Allelopathic interactions among algae

Five species of green algae isolated from the Cleveland County, Oklahoma, area and a commercially obtained yellow-green alga were tested for allelopathic interactions. Axenic cultures ofPandorina morum Bory were stimulated in three sterile filtrates from nonaxenic cultures ofScenedesmus incrassatulus var.mononae G.M. Smith, with the oldest filtrate showing the least stimulation. By measuring the growth of axenic cultures inoculated into sterile filtrates of old cultures, instances of inhibition and stimulation were recorded in three screening experiments.Cosmarium vexatum West filtrate was inhibitory to the five other species, a characteristic probably important in its role of producing waterblooms in ponds and swamps. The allelopathic effects of filtrates of the five other species onBolrydium becherianum Vischer could be a key to its restriction to terrestrial sites. Instances of heat lability of the active substances were noted. These interactions, both allelopathic and stimulatory, probably play a significant role in the succession of algal blooms in nature.     

Synergistic inhibitory effects of vanillic andp-hydroxybenzoic acids on radish and grain sorghum

Radish and grain sorghum germination and sorghum growth were inhibited in a synergistic manner by combinations of vanillic andp-hydroxybenzoic acids. At threshold inhibition levels, 2.5 × 10^–3 M vanillic acid-treated radish seeds had 71 % of control germination after 24 hr and 2.5 × 10^–3 Mp-hydroxybenzoic acid-treated radish yielded 95% germination. A mixture of 2.5 × 10^–3 M of each of these two phytotoxins showed 52% germination after 24 hr. Equimolar mixtures of 5 × 10^–3 M vanillic andp-hydroxybenzoic acids allowed sorghum germination of 60% of untreated seeds after 24 hr, whereas separate treatments of individual phenols had 93% and 96% of control seed germination. Sorghum root and shoot elongation and total seedling growth were more sensitive than germination to vanillic andp-hydroxybenzoic acid treatments, and synergistic effects also were apparent. A combination of 5 × 10^–3 M vanillic with 5 × 10^–3 Mp-hydroxybenzoic reduced root length more than either did individually, and a mixture of 5 × 10^–4 M vanillic with 5 × 10^–4 Mp-hydroxybenzoic acid reduced sorghum seedling growth to approximately that resulting from a 10^–3 M concentration of either phenol alone. Phytotoxin levels inhibitory to sorghum growth caused small increases in lower leaf surface diffusive resistance, but did not close stomates, and this effect was not judged to be the cause of reduced sorghum growth.     

Isolation,characterization and activity of phytotoxic compounds from quackgrass [Agropyron repens (L.)Beauv.]

Previous experiments showed that legumes grown in the presence of living or herbicidally treated quackgrass residues or extracts exhibited reduced seedling root and shoot growth and decreased nodulation and nitrogen fixation. Aqueous extracts of quackgrass shoots were most inhibitory to plant growth. Upon sequential partitioning of an aqueous extract of quackgrass shoots, the ether extract possessed the most activity and caused 50% reductions in radicle elongation of eight crop and weed species at concentrations of less than 240 g/ml (small-seeded species) and 1000 g/ml (large-seeded species). Snapbeans (Phaseolus vulgaris L. Bush Blue Lake) grown aseptically in agar containing an ether extract at 100 and 200 g/ml exhibited severe root browning, lack of root hair formation, and a two- to three-fold reduction in root and shoot dry weights. The ether extract of quackgrass shoots had no inhibitory effect on the growth of fourRhizobium species in Petri dishes or two species in broth culture. Inhibitors present in the ether extract may influence the legumeRhizobium symbiosis indirectly by reducing legume root growth and root hair formation. The ether extract of quackgrass shoots was separated using high-pressure liquid, thin-layer, and liquid column chromatography in an attempt to isolate and identify the inhibitors responsible for the inhibition of seedling growth. Two closely related flavonoid inhibitors were isolated from the ether extract. One was identified as 5,7,4-trihydroxy-3,5-dimethoxyflavone (tricin). Both flavonoids caused 50% inhibition of radicle elongation in cress (Lepidium sativum L. Burpee curly) seeds at concentrations of less than 125 g/ml. Both flavonoids were found in ether extracts of quackgrass shoots and rhizomes, but the largest amounts of both compounds occurred in quackgrass shoots collected from the field.Journal article No. 11887 of the Michigan Agricultural Experiment Station.     

Effects of Vaccinium myrtillus on Spruce Regeneration: Testing the Notion of Coevolutionary Significance of Allelopathy

