English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Different phytoplasmas were detected and identified in watercress and onion plants from Mauritius. Symptoms observed on watercress were purple coloration of leaves, plant stunting, and reduced leaf size. In onion, witches’ broom and virescence were observed in the inflorescence. Disease incidence in watercress ponds ranged from 30 to 70%, while in onion seed production plots, it was around 10%. PCR/RFLP analyses as well as sequencing of 16S ribosomal gene enabled the identification of phytoplasmas belonging to two ribosomal groups, namely stolbur and aster yellows, from the two aforementioned crops. Introduction Watercress (Nasturtium officinale) is a popular green leafy vegetable in Mauritius. It is grown in waterways all over the island, on an area of around 14 ha, with an annual production amounting to about 200 tonnes, and an economic value approximating US $200,000. Diseases recorded so far on watercress in Mauritius are fungal leaf spots caused by Cercospora, Septoria, and Colletotrichum and leaf mosaic caused by Turnip mosaic virus (TuMV). In a survey performed in year 2000 in all watercress cultivation of the island, 81% out of 231 symptomatic leaf samples were tested positive for TuMV by DAS ELISA (12). Onion is also an important crop in Mauritius, since it is a popular ingredient in the local cuisine. Annual onion production amounts to about 6,000 tonnes and imports can reach up to 11,600 tonnes. It is within government policy to boost seed production in Mauritius so as to promote onion cultivation and thus reduce imports. Major diseases recorded on onion so far in Mauritius include: purple blotch, pink root rot, rust, blast, Xanthomonas blight, root nematode, Phytophthora, onion yellow dwarf, and iris yellow spot viruses. To date, there are no official records of the presence of phytoplasmas in either watercress or onion in Mauritius. Over the past year, some abnormalities were reported in watercress and onion. Symptoms observed on watercress were reduced leaf size, plant stunting, and purple leaf coloration; infected plants died, leaving empty patches in ponds (Fig. 1A). In onion seed production plots of variety ‘Bellarose,’ several plants were stunted and showed witches′ broom and phyllody symptoms in their inflorescence (Fig. 1B). These symptoms, frequently associated with abiotic stress factors in the past, were strongly suggestive of possible phytoplasma association. 30 September 2010 Plant Health Progress Analyses to verify the presence of these prokaryotes in both onion and watercress were carried out using the polymerase chain reaction (PCR) assay with universal primers that amplify 16SrDNA sequences of phytoplasmas followed by molecular characterization of obtained amplicons. Sample collection and nucleic acids extraction. Inflorescences from onion variety ‘Bellarose’ and watercress leaf samples were collected respectively from Richelieu and Carreau Esnouf in Mauritius (Fig. 2) in 2008. Asymptomatic samples from both species were also collected as negative controls. Onion samples originated from seed production plots, whereas watercress samples were from commercial privately owned ponds. Total nucleic acids were extracted from 1 g of pooled tissues following the protocol described by Prince et al. (25) (extraction method 1), and/or from 0.7 g of pooled tissues following a CTAB protocol (extraction method 2) (2). Nucleic acid from both extraction systems were dissolved in TE buffer, and maintained at -20°C. Before performing PCR assays nucleic acids were quantified and diluted in sterile distilled water to the final concentration of 20 ng/μl. A B Fig. 1. (A) Empty patches (arrow) in a pond in which phytoplasma-infected watercress plants are dying, and (B) symptoms of phyllody and virescence on onion. 30 September 2010 Plant Health Progress Fig. 2. Map of Mauritius showing in the dark areas where onion and watercress were sampled. Reference phytoplasma strains. Phytoplasma reference strains maintained in collection in periwinkle [Catharanthus roseus (G.) Don.] (4) employed for phytoplasma identification were: koolsard aster yellows (KAY, ribosomal subgroup 16SrI-B), and stolbur from pepper from Serbia (STOL, ribosomal subgroup 16SrXII-A); moreover, ‘Candidatus Phytoplasma japonicum’ maintained in naturally infected Hydrangea from Japan (27) was also employed. 