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1.
A study was conducted to assess the phytotoxicity of Ageratum conyzoides, a weed of cultivated areas, to the growth and establishment of wheat (Triticum aestivum). The lengths of the radicle and coleoptile and the seedling dry weight of wheat were significantly reduced when wheat was grown in field soil previously infested with A. conyzoides, compared to control soil collected from an area devoid of this weed. Even extracts prepared from A. conyzoides soil were inhibitory, indicating the presence of some water‐soluble phytotoxins in the soil. To determine the possible contribution of the weed in releasing these phytotoxins, growth studies involving leaf residues and their extracts and amended soils (prepared by incorporating leaf residues and residue extracts) were also performed on wheat. With all treatments, an inhibitory effect of A. conyzoides was found, compared to respective controls. A significant amount of water‐soluble phytotoxins (the phenolics) was found to be present in the soil infested with A. conyzoides, leaf residues and the amended soils. The amount of phenolics correlated well with growth performance in the respective treatments. This study establishes the phytotoxicity of leaf residues of A. conyzoides to wheat through the release of phenolics into the soil, which may serve as possible tools in establishing its allelopathy.  相似文献   

2.
Unknown compounds in crop plants are inhibitory to seed germination and early seedling growth of weed plants. A Petri dish assay showed that barley (Hordeum vulgare L.), oats (Avena sativa L.), rice (Oryza sativa L.) and wheat (Triticum aestivum L.) extracts significantly reduced root growth of alfalfa (Medicago sativa L.), barnyard grass (Echinochloa crus‐galli, Beauv. var. oryzicola Ohwi.) and eclipta (Eclipta prostrata L.). As the concentration of crop extracts increased, root growth of the test plants were significantly reduced. A high‐performance liquid chromatography analysis with nine standard phenolic compounds showed that the concentrations and compositions of allelopathic compounds depend on the extracted plant extracts. Caffeic acid, hydro‐cinnamic acid, ferulic acid, m‐coumaric acid, p‐coumaric acid and coumarin were present in all the crop plant species, and hydro‐cinnamic acid were detected as the highest amount. Coumarin at 10?3 m significantly inhibited root growth of alfalfa and barnyard grass more than that of eclipta. The research suggests that extracts of barley, oats, rice and wheat have an allelopathic effect on alfalfa, barnyard grass and eclipta and that the findings of bioassay were considerably correlated with the type and amount of causative allelochemicals, indicating that the allelopathic effects on three test plants were ranked in order of wheat (highest), barley, rice and oats (lowest). The results may have value in enabling weed control based on natural plant extracts or crop residues in the fields.  相似文献   

3.
Root activity plays a dominant role in grain filling in cereal crops. However, the importance of deep roots for regulating post‐anthesis leaf senescence is not clearly understood in wheat (Triticum aestivum L.). In this study, we used 32P tracing to estimate the difference in wheat root activity at soil depths of 30 and 70 cm and the root restriction method to investigate the effects of vertical distribution of deep roots on leaf senescence, with non‐restricted plants as controls. Recovery of radioactive 32P indicated that deep roots had significantly higher activity than upper roots in wheat. Root restriction at a soil depth of 50 cm caused significant decreases in the activities of superoxide dismutase (EC 1.15.1.1), peroxidase (EC 1.11.1.7), catalase (EC 1.11.1.6) and ascorbate peroxidase (EC 1.11.1.11) at 16 days after anthesis and thereafter resulting in an increase in malondialdehyde. As a result, chlorophyll levels and net photosynthesis decreased. Ultimately, the root‐restricted wheat produced a significantly lower grain yield than the non‐restricted controls. These data suggest that deep roots are pivotal for regulating plant senescence, duration of grain filling, and yield formation.  相似文献   

