Two phytoalexin glycosides from potato tubers infected with Phoma

Four coumarins and seven isoprenoid compounds have been identified in potato tubers infected with Phoma exigua var. foveata. Among these were the 7-O-β-D-glucopyranoside of 7-hydroxy-6,8-dimethoxycoumarin (isofraxidin) and the sesquiterpene 2-(11,12-dihydroxy-11-methylethyl)-6,10-dimethyl-spiro[4,5]dec-6-en-8-one and its 12-O-β-D-glucopyranoside, which apparently have not been previously identified in potato tubers. At least two diastereoisomers of the latter glucoside were present. Analysis of eight fluorescent compounds in different parts of infected potatoes was performed by an improved HPLC technique.     

Actions of a versatile fluorene-degrading bacterial isolate on polycyclic aromatic compounds.

Pseudomonas cepacia F297 grew with fluorene as a sole source of carbon and energy; its growth yield corresponded to an assimilation of about 40% of fluorene carbon. The accumulation of a ring meta-cleavage product during growth and the identification of 1-indanone in growth media and washed-cell suspensions suggest that strain F297 metabolizes fluorene by mechanisms analogous to those of naphthalene degradation. In addition to fluorene, strain F297 utilized for growth a wide variety of polycyclic aromatic compounds (PACs), including naphthalene, 2,3-dimethylnaphthalene, phenanthrene, anthracene, and dibenzothiophene. Fluorene-induced cells of the strain also transformed 2,6-dimethylnaphthalene, biphenyl, dibenzofuran, acenaphthene, and acenaphthylene. The identification of products formed from those substrates (by gas chromatography-mass spectrometry) in washed-cell suspensions indicates that P. cepacia F297 carries out the following reactions: (i) aromatic ring oxidation and cleavage, apparently using the pyruvate released for growth, (ii) methyl group oxidations, (iii) methylenic oxidations, and (iv) S oxidations of aromatic sulfur heterocycles. Strain F297 grew with a creosote-PAC mixture, producing an almost complete removal of all aromatic compounds containing 2 to 3 rings in 14 days, as demonstrated by gas chromatography analysis of the remaining PACs recovered from cultures. The identification of key chemicals confirmed that not only are certain compounds depleted but also the anticipated reaction products are found.     

Oxidation of Methyl-Substituted Naphthalenes: Pathways in a Versatile Sphingomonas paucimobilis Strain

Aromatic compounds with alkyl substituents are abundant in fossil fuels. These compounds become important environmental sources of soluble toxic products, developmental inhibitors, etc. principally through biological activities. To assess the effect of methyl substitution on the completeness of mineralization and accumulation of pathway products, an isolate from a phenanthrene enrichment culture, Sphingomonas paucimobilis 2322, was used. Washed cell suspensions containing cells grown on 2,6-dimethylnaphthalene in mineral medium were incubated with various mono-, di-, and trimethylnaphthalene isomers, and the products were identified and quantified by gas chromatography and mass spectrometry. The data revealed enzymes with relaxed substrate specificity that initiate metabolism either by methyl group monoxygenation or by ring dioxygenation. Congeners with a methyl group on each ring initially hydroxylate a methyl, and this is followed by conversion to a carboxyl; when there are two methyl groups on a single ring, the first reaction is aryl dioxygenation of the unsubstituted ring. Intermediates are channeled to primary ring fission via dihydrodiols to form methyl-substituted salicylates. Further evidence that there are multiple pathways comes from the fact that both phthalate and (methyl)salicylate are formed from 2-methylnaphthalene.     

Metabolism of ipomeamarone in sweet potato root slices before and after treatment with mercuric chloride or infection with Ceratocystis fimbriata

Furanoterpenes produced in sweet potato (Ipomoea batatas) root tissue in response to fungal infection or injury with mercuric chloride were metabolized to compounds negative to Ehrlich's reagent. The metabolism of ipomeamarone in sweet potato root tissue was enhanced in response to cut injury. The enhanced metabolism of ipomeamarone in the cut tissue was partly prevented by HgCl₂ treatment. The initial metabolite of ipomeamarone was identified as ipomeamaronol, 15-hydroxyipomeamarone. A time-course analysis of the metabolism of [¹⁴C]ipomeamarone by cut tissue indicated that ipomeamarone was converted to ipomeamaronol, which was further metabolized to unknown compounds.     

