European Journal of Plant Pathology

Ntushelo, K.; Harrison, N.; Elliott, M.

doi: 10.1007/s10658-012-0007-4pmid: N/A

A comparison was made of the two palm yellows phytoplasmas affecting palms to determine if the entire ribosomal RNA operon portion of the phytoplasma genome, or portions thereof, could account for the observed palm host differences. Polymerase chain reaction (PCR) was used to amplify a 5.0 kb DNA fragment consisting of the entire ribosomal RNA operon from a subgroup 16SrIV-D phytoplasma that causes Texas Phoenix palm decline (TPD) in cabbage (Sabal palmetto) palm in west central Florida and from a subgroup 16SrIV-A phytoplasma that causes lethal yellowing (LY) in coconut (Cocos nucifera) palm in Jamaica. Before the PCR reaction, we sequenced by 454 sequencing a draft genome of the coconut LY phytoplasma, strain LYFL, that infects C. nucifera in Florida, and obtained from this draft sequence both copies of the entire ribosomal operon. Sequence analysis of the ribosomal RNA operons from both the LY and TPD phytoplasmas revealed the gene composition and orientation for the operons to be 5′16S rRNA-tRNAIle-23S rRNA-5S rRNA3′ and a tRNAVal3′ downstream of the 5S rRNA gene. Based on molecular comparisons using the sequences of the ribosomal RNA operon, the TPD (16SrIV-D) strain was 98 % similar to the LY (16SrIV-A) strains.

Khatabi, B.; Wen, R.-H.; Hershman, D.; Kennedy, B.; Newman, M.; Hajimorad, M.

doi: 10.1007/s10658-012-9969-5pmid: N/A

Soybean vein necrosis-associated virus (SVNaV) is a newly isolated tospovirus from field-grown soybeans in the United States. Polyclonal antibodies generated against the recombinant Escherichia coli-expressed nucleocapsid protein (NP) of the virus, reacted specifically with SVNaV and exhibited low, if any, cross-reactivity with other species within the genus Tospovirus. The serological results are in agreement with low sequence homology of the SVNaV-NP gene when compared with those of other tospovirus species, some of which are capable of infecting soybean naturally. Phylogenetic analysis utilizing NP sequences from several SVNaV isolates collected from different geographical regions and various soybean genotypes over 4 years showed close relationships, but distinct from the representatives of all the established serogroups or distinct serotypes within the genus of Tospovirus. All SVNaV isolates examined reacted strongly with the generated polyclonal antibodies. Collectively, our serological analyses suggest that SVNaV represents a new and distinct soybean-infecting tospovirus serotype. Furthermore, our data demonstrate that antiserum against NP has the potential to serve as a reliable probe for SVNaV detection in field-grown soybeans.

Alfaro-Fernández, Ana; Ali, Mai; Abdelraheem, Fadia; Saeed, Ebrahim; Font San Ambrosio, María

doi: 10.1007/s10658-012-9975-7pmid: N/A

In January 2011, symptomatic chickpea and faba bean plants were observed in fields located in the Gezira state (Sudan). Faba bean plants showed yellowing and stunting, whereas chickpea plants presented yellowing, reddening and little leaves. The disease etiology was investigated using nested polymerase chain reaction (PCR) with phytoplasma-specific primers which amplify a fragment of the 16S rRNA gene. Sequencing and restriction fragment length polymorphism (RFLP) analyses revealed that the tested phytoplasmas belonged to the group 16SrII. Phylogenetic analyses of the 16S rRNA gene of the obtained sequences indicated that the chickpea and faba bean phytoplasmas from Sudan were more closely related to the phytoplasmas subgroup 16SrII-D. To our knowledge, this is the first report of phytoplasmas from the group 16SrII-D infecting chickpea in Sudan, and faba bean worldwide.

