Influence of Mycorrhizal Tobacco Roots, Incorporated Into the Soil, on the Development of Thielaviopsis basicola

The interaction between the soil-borne pathogen Thielaviopsis basicola and mycorrhizal roots infected by Glomus microcarpum has been studied during 4 months. A significant reduction in the number of propagules was observed in soils treated with mycorrhizal roots and an inhibition of T. basicola growth by a substance produced by mycorrhizal roots is suggested.     

Effects of root residues on growth ofPinus radiata seedlings and a mycorrhizal fungus

The height of Pinus radiata Don seedlings grown on soils incorporating different proportions of root tissues (25 and 50%) was shown to be reduced by 20–80%. Seedlings watered with aqueous extracts from soil/root mixtures also showed a significant reduction in growth. This growth-retarding effect was partially overcome by the addition of nutrients or by soil sterilisation. It is postulated that growth retardation was caused not only by nutrient deficiency resulting from the addition of organic matter with a high C/N ratio, but also by phytotoxic substances present in the root tissue. The effect of water extracts of roots from old P. radiata trees on the growth of young P. radiata seedlings and on a mycorrhizal fungus (Rhizopogon sp.) under aseptic conditions was also studied. Extracts from the inner bark of roots caused complete growth inhibition of the mycorrhizal fungus as well as root necrosis and wilting of P. radiata seedlings. A water-soluble substance or substances, toxic both to the roots of P. radiata and to its mycorrhizal fungus, is postulated as the causal agent.     

An alternative explanation for plant growth promotion by bacteria of the genus Azospirillum

Experiments were performed to identify the substances that are excreted by the soil bacterium Azospirillum brasilense Sp7 and that were reported to stimulate the formation of lateral roots and of root hairs of grasses. Azospirillum forms indole-3 acetic acid (IAA) but only in the late stationary growth phase or when tryptophan is present in the medium, but not in continuous cultures or in the logarithmic growth phase of batch cultures. Formation of IAA by Azospirillum requires aerobic conditions. Nitrite can replace IAA in several phytohormone assay, and is even more active than IAA in a test with wheat root segments in which the increase of wet weight is determined. Higher amounts of nitrite are necessary for activity in other classical auxin assays. Nitrite shows 40–60% of the activity of IAA in the straight-growth test of Avena coleoptiles and in the formation of C₂H₄ by pea epicotyl segments. Like IAA, nitrite is inactive in promoting C₂H₄ formation by ripe apple tissues. Since nitrite alone can hardly exert phytohormonal effects, it is postulated that nitrite reacts with a substance in the cells and that a product formed by this reaction functions as auxin. Such a substance could be ascorbate. Exogenously added ascorbate enhances the rate of nitrite-dependent C₂H₄ formation by pea epicotyl sections and the nitrite-dependent increase in the wet weight of wheat root segments. Nitrite is formed by nitrate respiration of Azospirillum. The findings that nitrite can have phytohormonal effects offers an alternative explanation of the promotion of the growth of roots and the enhancement of mineral uptake of grasses by Azospirillum. Indole-acetic acid completely and nitrite partly substitute for an inoculation with Azospirillum in an assay where the increase of the dry weight of intact wheat roots is determined after an incubation for 10 d. Nitrite and IAA are, therefore, possibly the only factors causing an enhancement of the growth of roots of grasses.Abbreviations HPLC high-performance liquid chromatography - IAA indole-3-acetic acid     

Isolation and identification of a potent allelopathic substance in Bangladesh rice

Aqueous methanol extracts of Bangladesh rice (Oryza sativa L. cv. BR17) inhibited the growth of roots and shoots of cress (Lepidium sativum), lettuce (Lactuca sativa), alfalfa (Medicago sativa), timothy (Phleum pratense), Digitaria sanguinalis, Echinochloa crus-galli and Echinochloa colonum. Increasing the extract concentration increased the inhibition, suggesting that the BR17 may have growth inhibitory substances and possess allelopathic potential. The aqueous methanol extract of the BR17 was purified and a main inhibitory substance was isolated and determined by spectral data as 2,9-dihydroxy-4-megastigmen-3-one. This substance inhibited root and shoot growth of cress and E. crus-galli seedlings at concentrations greater than 0.03 and 3 μM, respectively. The concentrations required for 50% growth inhibition on cress roots and shoots were 0.22 and 0.47 μM, respectively, and on E. crus-galli roots and shoots were 36 and 133 μM, respectively. These results suggest that 2,9-dihydroxy-4-megastigmen-3-one may contribute to the growth inhibitory effect of BR17 and may play an important role in the allelopathy of BR17. Thus, Bangladesh rice BR17 may be potentially useful for weed management in a field setting. An erratum to this article can be found at     