Failure of natural regeneration of conifers, such as subalpine spruce (Picea abies) and black spruce (Picea mariana), has been reported in the presence of dominant ericaceous understory plants of boreal forests of North America, Fino-Scandinavia, and northern Europe. Among other factors such as competition for light and nutrients, conifer regeneration failure has been attributed to allelopathic effects of the understory ericaceous plants. Rabotnov theorized that (the manifestation of) allelopathy is a result of long-term coevolution within established plant communities and that it may have maximum inhibitory effects on introduced species. Our objectives were to determine what components of the understory ericaceous plant, Vaccinium myrtillus, affect spruce regeneration and to test Rabotnov's hypothesis. Field experiments were complemented with laboratory studies in which seed germination and primary growth of the two spruces were used as response variables. We found that P. mariana was generally more affected than P. abies by V. myrtillus allelochemicals, both in field and in vitro experiments. Field germination of P. abies was only 2% and 3% in the undisturbed sowed plots and in Vaccinium-removed sowed plots, respectively, but P. marana did not germinate at all in these treatments. In humus-removed sowed plots, P. abies had 27% germination, while P. marian had only 15%. In a controlled experiment, P. mariana had the highest decrease in dry weight of primary root in the fresh leaf treatment of V. myrtillus (77%), followed by its leaf leachate (71%), humus (29%), and humus leachate (13%). The decreases in root dry weights of P. abies due to these treatments were 67, 47, 30, and 10%, respectively. Our results provide support for Rabotnov's hypothesis. It is possible that both V. myrtillus and Kalmia angustifolia, involved in the growth inhibition process of P. abies and P. mariana, respectively adopted similar "strategies" of allelopathic inhibition of conifers, by allocating a large part of their carbon pool to the production of secondary metabolites.     

Effect of apiforol and apigeninidin on growth of selected fungi

Selected fungi were grown on agar plates in the presence of naringenin, apiforol, apiforol 7-O-rhamnoglucoside, or apigeninidin. Of the four compounds tested, only apigeninidin inhibited the growth ofFusarium oxysporum, Gibberella zeae, Gliocladium roseum, Altemaria solani, and Phytophthora infestons. In contrast, the growth ofRhizoctonia solani, Sclerotium rolfsii, and Rhizopus stolonifer (– and +) was not effected by any compound. Since apigeninidin is present in seeds ofSorghum sp., we hypothesize that apigeninidin may play a role in mold resistance and that apiforol accumulates as a biosynthetic precursor of apigeninidin, not as a fungal defense compound.     

Effects of juglone on growth,photosynthesis, and respiration

The impacts of juglone on plant growth and several other physiological functions were evaluated in this study. Juglone inhibitedLemna minor growth, chlorophyll content, and net photosynthesis at treatments between 10 and 40M. Soybean leaf disks vacuum infiltrated with as little as 10M juglone had reduced photosynthesis. Oxygen evolution by chloroplasts isolated fromPisum sativum was inhibited by juglone with an I₅₀ of 2M. Micromolar treatments of juglone stimulated oxygen uptake in mitochondria isolated fromGlycine max. These data suggest perturbations of chloroplast and mitochondrial functions may contribute to plant growth reductions observed in juglone-mediated allelopathy.This study was supported by National Science Foundation grant STI-8902066.     

A 75% reduction in herbicide use through integration with sorghum + sunflower extracts for weed management in wheat

BACKGROUND: To reduce herbicide use by 75%, integrated use of sorghum and sunflower extracts each at 18 L ha^?1 combined with 1/4^th (75% less) of label rates of four herbicides (mesosulfuron + idosulfuron, metribuzin, phenoxaprop‐p‐ethyl and isoproturon) were investigated for the management of wild oat and canary grass, the two pernicious weeds in wheat fields worldwide. RESULTS: The results revealed that sorghum + sunflower extracts combined with 1/4^th (75% less) of label rates of herbicides inhibited dry matter production of wild oat by up to 89% and canary grass by up to 92%. The wild oat and canary grass persistence index in sorghum + sunflower extracts combined with 1/4^th (75% less) of label rates of herbicides was either lower or equal to respective label rates of herbicides, except sorghum + sunflower extract + 1/4^th phenoxaprop‐p‐ethyl. Lower herbicide rates + water extracts also produced wheat grain yield statistically equal with label rates of respective herbicides. Two treatments having water extracts + lower herbicides rates were economical and sorghum + sunflower + 1/4^th mesosulfuron + idosulfuron produced the highest (4404%) marginal rate of return. CONCLUSION: Herbicides use can be reduced by 75% through integration with sorghum + sunflower extracts without compromising yield and net benefits for cost‐effective and eco‐friendly management of wild oat and canary grass in wheat. Copyright © 2010 Society of Chemical Industry     

Allelopathic potentials of alfalfa (Medicago sativa) saponins: Their relation to antifungal and hemolytic activities

A wheat seedling bioassay was used to indicate the relationship between the chemical structure of alfalfa saponins and their allelopathic activity. None of the tested saponins significantly influenced wheat germination. Seedling growth bioassays indicated significant differences among the activities of individual glycosides. The most active were medicagenic acid, its glycosides substituted at the C-3 position with glucose, and hederagenin monoglycoside. Medicagenic acid glycosides, substituted at the C-3 position with glucuronic acid, and zahnic acid tridesmoside were less active. No significant correlation was found among the allelopathic, hemolytic, and antifungal activities of the individual glycosides.     

Effect of temperature and sucrose concentration on hydroquinone toxicity in leafy spurge suspension culture cells

Euphorbia esula (leafy spurge) suspension culture cell bioassays were used to determine whether sucrose accumulation enhanced the glucosylation (detoxification) of hydroquinone in this noxious weed. The bioassay results indicate that cold temperatures and exogenous hydroquinone represent a dual stress to spurge cell growth that can be partially ameliorated by hydrolysis of sucrose. The persistent susceptibility of leafy spurge suggests that hydroquinone-producing forage plants (which are not toxic to animals) might be used as natural competitors.