Identification of the causal agents of crazy root disease on hydroponically cultivated cucumber plants in Poland

In April 2019, hydroponically cultivated cucumber plants with characteristic symptoms of crazy root disease were found in two different commercial production cucumber greenhouses in Poland. Due to excessive and inappropriate root growth, this disease led to a reduction in yield and deterioration of the general conditions of infected plants. Bacteria isolated from the roots were subjected to a morphological evaluation, as well as molecular, biochemical and pathogenicity tests. To identify the bacteria causing the disease, Agrobacterium-like colonies were subjected to PCR with primers complementary to the pathogenicity-related genes located on the crazy root-inducing plasmid (Ri-plasmid): the virD2A + virD2E primers complementary to the virD2 gene and the rolBF + rolBR primers complementary to the rolB gene. The pathogenicity of the isolated strains was studied in sunflowers and cucumbers. Twelve strains positive for the Ri plasmid, as determined by PCR, and pathogenic to sunflowers were identified based on sequence analysis of the 16S rRNA and recA genes. One strain was classified as belonging to the genus Pararhizobium, three to Rhizobium, and eight to Agrobacterium biovar 1, with the highest similarity to genomospecies G3. The results of the analyses suggest that these strains may belong to a new, thus far, undescribed species. To confirm this hypothesis, further phylogenetic studies are required.

The genome sequence of hairy root Rhizobium rhizogenes strain LBA9402. Bioinformatics analysis suggests the presence of a new opine system in the agropine Ri plasmid

We report here the complete genome sequence of the Rhizobium rhizogenes (formerly Agrobacterium rhizogenes) strain LBA9402 (NCPPB1855rifR), a pathogenic strain causing hairy root disease. In order to assemble a complete genome we obtained short-reads from Illumina sequencing as well as long-reads from Oxford Nanopore Technology sequencing. The genome consists of a 3,958,212 bp chromosome, a 2,005,144 bp chromid (secondary chromosome) and a 252,168 bp Ri plasmid (pRi1855), respectively. The primary chromosome was very similar to that of the avirulent biocontrol strain K84, but the chromid showed a 724 kbp deletion accompanied by a large 1.8 Mbp inversion revealing the dynamic nature of these secondary chromosomes. The sequence of the agropine Ri plasmid was compared to other types of Ri and Ti plasmids. Thus we identified the genes responsible for agropine catabolism, but also a unique segment adjacent to the TL-region that has the signature of a new opine catabolic gene cluster including the three genes that together encode an opine dehydrogenase. Our sequence analysis also revealed a novel gene at the very right end of the TL-DNA, which is unique for the agropine Ri plasmid. The protein encoded by this gene was most related to the succinamopine synthases of chrysopine and agropine Ti plasmids and thus may be involved in synthesis of the unknown opine that can be degraded by the adjacent catabolic cluster. The available sequence will facilitate the use of R. rhizogenes and especially LBA9402 in both the laboratory and for biotechnological purposes.

First report of root mat disease in a hydroponic tomato production system caused by rhizogenic Agrobacterium biovar 1 in South Korea