4.
Black mustard [Brassica nigra (L.) Koch.] contains water‐soluble allelochemicals that inhibit the germination and growth of other species. This characteristic could be used in weed management programmes. Greenhouse and laboratory experiments were conducted to determine the effects on wild barley (Hordeum spontaneum Koch.) germination and seedling growth of (i) preceding crops, (ii) fresh black mustard residue incorporation, and (iii) black mustard leaf, stem, flower and root water extract concentrations. Growth of wild barley, as indicated by plant height and weight, was significantly reduced when grown in soil previously cropped to black mustard compared with that cropped to wild barley. Soil incorporation of fresh black mustard roots and both roots and shoots reduced wild barley germination, plant height and weight when compared with a no‐residue control. In bioassays, black mustard extracts reduced wild barley hypocotyl length, hypocotyl weight, radicle weight, seed germination, and radicle length by as much as 44, 55, 57, 63 and 75 %, respectively, when compared with a water control. Increasing the water extract concentrations from 4 to 20 g per 100 ml of water of all black mustard parts significantly increased the inhibition of wild barley germination, seedling length and weight. Based on 8‐day‐old wild barley radicle length, averaged across all extract concentrations, the degree of toxicity of different black mustard plant parts can be ranked in the following order of inhibition: leaves > flowers > mixture of all plant parts > stems > roots.  相似文献   

5.
Autotoxicity restricts reseeding of alfalfa (Medicago sativa L.) after alfalfa until autotoxic chemical(s) breaks down or is dispersed into external environments. A series of aqueous extracts from leaves, stems, roots and seeds of alfalfa ‘Vernal’ were bioassayed against alfalfa seedlings of the same cultivar to determine their autotoxicity. The highest inhibition was found in the extracts from the leaves. Extracts at 40 g dry tissue l?1 from alfalfa leaves were 15.4, 17.5 and 28.7 times more toxic to alfalfa root growth than were those from roots, stems and seeds, respectively. A high‐performance liquid chromatography (HPLC) analysis with nine standard compounds showed that the concentrations and compositions of allelopathic compounds depended on the plant parts. In leaf extracts that showed the most inhibitory effect on root growth, the highest amounts of allelochemicals were detected. Among nine phenolic compounds assayed for their phytotoxicity on root growth of alfalfa, coumarin, trans‐cinnamic acid and o‐coumaric acid at 10?3 m were most inhibitory. The type and amount of causative allelochemicals found in alfalfa plant parts were highly correlated with the results of the bioassay, indicating that the autotoxic effects of alfalfa plant parts significantly differed.  相似文献   

6.
Crop establishment, determined by shoot and root growth during early growth is a vital component in procuring desired plant populations and high yields in rainfed tropical smallholder farming systems, where green manures help maintain soil fertility and sustainability. As green manure incorporation could affect early seedling growth, studies were conduced in a plant house using soils from fields, to evaluate the impact of incorporating two popular tropical green manures (Crotalaria juncea and Tithonia diversifolia) into soil under rainfed field conditions over 3 years, on selected physico‐chemical properties of the soils and on establishment and early shoot and root growth of maize (Zea mays), with and without inorganic fertilizers. In a given year, green manure was grown in one season while maize was grown in the other. A soil that did not receive green manures but was left fallow during the period of green manure cultivation was used as the control treatment. The incorporation of green manures over the 3 years showed trends of increasing soil physical properties, and also the available nitrogen, phosphorus and potassium contents. Incorporation of Crotalaria, with its higher nitrogen content, promoted shoot growth, while Tithonia induced the development of an extended root system. The use of inorganic fertilizers stimulated the beneficial impact of the green manures in promoting shoot and root growth. The use of green manures, especially Tithonia, promoted the development of seminal and nodal roots of maize seedlings, both in the form of length and thickness (based on root surface area) and root length densities, which could assist in successful crop establishment and resource utilization, rather than primary roots. The benefits of using green manures, especially Tithonia, in promoting root growth and Crotalaria in shoot development of maize seedlings even without inorganic fertilizers is presented.  相似文献   

7.
Waterlogging causes long‐lasting damage to wheat (Triticum aestivum). Root growth and respiration were investigated after heading in waterlogged, pot‐grown, wheat plants and also in hydroponically grown, wheat seedlings exposed to a hypoxic treatment. In the pot experiment, plants were subjected to 8 days of waterlogging after heading. This period of waterlogging resulted in reduced shoot and root growth through to maturity. The root CO2 emission rates of previously waterlogged and well‐drained plants were about 220 and 140 nmol g?1 per s, respectively, with the rate differences persisting from 10 days after anthesis through to maturity. In the hydroponic experiments, seedlings (Feekes stage 2.0) were exposed to root‐zone, hypoxic treatment for 10–19 days. The roots showed 27 % higher CO2 emission rates and 37 % higher O2 consumption rates, compared with untreated roots. In whole root systems, the high respiration rates found during hypoxic treatment disappeared during recovery under aerated conditions as a result of the appearance of newly initiated roots. However, measurements of the respiration of the previously hypoxic roots showed abnormally high respiration rates. In roots exposed to hypoxic treatment, total sugar concentrations were 3.6‐times higher than in untreated roots indicating that this elevation of sugar may be responsible for the continued high respiration rate. This study shows that roots exposed to waterlogging or to hypoxic treatments do not increase their weights and thus recover from the metabolic disturbances resulting from these treatments.  相似文献   

8.
Sorghum (Sorghum bicolor L. Moench) seeds were examined to determine the influence of exposure to ascending and descending imbibition temperature regimes on plumule and radicle axes behaviour of seed after treatment. Treatments included soaking in distilled water, 4.5 % NaCl or 4.5 % KCl for 3 days at three ascending or descending temperatures ranging from 11 to 21 °C. Root growth was enhanced by descending temperatures (21, 16 and 11 °C) over the 3‐day period, whereas ascending temperatures (11, 16 and 21 °C) increased growth differences between shoots and roots. Shoot–root growth was affected by imbibition temperature to a greater extent than germination. However, seed soaking treatments in NaCl or KCl did not improve root or shoot growth, but did improve germination rates.  相似文献   

9.
Stylosanthes guianensis is a popular pasture legume and cover crop. The legume possessed strong allelopathic potential and suppressed spontaneous growth of paddy weeds. In a bioassay, aqueous extract of S. guianensis remarkably inhibited germination and growth of barnyardgrass and monochoria. Application of 1 ton ha?1 upland parts of S. guianensis significantly reduced paddy weed biomass by 80 % and increased rice yield by 40 % when compared with the control. Gas chromatography‐mass spectrometry analysis reveals the presence of several allelochemicals in S. guianensis including phenolic acids, coumarin and long‐chain fatty acids. Stylosanthes guianensis may be used as a source of natural herbicide for reducing the dependency on synthetic herbicides in agricultural production.  相似文献   

10.
Root penetration (RP) ability into compacted soil is an important breeding target for drought avoidance by durum (Triticum turgidum L. var. durum) and bread wheat (T. aestivum L.) in regions with compacted soils and water deficits. However, it is said generally that yield of the current cultivars introduced the reduced height gene (Rht-B1b or Rht-D1b) are more sensitive to drought stress than that of old landraces. This study investigated the effect of the Rht genes on RP ability using the seedlings of near-isogenic lines (NILs) of Rht genes of LD222 durum wheat and April Bearded bread wheat, and 110 recombinant inbred lines (RILs) of durum wheat derived from the cross between the tall landrace (Jennah Khetifa; Rht-B1a Rht-B1a) and semi-dwarf cultivar (Cham1; Rht-B1b Rht-B1b). One seedling of each genotype was grown in a pot (6 cm diameter, 15 cm height) with a disc of 3 mm thickness made from paraffin and Vaseline mixture (PV) in 10 cm depth, as a substitute for a compacted soil layer. The RP index [number of roots penetrating through the PV disc per plant (PVRN)/total number of seminal and crown roots per plant (TRN)] was measured at eight weeks after sowing and used as the indicator of RP ability of seedling. In NILs, the shoot length decreased significantly because of the introduction of either Rht-B1b or Rht-D1b dwarfing genes, but the RP index was similar to those of tall parents. In RILs, although the RP index and shoot length were higher in Jennah Khetifa than in Cham1, the relationship between RP index and shoot length was not significant (r = 0.156). Both results indicate that RP ability of wheat does not link to dwarfness regulated by Rht genes. We suppose therefore that it would be possible to develop a high yielding semi-dwarf cultivar with excellent RP ability.  相似文献   

11.
Large mounds amended with plant residues are a common cultivation method for sweetpotato (Ipomoea batatas) in the western parts of the Papua New Guinea highlands, with a suggested benefit of elevated root zone temperature (RZT) from decomposition. This study aimed to evaluate whether RZT affects the formation and growth of sweetpotato storage roots. Experiments evaluated the effects of a constant elevated RZT on the Beauregard cultivar and of a short‐term increase in RZT on the Beauregard and Northern Star cultivars. Plants were grown in 18‐L pots divided into a control compartment (constant RZT at 20°C) and a treated compartment (RZT at 30, 40 or 50°C). Constant elevated RZT was maintained until harvest, while short‐term increase in RZT occurred in weeks 2 and 3 only. Constant elevated RZT did not affect the total number of storage roots, but RZT of 30°C and above reduced the dry‐biomass of storage roots. The short‐term increase in RZT did not alter the total number or dry‐biomass of storage roots in Beauregard, while both of these attributes were reduced at RZT of 40°C or above in Northern Star. Elevated RZT inhibited dry‐biomass accumulation of storage root, with a more pronounced impact at constant elevated RZT. These results demonstrate that any benefits of the mound culture on sweetpotato yield production do not arise through the influence of temperature elevation.  相似文献   

12.
The root mass of winter barley ( Hordeum vulgare cv. Niki) at growth stages 5, 9 and 16 of the Feekes scale increased from 100 % (0.272 mg cm–3 soil) to 132 % and 139 %, respectively. Root mass was always greater in no-tillage (NT) plots than in ploughed-tillage (CT) plots and was also greater where manure was applied in comparison to plots without manure. The root density at growth stages 5, 9 and 16 over all treatments was 0.197, 0.224 and 0.238 cm cm–3 soil, respectively. At growth stage 5, the root density in NT plots was 9 % greater than that in CT plots, and in rotary hoed (MT) plots it was 3 % greater. At this same growth stage, soil fertilization with NP, farmyard manure (30 t ha−1) and NP plus farmyard manure improved the root density of barley by up to 5, 10 and 11 %, respectively, in comparison with control plots. The diameter of barley roots was clearly biggest in CT plots, while in NT plots the thinnest roots were found. The mean diameter was 0.63, 0.75 and 0.78 mm at growth stages 5, 9 and 16, respectively (over all treatments). Significant correlation coefficients were found between root density (RD) and the soil properties bulk density (BD), porosity (P), penetration resistance (PR) and mean weight diameter of aggregates (MWD). For example, the highest r values were as follows: at growth stage 5, r=0.95 (P < 0.001) for P and r=0.86 (P < 0.001) for MWD; at growth stage 9, r=−0.97 (P < 0.001) for PR and r=0.96 (P < 0.001) for P, and finally at growth stage 16, r=0.97 (P < 0.001) for P and r=−0.97 (P < 0.001) for PR.  相似文献   

13.
Laboratory bioassay and high‐performance liquid chromatography (HPLC) analysis were conducted to determine the allelopathic potentials of aqueous or methanol extracts from three different coloured sweet potato [Ipomoea batatas L. (Lam)] cultivars by plant part. The aqueous extracts applied on filter paper significantly inhibited root growth of alfalfa (Medicago sativa L.). Aqueous leaf leachates at 40 g dry tissue l?1 (g l?1) from white sweet potato cultivar ‘Sinyulmi’ showed the highest inhibition against alfalfa, followed by yellow ‘Sinhwangmi’ and purple ‘Jami’. Alfalfa root growth was significantly inhibited by methanol extracts of the same plants as the concentration increased. Aqueous and methanol extracts from leaves showed the most inhibitory effect on alfalfa root growth followed by stems and roots. By means of HPLC analysis, leaf samples of sweet potato had the highest amount of phenolic compounds followed by stems and roots. Total content of these compounds was highest for leaf extracts (37.7 mg 100 g?1), detected in EtOAc fraction, especially trans‐cinnamic acid (20.9 mg 100 g?1). These results suggest that sweet potato plants are allelopathic and that their activities differ depending on plant part as well as root periderm colour.  相似文献   

14.
The observed delayed emergence and seedling development in wheat ( Triticum aestivum L.) planted into soybean ( Glycine max [L.] Merr.) residues in the field were reproduced in the greenhouse. Severity of the effects were increased as the rate of residue increased. Residues, and leachates from residues, inhibited wheat growth and reduced yields 19–29 % in the field. Shallow incorporation of residues into soil resulted in delayed emergence, thinner stands, and greatly shortened coleoptile length. Emergence was reduced more under "moderately dry" soil conditions while stunting was more pronounced under "wet" soil conditions. Residues appeared to have no direct effect on Rhizoctonia winter-kill. Based on this research, even distribution of soybean residues across the field at harvest and deep placement of the residue should reduce these allelopathic effects on a subsequent wheat crop.  相似文献   

15.
Seedling Growth of Agronomic Crops in Crude Oil Contaminated Soil   总被引：1，自引：0，他引：1  
Phytoremediation of hydrocarbon‐contaminated soil shows promise as a low‐cost alternative to most remediation methods. This study evaluated seedling growth of six crop species in crude oil contaminated soils. The experiments were conducted in a greenhouse. Weathered crude oil was added to an Ipava silt loam soil at the rate of 0 (control), 10, 50 and 100 g of crude oil kg?1 of soil, which was then placed into pots. Irrigation was used to maintain soil moisture at approximately field capacity. Five seeds of Zea mays, Meticago sativa, Lolium perenne, Triticum aestivum, Glycine max or Vicia villosa were sown per pot. The experimental design was completely randomized with five replications per treatment. Germination and seedling height data were recorded on day 7, 14, 21 and 28. Plants were harvested on day 28, separated into shoots and roots and dried to measure biomass. Analysis of variance was used to determine treatment significance. Significant treatment mean values were separated using Tukey's Honestly Significant Difference Test. Based upon percent emergence and plant biomass production in contaminated soil, Z. mays and G. max seedlings show the greatest potential to enhance remediation.  相似文献   

16.
Intensive irrigated rice system is the most important food production system in the world. Continued population growth necessitates increased rice production to meet the increased need of food production through increased rice productivity to ensure food security. In contrast, the recent slowdown in yield growth in intensive irrigated rice‐based cropping systems as a result of deterioration of soil health and decline in productivity level is a serious cause for concern. The objective of this research was to investigate the soil organic carbon (SOC) build‐up and its dynamics in rice–rice cropping system by including a green manure (GM) crop Sesbania rostrata Berm. either during fallow and/or intercrop at 4 : 1 ratio as additive series without changing rice geometry. The results revealed that there is a gradual build‐up of SOC when S. rostrata included and in situ incorporated at flowering stage as a basic means of improving soil quality in rice–rice cropping system. Further, the soil organic matter fractions viz. humic acid and fulvic acid were also improved in all GM‐incorporated systems. In general, the proportion of fulvic acid was higher than humic acid. Cropping system involving three GMs viz. S. rostrata‐rice/S. rostrata‐rice/S. rostrata registered significantly higher SOC and was 10.63 percent higher than traditional rice–rice cropping system (A1). This was followed by S. rostrata‐rice/S. rostrata‐rice system. Although the traditional rice–rice cropping system (A1) also conserved SOC (0.29 and 1.69 % higher than initial during first and second annual cropping cycle, respectively), the magnitude was very low. Repeated application of S. rostrata as GM improved SOC, which formed the basis for sustainable management of soil resources. It can be concluded that S. rostrata would affect the rate of loss of SOC in cropping systems and its ultimate level in soils.  相似文献   

