Agronomy Journal Journal of Natural Resources and Life Sciences Education
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (21)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Chon, S.-U.
Right arrow Articles by Nelson, C. J.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Chon, S.-U.
Right arrow Articles by Nelson, C. J.
Agricola
Right arrow Articles by Chon, S.-U.
Right arrow Articles by Nelson, C. J.
Related Collections
Right arrow Allelopathy
Right arrow Alfalfa
Right arrow Root Development
Agronomy Journal 92:715-720 (2000)
© 2000 American Society of Agronomy

ALFALFA

Effects of Light, Growth Media, and Seedling Orientation on Bioassays of Alfalfa Autotoxicity

Sang-Uk Chon, John H. Coutts and C. Jerry Nelson

Dep. of Agronomy, 210 Waters Hall, University of Missouri, Columbia, MO 65211 USA

nelsoncj{at}missouri.edu


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 Materials and methods
 Results and discussion
 Summary and conclusions
 REFERENCES
 
Most assessments of allelopathy involve bioassays. Our objective was to improve the sensitivity of an alfalfa (Medicago sativa L.) seedling bioassay for evaluating genetic tolerance to autotoxic leaf extracts. In a petri dish assay on imbibed seed, light inhibited hypocotyl elongation of controls and increased root elongation. Root growth was sensitive to the autotoxin in both light and darkness. An agar medium gave better root growth of controls and lower standard errors than did filter paper when petri dishes were placed on edge to encourage downward root growth or were placed flat where roots grew laterally. Hypocotyl growth was not very sensitive to the autotoxic chemical(s) on either agar or paper medium when the plate was flat, because the hypocotyl arched upward to escape contact with the extract. Hypocotyl growth was sensitive in a rolled paper towel treatment held vertically because the hypocotyl remained in continuous contact with the extract. On agar plates placed flat, 50% inhibition of root length occurred at an extract concentration that was about 8% of that needed for 50% inhibition of germination at 36 and 48 h. Root growth was stimulated up to 15% above controls at very low concentrations of leaf extract. Root length at 120 h was the best indicator of autotoxic effects of alfalfa leaf extracts. We evaluated 17 germplasms and three cultivars of alfalfa for root growth response to the autotoxic chemical and found a twofold range (P < 0.05) in tolerance.

Abbreviations: G50, concentration causing 50% germination • Gt50, time to reach 50% germination • H50, concentration causing 50% inhibition of hypocotyl length • L50, concentration causing 50% inhibition of root length • LSD, least significant difference • PAR, photosynthetically active radiation


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
Materials and methods
 Results and discussion
 Summary and conclusions
 REFERENCES
 
ALLELOPATHY IS A CHEMICAL INTERACTION between plants (microbes and higher plants) that includes stimulatory as well as inhibitory influences (Molisch, 1937). It was later defined as any direct or indirect harmful or beneficial effect of one plant (donor plant) on another (recipient plant) through the production of chemical compounds that escape into the environment (Rice, 1984). Reseeding of alfalfa (Medicago sativa L.) is often not successful due to autotoxicity (Jensen et al., 1981; Miller, 1996), a special type of allelopathy by which plants have a detrimental effect on other plants of the same species (Putnam, 1985).

Autotoxicity may exist where alfalfa has lower germination, poorer establishment, and lower productivity immediately after alfalfa compared with after another species or after fallow (Jensen et al., 1981). The common field recommendation to avoid autotoxicity is to delay seeding of alfalfa after alfalfa for at least 2 wk (Tesar, 1993), and in some cases up to 2 yr (Jennings et al., 1996). Alfalfa plants contain water-soluble substances that are toxic to plants (Lawrence and Kilcher, 1962; Guenzi et al., 1964; McCalla and Haskins, 1964; Klein and Miller, 1980; Jensen et al., 1981; Jennings and Nelson, 1998), but the causative chemical(s) have not been unequivocally identified. Autotoxicity in alfalfa may result from an interaction of more than one chemical present in the shoot, especially in the leaves (Chung and Miller, 1995).

