<Emphasis Type="Italic">Ageratum</Emphasis><Emphasis Type="Italic">yellow vein virus</Emphasis> isolated from tomato plants with leaf curl on Ishigaki Island,Okinawa, Japan

In 2005, severe leaf curling and yellowing were observed on tomato plants on Ishigaki Island. Because the symptoms were consistent with infection by a begomovirus, we used a polymerase chain reaction (PCR) with specific primers for begomovirus DNA-A and DNA satellite component (DNA-β) and detected products of the expected sizes from symptomatic tomato plant samples. DNA sequence analyses of the PCR products revealed that the symptomatic tomato plants were associated with Ageratum yellow vein virus (AYVV) infection. We confirmed AYVV transmission from the naturally infected weed host, Ageratum conyzoides, to healthy tomato plants by the insect vector Bemisia tabaci B biotype. This report is the first of AYVV occurrence in Japan.     

The first report of tomato foot rot caused by <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> AG-3 PT and AG-2-Nt and its host range and molecular characterization

Foot rot of mature tomato plants was found in four cities of Hokkaido, Japan, from 2004 to 2007. Six of eight isolates obtained from damaged tissues were identified as Rhizoctonia solani anastomosis group (AG)-3, and the remaining two isolates belonged to AG-2-1. We compared these isolates with nine reference isolates including the different subgroups in AG-3 (PT, TB and TM) and AG-2-Nt (pathogen of tobacco leaf spot) within AG-2-1 in terms of pathogenicity to tomato, tobacco and potato. All eight isolates caused foot rot on tomato. The six AG-3 isolates caused stem rot on young potato plants. While, all reference isolates of AG-3 PT causing stem rot of young potato plants incited foot rot on tomato. The two AG-2-1 isolates and an AG-2-Nt reference isolate caused severe leaf spot on tobacco leaves. The sequences of rDNA- ITS region and rDNA-IGS1 region of the AG-3 isolates showed high similarity to that of AG-3 PT isolates. Phylogenetic tree based on ITS and IGS1 regions of rDNA indicated that the AG-2-1 isolates from tomato formed a single clade with AG-2-Nt isolates and that they were separate from Japanese AG-2-1 isolates (culture type II). Pathogenicity tests and DNA sequence evaluation of the causal fungi revealed that the present isolates of AG-3 and AG-2-1 belonged to AG-3 PT and AG-2-Nt, respectively. This is the first report of tomato foot rot caused by R. solani in Japan.     

Distribution and multiplication of <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> in tomato plants with resistance derived from different origins

The distribution and multiplication of Ralstonia solanacearum in tomato plants of 11 resistant cultivars derived from different genetic sources and susceptible cultivar Ponderosa were examined. Bacterial multiplication in stems of resistant tomato plants was suppressed owing to the limitation of pathogen movement from the protoxylem or the primary xylem to other xylem tissues. The limitation was most conspicuous in Hawaii 7996. Grafting experiments indicated that the percentage of wilting of Ponderosa scions was less on Hawaii 7996 rootstocks than that on the most resistant rootstock (LS-89) used in Japan. Hawaii 7996 could be an alternative genetic source for breeding for resistance to bacterial wilt.     

The first occurrence of leaf mold of tomato caused by races 4.9 and 4.9.11 of <Emphasis Type="Italic">Passalora fulva</Emphasis> (syn. <Emphasis Type="Italic">Fulvia fulva</Emphasis>) in Japan

Tomato leaf mold caused by Passalora fulva was found on two tomato varieties carrying the Cf-9 gene in Japan, in 2007. The isolates obtained from Chiba and Fukushima were identified as race 4.9.11, and those from Gunma were races 4.9 or 4.9.11. This is the first report in Japan of tomato leaf mold caused by P. fulva strains that can overcome the Cf-9 gene.     

Transmission of <Emphasis Type="Italic">Tomato chlorotic dwarf viroid</Emphasis> by bumblebees (<Emphasis Type="Italic">Bombus ignitus</Emphasis>) in tomato plants

Quantitative PCR revealed that Tomato chlorotic dwarf viroid (TCDVd) was present in substantial amounts in viroid-infected tomato flowers. Healthy tomato plants were arranged in two different glasshouses, and plants were mechanically inoculated with TCDVd. Bumblebees (Bombus ignitus) were then introduced into the glasshouses to reveal whether the viroid was transmitted from infected source plants to neighbouring healthy plants. TCDVd infection was found in neighbouring tomato plants more than 1 month after the introduction of the bees, some of which expressed symptoms, in both glasshouses. Thus, bumblebees transmitted TCDVd from tomato to tomato by pollination activities.     