In June 2019, root mat disease was observed in hydroponically cultivated tomatoes in Jinju, South Korea, which occurred in at least 30% of the plants in the greenhouse. To isolate the causal bacteria, 10 g of infested tomato root mat sample was ground with 50 mL of sterile water. A 100-µL aliquot of the homogenate was serially diluted and spread on Mannitol-Glutamate (MG) medium amended with 0.1% yeast extract (MGY) and incubated at 28°C for 48 hours. Fifteen dominant colonies that formed on the MGY medium were purified and subjected to diagnostic polymerase chain reaction (PCR) based on the virD2–ipt gene loci. Because Ti-plasmid harbors both virD2 and ipt genes, Ri-plasmid-borne Agrobacterium species with only virD2 can be differentiated using virD2–ipt PCR. To amplify virD2, the primers 5'-ATG CCC GAT CGA GCT CAA GT-3' and 5'-TCG TCT GGC TGA CTT TCG TCA TAA-3' were used; for ipt amplification, the primers 5'-GAT CG(G/C) GTC CAA TG(C/T) TGT-3' and 5'-GAT ATC CAT CGA TC(T/C) CTT-3' were used. Amplification involved an initial 94°C for 1 min and then 40 cycles at 94°C, 50°C, and 72°C for 1 min at each temperature, with a final 5-min extension at 72°C. For three strains (GNIY2, J10, and J11), virD2 PCR products, but no ipt PCR products, were identified, indicating that three strains are Ri-plasmid-borne Agrobacterium species. A pathogenicity test was performed on 2-week-old tomato plants. Bacteria isolates (GNIY2, J10, and J11) cultured overnight in LB were made into a bacterial suspension (107 cfu/mL) in 50 mM phosphate buffer. Five tomato seedling roots were cut with sterilized scissors and soaked in each bacterial suspension for 1 hour. Phosphate buffer was used as a negative control. The inoculated tomato seedlings were transplanted in new pots and placed in a greenhouse with 25°C day and 20°C night temperature set points in natural light. After 9 weeks, all inoculated tomato plants produced overgrown roots, while the negative control plants had no symptoms. To satisfy Koch’s postulates, re-isolation was performed from the diseased tomato and was the re-isolated bacteria were subject to partial 16S rDNA sequencing. Biovar tests performed as previously described revealed that all three isolates were biovar 1. A representative strain (GNIY2) was deposited in the Korean Agricultural Culture Collection (KACC 21759). To confirm the identity, four housekeeping genes of KACC 21759 were sequenced (16S rRNA, trpE, rpoB, and recA) and deposited in GenBank (accession nos. MT071560, MT444428, MT444429, and MT444430). Multilocus sequence analysis performed as previously described showed that the KACC 21759 strain was grouped in Agrobacterium genomospecies 4. This is the first report on mat root disease caused by Agrobacterium biovar 1 in hydroponic tomatoes in South Korea.

The Presence of the Hairy-Root-Disease-Inducing (Ri) Plasmid in Wheat Endophytic Rhizobia Explains a Pathogen Reservoir Function of Healthy Resistant Plants

ABSTRACT A large number of strains in the Rhizobium radiobacter species complex (biovar 1 Agrobacterium) have been known as causative pathogens for crown gall and hairy root diseases. Strains within this complex were also found as endophytes in many plant species with no symptoms. The aim of this study was to reveal the endophyte variation of this complex and how these endophytic strains differ from pathogenic strains. In this study, we devised a simple but effective screening method by exploiting the high resolution power of mass spectrometry. We screened endophyte isolates from young wheat and barley plants, which are resistant to the diseases, and identified seven isolates from wheat as members of the R. radiobacter species complex. Through further analyses, we assigned five strains to the genomovar (genomic group) G1 and two strains to G7 in R. radiobacter. Notably, these two genomovar groups harbor many known pathogenic strains. In fact, the two G7 endophyte strains showed pathogenicity on tobacco, as well as the virulence prerequisites, including a 200-kbp Ri plasmid. All five G1 strains possessed a 500-kbp plasmid, which is present in well-known crown gall pathogens. These data strongly suggest that healthy wheat plants are reservoirs for pathogenic strains of R. radiobacter. IMPORTANCE Crown gall and hairy root diseases exhibit very wide host-plant ranges that cover gymnosperm and dicot plants. The Rhizobium radiobacter species complex harbors causative agents of the two diseases. Recently, endophyte isolates from many plant species have been assigned to this species complex. We isolated seven endophyte strains belonging to the species complex from wheat plants and revealed their genomovar affiliations and plasmid profile. The significance of this study is the finding of the genomovar correlation between the endophytes and the known pathogens, the presence of a virulence ability in two of the seven endophyte strains, and the high ratio of the pathogenic strains in the endophyte strains. This study therefore provides convincing evidence that could unravel the mechanism that maintains pathogenic agents of this species and sporadically delivers them to susceptible plants.

Unexpected conservation and global transmission of agrobacterial virulence plasmids

The accelerated evolution and spread of pathogens are threats to host species. Agrobacteria require an oncogenic Ti or Ri plasmid to transfer genes into plants and cause disease. We developed a strategy to characterize virulence plasmids and applied it to analyze hundreds of strains collected between 1927 and 2017, on six continents and from more than 50 host species. In consideration of prior evidence for prolific recombination, it was surprising that oncogenic plasmids are descended from a few conserved lineages. Characterization of a hierarchy of features that promote or constrain plasticity allowed inference of the evolutionary history across the plasmid lineages. We uncovered epidemiological patterns that highlight the importance of plasmid transmission in pathogen diversification as well as in long-term persistence and the global spread of disease.