Effect of indoleacetic acid,abscisic acid,root tips and coleoptile tips on growth and curvature of maize roots

The effect of externally applied indoleacetic acid (IAA) and abscisic acid (ABA) on the growth of roots of Zea mays L. was measured. Donor blocks of agar with IAA or ABA were placed laterally on the roots and root curvature was measured. When IAA was applied to vertical roots, a curvature directed toward the donor block was observed. This curvature corresponded to a growth inhibition at the side of the root where the donor was applied. When IAA was applied to horizontal roots from the upper side, normal geotropic downward bending was delayed or totally inhibited. The extent of retardation and the inhibition of curvature were found to depend on the concentration of IAA in the donor block. ABA neither induced curvature in vertical roots nor inhibited geotropic curvature in horizontal roots; thus the growth of roots was not inhibited by ABA. However, when, instead of donor blocks, root tips or coleoptile tips were placed onto vertical roots, a curvature of the roots was observed.Abbreviations ABA abscisic acid - IAA 3-indoleacetic acid     

Diterpene Phytoalexins Are Biosynthesized in and Exuded from the Roots of Rice Seedlings

Rice (Oryza sativa L.) produces a variety of diterpene phytoalexins, such as momilactones, phytocassanes, and oryzalexins. Momilactone B was previously identified as an allelopathic substance exuded from the roots of rice. We identified in this present study momilactone A and phytocassanes A–E in extracts of, and exudates from, the roots of rice seedlings. The concentration of each compound was of the same order of magnitude as that of momilactone B. Expression analyses of the diterpene cyclase genes responsible for the biosynthesis of momilactones and phytocassanes suggest that these phytoalexins found in roots are primarily biosynthesized in those roots. None of phytocassanes B–E exhibited allelopathic activity against dicot seedling growth, whereas momilactone A showed much weaker allelopathic activity than momilactone B. The exudation of diterpene phytoalexins from the roots might be part of a system for defense against root-infecting pathogens.     

THE ROLE OF ALLELOPATHIC SUBSTANCES IN THE “SMOTHER CROP” BARLEY

The high degree of success of barley as a “smother crop” generally has been attributed to physical competition for nutrients and water. However, it was found that even in the absence of such competition, barley still inhibits germination and growth. This occurred both in mixed cultures receiving adequate nutrients and water and in germination tests. Aqueous leachates of seeds and roots of barley caused similar inhibition of germination and growth, thereby indicating an inhibitory allelopathic substance. A specificity of reaction was found, with the greatest inhibition occurring with Stellaria media (L.) Cyr., less with Capsella bursa-pastoris (L.) Medic. and tobacco (Nicotiana tabacum L.), and no significant effect with wheat (Triticum aestivum L.). A concentration effect and possible periodic production of the inhibitor were indicated. Living plants and aqueous leachates of living roots were more inhibitory than dead ones, thereby supporting the hypothesis of an active metabolic secretion of the allelopathic substance. Preliminary attempts to identify the active inhibitory components demonstrated the presence of alkaloids, with a much greater concentration of substance in the living than in the dead root leachates. The alkaloid, gramine, known to occur in barley, was found to have an inhibitory effect on the growth of Stellaria media and it is suspected as an active component of the root leachates. These results suggest that factors other than the previously assumed physical competition are involved in the mechanism of the “smother crop” barley.     