Powell, Michelle; Cuthbertson, Andrew; Bell, Howard; Boonham, Neil; Morris, Jane; Northing, Phil

doi: 10.1007/s10658-012-9976-6pmid: N/A

For the UK, Bemisia tabaci poses a threat primarily to protected vegetable crops due to the transmission of several plant-pathogenic viruses. There are at least 24 different biotypes of B. tabaci that cannot be differentiated through morphological traits. The B (Middle East-Asia Minor 1 species) and Q (Mediterranean species) biotypes are widely considered to be the most important and, as such, the ability to rapidly and precisely biotype B. tabaci interceptions is vital when developing effective control strategies. Intercepted adult/pupal B. tabaci received from the UK Plant Health and Seeds Inspectorate (PHSI) during 2002–2003 (n = 60) and 2010–2011 (n = 42) were both biotyped and tested for the presence of Tomato yellow leaf curl virus (TYLCV) and Tomato yellow leaf curl Sardinia virus (TYLCSV) using a real-time PCR assay based on TaqMan® chemistry. The positive results indicated that during 2002–2003 the Q biotype comprised 68.3 % of the interceptions whilst in 2010–2011 it comprised 66.7 % of the B. tabaci samples intercepted. Only three of the B biotypes collected during 2002–2003 were positive for TYLCSV, two originating from Israel and the other of unknown origin. The implications in regards to pest management of the insect are discussed.

Verhoeven, J.; Botermans, M.; Meekes, E.; Roenhorst, J.

doi: 10.1007/s10658-012-0005-6pmid: N/A

In the Netherlands a survey for pospiviroids was performed in ornamental plants from 2006 up to 2011. Tomato apical stunt viroid (TASVd) was the most frequently found pospiviroid, causing infections in Brugmansia sp., Cestrum sp., Lycianthes rantonnetii, Solanum jasminoides and Streptosolen jamesonii. In addition, five other pospiviroids were detected. In 2011 TASVd also was found in tomato plants in a single greenhouse. The genotype of this isolate was identical to the TASVd genotype found most frequently in ornamentals. This indicates that an ornamental species has been the source of inoculum for the tomato crop.

Chidamba, Lizyben; Bezuidenhout, Cornelius

doi: 10.1007/s10658-012-0002-9pmid: N/A

The genetic diversity of Xanthomonas campestris pv. campestris isolates from South Africa was evaluated using 28 isolates obtained from the Johannesburg Fresh Produce Market. Samples were collected from cabbage supplies from farms in Gauteng, Mpumalanga and North West Provinces. Strains were isolated from small sections of infected cabbage leaf samples and cultured on Yeast Dextrose Agar. Isolates identity was confirmed by ELISA and Pathogenicity test. Pathogenicity tests were performed by inoculating leaves of known susceptible cabbage seedlings. Infection symptoms induced could be categorized into three groups, ranging from typical to non-typical black rot symptoms. Four differential Brassica cultivars with known avirulence genes were used for race typing done by spray inoculation. Four races, namely 1, 3, 4 and 6, were identified. Of the 28 isolates, four were identified as race 1, two as race 3, 19 as race 4 and three as race 6. Repetitive DNA polymerase chain reaction-based fingerprinting using Eric- and Box-primers was used to assess the genetic diversity. Generated fingerprints of X. c pv. campestris were relatively similar. Cluster analysis could not strictly group isolates by their geographical origin, suggesting limited diversity of Xanthomonas campestris pv. campestris strains within cabbage producing regions in South Africa.

Ni, Hui-Fang; Yang, Hong-Ren; Chen, Ruey-Shyang; Hung, Ting-Hsuan; Liou, Ruey-Fen

doi: 10.1007/s10658-012-0003-8pmid: N/A

Lasiodiplodia theobromae (Pat.) Griff. & Maubl, Neofusicoccum parvum Pennycook & Samuels, N. mangiferae Syd. & P. Syd., and Fusicoccum aesculi Corda, all anamorphs of Botryosphaeriaceae species, are the causal agents of mango stem-end rot and fruit rot in Taiwan. Identification of these fungal species based on morphology has not been easy due to their extensive plasticity for some of the morphological characters. To aid reliable identification of Botryosphaeriaceae species associated with mango fruits, four pairs of species-specific primers were designed according to sequences of the ribosomal internal transcribed spacers (ITS), and a rapid method was established based on nested multiplex polymerase chain reaction (PCR) in this study. To perform the analysis, PCR was first run with ITS1 and ITS4 as the primers, followed by a second PCR with the addition of all four sets of species-specific primers. With this method, a low limit of 100 fg-1 pg of purified fungal DNA was detectable. It could also successfully detect L. theobromae, N. parvum, N. mangiferae and F. aesculi in total DNA extracted from inoculated mango fruits. This assay provides a rapid and sensitive method for the identification of Botryosphaeriaceae species and diagnosis of mango fruit rot and stem-end rot as well.