Kultur akar rambut Cinchona ledgeriana dan C. succirubra dalam kultur in vitro Hairy root culture of Cinchona ledgeriana and C. succirubra by in vitro culture

Summary Problems encountered in hairy root culture of C. ledgeriana and C. succirubra are low percentage of transformation of explants by Agrobacterium rhizogenes and slow growth of hairy root. The objective of this research was to evaluate the potential of several A. rhizogenes strains for initiation hairy roots of C. succirubra and C. ledgeriana, and to obtain the best medium for hairy root culture of Cinchona spesies. Axenic shoot and leaves explants of eight-month-old of C. ledgeriana and C. succirubra seedlings were inoculated with A. rhizogenes strain ATCC-15834, ATCC-8196, R-20001, 07-20001, A4, R-MAFFA, TISTR509, TISTR510 and LBA9457. Inoculated explants were cultured in solid MS medium with the addition of 100 mg/L amphicylin. Subculture of the hairy root was performed by transferred of root pieces into fresh liquid basal medium MS, B5, White and Heller. Hairy roots from the best of basal medium were subcultured on the same medium with the addition of 50 and 100 mg/L L-tryptophane, three or five times concentration of MS vitamins. The integration of T-DNA of A. rhizogenes in hairy root was confirmed with specific primer for TL and TR-DNA of plasmid by Polymerase Chain Reaction analysis. The results showed that only A. rhizogenes strain LBA 9457 were effective for transformation of explants from both Cinchona species. The fastest hairy roots growth were found in MS medium, while growth in others medium was poor. Hairy roots of C. ledgeriana has vigor and growth better than hairy roots of C. succirubra. MS with the addition of 50 mg/L L-tryptophane and three times the concen-trations of vitamin is the best medium for hairy root growth and vigor. Hairy roots of C. succirubra and C. ledgeriana used in this studies were confirmed that hairy roots contained TL and TR-DNA region of Ri plasmid with molecular weight 780 and 1600 bp. The results showed that strain of A. rhizogenes, plant species, source of explant and composition of medium affect the initiation, growth, development and vigor of hairy roots.Ringkasan Masalah dalam kultur akar rambut C. ledgeriana dan C. succirubra adalah rendahnya tingkat keberhasilan transformasi eksplan dengan Agrobacterium rhizogenesdan pertumbuhannya yang lambat. Penelitian ini bertujuan untuk mengevaluasi potensi dari beberapa galur A. Rhizogenes untuk inisiasi, mendapatkan komposisi medium terbaik untuk pertumbuhan akar rambut C. ledgeriana dan C. succirubra, serta konfirmasi terintegrasinya TR dan TL-DNA Ri plasmid ke dalam jaringan eksplan. Eksplan batang dan daun berasal dari kecambah aksenik C. ledgeriana dan C. succirubra berumur delapan bulan diinokulasi dengan A. rhizogenes galur 15834, 8196, R-20001, 07-20001, A4, R.MAFFA,TISTR 509, TISTR 510 dan LBA 9457. Eksplan yang sudah diinokulasi dikulturkan dalam medium MS padat. Subkultur dilakukan dengan cara mentransfer potongan ujung akar rambut ke dalam medium cair MS, B5, White dan Heller. Akar rambut dari medium kultur yang terbaik kemudian disubkultur ke dalam medium yang sama dengan penambahan 50 dan 100 mg/L L-triptofan dengan konsentrasi vitamin sebanyak tiga kali dan lima kali dari konsentrasi normal MS. Integrasi T-DNA dalam akar rambut dikonfirmasi meng-gunakan Polymerase Chain Reaction dengan primer spesifik untuk TL dan TR-DNA plasmid. Hasil yang diperoleh menunjukkan bahwa hanya A.rhizogenes galur LB9457 yang efektif menginfeksi eksplan baik batang maupun daun dari kedua spesies kina. Induksi, pertumbuhan dan vigor akar rambut yang terbaik diperoleh dari medium MS dengan penambahan 50 mg/L L-triptofan dan tiga kali konsentrasi vitamin. Hasil konfirmasi akar rambut baik dari batang maupun daun menggunakan PCR, menunjukkan bahwa TL dan TR-DNA dari Ri plasmid A. rhizogenes mampu menghasilkan pita-pita DNA dengan BM780 dan 1600 pb. Hasil yang diperoleh menunjukkan bahwa galur A. rhizogenes, spesies tanaman, sumber eksplan dan komposisi medium berpengaruh terhadap inisiasi, pertumbuhan, perkembangan dan vigor akar rambut.