The allelopathic potential of alfalfa root medicagenic acid glycosides and their fate in soil environments

Summary The allelopathic effect of alfalfa (Medicago media Pers.) and red clover (Trifolium pratense L.) root saponins on winter wheat seedling growth and the fate of these chemicals in soil environments were studied. Seed germination, seedling and test fungus growth were suppressed by water and by alcohol extracts of alfalfa roots, and by crude saponins of alfalfa roots, indicating that medicagenic acid glycosides are the inhibitor. Powdered alfalfa roots inhibited wheat seedling growth when added to sand. At concentrations as low as 0.25% (w/w) the root system was completely destroyed whereas seedling shoots suffered little damage. Red clover roots caused some wheat growth inhibition when incorporated to sand, but their effect was much lower than in the alfalfa root treatment. Soil textures had a significant influence on the inhibitory effect of alfalfa roots. The inhibition of seedling growth was more pronounced on light than on heavy soils. This was attribted to the higher sorption of inhibitors by heavy soils. Incubation of alfalfa roots mixed into loose sand, coarse sand, loamy sand and clay loam for a period of 0–8 days resulted in decreased toxicity to bothT. viride and wheat seedlings. This decrease occurred more quickly in heavier soils than in loose sand, due to the hydrolysis of glycosides by soil microorganisms. Soil microbes were capable of detoxifying medicagenic acid glycosides by partial hydrolysis of sugar chain to aglycone. These findings illustrate the importance of medicagenic acid glycosides as an inhibitor of wheat seedling growth, and of their fate in different soil environments.     

Effect of applied and endogenous indol-3-yl-acetic acid on maize root growth

The level of endogenous Indol-3-yl-acetic acid (IAA) measured by gas chromatography-mass spectrometry in the elongating zone of intact primary roots of Zea mays showed a good linear correlation with the growth rate of these roots. When they were treated with IAA, their relative elongation decreased; this indicates a supraoptimal content of endogenous IAA. However, the growth of some of the relatively rapidly extending roots was enhanced by such treatment. Interactions between endogenous and applied IAA in the control of root growth are discussed.Abbreviations GC-MS gas chromatography-mass spectrometry - IAA Indol-3-yl-acetic acid     

Growth promotion effect of Fusarium spp. PPF1 from bermudagrass (Cynodon dactylon) rhizosphere on Indian spinach (Basella alba) seedlings are linked to root colonisation

A rhizosphere fungus was isolated from roots of bermudagrass (Cynodon dactylon) and identified as Fusarium spp. PPF1. A pot experiment was conducted to test its ability to promote the vegetative growth of Indian spinach seedlings (Basella alba). Indian spinach seeds were sown in sterilised field soil amended with wheat grain inoculum of PPF1 at the rate of 0.5 and 1.0% w/w, and plants were grown for 21?days in a net house. Significantly, higher germination percentage and vigour index were observed due to application of PPF1 in the potting soil. Treatment with PPF1 also significantly increased shoot length, shoot fresh weight, shoot dry weight, root length, root fresh weight, root dry weight, leaf area and leaf chlorophyll content of cucumber plants compared to non-treated control. The growth promotion rate increased with the increasing concentration of inoculum of PPF1 applied to the soil. The fungus was re-isolated from the roots of cucumber plants at higher frequencies, while a positive co-relation was found between the root colonisation ability and the plant growth enhancement by the isolate. These results suggest that growth promotion effect of Fusarium spp. PPF1 on Indian spinach (B. alba) are linked to root colonisation ability of the fungus.     

Biofumigation: Isothiocyanates released frombrassica roots inhibit growth of the take-all fungus

The presence of root tissue of the brassicas canola and Indian mustard inhibited growth of pure cultures of the fungal pathogen which causes take-all of wheat [Gaeumannomyces graminis (Sacc.) Arx and Oliver var.tritici, abbreviated as Ggt]. Ggt growth was generally inhibited more in the presence of Indian mustard roots than canola roots. Dried irradiated roots were consistently effective in reducing Ggt growth, but growth inhibition by young live roots and macerated roots was not consistent. The inhibitory compound(s) were shown to be volatile because the symmetry of Ggt growth was not affected by the proximity of theBrassica tissue. Volatile breakdown products from maceratedBrassica roots were identified using a gas chromatograph-mass spectrometer. The major compounds found were isothiocyanates (ITCs). Canola roots released mostly methyl ITC and Indian mustard roots released mostly phenylethyl ITC. Low concentrations of these and related compounds inhibited growth of Ggt in pure culture when supplied as the vapour of pure chemicals in concentrations within the range expected during breakdown ofBrassica roots in soil.     