Rappussi, M.; Eckstein, B.; Flôres, D.; Haas, I.; Amorim, L.; Bedendo, I.

doi: 10.1007/s10658-012-0004-7pmid: N/A

Since 2000, a disease has occurred with high levels of incidence in crops of cauliflower grown in the green belt area of the city of São Paulo, Brazil. The symptoms are characterized by stunting, malformation of the inflorescence, reddening leaves, and vascular necrosis, suggesting infection by phytoplasma. These symptoms are similar to those described in Brassicas species affected by the aster yellows (16SrI) group of phytoplasma. In the present study, a phytoplasma from the 16SrIII-J subgroup was identified in cauliflower plants based on actual and virtual RFLP patterns and phylogenetic analysis, and was distinct from the phytoplasmas frequently associated with aster yellows disease in Brassicas. Pathogenicity assays using dodder confirmed that the identified phytoplasma is the agent of the observed disease, which is here designated as cauliflower stunt. Consequently, this species of Brassica may be recognized as a new host for subgroup 16SrIII-J, which has frequently been found in diverse species cultivated in Brazil. The spatial pattern of diseased plants was determined in ten cauliflower plots of 300 to 728 plants each. All plants in these plots were evaluated by visual assessments, assigned as diseased or healthy and mapped. The dispersion index and Taylor’s power law were determined for various quadrat sizes and the results showed that the diseased plants were distributed in a random pattern in fields with a low disease incidence and in an aggregated pattern in fields with a disease incidence greater than 25 %. According to an isopath area analysis, diseased plants were predominantly present in the field borders, suggesting that the pathogen is possibly introduced by vector(s) from the external area.

Aghighi, Sonia; Hardy, Giles; Scott, John; Burgess, Treena

doi: 10.1007/s10658-012-0006-5pmid: N/A

A new homothallic Phytophthora species, isolated from rhizosphere soil and roots of declining or dead Rubus anglocandicans (European blackberry) in south-west Western Australia, is described as Phytophthora bilorbang sp. nov. It produces non-papillate sporangia, smooth-walled oogonia containing thick-walled oospores, and paragynous antheridia. Although morphologically similar to several species within ITS Clade 6 and sub-clade II, namely P. gibbosa, P. gregata and P. megasperma, phylogenetic analyses of the ITS, cox1, HSP90, BT and NADH gene regions demonstrate that P. bilorbang sp. nov. is a distinct species. Additionally, P. bilorbang differs from these species in its growth and colony morphology on several media. Pathogenicity tests indicate that P. bilorbang could be responsible for the decline syndrome of blackberry within the Warren and Donnelly River catchments in the south-west of Western Australia.

García-Ibarra, Ana; Dicenta, Federico; Martínez-Gómez, Pedro; Rubio, Manuel

doi: 10.1007/s10658-012-0009-2pmid: N/A

Apple chlorotic leaf spot virus (ACLSV) seems to be the causal agent of apricot viruela disease. This disease has become an important problem for apricot production in Spain, mainly affecting the ‘Búlida’ cultivar, although no information is available about the behaviour of other cultivars with regards to ACLSV. In this study, the behaviour of 29 apricot cultivars against ACLSV (Apr 62 isolate) was evaluated under controlled conditions in an insect-proof greenhouse. Three different rootstocks, ‘GF305’ peach, ‘Real Fino’ apricot and ‘Adesoto’ plum, were first inoculated by grafting ACLSV-infected bark and were later grafted with the apricot cultivar to be evaluated. Apricot cultivars were evaluated during three cycles of study. ACLSV was asymptomatic on the leaves of all cultivars and rootstocks, so level of susceptibility or resistance was determined by virus detection through RT-PCR. ‘GF305’ rootstock showed a greater susceptibility level than ‘Real Fino’ and ‘Adesoto’. Most of the cultivars were susceptible to ACLSV with different levels of susceptibility, and only ‘Bergeron’ and ‘Mauricio’ were resistant.