), sweet cherry (P. avium L.), and flowering cherry (P. serrulata L.), grown in Hubei, Henan, and Shandong provinces in central and northern China. Most of sampled trees showed trunk gummosis or stem pitting. The presence of PBNSPaV was tested by reverse transcription (RT)-PCR using primer set PBN195F/PBN195R (5-CTGGTCTTCCTGCTACTCCTT-3/5-AAGCCCACAATCTCAGAGCG-3) designed for the detection of the coat protein (CP) gene of the virus. Total RNA was extracted from leaves using a CTAB protocol reported by Li et al. (2). Products of the expected size of 190 bp were amplified from 20 samples, including seven cultivated peach, four ornamental peach, one nectarine, two plum, one ornamental plum, three sweet cherry, and two flowering cherry samples. All trees positive for PBNSPaV showed stem pitting symptoms on the base of the trunk. To further confirm these results, a 590-base region of the heat shock protein 70 homolog (HSP70h) gene was amplified by RT-PCR using primers HSP-P1/HSP-P2 (5-GGAATTGACTTCGGTACAAC-3/5-TCGAAAGTACCACCACCGAA-3). Amplicons of the expected size were cloned into the vector pMD18-T (TaKaRa, Dalian, China) and sequenced by Genscript Corp. (Nanjing, China). Sequences of 18 PBNSPaV isolates were deposited in GenBank with Accession Nos. JF810177-JF810194. Sequence comparisons showed that the partial HSP70h gene from the Chinese PBNSPaV isolates shared 82.2 to 100% nucleotide (nt) and 94.0 to 100% amino acid (aa) similarities between them and 83.6 to 99.1% nt and 94 to 100% aa similarities with the corresponding region of the other PBNSPaV isolates deposited in GenBank. In July 2010, peach GF305 seedlings were inoculated by side grafting with budwoods from two PBNSPaV-positive ornamental peach plants. In June 2011, grooving symptom was observed on the stems of the seedlings and the virus was detected by RT-PCR. The results further confirmed PBNSPaV infection in China. These results show that PBNSPaV and the associated disease occur in main cultivated and ornamental Prunus species in China. Given the importance and the devastating symptoms of the disease, it is important to prevent virus spread by using virus-tested propagation materials. References: (1) M. Al Rwahnih et al. Arch. Virol. 152:2197, 2007. (2) R. Li et al. J. Virol. Methods 154:48, 2008. (3) D. B. Marini et al. Plant Dis. 86:415, 2002.

First Report of Citrus exocortis viroid from Grapevine in China

Taro (Colocasia esculenta L. Schott) is an important crop worldwide. In China, the growing area and productivity of taro increased greatly in recent years. During the 2010 to 2013 growing seasons (from May to July), the incidence of Cucumber mosaic virus (CMV) in taro was determined. Leaf samples from 91 taro plants, including 26 plants of cv. Hongyayu grown in Jiangxi Province in eastern China, 33 plants of cv. Eyu no.1 grown in Hubei Province in central China, and 32 plants of cv. Baiyu grown in Guangxi Province in southwest China were collected randomly and tested for the presence of CMV by reverse transcription (RT)-PCR. Some sampled plants of cv. Hongyayu and Eyu no.1 showed leaf chlorosis or chlorotic spots, and most of the plants of these three cultivars showed feather-like mosaic symptom on their leaves, which was confirmed to be associated with the infection of Dasheen mosaic virus (DsMV) in our previous studies (3). Total RNA was extracted from leaves using CTAB protocol reported by Li et al. (1). Primer set forward 5-ATGGACAAATCTGAATCAACC-3/reverse 5-TAAGCTGGATGGACAACCCGT-3 (4) was used for the amplification of a 777-bp fragment, which contains the complete capsid protein (CP) gene of 657 bp. PCR products of the expected size were identified from 11 taro samples, including two samples of Hongyayu, three Eyu no.1, and six Baiyu plants. The result did not show any specific association between the symptoms observed and CMV infection. The obtained PCR products were cloned individually into the vector pMD18-T (TaKaRa, Dalian, China). Three independent clones derived from each product were sequenced by Genscript Corp., Nanjing, China. Pairwise comparison of CP gene sequences (Accession No. of one representation CP sequence: KF564789) showed 99.7 to 99.8% nucleotide (nt) and 99.1 to 99.5% deduced amino acid (aa) sequence identity among themselves, and 92.0 to 94.3% and 76.5 to 77.7% nt identities with corresponding sequences of CMV isolates in subgroup I and subgroup II (2), respectively. The maximum likelihood phylogenetic trees of nt and aa sequences generated by Clustal X v1.8 revealed that all these CMV isolates from taro in China fell into subgroup I. To further confirm the CMV infection, leaf saps of CMV infected taro plants of cv. Eyu no.1 were mechanically inoculated onto Pinellia ternate and Cucumis sativus. Plants of P. ternate showed local chlorotic lesions on the inoculated leaves and downward curl of newly grown leaves, and C. sativus showed local chlorotic lesions on the inoculated leaves and crinkle of newly grown leaves at 10 to 15 days post inoculation. The RT-PCR detection confirmed the CMV infection in those inoculated plants, and that the plants of P. ternate were also positive to DsMV, further complementing the results obtained above. To our knowledge, this is the first report of CMV occurrence in taro plants grown in China. Our results indicated that taro plants were widely infected by CMV isolates in subgroup I. This study provides important information for further evaluating the viral sanitary status of taro germplasm and improving the certification program of taro propagation materials in China. References: (1) R. Li et al. J. Virol. Methods 154:48, 2008. (2) P. Palukaitis et al. Adv. Virus. Res. 62:241, 2003. (3) S. M. Shi et al. Acta Hortic. Sin. 39:509, 2012. (4) P. D. Xu et al. Chinese J. Virol. 15:164, 1999.