Effects of lemon balm (Melissa officinalis L.) extract on germination and seedling growth of six plants

The n-hexane-, acetone- and water-soluble fractions obtained from an aqueous acetone extract of lemon balm (Melissa officinalis L.) shoots inhibited the germination and the growth of roots and shoots of cockscomb (Amaranthus caudatus L.), cress (Lepidium sativum L.), crabgrass (Digitaria sanguinalis L.), timothy (Phleum pratense L.), lettuce (Lactuca sativa L.) and ryegrass (Lolium multiflorum Lam.). The inhibitory activity of the water-soluble fraction was the greatest, followed by that of acetone- and n-hexane-soluble fractions in all bioassays. The effectiveness of these fractions on the roots was greater than that of the shoots of the test plants. Significant reductions in the germination and growth of the roots and shoots were observed as the extract concentration increased. Such rate-dependent responses of the test plants to the fractions suggest that each fraction might contain allelochemical(s), but that the greatest potential was in the water-soluble fraction.     

Stimulation of artemisinin production in Artemisia annua hairy roots by the elicitor from the endophytic Colletotrichum sp.

Artemisinin content in hairy roots of Artemisia annua was increased from 0.8 mg g^–1 dry wt to 1 mg g^–1 dry wt by using elicitor treatment of mycelial extracts from the endophytic fungus Colletotrichum sp. The increase of artemisinin was dependent on the growth stage of hairy roots as well as on the dose of the elicitor applied. When hairy roots of 23-day-old cultures (later growth phase) were exposed to the elicitor at 0.4 mg total sugar ml^–1 for 4 days, the maximum production of artemisinin reached to 13 mg l^–1, a 44% increase over the control. This is the first report on the stimulation of artemisinin production in hairy roots by the elicitor from an endophytic fungus of A. annua.     

Effect of Lysophosphatidylethanolamine and Brassinosteroids on Development of <Emphasis Type="Italic">Arabidopsis</Emphasis> Roots

Exogenously applied lysophosphatidylethanolamine (LPE) increased the growth of primary roots and the formation of lateral roots in Arabidopsis thaliana. In the presence of brassinolide, lateral root formation induced by LPE was enhanced, implying that both LPE and brassinosteroids (BR) interact positively in the development of Arabidopsis roots. Co-treatment with LPE and BRs increased the bending activity in the rice lamina inclination assay compared to that when BRs were applied alone, suggesting that LPE seems to exert its activity via BRs activity. RT-PCR revealed that LPE did not alter the expressions of genes involved in the biosynthesis of BRs but did activate the expressions of BR signaling genes in A. thaliana. In a BR-insensitive mutant, bri1, enhanced gravitropic response by LPE in wild-type A. thaliana was diminished. In conclusion, LPE is a positive regulator for the growth and development of Arabidopsis roots, and this process seems to be enhanced by BR signaling rather than by increase in endogenous levels of BRs in A. thaliana.     

Cytokinin Production by Tomato Root: Occurrence of Cytokinins in Staled Medium of Root Culture

Cytokinins were released into the medium by cultures of excised tomato (Lycopersicon esculentum Mill.) root tips. A large portion was directly released from the proximal cut-end of the roots. The most active substance was found to co-chromatograph with zeatin riboside in both paper and Sephadex column chromatographies. The cytokinin activity after 7 days of growth was found about eight times higher in the medium as compared with that in the root tissues. When freshly excised root tips were subcultured throughout eight passages, the accumulation of cytokinin in the medium of each passage was approximately the same. These results show that the root tip is a main site of cytokinin synthesis.     