A chromosome-level genome assembly of the potato grouper (Epinephelus tukula)

The potato grouper, Epinephelus tukula, is one of the largest coral reef teleost, and it is an important germplasm resource for selection and cross breeding. Here we report a potato grouper genome assembly generated using PacBio long-read sequencing, Illumina sequencing and high-throughput chromatin conformation capture (Hi-C) technology. The genome size was 1.13 Gb, with a total of 508 contigs anchored into 24 chromosomes. The scaffold N50 was 42.65 Mb. For the genome models, our assembled genome contained 98.11% complete BUSCO with the vertebrata_odb9 database. One more copies of Gh and Hsp90b1 were identified in the E. tukula genome, which might contribute to its fast growth and high resistance to stress. In addition, 435 putative antimicrobial peptide (AMP) genes were identified in the potato grouper. This study provides a good reference for whole genome selective breeding of the potato grouper and for future development of novel marine drugs.     

Age- and Organ-Specific Differences of Potato (<Emphasis Type="Italic">Solanum phureja</Emphasis>) Plants Metabolome

Potato Solanum phureja Juz. & Bukasov crop species' metobolome at the flowering stage includes 234 compounds, 117 of which were identified. The most represented group among them contains sugars and their derivatives that are in accordance with intensive carbohydrate exchange of potato tissues and organs. Young leaves and developing reproductive organs are characterized by a wide spectrum of organic and amino acids, nitrogen-containing compounds, and lipids as well as compounds of secondary metabolism that may indicate the intensity of metabolic processes and the formation of defense mechanisms. Depletion of metabolites’ profile in senescent leaves agrees with the idea of weakening synthetic processes in them and the onset of metabolites’ outflow to new forming attracting potato organs. Specificity of metabolic profiles, which corresponds to age and physiological status of potato organ or tissue, was revealed.     

Isolated Phosphate-Solubilizing Soil Bacteria Promotes In vitro Growth of Solanum tuberosum L.

The capacity of four bacterial strains isolated from productive soil potato fields to solubilize tricalcium phosphate on Pikovskaya agar or in a liquid medium was evaluated. A bacterial strain was selected to evaluate in vitro capacity of plant-growth promotion on Solanum tuberosum L. culture. Bacterial strain A3 showed the highest value of phosphate solubilization, reaching a 20 mm-diameter halo and a concentration of 350 mg/l on agar and in a liquid medium, respectively. Bacterial strain A3 was identified by 16S rDNA analysis as Bacillus pumilus with 98% identity; therefore, it is the first report for Bacillus pumilus as phosphate solubilizer. Plant-growth promotion assayed by in vitro culture of potato microplants showed that the addition of bacterial strain A3 increased root and stems length after 28 days. It significantly increased stem length by 79.3%, and duplicated the fresh weight of control microplants. In this paper, results reported regarding phosphorus solubilization and growth promotion under in vitro conditions represent a step forward in the use of innocuous bacterial strain biofertilizer on potato field cultures.Key words: Bacillus sp., phosphorus soluble, Pikovskaya agar, potato rhizosphere, plant growth promoting rhizobacteria     

Potato-associated arbuscular mycorrhizal fungal communities in the Peruvian Andes

The world's fourth largest food crop, potato, originates in the Andes. Here, the community composition of arbuscular mycorrhizal fungi (AMF) associated with potato in Andean ecosystems is described for the first time. AMF were studied in potato roots and rhizosphere soil at four different altitudes from 2,658 to 4,075 m above mean sea level (mamsl) and in three plant growth stages (emergence, flowering, and senescence). AMF species were distinguished by sequencing an approx. 1,500 bp nuclear rDNA region. Twenty species of AMF were identified, of which 12 came from potato roots and 15 from rhizosphere soil. Seven species were found in both roots and soil. Interestingly, altitude affected species composition with the highest altitude exhibiting the greatest species diversity. The three most common colonizers of potato roots detected were Funneliformis mosseae, an unknown Claroideoglomus sp., and Rhizophagus irregularis. Notably, the potato-associated AMF diversity observed in this Andean region is much higher than that reported for potato in other ecosystems. Potato plants were colonized by diverse species from 8 of the 11 Glomeromycota families. Identification of the AMF species is important for their potential use in sustainable management practices to improve potato production in the Andean region.     