17.
通过室内生物测定法,研究了黄芪根水浸液对4种作物种子萌发及幼苗生长的化感影响。结果表明,黄芪根水浸液对4种作物种子萌发及幼苗生长均有明显的化感作用,其中根受到的化感抑制大于地上部分,种子萌发阶段受到的化感抑制大于幼苗生长阶段。不同受体的发芽势、最长根长和根冠比受到的化感抑制最强。4种作物的化感敏感性为小麦>板蓝根>大麦>大豆。因此,选择与黄芪轮作、套作的作物时,优先选择大豆和大麦,其次为板蓝根。  相似文献   

18.
Salicornia bigelovii is a novel crop for salty soils, which can contribute to arid‐zone management where irrigation with salty water, including sea water, is now a necessity. Nitrogen fixation by bacteria associated with the roots of S. bigelovii and similar halophytes is an important source of available nitrogen in salt marsh ecosystems. However, the diversity of the rhizosphere of Salicornia is unknown. Five areas around the Bay of La Paz in Baja California Sur, Mexico were sampled to detect nitrogen‐fixing bacteria associated with this halophyte; from these, 18 colonies were isolated. Only one showed high acetylene reduction activity. This bacterium was identified as Klebsiella pneumoniae. The effects of K. pneumoniae were evaluated at the germination and early seedling growth stages of two genotypes of S. bigelovii (‘wild genotype’ and cultivar SOS‐10), as an alternative crop for semiarid and saline environments. This bacterium, in conjunction with Azospirillum halopraeferens, was tested for growth‐promoting ability when inoculated on S. bigelovii genotypes under various saline concentration conditions. During germination and early seedling growth, K. pneumoniae showed high specificity for the wild S. bigelovii genotype, while A. halopraeferens was more specific for the improved S. bigelovii genotype SOS‐10. This is the first report of K. pneumoniae as a nitrogen‐fixing bacterium associated with the oilseed S. bigelovii, a novel halophyte crop. A reliable biological method, based on beneficial bacteria, is suggested to help maintain or improve the fertility of soils sustaining Salicornia fields.  相似文献   

19.
The present study was conducted to investigate the allelopathic effects of Parthenium hysterophorus weed on seed germination and seedling growth of tef. Flower, stem, root and leaf aqueous extracts of Parthenium at 0, 1, 5, and 10 % concentrations were applied to determine their effect on tef seed germination and seedling growth under laboratory conditions. Increasing concentrations of aqueous extracts of Parthenium from leaf and flower inhibited seed germination and complete failure of seed germination was recorded when the extract concentration from the leaf part was 10 %. In contrast, aqueous extracts from stem and root had no effect on tef seed germination. Roots appeared more sensitive to allelopathic effect than shoots. Extracts from flower, root and stem had a stimulatory effect on shoot length at all concentration levels, as against an inhibitory effect of leaf extracts. Root extracts at low concentration (1 %) greatly promoted root length but aqueous extracts from leaf and flower inhibited root length.  相似文献   

20.
To increase the inhibitory effect of soil-incorporated cover crop residues on germination and early growth of weeds, the allelochemical content of the cover crop at the time of soil incorporation should be maximal. We investigated whether mechanical damaging in spring induced the production of allelochemicals in late-summer sown lucerne, winter rye and winter oilseed rape. Allelopathic activity and biomass of intact cover crop plants were determined throughout spring, and mechanically damaged plants were monitored till 14 days after wounding. Allelopathic activity was determined directly by lettuce seedling bioassays (lucerne and winter rye) or indirectly by glucosinolate quantification (winter oilseed rape). During spring, the allelopathic activity per unit biomass of intact plants showed a gradual decline for winter rye and lucerne, and a steep decline at the onset of flowering for winter oilseed rape. All cover crop species attained the highest allelopathic activity per unit area at the end of the sampling period as the increase in biomass surpassed the decline in allelopathic activity per unit biomass. Although mechanical wounding enhanced the allelopathic activity per unit biomass of all three species, the effect was only minor and often just sufficient to compensate for the loss in biomass resulting from wounding. This study therefore indicates that the best option for maximizing the inhibitory effect is to incorporate residues of intact cover crops as late as possible.  相似文献   

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