Use of morphometric analysis for characterization of tobacco root growth in relation to infection byPhytophthora parasitica var.nicotianae

Development of tobacco root systems was characterized under controlled environmental conditions by use of morphometric root analysis. According to the classification scheme of this system, roots terminating in apical meristems are defined as first-order roots. Elements of second-order roots begin where two first-order roots merge, and so forth. Growth of root systems was similar for susceptible and resistant tobacco cultivars in nonautoclaved and autoclaved soils. During 15 days of growth subsequent to transplanting of 2-week-old plants, relative multiplication and extension rates of first-order and second-order roots were constant. Apparent unit extension rates of first-order and second-order root elements increased through 15 days of root system growth. Classification of tobacco root systems by the morphometric scheme provided a useful means of partitioning susceptibility of tissues to infection byPhytophthora parasitica var.nicotianae. Zoospores applied at the tips of first-order roots were most successful in causing infections; 73.3% of the roots inoculated with 16 zoospores per root tip became infected. Percentages of infections after inoculation of first-order root tissues 2 cm behind root tips or after inoculation of second-order roots were 10 and 4.3%, respectively.Florida Agricultural Experiment Station, Journal Series Paper 8106.     

Growth of transformed roots in a nutrient mist bioreactor: reactor performance and evaluation

Summary A nutrient mist bioreactor was modified for culturing transformed roots of Beta vulgaris and Carthamus tinctorius on a nylon support. Culture conditions of misting cycle, inoculum size, batch or continuous operation and sucrose concentration were varied in order to maximize growth over a 1-week period. Root tissue cultured in nutrient mists in a 1.8-1 culture chamber achieved levels of growth equivalent to hairy roots cultured in shake flasks with identical medium. Our results demonstrate the effectiveness of nutrient mist culture as applied to hairy roots, thereby providing an alternative means for successful culture of these tissues. Correspondence to: A. A. DiIorio     

Growth retarding and stimulating effects of CCC on Antirrhinum majus L.

Summary Stimulation of stem growth on snapdragon, Antirrhinum majus, by foliar sprays with CCC has been reported by Halevy and Wittwer (1965). Soil application gave little or no effect on growth. Our results confirm the observations by Halevy and Wittwer on stimulated stem elongation when CCC is applied as a foliar spray. However, growth was significantly retarded when the growth regulator was applied to the roots. At present there is no explanation for these findings.     

Isolation and structural elucidation of a growth stimulant for arbuscular mycorrhizal fungus from Laminaria japonica Areschoug

Arbuscular Mycorrhizal (AM) fungi enhance terrestrial plant growth by forming a symbiotic relationship with the roots of its host plant. A growth stimulant for AM fungi was isolated from a brown alga Laminaria japonica Areschoug. The active substance for in vitro AM hyphal growth was isolated from 75% methanol extracts of L. japonica using a succession of chromatographic procedures, including flash chromatography equipped with an octa decyl silane (ODS) column, gel filtration chromatography and HPLC using an ODS column. Spores of Gigaspora margarita Becker & Hall, an AM fungus, were exposed to the compound in vitro, and hyphal growth of G. margarita was measured after two weeks of incubation. At 40 mg L⁻¹, the compound significantly stimulated the in vitro hyphal growth of G. margarita, compared to the control. This compound was elucidated as 5′-deoxy-5′-methylamino-adenosine by EIMS and NMR spectrum.     

雷公藤组培产物的杀虫杀菌活性研究

采用室内生测法研究了雷公藤愈伤组织、悬浮细胞、不定根等组培产物对小菜蛾毒杀、生长发育影响以及不定根提取物对番茄灰霉病等植物病原真菌菌丝生长抑制作用,以明确雷公藤组培产物的生物活性及其应用前景。结果表明,不同雷公藤组培产物对小菜蛾3龄幼虫都具有明显的毒杀作用,悬浮细胞以及不定根的LC50均超过了根皮粉的效果,其中的不定根提取物对小菜蛾3龄幼虫毒杀作用的LC50为根皮粉的1.95倍;不同组培产物提取物对小菜蛾幼虫的生长均有明显的抑制作用,其中不定根提取物处理后每天的小菜蛾体重显著下降,72h后70%左右已经死亡,存活的试虫体重比试验前下降了18.33%;雷公藤不定根提取物对供试的11种植物病原真菌菌丝生长均有一定的抑制作用,有5种的抑制率超过60%,并对番茄灰霉病菌的抑制作用最强,其EC50为10.074mg/mL,且不定根的抑制效果均超过了根皮粉的抑制效果。