Needle in a haystack: Antibacterial activity-guided fractionation of a potato wound tissue extract

Erwinia carotovora is a major cause of potato tuber infection, which results in disastrous failures of this important food crop. There is currently no effective antibiotic treatment against E. carotovora. Recently we reported antibacterial assays of wound tissue extracts from four potato cultivars that exhibit a gradient of russeting character, finding the highest potency against this pathogen for a polar extract from the tissue formed immediately after wounding by an Atlantic cultivar. In the current investigation, antibacterial activity-guided fractions of this extract were analyzed by liquid chromatography-mass spectrometry (LC-MS) utilizing a quadrupole-time-of-flight (QTOF) mass spectrometer. The most active chemical compounds identified against E. carotovora were: 6-O-nonyl glucitol, Lyratol C, n-[2-(4-Hydroxyphenyl)] ethyldecanamide, α-chaconine and α-solanine. Interactions among the three compounds, ferulic acid, feruloyl putrescine, and α-chaconine, representing metabolite classes upregulated during initial stages of wound healing, were also evaluated, offering possible explanations for the burst in antibacterial activity after tuber wounding and a chemical rationale for the temporal resistance phenomenon.     

Involvement of Quinolinate Phosphoribosyl Transferase in Promotion of Potato Growth by a Burkholderia Strain

Burkholderia sp. strain PsJN stimulates root growth of potato explants compared to uninoculated controls under gnotobiotic conditions. In order to determine the mechanism by which this growth stimulation occurs, we used Tn5 mutagenesis to produce a mutant, H41, which exhibited no growth-promoting activity but was able to colonize potato plants as well as the wild-type strain. The gene associated with the loss of growth promotion in H41 was shown to exhibit 65% identity at the amino acid level to the nadC gene encoding quinolinate phosphoribosyltransferase (QAPRTase) in Ralstonia solanacearum. Complementation of H41 with QAPRTase restored growth promotion of potato explants by this mutant. Expression of the gene identified in Escherichia coli yielded a protein with QAPRTase activities that catalyzed the de novo formation of nicotinic acid mononucleotide (NaMN). Two other genes involved in the same enzymatic pathway, nadA and nadB, were physically linked to nadC. The nadA gene was cotranscribed with nadC as an operon in wild-type strain PsJN, while the nadB gene was located downstream of the nadA-nadC operon. Growth promotion by H41 was fully restored by addition of NaMN to the tissue culture medium. These data suggested that QAPRTase may play a role in the signal pathway for promotion of plant growth by PsJN.     

Sesquiterpene-α-amino acid quaternary ammonium hybrids from Stereum complicatum (Steraceae)

Five sesquiterpene-α-amino acid quaternary ammonium hybrids and the sesquiterpene core with no amino acid moiety linked were isolated from the n-butanol partition of the Stereum complicatum fungal culture grown on potato dextrose broth. Chemical structures were unambiguously elucidated by high resolution electrospray ionization mass spectrometry (HR-ESI-MS) in positive ion mode and NMR experiments and were identified as sterostrein Q and stereumamides A - E. The isolation and structure elucidation of these hybrid compounds is reported herein for the first time from S. complicatum. The phytotoxic, antifungal and antibacterial activities of these compounds were evaluated, but no significant activity was found. The HR-ESI-MS fragmentation pattern of the sesquiterpene-α-amino acid quaternary ammonium hybrid metabolites and its chemotaxonomic implication are discussed.     