Most assessments of allelopathy or autotoxicity involve bioassays of plant or soil extracts based on seed germination or seedling growth. Generally, germination is less sensitive than is seedling growth, especially root growth (Miller, 1996). Autotoxic and allelopathic extracts have been assayed in petri plates with filter paper (Cope, 1982; Luu et al., 1982; Hall and Henderlong, 1989; Hedge and Miller, 1990; Chung and Miller, 1995), but results can be inconsistent due to nonuniform moisture conditions or swelling of the paper in localized areas (Peters, 1968; Pederson, 1986). Mixing the extract in agar provides an alternative and perhaps more sensitive assay (Carlson et al., 1983; Pederson, 1986; Dornbos and Spencer, 1990; Ben-Hammouda et al., 1995). Dornbos and Spencer (1990) reported that the modified agar bioassay required smaller quantities of compound per seed for results comparable to a commonly used filter paper procedure.

Some researchers conducted seedling assays in light, while others did them in darkness. Arnim and Deng (1996) found that hypocotyl growth is negatively associated with light intensity and is affected by light quality. Thus, light may alter the relative growth of the hypocotyl, root, and shoot to alter the sensitivity of the assay.

An appropriate bioassay that is sensitive and distinguishes autotoxic factors from competitive or inherent growth properties of alfalfa seedlings is needed for more in-depth studies of the growth mechanisms involved and for developing initial analytical procedures to determine the chemical(s) responsible. Our objectives were (i) to develop an appropriate culture medium, (ii) to determine the light effects on bioassays of alfalfa autotoxicity, and (iii) to find critical extract concentrations that optimize sensitivity for genetic studies.


   Materials and methods
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
Results and discussion
 Summary and conclusions
 REFERENCES
 
Sampling and Preparation of Extracts
Topgrowth of 3-yr-old `Cody' alfalfa plants was harvested at a vegetative stage from a field near West Plains, MO, in November 1995 and oven-dried at 40°C for 5 d. Dried alfalfa plants were separated into leaves (blades and petioles) and stems. Leaf samples were ground to pass a 1-mm screen and then stored at 2°C until used. Twenty grams of ground tissue was extracted by soaking, with occasional swirling, in 1 L distilled water for 24 h at 24°C in a lighted room. The extract was filtered through four layers of cheesecloth to remove the fiber debris, then centrifuged at low speed (3000 revolutions min-1) for 4 h. The supernatant was vacuum-filtered through No. 42 paper (Whatman, Clifton, NJ) and diluted with distilled water to the desired concentration. Stock extract was made fresh for each experiment. Dilutions of this extract are reported as g of dry alfalfa leaf tissue L-1.

General Culture and Data Analysis
For all experiments, seed was surface-sterilized for 15 min in sodium hypochlorite (0.525 g L-1), rinsed, imbibed for 10 or 12 h in deionized water at 25°C, and carefully blotted using a folded paper towel. Twenty or 25 swollen seeds were distributed evenly on the paper or agar surface in each petri dish. The petri dishes were covered, sealed by wrapping in parafilm, and placed flat in a growth chamber held at 24°C during the 14-h light period and 22°C during the 10-h dark period. Plates were illuminated at 400 µmol photons m-2 s-1 photosynthetically active radiation (PAR) provided by a mixture of incandescent and fluorescent lamps.

Number of germinated seeds (radicles 1 mm long) was determined at 12- or 24-h intervals over a defined period. Hypocotyl and root lengths were measured on all seedlings in each petri dish at 120 or 144 h after placing seed on the medium. Data were transformed to percentage of control for analysis. When the F-test was significant (P < 0.05), means were separated on the basis of least significant difference (LSD).

