Tran Dang Xuan

Screening for allelopathic potential of higher plants from Southeast Asia

Abstract A preliminary survey on allelopathic plants found in Southeast Asia including Vietnam was carried out during 2000–2002. Nineteen species consisting of weeds, shrubs and trees were selected for their effects on bioassays. Some of these plants have been traditionally used by Vietnamese farmers as field manures and mulches. The allelopathic potential of these plants was elucidated by evaluating the inhibitory exhibition from their leaves, stem and root on germination and growth of radish. The three species showing the greatest allelopathic potential were Galactia pendula , Leucaena glauca and Melia azedarach . Four other species including Desmodium rezoni , Euphobia hirta , Manihot esculenta and Morus alba were assessed to be the second most suppressive to radish germination and growth. Findings also indicated inhibitory exhibition of allelopathic plants were species dependent. Moreover, inhibitory effects varied among plant parts such as the leaves, stem and root.

Molecular Breeding to Improve Salt Tolerance of Rice (Oryza sativa L.) in the Red River Delta of Vietnam

Rice is a stable food in Vietnam and plays a key role in the economy of the country. However, the production and the cultivating areas are adversely affected from the threats of devastation caused by the rise of sea level. Using marker-assisted backcrossing (MABC) to develop a new salt tolerance rice cultivar is one of the feasible methods to cope with these devastating changes. To improve rice salt tolerance in BT7 cultivar, FL478 was used as a donor parent to introgress the Saltol QTL conferring salt tolerance into BT7. Three backcrosses were conducted and successfully transferred positive alleles of Saltol from FL478 into BT7. The plants numbers IL-30 and IL-32 in BC3F1 population expected recurrent genome recovery of up to 99.2% and 100%, respectively. These selected lines that carried the Saltol alleles were screened in field for their agronomic traits. All improved lines had Saltol allele similar to the donor parent FL478, whereas their agronomic performances were the same as the original BT7. We show here the success of improving rice salt tolerance by MABC and the high efficiency of selection in early generations. In the present study, MABC has accelerated the development of superior qualities in the genetic background of BT7.

Correlation between Growth Inhibitory Exhibition and Suspected Allelochemicals (Phenolic Compounds) in the Extract of Alfalfa (Medicago sativa L.)

Abstract Acidic fractions of the extracts from the three alfalfa cultivars Batasu, Rasen, and Yuba exhibited a varietial difference in the inhibitory effect on hypocotyls and radicle growth of alfalfa (cv. Nasuwakaba) and rice (cv. Koshihikari) seedlings. The extract from Rasen possessed the strongest inhibitory activity, and that of Batasu was the lowest. In a TLC bioassay with lettuce seedlings, inhibitory zones of the extracts were located at an Rf value of 0.6 -0.8, and maximum exhibitory zones at Rfs of 0.7-0.8. However, the extracts of Rasen and Yuba contained an additional inhibitory zone at Rf of 0.1-0.2. Inhibitory zones were analyzed by HPLC. Eight phenolic compounds were identified in the extracts from Rasen and Batasu, and six compounds in that from Yuba. However, the content of these phenolic compounds varied with the cultivar. The content of each phenolic compound was the highest in Rasen, followed by Yuba and Batasu, although the content of jft-hydroxybenzoic acid was equivalent in all cultivars. We suppose that the degree of inhibitory exhibition of allelopathy may be related to the presence and concentrations of allelochemicals (phenolic compounds), however, the allelopathic activity of the plant might be determined by interactions of all these compounds, not just a single chemical.

Kava and kava hepatotoxicity: requirements for novel experimental, ethnobotanical and clinical studies based on a review of the evidence.

Kava hepatotoxicity is a well described disease entity, yet there is uncertainty as to the culprit(s). In particular, there is so far no clear evidence for a causative role of kavalactones and non‐kavalactone constituents, such as pipermethystine and flavokavain B, identified from kava. Therefore, novel enzymatic, analytical, toxicological, ethnobotanical and clinical studies are now required. Studies should focus on the identification of further potential hepatotoxic constituents, considering in particular possible adulterants and impurities with special reference to ochratoxin A and aflatoxins (AFs) producing Aspergillus varieties, which should be urgently assessed and published. At present, Aspergillus and other fungus species producing hepatotoxic mycotoxins have not yet been examined thoroughly as possible contaminants of some kava raw materials. Its occurence may be facilitated by high humidity, poor methods for drying procedures and insufficient storage facilities during the time after harvest. Various experimental studies are recommended using aqueous, acetonic and ethanolic kava extracts derived from different plant parts, such as peeled rhizomes and peeled roots including their peelings, and considering both noble and non‐noble kava cultivars. In addition, ethnobotanical studies associated with local expertise and surveillance are required to achieve a good quality of kava as the raw material. In clinical trials of patients with anxiety disorders seeking herbal anxiolytic treatment with kava extracts, long‐term safety and efficacy should be tested using traditional aqueous extracts obtained from peeled rhizomes and peeled roots of a noble kava cultivar, such as Borogu, to evaluate the risk: benefit ratio. Concomitantly, more research should be conducted on the bioavailability of kavalactones and non‐kavalactones derived from aqueous kava extracts. To be on the side of caution and to ensure lack of liver injury, kava consuming inhabitants of the kava producing or importing South Pacific islands should undergo assessment of their liver function values and serum aflatoxin levels. The primary aim is to achieve a good quality of kava raw material, without the risk of adulterants and impurities including ochratoxin A and AFs, which represent the sum of aflatoxin B1, B2, G1 and G2. Although it is known that kava may naturally be contaminated with AFs, there is at present no evidence that kava hepatotoxicity might be due to aflatoxicosis. However, appropriate studies have yet to be done and should be extended to other mould hepatotoxins, with the aim of publishing the obtained results. It is hoped that with the proposed qualifying measures, the safety of individuals consuming kava will substantially be improved. Copyright