16S ribosomal DNA. Detection of phytoplasmas was done using PCR assays with phytoplasma universal primer pair P1/P7 (8,28) in direct PCR reaction, followed by nested PCR by R16F2/R2 primers (18). Further nested PCR reactions on P1/P7 amplicons were performed with R16(I)F1/R1 primer pair, specific for phytoplasmas belonging to aster yellows (16SrI) (20), faba bean phyllody (16SrII) (32), and stolbur (16SrXII) (21) groups. Each 25 μl PCR reaction mix contained 20 ng template DNA, 2.5 μl 10× PCR buffer, 0.8 U Taq polymerase (Sigma-Aldrich Co., St. Louis, MO), 0.2 mM dNTPs, 1.5 mM MgCl and 0.4 μM of each primer. Asymptomatic samples were run as negative controls in each PCR reaction. One μl of amplicon from direct PCR diluted 1:30 in sterile distilled water, was used as template in nested PCR reactions. Thirty-five PCR cycles were performed under the following 2 30 September 2010 Plant Health Progress conditions: 1 min (2 min for the first cycle) for denaturation at 94°C, 2 min for annealing at 50°C, and 3 min (10 min for the last cycle) for primer extension at 72°C. Six μl of PCR products were separated in 1% agarose gel, stained with ethidium bromide, and photographed under UV at 312 nm using a transilluminator. Identification of detected phytoplasmas was done using RFLP analyses with TruI, HhaI, and TaqI (Fermentas, Vilnius, Lithuania) restriction enzymes on amplified ribosomal DNA sequences. Visualization of RFLP products was performed in a 5% polyacrylamide gel, stained with ethidium bromide, and visualized with UV transilluminator. For better molecular identification longer 16S rDNA sequences were obtained with further nested amplification on P1/P7 amplicons with F1/B6 primers (9) on samples WatM-1, WatM-2, and OnM-2 (Table 1) and the amplified products (about 1,700 bp) were purified using Qiagen PCR Purification Kit (Qiagen GmbH, Hilden, Germany, EU), and then sequenced in both directions with primers F1, 350R (24), and B6 from Eurofins MWG Operon (Ebersberg, Germany). These sequences were aligned with those of representative strains of the genus ‘Candidatus Phytoplasma’ (14) retrieved from GenBank and aligned using CLUSTAL X and BioEdit (13,31). The obtained sequences of samples WatM-1 (1,625 bp), WatM-2 (1,513 bp), and OnM-2 (1,524 bp) were deposited in the National Center for Biotechnology Information (NCBI, Bethesda, MD, USA) NCBI under accession No. GU129975, GU129976, GU129974, respectively. Maximum parsimony analysis using the close neighbour interchange algorithm was performed with MEGA version 4 (30) to construct a phylogenetic tree from the aligned 16S ribosomal sequences and related sequences from 39 phytoplasma strains (Table 1). The initial tree was created by random addition for 10 replications. Bootstrap analysis was also performed and replicated 1,000 times for estimation of stability and support for the clades. Acholeplasma laidlawii (a cultivable Mollicute, phylogenetically related to phytoplasmas) was designated as the out-group to root the tree. Virtual RFLP analyses on R16F2/R2 amplicons were performed using pDRAW32 program version 1.0 to verify consistency of sequences with RFLP results obtained. Table 1. Phytoplasma 16S rDNA sequences retrieved from GenBank, including strains from watercress and onion from Mauritius, employed for phylogenetic analysis. (continued) GenBank # Phytoplasma strain Origin Disease Ref. # M30790 ‘Candidatus. Phytoplasma asteris’ Michigan (US) Aster yellows 14 U15442 ‘Ca. P. aurantifolia’ Oman Lime witches broom 14 L04682 ‘Ca. P. pruni’* California (US) X disease 14 U18747 ‘Ca. P. palmae’* Florida (US) Palm lethal yellowing 14 X80117 ‘Ca. P. cocostanzianae’* Tanzania Palm lethal yellowing 14 Y14175 ‘Ca. P. cocosnigerianae’* Nigeria Palm lethal yellowing 14 AF122910 ‘Ca. P. ulmi’ New York (US) Elm yellows 14 AF305240 ‘Ca. P. ziziphi’ South China Jujube witches broom 14 X76560 ‘Ca. P. vitis’* France Flavescence dorée 14 AY390261 ‘Ca. P. trifolii’ Canada Clover proliferation 14 AF092209 ‘Ca. P. fraxini’ New York (US) Ash yellows 14 AF086621 ‘Ca. P. luffae’* Taiwan Luffa witches broom 14 AF515637 ‘Ca. P. phoenicium’ Lebanon Almond witches broom 14 AJ542541 ‘Ca. P. mali’ Italy Apple proliferation 14 30 September 2010 Plant Health Progress Table 1 (continued). Disease status. Disease incidence varied from 40 to 70% across watercress ponds; the surveillance program started in January 2009, revealed that these symptoms are present on all three locally grown watercress varieties (‘Cresson Filant,’ ‘Brede Doux,’ and ‘Cresson Constance’), and 60% of sites surveyed were affected. Disease incidence of symptomatic onion plants did not exceed 10% on variety ‘Bellarose,’ the only onion variety presently cultivated for seed production in Mauritius. 16S Ribosomal DNA. All symptomatic samples from both species examined were positive in direct and/or nested PCR analyses. Selected samples from both species were also examined with RFLP analyses and results are summarized in Table 2. The asymptomatic samples of onion and watercress were negative in all GenBank # Phytoplasma strain Origin Disease Ref. # AJ542544 ‘Ca. P. prunorum’ Germany European stone fruit yellows 14 AJ542543 ‘Ca. P. pyri’ Germany Pear decline 14 X92869 ‘Ca. P. spartii’ Italy Spartium witches broom 14 D12581 ‘Ca. P. oryzae’ Japan Rice yellows 14 L76865 ‘Ca. P. australiense’ Australia Australian grapevine yellows 14 AF147708 ‘Ca. P. brasiliense’ Brasil Hibiscus witches broom 14 AY725228 ‘Ca. P. graminis’ Cuba Yellow leaf syndrome 3 DQ174122 ‘Ca. P. americanum’ Nebraska (US) American potato purple top wilt 19 AY725234 ‘Ca. P. caricae’ Cuba Pap

Impact of Crop Rotation and Bio-covers on Soybean Cyst Nematode