Characterization of Rehmannia mosaic virus isolated from chili pepper (<Emphasis Type="Italic">Capsicum annuum</Emphasis>) in Japan

In 2010, severe necrotic mosaic disease and fruit distortion were observed on greenhouse-grown chili pepper (Capsicum annuum cv. Fushimi-amanaga) plants in Kyoto Prefecture, Japan. Electron microscopic imaging and genomic RNA sequencing indicated that the virus responsible was a new isolate of Rehmannia mosaic virus (ReMV), which had not been previously reported in Japan. Although ReMV systemically infected many Solanaceae species, including chili pepper and tomato (Solanum lycopersicum), tobamovirus-resistance genes from species of Capsicum (L ^1a , L ² , L ³ , and L ⁴ ) and tomato (Tm-1, Tm-2, and Tm-2 ^a ) conferred resistance against ReMV.     

Repeated applications of Penicillium oxalicum prolongs biocontrol of fusarium wilt of tomato plants

The suppression of fusarium wilt of tomato achieved by Penicillium oxalicum (PO) applied one or several times (up to four) was assessed during three glasshouse experiments. The first application of PO (10⁶ conidia g^-1 substrate) to the growing substrate (peat and vermiculite, 1 : 1, v : v) was performed prior to its infestation with Fusarium oxysporum f. sp. lycopersici (FOL) (10⁴–10⁶ chlamydospores g^-1). Repeated applications of PO prolonged the duration of control of fusarium wilt especially when disease incidence was high. The timing of repeated applications of PO did not affect the efficacy of the control. Disease reduction was not associated with a decrease in density of FOL in the rhizosphere, irrespective of the number of applications of PO. Density of PO in the tomato rhizosphere was higher when repeated applications were made. No relationship was observed between reduction of disease and high densities of PO. Reasons for a longer disease reduction in tomato plants following several applications with PO are discussed.     

<Emphasis Type="Italic">Spongospora subterranea</Emphasis> soil contamination and its relationship to severity of powdery scab on potatoes

We investigated soil contamination by Spongospora subterranea f. sp. subterranea (Sss) and disease severity of powdery scab in 29 potato fields in Hokkaido, Japan, using a hydroponic culture method with tomato seedlings as bait plants. The quantity of Sss infection on the roots of bait plants was evaluated using the polymerase chain reaction (PCR) and expressed in terms of the infection potential in the soil. The infection potential was positively correlated with the disease severity of harvested tubers, whereas the spore ball density determined using PCR had an indistinct relationship with disease severity. The infection potential can be useful in evaluating soil contamination and in applying countermeasures against powdery scab.     

First report of tomato chlorotic dwarf viroid isolated from symptomless petunia plants (Petunia spp.) in Japan

A viroid was detected for the first time in symptomless petunia plants (Petunia spp.) and identified as Tomato chlorotic dwarf viroid (TCDVd) based on an analysis of the complete genomic sequence. These petunia plants are a likely source of inoculum for tomato or potato plants because TCDVd induces severe symptoms on these plants. The genomic sequence of this petunia isolate from Japan shared 100 % identity with petunia isolates from the Netherlands and United Kingdom and a tomato isolate from Japan. Phylogenetic analysis showed that all petunia isolates and the tomato isolate from Japan formed a monophyletic clade.     

Tomato can be a latent carrier of ‘Candidatus Liberibacter solanacearum’, the causal agent of potato zebra chip disease

‘Candidatus Liberibacter solanacearum’ was recently described as the causal agent of potato zebra chip disease. This pathogen occurs in North America, New Zealand, and Northern Europe on various crops, and may spread to other potato growing regions. Observation on ‘Ca. L. solanacearum’‐infected tomato and potato plants propagated in growth chambers over 5 years indicated that tomato plants (cvs Moneymaker and Roma) can be a latent carrier of ‘Ca. L. solanacearum’. Tomato plants graft‐inoculated with scions from latently infected tomato plants remained symptomless, but tested positive in a species specific PCR assay. ‘Ca. L. solanacearum’ was consistently detected in the top, middle and bottom portion of the symptomless tomato plants, including stem, petiole, midrib, vein, flowers and fruits. In tomato fruits, ‘Ca. L. solanacearum’ was evenly distributed in the tissues at the peduncle and style ends, as well as in the pericarp, and columella placenta tissues. This is the first report that ‘Ca. L. solanacearum’ is present in a plant reproductive organ. In contrast, potato plants (cvs. Jemseg, Atlantic, Shepody, Frontier Russet, Russet Burbank, Red Pontiac, and Russet Norkotah) grafted with scions from the same latently infected tomato plants resulted in typical symptoms of purple top, leaf scorch, and other disease symptoms in plants and brown discoloration in the vascular ring and medullary rays in tubers.     