Light Effect
Seed of Cody alfalfa were germinated on filter paper wetted with distilled water for 36 h at 24/20°C (14 h light/10 h dark). Mean radicle length was 4.2 mm, and mean hypocotyl length was 2.8 mm. Twenty seedlings were carefully transferred to the agar surface of petri dishes containing extract at 0.0, 0.5, and 2.0 g dry tissue L-1. Agar containing distilled water was the control. Four replications were used in a randomized block design. Plates were placed horizontally in a growth chamber at 24/20°C in darkness or with a 14-h photoperiod with PAR of 400 µmol photons m-2 s-1. Hypocotyl and root lengths were measured on all seedlings at 36-h intervals for 144 h. The experiment was repeated with very similar results. These data showed shorter hypocotyls and longer roots for the light/dark treatment compared with darkness. Subsequent studies were conducted using a growth chamber with light/dark conditions as described above.

Growth Media and Seedling Orientation
Four bioassay procedures, each with four replications in a randomized complete block design, were compared to develop an appropriate growth medium (Fig. 1) . Our goal was to maximize root growth, ease of measurement, and precision of the assay. We evaluated extracts from 0.0, 1.0, 2.0, 4.0, and 8.0 g dry tissue L-1 on root and hypocotyl growth in light on agar and filter paper when roots grew downward or laterally.



View larger version (63K):
[in this window]
[in a new window]
  		Fig. 1 Schematic of four growth media techniques: (A) paper flat, (B) paper vertical, (C) agar flat, and (D) agar vertical

 
Paper Flat
Two layers of Whatman No. 1 filter paper were placed in each 9-cm-diam. plastic petri dish and 5 mL of diluted extract was pipetted onto the filter paper. Twenty seeds that had been imbibed for 10 h with distilled water at 22°C were placed on the wetted paper. The plate was covered and sealed with parafilm. Plates were placed horizontally.

Paper Vertical
A piece of Kimwipes (Kimberly-Clark, Atlanta, GA) lab tissue paper (22 by 11 cm) was placed onto half (27 by 12 cm) of a single-fold, natural, brown paper towel beginning 1 cm from the upper edge of the towel. Twenty imbibed seeds were placed evenly along the edge of the lab tissue paper; i.e., 1 cm below the edge of the paper towel. The seeds were covered with another paper towel. The towels were rolled and inserted vertically into a glass test tube, which was inverted and placed in a 125-mL Erlenmeyer flask containing 50 mL of water or extract solution (Fig. 1). The test tube was sealed to the flask with parafilm. The extract moved up the rolled towels within a few minutes. We assumed the allelochemical(s) moved with the water (Jennings and Nelson, 1998).

Agar Flat
Bacto agar (Difco Laboratories, Detroit, MI) (16 g L-1) was autoclaved for 25 min at 125°C and then equilibrated in a 50°C water bath along with a flask of stock extract and another of sterile distilled water. An aliquot of stock extract (20 g dry tissue L-1) was diluted with warm water to twice each desired test concentration, then mixed in a 1:1 ratio with the agar solution to give the final concentration. About 10 mL of extract-agar or water-agar solution (control) was poured into 9-cm-diam. plastic petri dishes, covered, and allowed to solidify for 4 h at room temperature. Twenty seeds were imbibed for 10 h and placed uniformly on the agar, resulting in agar surface area of 3.2 cm2 seed-1. Dishes were covered, sealed, and placed horizontally.

Agar Vertical
The agar solutions and dishes were prepared as described above. A semicircular section of the solidified agar-extract was cut about 2 cm from the center of the dish and removed (Fig. 1). The dish was positioned vertically with the cut-line horizontal. Twenty imbibed seeds were placed on the cut surface of agar, resulting in agar surface area of 0.23 cm2 seed-1. The dish was covered and sealed, then placed in a rack at 70° from horizontal.

The four methods were evaluated simultaneously in the same growth chamber. Hypocotyl and root lengths were measured on all seedlings 144 h after transfer of the imbibed seeds to the treatments. Extract concentrations resulting in 50% inhibition of hypocotyl length (H50) and root length (L50) of controls were determined by interpolation. The agar treatments yielded longer and more consistent root lengths than did the paper treatments. Relative results were very similar on agar whether the roots grew vertically or horizontally. Thus, for convenience we used the agar-flat method (Fig. 1C) for subsequent studies.