Comparative efficacies in vitro of antibacterial, fungicidal, antioxidant, and herbicidal activities of momilatones A and B

Abstract Momilactones A (MA) and B (MB) are phytoalexins derived from rice plant (Oryza sativa) and were considered to be a part of the mechanism of rice self-defense system. The present study was to evaluate the comparative efficacies in vitro of antibacterial, fungicidal, antioxidant, and herbicidal activities of MA and MB. In general, MB shows higher antifungal, antibacterial, and herbicidal action than MA, although its antioxidant property was less than MA. In herbicidal trial, the IC50 values of MB against germination, shoot and root elongation of barnyardgrass and monochoria were 40.9, 45.5, and 27.5, and 27.1, 17.3, and 0.9 µg, respectively. For MA, these values were 40.3, 35.6, and 55.1, and 43.9, 24.3, and 0.5 µg, respectively. For antifungal activity, momilactone B (IC50: 1.2, 123.9, and 53.4 µg) exerted significantly greater inhibition than MA (IC50: 78.1, 198.1, and 95.3 µg) against Botrytis cinerea, Fusarium solani, Colletrotrichum gloeosporioides, respectively, except for Fusarium oxysporum that both MA and MB showed no marked difference. In addition, MB exhibited significantly stronger antibacterial activity than MA against Pseudomonus ovalis, Bacillus cereus, and Bacillus pumilus, whereas the inhibitory activity of the two compounds was similar against Escherichia coli. Both MA and MB exerted rather weak antioxidant activity (EC50 was 783.9 and 790.7 µg, respectively), of which MA showed a slightly stronger antioxidant activity than MB. This study is the first to examine antifungal, antibacterial, and antioxidant activities of two phytoalexins, as well as their comparative efficacies against growth of the noxious weeds barnyardgrass and monochoria.

Phenolic Profiles and Antioxidant Activity of Germinated Legumes

Bioactive compounds, which are naturally produced in plants, have been concerned with the food and pharmaceutical industries because of the pharmacological effects on humans. In this study, the individual phenolics of six legumes during germination and antioxidant capacity from sprout extracts were determined. It was found that the phenolic content significantly increased during germination in all legumes. Peanuts showed the strongest antioxidant capacity in both the DPPH• (1,1-diphenyl-2-picrylhydrazyl) method and the reducing power assay (32.51% and 84.48%, respectively). A total of 13 phenolic acids were detected and quantified. There were 11 phenolic constituents identified in adzuki beans; 10 in soybeans; 9 in black beans, mung beans, and white cowpeas; and 7 compounds in peanuts. Sinapic acid and cinnamic acid were detected in all six legume sprouts, and their quantities in germinated peanuts were the highest (247.9 µg·g−1 and 62.9 µg·g−1, respectively). The study reveals that, among the investigated legumes, germinated peanuts and soybeans obtained maximum phenolics and antioxidant capacity.

Chemical Interaction in the Invasiveness of Cogongrass (Imperata cylindrica (L.) Beauv.)

From gas chromatography-mass spectrometry (GC-MS), numerous plant growth inhibitors were found in the rhizome and root exudates of cogongrass, one of the most problematic weeds in the world. iso-Eugenol, iso-ferulic acid, linoleic acid, ferulic acid, and vanillin were the major chemicals in the rhizome (88.1-392.2 microg/g of fresh root), while 4-acetyl-2-methoxyphenol was the principle substance (872.6 microg/plant) in the root exudates. In fields, the use of cutting and plowing reduced weed biomass and weed density of cogongrass >70%. However, the alternative invasion of beggar tick might be a problem, because its density and biomass increased 33.3 and 62.5%, respectively. Chemicals from cogongrass showed selective effects against tested invasive species. Of them, 2,4-di-tert-butylphenol was the most potent (78.3-100% of inhibition), followed by iso-eugenol and 4-acetyl-2-methoxyphenol. These compounds may play important roles in the invasiveness of cogongrass and might be promising parent constituents of synthesis to develop novel herbicides for control of invasive plants.