Kultur akar rambut Cinchona ledgeriana dan C. succirubra dalam kultur in vitro Hairy root culture of Cinchona ledgeriana and C. succirubra by in vitro culture

Summary Problems encountered in hairy root culture of C. ledgeriana and C. succirubra are low percentage of transformation of explants by Agrobacterium rhizogenes and slow growth of hairy root. The objective of this research was to evaluate the potential of several A. rhizogenes strains for initiation hairy roots of C. succirubra and C. ledgeriana, and to obtain the best medium for hairy root culture of Cinchona spesies. Axenic shoot and leaves explants of eight-month-old of C. ledgeriana and C. succirubra seedlings were inoculated with A. rhizogenes strain ATCC-15834, ATCC-8196, R-20001, 07-20001, A4, R-MAFFA, TISTR509, TISTR510 and LBA9457. Inoculated explants were cultured in solid MS medium with the addition of 100 mg/L amphicylin. Subculture of the hairy root was performed by transferred of root pieces into fresh liquid basal medium MS, B5, White and Heller. Hairy roots from the best of basal medium were subcultured on the same medium with the addition of 50 and 100 mg/L L-tryptophane, three or five times concentration of MS vitamins. The integration of T-DNA of A. rhizogenes in hairy root was confirmed with specific primer for TL and TR-DNA of plasmid by Polymerase Chain Reaction analysis. The results showed that only A. rhizogenes strain LBA 9457 were effective for transformation of explants from both Cinchona species. The fastest hairy roots growth were found in MS medium, while growth in others medium was poor. Hairy roots of C. ledgeriana has vigor and growth better than hairy roots of C. succirubra. MS with the addition of 50 mg/L L-tryptophane and three times the concen-trations of vitamin is the best medium for hairy root growth and vigor. Hairy roots of C. succirubra and C. ledgeriana used in this studies were confirmed that hairy roots contained TL and TR-DNA region of Ri plasmid with molecular weight 780 and 1600 bp. The results showed that strain of A. rhizogenes, plant species, source of explant and composition of medium affect the initiation, growth, development and vigor of hairy roots.Ringkasan Masalah dalam kultur akar rambut C. ledgeriana dan C. succirubra adalah rendahnya tingkat keberhasilan transformasi eksplan dengan Agrobacterium rhizogenesdan pertumbuhannya yang lambat. Penelitian ini bertujuan untuk mengevaluasi potensi dari beberapa galur A. Rhizogenes untuk inisiasi, mendapatkan komposisi medium terbaik untuk pertumbuhan akar rambut C. ledgeriana dan C. succirubra, serta konfirmasi terintegrasinya TR dan TL-DNA Ri plasmid ke dalam jaringan eksplan. Eksplan batang dan daun berasal dari kecambah aksenik C. ledgeriana dan C. succirubra berumur delapan bulan diinokulasi dengan A. rhizogenes galur 15834, 8196, R-20001, 07-20001, A4, R.MAFFA,TISTR 509, TISTR 510 dan LBA 9457. Eksplan yang sudah diinokulasi dikulturkan dalam medium MS padat. Subkultur dilakukan dengan cara mentransfer potongan ujung akar rambut ke dalam medium cair MS, B5, White dan Heller. Akar rambut dari medium kultur yang terbaik kemudian disubkultur ke dalam medium yang sama dengan penambahan 50 dan 100 mg/L L-triptofan dengan konsentrasi vitamin sebanyak tiga kali dan lima kali dari konsentrasi normal MS. Integrasi T-DNA dalam akar rambut dikonfirmasi meng-gunakan Polymerase Chain Reaction dengan primer spesifik untuk TL dan TR-DNA plasmid. Hasil yang diperoleh menunjukkan bahwa hanya A.rhizogenes galur LB9457 yang efektif menginfeksi eksplan baik batang maupun daun dari kedua spesies kina. Induksi, pertumbuhan dan vigor akar rambut yang terbaik diperoleh dari medium MS dengan penambahan 50 mg/L L-triptofan dan tiga kali konsentrasi vitamin. Hasil konfirmasi akar rambut baik dari batang maupun daun menggunakan PCR, menunjukkan bahwa TL dan TR-DNA dari Ri plasmid A. rhizogenes mampu menghasilkan pita-pita DNA dengan BM780 dan 1600 pb. Hasil yang diperoleh menunjukkan bahwa galur A. rhizogenes, spesies tanaman, sumber eksplan dan komposisi medium berpengaruh terhadap inisiasi, pertumbuhan, perkembangan dan vigor akar rambut.