Concentration Effects on Germination and Seedling Length
Twenty seeds were imbibed in distilled water for 10 h and placed on the agar surface with extract concentrations of 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 2.0, 4.0, and 8.0 g dry tissue L-1. Agar containing distilled water was used as a control. Dishes were placed horizontally. Four replications were used in a randomized complete block design. Cumulative germination was determined by counting the number of germinated seeds at 12-h intervals over an 84-h period. Root and hypocotyl lengths of all seedlings were measured 120 h after transfer of seed to agar. The experiment was conducted twice. Data for the two experiments were very similar and showed no interaction and so were combined for presentation. Germination data were plotted vs. time, and the times needed to reach 50% germination (G50) at 24 and 36 h were determined by interpolation.

Germplasm Evaluation
We used the bioassay as developed above to evaluate an autotoxic effect on root length of 17 germplasms and three cultivars of alfalfa. Seed were imbibed in water for 12 h in light, then transferred to the agar surface containing extract concentrations of 1.0 and 4.0 g dry tissue L-1. Agar containing distilled water was the control. Dishes were sealed, placed flat, and arranged in a randomized complete block design with four replications. Root and hypocotyl lengths were measured after 120 h at 24/22°C (light/dark) with a 14-h photoperiod. Cultivars and germplasms differed (P < 0.05) in inherent root lengths of the controls, so responses to the extract were expressed as percentage of control. A similar experiment was conducted using the same entries at concentrations of 1.0, 2.0, and 4.0 g dry tissue L-1. Responses and germplasm rankings were similar for the two experiments. Data from the first experiment are presented.


   Results and discussion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
Summary and conclusions
 REFERENCES
 
Light Effect
Using flat petri dishes, hypocotyl growth rates were near linear for 108 h in both light and darkness, with no response to the extract except a transient inhibition at 2.0 g L-1 in darkness (Fig. 2) . In darkness, the growth rate decreased as hypocotyl length approached 40 mm. A finite maximum hypocotyl length appeared to be about 43 mm. In light, the maximum hypocotyl length was 8 to 10 mm. Hypocotyls grow by cell division and especially cell elongation (Cavalieri and Boyer, 1982), and light is known to reduce hypocotyl growth (Arnim and Deng, 1996).



View larger version (33K):
[in this window]
[in a new window]
  		Fig. 2 Effect of extract concentrations on (A) hypocotyl and (B) root length of alfalfa seedlings in light and darkness

 
Light also affects potential photosynthesis of the green cotyledons. In light, the cotyledons turned green at about 72 h, and CO2 concentrations were probably high in the covered plates so photosynthesis could occur. Although roots of some species are sensitive to light, those of alfalfa controls were longer in the light-grown seedlings. The reduced growth of the hypocotyl in light apparently allowed more resources, including photosynthate, to be allocated to root growth.

Root growth was responsive to autotoxin concentration in both light and darkness, with final length at 2 g L-1 in both conditions being restricted to about 5 mm (Fig. 2B). In other experiments, we noted that roots inhibited by high concentrations of the autotoxic extract grew slowly to reach 5 to 8 mm, then stopped. By 108 and 144 h, roots of the control and 0.5 g L-1 treatment were about 25% longer in light than in darkness. Standard errors in light were generally lower, indicating a bioassay in light can improve the ability to discriminate between treatments.

The optimum temperature and radiation density for the bioassay were not determined, and would depend on the relative effects of both on hypocotyl growth and net photosynthesis. We did not stack the plates, and in our agar-flat experiments the light source was perpendicular to the agar surface. Phototropism as a supplement to geotropism causes the hypocotyls to curve upward and away from the agar surface, which probably reduces contact with the autotoxic chemical(s). This also indicates that the autotoxin is probably not translocated from the root tip to growing cells of the hypocotyl. We repeated the experiment two more times in light, but shortened the imbibition and early germination period from 36 to 12 h before transfer to agar, to ensure that the seedlings had enough reserves. In both cases the root growth rates were near linear for 144 h after a short lag phase, verifying that the hypocotyls were short and arched, and that the roots had enough resources for linear growth during the assay.