Weed-Suppressing Potential of Dodder (Cuscuta hygrophilae) and its Phytotoxic Constituents

Abstract Dodder is a parasitic weed that is troublesome to the growth of many plants. Our study shows that this invasive species contains strong allelopathic potential, exerting strong inhibition against the growth of indicator plants and noxious paddy weeds in bioassay and pot trials. In a greenhouse, incorporation of 0.5 t ha−1 of dried dodder plants to paddy soil reduced spontaneous growth of paddy weeds by about 50%, whereas the 1.5 to 2 t ha−1 dose suppressed biomass of paddy weeds by more than 75% and completely controlled emergence of barnyardgrass and monochoria. By the use of a separation resin, 22 compounds were separated from dodder and identified by gas chromatography–mass spectrometry as belonging to terpenes, long-chain fatty acids, phenols, phenolic acids, and lactone. Among these compounds, 15 substances were quantified and tested for their herbicidal activity. Quantity of cinnamic acid was the highest (37.3 mg g−1), followed by dihydro-5,6-dehydrokavain (DDK; 6.0 mg g−1), myristic acid (3.2 mg g−1), and methyl cinnamate (2.1 mg g−1), whereas the amounts of other compounds were between 0.01 and 0.1 mg g−1. It is suggested that the content of the terpenes within dodder, which was rather high in amount (0.41–2.1 mg g−1), correlated to its strength of chemical cues to find host plants. Cinnamic acid, DDK, methyl cinnamate, and vanillin exerted the most potent herbicidal activities against radish growth. Findings of this study propose that cinnamic acid, DDK, and methyl cinnamate are responsible for its strong phytotoxic action of dodder plants. However, whether these plant growth inhibitors and other compounds detected from the dodder can suppress emergence of their hosts as well as contributing to its strong invasiveness needs further elucidation. Nomenclature: Barnyardgrass, Echinochloa crus-galli P. Beauv. var. oryzicola OHWI; dodder, Cuscuta hygrophilae H. Pearson; monochoria, Monochoria vaginalis (Burm.f.) Presl var. plantaginea Solms; radish, Raphanus sativus L.

Potential biological control of weeds in rice fields by allelopathy of dwarf lilyturf plants

Dwarf lilyturf (Ophiopogonjaponicus Ker-Gawl), a medicinal plant, hasbeen used for sore throat therapy andinhibition of physiological thirst sinceancient times. Experimental studies wereconducted to determine the allelopathic effectsof dwarf lilyturf plants on germination andgrowth of three main weed species, viz.,barnyardgrass (Echinochloa crusgalli L.),monchoria (Monocharia vaginalis P.) andsmallflower umbrella (Cyperus difformisL.), in rice production and on emergence andgrowth of weeds in rice fields in Japan. Theseresults showed that all aqueous extracts (1, 2,4, 8%, w/v) from the dried powders ofunderground parts of dwarf lilyturf containedwater-soluble substances that significantlyinhibited seed germination and seedling growthfor monchoria and smallflower umbrella. Withrespect to barnyardgrass, all aqueous extractshad less effect on germination, but lowconcentrations (<2%, w/v) had stimulatoryeffects on growth. However, higherconcentrations (>4%, w/v) had significantinhibitory effects. In a glasshouse experiment,all treatments (50, 100, 150 g m−2) of thedried powders significantly inhibited theemergence and dry weights of weeds in ricepaddy fields and the inhibition became strongeras the concentration increased, except that50 g m−2 concentration had slightstimulatory effects on the emergence ofbarnyardgrass. The 150 g m−2 concentrationmarkedly inhibited emergence (77.6%) and dryweight (91.1%) of rice field weeds. Inaddition, all treatments had no inhibition oninitial rice plant growth. Dwarf lilyturfplants may have inhibitory potential on weedsas a natural rice field herbicide.

Rapid and high-precision marker assisted backcrossing to introgress the SUB1 QTL into the Vietnamese elite rice variety

Submergence stress regularly influences about 15 million hectares of rice growing areas in South and Southeast Asia. Vietnam is one of the most vulnerable countries affected by submergence stress in Asia. Submergence caused by typhoons and floods is one of the major reasons for rice production losses in this country. A major quantitative trait locus (QTL) on chromosome 9, SUB1, has provided the opportunities to apply marker-assisted backcrossing (MABC) to develop submergence tolerant for an elite variety that is popularly grown in Vietnam. Improving rice tolerance with submergence is vital to minimize the risks from submergence stress. In this study, we reported a successful application of MABC method to select a line number 19 in BC2F1 populations that has genetic background up to 89.8%.