Diversity and effect of Trichoderma spp. associated with green mold disease on Lentinula edodes in China

Citrus exocortis viroid (CEVd) can induce bark scaling, dwarfing, leaf epinasty, and fruit yield loss in susceptible hosts. In citrus, CEVd is reported from around the world, but in grape, it is reported from fewer locations (Australia, Brazil, California, and Spain [1]). In 2009, leaves were collected from 40 grapevines (of several different cultivars and species) from Henan, Hubei, Shandong, and Liaoning provinces, China. Total RNA or double-stranded RNA was extracted from the leaves by a described method (3) and subjected to reverse transcription with a random primer (Takara, Dalian, China) and then PCR with primer CEV-AM3 and CEV-AP3 (2). Results showed that the target DNA fragments of 372 bp long were amplified only from the symptomless leaves collected from two grapevines of cv. White Rose grown for approximately 26 years within a small garden in Hubei Province. Amplified products were recovered and cloned into pMD18-T (Takara) and 10 positive clones of each isolate were sequenced and aligned. For both isolates, 20% of the clones represented the same variant (CEVd-hn-g-1; GenBank Accession No. GU592444). It showed a max identity of 94 to 99% with the variants (GenBank Accession Nos. Y00328.1 and DQ471996.1) from grape registered in NCBI, 91 to 100% (GenBank Accession Nos. DQ431993.1 and DQ831485.1) from citrus, 91 to 98% (GenBank Accession Nos. EF488068.1 and EF488050.1) from broad bean, and 89 to 94% (GenBank Accession Nos. AY671953.1 and S67446.1) from tomato. To our knowledge, this is the first report of CEVd from grape in China. References: (1) M. Eiras et al. Fitopatol. Bras. 31:440, 2006. (2) H. J. Gross et al. Eur. J. Biochem. 121:249, 1982. (3) W. X. Xu et al. J. Virol. Methods 135:276, 2006.

First Report of Valsa leucostoma Causing Valsa Canker of Pyrus communis (cv. Duchess de' Angouleme) in China

Lentinula edodes, one of the most important edible mushrooms in China, is affected heavily by the infection of green mold that overgrows mushroom mycelia. We collected the diseased samples from main L. edodes cultivation regions in China to characterize the pathogen and to study the effect of Trichoderma spp. on L. edodes species. We identified six Trichoderma species, that is, T. harzianum, T. atroviride, T. viride, T. pleuroticola, T. longibrachiatum, and T. oblongisporum based on the internal transcribed spacer or tef1‐α sequences and morphology characteristics. In confrontation cultures on Petri plates or in tubes, and in L. edodes cultures in a medium containing Trichoderma metabolites, L. edodes mycelia were not only distorted and swollen, but also inhibited by Trichoderma isolates. It is not possible that adjusting pH value or temperature is used for controlling L. edodes green disease, because the growth of most of Trichoderma isolates and L. edodes shared similar pH and temperature conditions.