Growth Media and Seedling Orientation
Roots were longest in the agar-vertical treatment, nearly 50% longer than in the agar-flat treatment (Fig. 3) . Controls grew least in the paper-flat treatment, perhaps because the roots grew horizontally on the paper surface instead of more vertically as was the case in the agar-flat treatment, and especially in the agar-vertical treatment. Roots on the paper also appeared to have less contact with the medium, likely making it harder for the seedling to absorb water for growth (Pederson, 1986).



View larger version (29K):
[in this window]
[in a new window]
  		Fig. 3 Effect of growth media and extract concentrations on hypocotyl and root length of alfalfa seedlings at 144 h. Within a growth medium, means of total length (upper case), root length (lower case), or hypocotyl length (lower case italics) are not significantly different (0.05) from those with the same letter in or above the bar. Extract concentrations are expressed as g dry leaf tissue L-1

 
At the same extract concentrations, roots were more sensitive to the alfalfa extract in the agar-flat or agar-vertical treatment than in the paper-flat or paper-vertical treatment (Fig. 3). This corroborates previous reports (Carlson et al., 1983; Pederson, 1986; Dornbos and Spencer, 1990) that extracts in agar are more inhibitory than are the same concentrations in paper. As above, hypocotyl length was not very sensitive to the extract concentrations except in the paper-vertical treatment, in which the basal 10 mm of hypocotyl could not escape contact with the extract. We expected long hypocotyls in this treatment because seedlings were in darkness (Fig. 2). At concentrations of 0.1, 0.2, and 0.4 g L-1 , at which the hypocotyl remained shaded and in contact with the paper roll, the ratio of hypocotyl length (12.7, 8.8, and 4.0 mm, respectively) to root length was near 1.0, indicating near equal sensitivity. This contrasts with earlier conclusions based on flat petri dish assays of allelopathy (Luu et al., 1982; Smith, 1989; Hedge and Miller, 1990; Chung and Miller, 1995) that hypocotyl growth was rather insensitive.

The paper-vertical treatment provides for initial hypocotyl growth in darkness, and should best simulate a field measurement if the autotoxic chemical(s) are present near or at the soil surface. In our assay, the imbibed seed germinated about 1 cm below the paper edge and needed to grow at least that distance to expose the cotyledons to light. Darkness stimulates hypocotyl growth and indirectly causes a reduced growth of the root. Earlier data indicate the autotoxic chemical moves in the soil with water (Jennings and Nelson, 1998), probably moving downward when rainfall infiltration exceeds evaporation, allowing the hypocotyl to escape the toxin whereas the root may not. Root length in the paper-vertical treatment was more sensitive to the extract than in the paper-flat treatment, likely because of better contact between the root and the extract solution, something that may also occur in soil.

Comparative Effects on Seedling Length and Germination
Both agar treatments (Fig. 3) had similar L50 concentrations for root length (0.58 g L-1), indicating the orientation of the dishes affected absolute root growth rates but did not alter the relative response to the extract. Further, the L50 concentrations for the paper-flat (4.1 g L-1) and paper-vertical (0.91 g L-1) treatments were seven and 1.6 times higher, respectively, than those of the two agar treatments, indicating smaller concentrations of extracts were required in agar than in paper treatments to express the same autotoxic response. We continued using the agar-flat method because there was more surface area, allowing us to use more seed per dish to help overcome plant-to-plant variation.