The use of natural plant volatile compounds for the control of the potato postharvest diseases,black dot,silver scurf and soft rot

Many naturally occurring plant volatile compounds are known for their anti-fungal properties. In this study, acetaldehyde and 2E-hexenal were chosen as prototype volatiles in order to investigate the use of volatile compounds for control of blemish pathogens in fresh-pack potato packaging. Pure cultures of the three main potato blemish pathogens, Pectobacterium atrosepticum (bacterial soft rot), Colletotrichum coccodes (black dot), and Helminthosporium solani (silver scurf), were used in the study. Pathogen cultures were exposed to the pure volatiles that were injected into the atmosphere of sealed jars for 4–8 days at 23 °C. Results showed that 2E-hexenal was the most effective of the two volatiles with 5 μL/L providing complete inhibition of growth for all three pathogens in vitro. Cytological studies showed that a concentration of 2.5 μL/L of 2E-hexenal was capable of inhibiting germination in both fungal pathogens. These results suggest that the primary mode of action of 2E-hexenal was inhibiting germination for fungi and suppressing bacterial growth. The quantities required to achieve pathogen inhibition are extremely low. This study suggests that these volatiles may be used to effectively manage potato postharvest blemish diseases in storage.     

α and β-solamarine in kennebec Solanum tuberosum leaves and aged tuber slices

Two major steroid glycoalkaloids, in addition to α-solanine and α-chaconine, were isolated from leaves and aged tuber slices of potato, Solanum tuberosum L. var Kennebec. They are glycosides of tomatidenol and have been identified as α- and β-solamarine. The compounds were not found in tuber peel or freshly sliced Kennebec tubers or in 20 other cultivars.     

Pyrrolnitrin Production by Biological Control Agent Pseudomonas cepacia B37w in Culture and in Colonized Wounds of Potatoes

Bacterial strain B37w (= NRRL B-14858), an isolate noteworthy because it inhibits the growth of the bioherbicide fungus Colletotrichum truncatum, was selected for further studies of bacterial antifungal properties. This isolate was identified as a Pseudomonas cepacia strain by performing carbohydrate utilization and fatty acid profile analyses, as well as other biochemical and physiological tests. Petri plate assays revealed that strain B37w exhibited antifungal activity against the potato dry rot fungus Fusarium sambucinum. Using bioautography, we correlated antifungal activity with production of a specific compound. Isolation from strain B37w and identification of the antifungal antibiotic pyrrolnitrin are described. A whole-potato assay revealed B37w's ability to colonize potato wounds. Wounded potatoes were inoculated with B37w, and pyrrolnitrin was detected in these potatoes by thin-layer chromatography-bioautography at a concentration on the order of nanograms per wound. We performed an assay in which we examined efficacy against F. sambucinum-incited potato dry rot and found that B37w inhibited disease development. This is the first report of P. cepacia or pyrrolnitrin activity against the economically important potato pathogen F. sambucinum.     

Contitions for optimal growth of a PSTV-infected potato cell suspension and detection of viroid-complementary longer-than-unit-length RNA in these cells

A suspension culture from potato spindle tuber viroid (PSTV)-infected cells of the wild type potato (Solanum demissum) has been established, which is a suitable model system for studying PSTV replicationin vivo. The conditions for rapid growth of these cells and for permanent extensive viroid biosynthesis within them are described. Biosynthesis of PSTV in the potato cells was demonstrated by³²P-incorporation into nucleic acids and their subsequent electrophoretic analysis on polyacrylamide gels. Under optimum culture conditions the amount of³²P-orthophosphate incorporation into PSTV reached 10% of that incorporated into the 2 M LiCl-soluble cellular RNA. (+)PSTV and its complementary form, i.e. (?)PSTV were identified after their electrophoretic separation on polyacrylamide and agarose gels by molecular hybridization. This analysis revealed the presence of six high molecular weight(?)PSTV species, which are possibly multimers of the unit length(+)PSTV molecule consisting of 359 nucleotides.     

Nep1-like proteins as a target for plant pathogen control

The lack of efficient methods to control the major diseases of crops most important to agriculture leads to huge economic losses and seriously threatens global food security. Many of the most important microbial plant pathogens, including bacteria, fungi, and oomycetes, secrete necrosis- and ethylene-inducing peptide 1 (Nep1)-like proteins (NLPs), which critically contribute to the virulence and spread of the disease. NLPs are cytotoxic to eudicot plants, as they disturb the plant plasma membrane by binding to specific plant membrane sphingolipid receptors. Their pivotal role in plant infection and broad taxonomic distribution makes NLPs a promising target for the development of novel phytopharmaceutical compounds. To identify compounds that bind to NLPs from the oomycetes Pythium aphanidermatum and Phytophthora parasitica, a library of 587 small molecules, most of which are commercially unavailable, was screened by surface plasmon resonance. Importantly, compounds that exhibited the highest affinity to NLPs were also found to inhibit NLP-mediated necrosis in tobacco leaves and Phytophthora infestans growth on potato leaves. Saturation transfer difference-nuclear magnetic resonance and molecular modelling of the most promising compound, anthranilic acid derivative, confirmed stable binding to the NLP protein, which resulted in decreased necrotic activity and reduced ion leakage from tobacco leaves. We, therefore, confirmed that NLPs are an appealing target for the development of novel phytopharmaceutical agents and strategies, which aim to directly interfere with the function of these major microbial virulence factors. The compounds identified in this study represent lead structures for further optimization and antimicrobial product development.     

Abundance,diversity and spatio-temporal dynamics of nirS gene-harbouring denitrifiers in a potato field over the course of a growth season

The abundance and diversity of nirS-harbouring bacteria were evaluated in a potato field during a growth season using culture-independent techniques. A total of 182 operational taxonomical units were identified and most had low homology to known nirS sequences, which suggested the discovery of new denitrifiers. The diversity was significantly higher in the furrow, followed by the hill and the near-plant region and was inversely proportional to the denitrification enzyme activity. In contrast, the abundance was not altered by soil locations but was significantly lower at the end of the growth season.     

Temporal shifts of fungal communities in the rhizosphere and on tubers in potato fields

Soil fungal communities perform important ecological roles determining, at least in part, agricultural productivity. This study aimed at examining the fungal community dynamics in the potato rhizosphere across different development stages in two consecutive growing seasons (winter and summer). Microbial fingerprinting of rhizosphere soil samples collected at pre-planting, tuber initiation, flowering and at senescence was performed using ARISA in conjunction with Next Generation Sequencing (Illumina MiSeq). The epiphytic fungal communities on tubers at harvest were also investigated. Alpha-diversity was stable over time within and across the two seasons. In contrast, rhizospheric fungal community structure and composition were different between the two seasons and in the different plant growth stages within a given season, indicating the significance of the rhizosphere in shaping microbial communities. The phylum Ascomycota was dominant in the potato fungal rhizosphere, with Operational Taxonomic Units (OTUs) belonging to the genus Peyronellaea being the most abundant in all samples. Important fungal pathogens of potato, together with potential biological control agents and saprophytic species, were identified as indicator OTUs at different plant growth stages. These findings indicate that potato rhizosphere fungal communities are functionally diverse, which may contribute to soil health.     

Allelopathic interference of sweet potato with cogongrass and relevant species

Cogongrass (Imperata cylindria) is an invasive weed and harmful to ecological systems and agricultural production in many countries. It was found that plant extracts and root exudates of sweet potato (Ipomoea batatas) exhibit allelopathic potential and inhibit the growth of cogongrass to a greater extent than either barnyardgrass (Echinochloa crus-galli), Indian goose-grass (Eleushine indica), or lettuce (Lactuca sativa) in bioassays. Greenhouse trials indicated that sweet potato soil reduced the emergence of the noxious weed by 50 %, yet exhibited either weaker inhibition or the promotion of barnyardgrass, Bidens (Bidens pilosa), and Leucaena (Leucaena leucocephala), while the desired growth of upland rice (Oryza sativa) was not affected. In cogongrass fields, the incorporation of 1–2 tons aboveground parts and cultivation of sweet potato provided 80–85 % weed control. On the other hand, the reduction of congograss in fields may be offset by the alternate invasion of B. pilosa which multiplied its biomass by 2–6 times with sweet potato amended soils. The findings of this study indicate that sweet potato is an effective crop in the biologic management of the invasive cogongrass in agricultural fields, thus the interactive mechanism between sweet potato and the invasive weed demands further investigation. Ecologically, this study highlights the specificity of allelopathic interactions between cogongrass and sweet potato that is helpful to minimize the disturbance from infestation of this invasive weed against native species and crops.