Biological control of grapevine crown gall by nonpathogenic <Emphasis Type="Italic">Agrobacterium vitis</Emphasis> strain VAR03-1

A nonpathogenic strain of Agrobacterium vitis VAR03-1 was tested as a biological control agent against crown gall of grapevine (Vitis vinifera L.). A mixture of the nonpathogenic strain VAR03-1 and a tumorigenic strain G-Ag-27 of A. vitis at cell ratios of 1 : 1, 3 : 1, 9 : 1, and 99 : 1 significantly inhibited gall formation and size on stems of tomato (Lycopersicon esculentum Mill.). Strain VAR03-1 also inhibited gall formation on stems of both tomato and grapevine at a 1 : 1 cell ratio with several tumorigenic A. vitis strains isolated from different fields of grapevine in Japan. In biological control tests, when roots of grapevine and tomato seedlings were soaked in a cell suspension of strain VAR03-1 for 24 h before a 1-h soaking in a cell suspension of the pathogen and subsequent planting in pots of infested soil, strain VAR03-1 significantly reduced the incidence of gall formation on both plants.     

Inhibitory effect of ACC deaminase‐producing bacteria on crown gall formation in tomato plants infected by Agrobacterium tumefaciens or A. vitis

This study showed that various rhizosphere bacteria producing the enzyme 1‐aminocyclopropane‐1‐carboxylate (ACC) deaminase (ACCD), which can degrade ACC, the immediate precursor of ethylene in plants, and thereby lower plant ethylene levels, can act as promising biocontrol agents of pathogenic strains of Agrobacterium tumefaciens and A. vitis. Soaking the roots of tomato (Solanum lycopersicum) seedlings in a suspension of the ACCD‐producing Pseudomonas putida UW4, Burkholderia phytofirmans PsJN or Azospirillum brasilense Cd1843 transformed by plasmid pRKTACC carrying the ACCD‐encoding gene acdS from UW4, significantly reduced the development of tumours on tomato plants injected 4–5 days later with pathogenic Agrobacterium strains via wounds on the plant stem. The fresh mass of tumours formed by plants pretreated with ACCD‐producing strains was typically four‐ to fivefold less than that of tumours formed on control plants inoculated only with a pathogenic Agrobacterium strain. Simultaneously, the level of ethylene evolution per amount of tumour mass on plants pretreated with ACCD‐producing bacteria decreased four to eight times compared with that from tumours formed on control plants or plants pretreated with bacteria deficient in ACCD production. Moreover, transgenic tomato plants expressing a bacterial ACCD were found to be highly resistant to crown gall formation relative to the parental, non‐transformed tomato plants. The results support the hypothesis that ethylene is a crucial factor in Agrobacterium tumour formation, and that ACCD‐produced rhizosphere bacteria may protect plants infected by pathogenic Agrobacteria from crown gall disease.     

Detection,characterization and host range studies of <Emphasis Type="Italic">Pepino mosaic virus</Emphasis> in Cyprus

Pepino mosaic virus (PepMV, Genus Potexvirus, Family Flexiviridae) is a mechanically transmitted viral disease that has emerged as a significant problem of greenhouse tomato crops in Europe and around the world. Although previous studies in Cyprus suggested that the virus was not present on the island, in 2009 tomato fruits from two major tomato production areas exhibited symptoms of yellow mosaic and discolouration, similar to those induced by PepMV. Consequently, an extensive survey was conducted in all tomato producing areas of the country to identify the incidence and prevalence of PepMV in protected and open field tomato crops. Analysis of 3500 leaf samples from tomato plants and weeds with DAS-ELISA and real-time RT-PCR showed that PepMV was present in all tomato growing areas of the island. The virus was detected in both protected and open field tomato plants, as well as in 20 weed species in the families of Amaranthaceae, Chenopodiaceae, Compositae, Convolvulaceae, Malvaceae, Plantaginaceae and Solanaceae. All Cypriot isolates assayed belonged to the CH2 genotype. Biological assays with two Cypriot isolates showed that they could infect cultivated and weed species including Vigna unguiculata, Solanum melongena, Nicotiana tabacum, Malva parviflora, Sonchus oleraceus, Solanum nigrum, Convolvulus arvensis, Chrysanthemum segetum and Calendula arvensis. To our knowledge, this is the first study to report Chrysanthemum segetum and Calendula arvensis as hosts of PepMV.     

Molecular and biological characterization of <Emphasis Type="Italic">Chrysanthemum stem necrosis virus</Emphasis> isolates from distinct regions in Japan

Three isolates of Chrysanthemum stem necrosis virus (CSNV) were obtained from chrysanthemum plants in distinct regions of Japan in 2006 and 2007. All the original host plants showed severe necrotic symptoms on the leaves and stems. Amino acid sequence data of the nucleocapsid protein genes of the three isolates (CbCh07A, TcCh07A, and GnCh07S) showed high identities with those of two other CSNV isolates, HiCh06A L1 from Japan and Chry1 from Brazil. Furthermore, for the first time the complete nucleotide sequence of the S RNA was determined for CSNV (isolate HiCh06A). In phylogenetic analysis based on the non-structural protein genes from the genus Tospovirus, HiCh06A L1 was placed in the same genetic group as Tomato spotted wilt virus (TSWV) and Impatiens necrotic spot virus. Host range examination for isolates HiCh06A L1 and CbCh07A showed that green pepper (cv. ‘Kyoyutaka’, ‘Saitamawase’, ‘Tosakatsura’, ‘L3 sarara’ and ‘L3 miogi’) and tomato (cv. ‘Sekaiichitomato’) were systemically susceptible hosts, whereas TSWV-resistant Solanaceae species, Capsicum chinense, Lycopersicon peruvianum and a TSWV-resistant cultivar of green pepper (cv. TSR miogi), were resistant.     

Long‐lasting β‐aminobutyric acid‐induced resistance protects tomato fruit against Botrytis cinerea

Minimizing losses to pests and diseases is essential for producing sufficient food to feed the world's rapidly growing population. The necrotrophic fungus Botrytis cinerea triggers devastating pre‐ and post‐harvest yield losses in tomato (Solanum lycopersicum). Current control methods are based on the pre‐harvest use of fungicides, which are limited by strict legislation. This investigation tested whether induction of resistance by β‐aminobutyric acid (BABA) at different developmental stages provides an alternative strategy to protect post‐harvest tomato fruit against B. cinerea. Soil‐drenching plants with BABA once fruit had already formed had no impact on tomato susceptibility to B. cinerea. However, BABA application to seedlings significantly reduced post‐harvest infection of fruit. This resistance response was not associated with a yield reduction; however, there was a delay in fruit ripening. Untargeted metabolomics revealed differences between fruit from water‐ and BABA‐treated plants, demonstrating that BABA triggered a defence‐associated metabolomics profile that was long lasting. Targeted analysis of defence hormones suggested a role of abscisic acid (ABA) in the resistance phenotype. Post‐harvest application of ABA to the fruit of water‐treated plants induced susceptibility to B. cinerea. This phenotype was absent from the ABA‐exposed fruit of BABA‐treated plants, suggesting a complex role of ABA in BABA‐induced resistance. A final targeted metabolomic analysis detected trace residues of BABA accumulated in the red fruit. Overall, it was demonstrated that BABA induces post‐harvest resistance in tomato fruit against B. cinerea with no penalties in yield.     

<Emphasis Type="Italic">Physalis ixocarpa</Emphasis> and <Emphasis Type="Italic">P. peruviana</Emphasis>, new natural hosts of <Emphasis Type="Italic">Tomato chlorosis virus</Emphasis>

Tomato chlorosis virus causes yellow leaf disorder epidemics in many countries worldwide. Plants of Physalis ixocarpa showing abnormal interveinal yellowing and plants of Physalis peruviana showing mild yellowing collected in the vicinity of tomato crops in Portugal were found naturally infected with ToCV. Physalis ixocarpa and P. peruviana were tested for susceptibility to ToCV by inoculation with Bemisia tabaci, Q biotype. Results confirmed that ToCV is readily transmissible to both species. The infection was expressed in P. ixocarpa by conspicuous interveinal yellow areas on leaves that developed into red or brown necrotic flecks, while P. peruviana test plants remained asymptomatic. Infected plants of both P. ixocarpa and P. peruviana served as ToCV sources for tomato infection via B. tabaci transmission. This is the first report of P. ixocarpa and P. peruviana as natural hosts of ToCV.