Seed germination was delayed dependent on extract concentration, with no difference in final germination at 60 h for concentrations less than 8 g L-1 (Fig. 4) . The mechanism for germination delay is not known, but may be an artifact of the method by which a seed is defined as germinated. Germination is usually acknowledged when the radicle has emerged and is visible, or has achieved a minimal length, in our case 1 mm. As shown above, root growth is very sensitive, and the autotoxic chemical may not delay the true onset of germination (when measured by enzyme activation, commencement of rapid O2 consumption, or initiation of root cell growth), but causes a reduced root growth within the seed and delays its appearance. The effect of the autotoxin on the activation of metabolic processes needs to be evaluated independently from the effect on root growth to clarify this response. In routine bioassays, we imbibe seeds in water for 10 or 12 h before exposing them to the extract so that the effect of the extract is primarily on root growth.



View larger version (26K):
[in this window]
[in a new window]
  		Fig. 4 Effect of extract concentration on cumulative germination of alfalfa seed that had been imbibed for 10 h and then transferred to the extract treatments in agar. Response was concentration-dependent and no stimulation of germination occurred, so data for concentrations of 0.1, 0.2, 0.3, 0.4, and 2.0 g dry tissue L-1 were omitted for clarity

 
We evaluated low concentrations of extract (Fig. 5) because Einhellig (1986) noted that biological activity of several allelochemicals had a response threshold before becoming concentration-dependent. Many herbicides act as growth stimulators at very low concentrations (Wiedman and Appleby, 1972), and stimulation effects have been reported for some allelochemicals (Rice, 1986). In our case, hypocotyl length was not affected at an extract concentration of 0.1 g L-1, whereas root length showed up to 15% stimulation over the control at extract concentrations of 0.1 and 0.2 g L-1 (Fig. 5). There are few reports of allelopathic stimulation between higher plants, but adding chopped alfalfa to the soil stimulated growth of other species (Rice, 1986).



View larger version (19K):
[in this window]
[in a new window]
  		Fig. 5 Effect of low extract concentrations on root and hypocotyl growth of alfalfa seedlings using the agar-flat method. Data are the mean of two experiments. Hypocotyl and root lengths at 2, 4, and 8 g dry tissue L-1 (not shown) were less than 10 percentage points lower than those at 1 g L-1

 
With increasing extract concentrations, agar-extract media showed increased inhibitory effects on seedling growth (Fig. 5). Root length was much more sensitive to the extracts than was hypocotyl length (H50 > 8 g L-1), and 11 to 13 times more sensitive than seed germination (interpolated from data in Fig. 4). These results corroborate earlier reports that root growth is more sensitive to extracts than is seed germination or hypocotyl growth (Luu et al.,1982; Smith, 1989; Hedge and Miller, 1990; Chung and Miller, 1995), and is the most sensitive bioassay for alfalfa autotoxicity.

Germplasm Evaluation
Ideally, an extract concentration to distinguish germplasms is one that is near the L50 for roots, but activities of extracts from alfalfa topgrowth differ depending on the season of year and stage of growth (Guenzi et al., 1964), and repeated extractions from the same dried leaf sample gradually weaken with time (Chon and Nelson, unpublished data, 1999). Therefore, selection of the best concentration beforehand may require a preliminary study. At an extract concentration of 1 g L-1 from the original dried leaf sample, the root lengths of germplasms ranged from 37 to 92% of the control (Fig. 6) . At 4 g L-1, the lengths ranged from 9 to 36% of the control. The correlation between responses at the two concentrations was , but the respective LSD was lower relative to the mean of 60.6% at 1 g L-1 than the mean of 15.5% at 4 g L-1.



View larger version (35K):
[in this window]
[in a new window]
  		Fig. 6 Effect of extract concentrations on relative root length of 17 germplasms and three cultivars of alfalfa after 120 h using a leaf extract in agar. Entries were significantly different (P < 0.05) at both extract concentrations. Correlation between responses at 4 and 1 g dry tissue L-1 was . `WL 252' (W), `Innovator' (In), and `Magnum IV' (M) were intermediate

 
The three cultivars were intermediate in tolerance. The range of responses indicates genetic improvement in tolerance to the alfalfa autotoxin is possible. This differs from earlier studies that used cultivars and concluded there was little genetic variation in tolerance (Goplen and Webster, 1969; Wyman-Simpson et al., 1991). But using a similar assay process, Pederson (1985) reported genetic tolerance among white clover (Trifolium repens L.) genotypes to allelochemicals extracted from tall fescue (Festuca arundinacea Schreb.) ranged from 58 to 86% of the control.


   Summary and conclusions
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Summary and conclusions
REFERENCES
 
We increased the sensitivity of a bioassay for alfalfa autotoxicity based on water-soluble extracts from alfalfa leaves. Seeds were imbibed for 10 or 12 h at room temperature, then transferred to petri dishes containing alfalfa leaf extract mixed with agar. Dishes were placed flat. We used light because hypocotyl growth was reduced and root growth was stimulated. Root growth was more sensitive to the autotoxic chemical(s) than was hypocotyl growth or seed germination. Low concentrations of the alfalfa extract stimulated root growth, but not hypocotyl growth or seed germination. Based on root length at 120 h, germplasms differ in tolerance to the autotoxin, suggesting that genetic progress can be made.


   ACKNOWLEDGMENTS
 
Appreciation is expressed to Forage Genetics, West Salem, WI, for germplasms and financial support.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Summary and conclusions
 REFERENCES
 
Contribution of the Missouri Agricultural Experiment Station. Journal Series No. 12822.

Received for publication March 13, 1999.
   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and methods
 Results and discussion
 Summary and conclusions
 REFERENCES
 




This article has been cited by other articles:


Home page
 Crop Sci.Home page
K. V. Dhima, I. B. Vasilakoglou, I. G. Eleftherohorinos, and A. S. Lithourgidis
Allelopathic Potential of Winter Cereal Cover Crop Mulches on Grass Weed Suppression and Sugarbeet Development
Crop Sci., June 20, 2006; 46(4): 1682 - 1691.
[Abstract] [Full Text] [PDF]

Home page
 Crop Sci.Home page
K. V. Dhima, I. B. Vasilakoglou, I. G. Eleftherohorinos, and A. S. Lithourgidis
Allelopathic Potential of Winter Cereals and Their Cover Crop Mulch Effect on Grass Weed Suppression and Corn Development
Crop Sci., January 24, 2006; 46(1): 345 - 352.
[Abstract] [Full Text] [PDF]

Home page
 Agron. J.Home page
S.-U. Chon, C. J. Nelson, and J. H. Coutts
Osmotic and Autotoxic Effects of Leaf Extracts on Germination and Seedling Growth of Alfalfa
Agron. J., November 1, 2004; 96(6): 1673 - 1679.
[Abstract] [Full Text] [PDF]

Home page
 Agron. J.Home page
J. A. Jennings and C. J. Nelson
Zone of Autotoxic Influence around Established Alfalfa Plants
Agron. J., September 1, 2002; 94(5): 1104 - 1111.
[Abstract] [Full Text] [PDF]

Home page
 Agron. J.Home page
P. Seguin, C. C. Sheaffer, M. A. Schmitt, M. P. Russelle, G. W. Randall, P. R. Peterson, T. R. Hoverstad, S. R. Quiring, and D. R. Swanson
Alfalfa Autotoxicity: Effects of Reseeding Delay, Original Stand Age, and Cultivar
Agron. J., July 1, 2002; 94(4): 775 - 781.
[Abstract] [Full Text] [PDF]

Home page
 Agron. J.Home page
J. A. Jennings and C. J. Nelson
Rotation Interval and Pesticide Effects on Establishment of Alfalfa after Alfalfa
Agron. J., July 1, 2002; 94(4): 786 - 791.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (21)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Chon, S.-U.
Right arrow Articles by Nelson, C. J.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Chon, S.-U.
Right arrow Articles by Nelson, C. J.
Agricola
Right arrow Articles by Chon, S.-U.
Right arrow Articles by Nelson, C. J.
Related Collections
Right arrow Allelopathy
Right arrow Alfalfa
Right arrow Root Development

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Crop Science Vadose Zone Journal
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome