Crop Science 40:103-109 (2000)
© 2000 Crop Science Society of America
CROP PHYSIOLOGY & METABOLISM
Host Variation in Traits Associated with Crown Nodule Senescence in Soybean
David Espinosa-Victoriaa,
Carrol P. Vanceb and
Peter H. Grahamc
a Programa Edafologia, Colegio de Postgraduados, Montecillo, Mexico
b USDA-ARS, Univ. of Minnesota, St Paul, MN 55108 USA
c Department of Soil, Water, and Climate, Univ. of Minnesota, St Paul, MN 55108 USA
pgraham{at}soils.umn.edu
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ABSTRACT
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Active N2 fixation in soybean [Glycine max (L.) Merr.] in Minnesota is limited by cool early-season soil temperatures and by postflowering nodule senescence. This study examined variation in onset of nodule senescence among Maturity Group I soybean cultivars and sought traits associated with this variation. Host genotype markedly affected onset of crown nodule senescence. For most cultivars, crown nodule fresh weight and specific nodule activity (SNA) peaked 31 to 38 d after emergence (DAE) and declined rapidly thereafter. In contrast, maximum crown nodule fresh weight in `Hardin' and `Hodgson 78' did not occur until 52 DAE, and SNA was still high 45 to 52 DAE. Two cultivars, Chippewa and Alpha, that exhibited early change in crown nodule mass and SNA, accumulated glyceollin I 10 to 45 DAE at rates significantly greater than for Hardin and Hodgson 78. The four cultivars also differed in phenylalanine ammonia lyase (PAL) and chalcone synthase (CHS) gene expression, nodule protease activity, and polyamine accumulation. Morphological changes within the nodule paralleled the biochemical differences, with Chippewa nodules 45 DAE showing more conspicuous deterioration than was evident in Hardin. Because crown-nodule mass and nitrogenase activity in Hardin and Hodgson 78 declined later than in other Maturity Group I cultivars, with less evidence of host–strain incompatibility, these two lines may have value in breeding programs to extend the period of active nodulation and N2 fixation in soybean.
Abbreviations: BSA, bovine serum albumin • CHS, chalcone synthase • DAE, days after emergence • PAL, phenylalanine ammonia lyase • SNA, specific nodule activity (µmol C2H4 produced g-1 fresh weight h-1)
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INTRODUCTION
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Symbiotic N2 fixation in soybean reduces the need for N fertilization, and in Brazil alone is estimated to save $1.8 billion annually (Dobereiner et al., 1995). Despite this benefit, improving N2 fixation in soybean is not a high priority in U.S. agriculture (Vance, 1998), although cultivar variation in nodulation and N2 fixation has been reported (Coale et al., 1985; Cregan and Yaklich, 1986; Neuhausen et al., 1988; Sinclair et al., 1991; Herridge et al., 1994) and some gains in N2 fixation through genetic selection have been made.
In the U.S. Midwest, the period of active N2 fixation in Maturity Group I soybeans is limited both by cool early-season soil temperatures and by the rapid senescence of nodules after flowering. Lateral root nodules may contribute to N2 fixation later in the growing season (McDermott and Graham, 1989) but often contain less-effective indigenous rhizobia. As a result, soybean plants may derive less than 50% of their N needs from symbiosis (Ham, 1978). Recently, Pazdernik et al. (1996, 1997a, 1997b) found genetic variation for early nodulation and N2 fixation in soybean and demonstrated moderate heritability for this trait. However, there have been no parallel studies aimed at extending the period of N2 fixation through the selection of cultivars that exhibit delayed onset of crown nodule senescence.
In this study, we evaluated differences in onset of nodule degeneration among soybean genotypes of Maturity Group I, and sought to identify traits associated with such differences that would be appropriate for screening germplasm or plant populations. Crown nodulation was emphasized both to minimize the confounding effects of nodule age and because later-formed lateral-root nodules are often occupied by indigenous rhizobia. In comparing cultivars for differences in nodule senescence, we also considered variation in nodule glyceollin I content, PAL and CHS gene expression, protease activity, and polyamine levels. Earlier studies identified these substances in senescing root nodules (Werner et al., 1985; Parniske et al., 1991; Karr et al., 1992; Osawa and Tsuji, 1992; Pladys and Vance, 1993; Werner et al., 1994) but did not examine variation between cultivars.
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Materials and methods
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Plant Culture and Growth
The experiments reported here each used the same plant culture and growth procedures. For each, 16.25 by 15 cm plastic pots were filled with a 1:1 mixture of silica sand and Sunshine-mix #2 (J.R. Johnson, Roseville, MN) and autoclaved at 121°C for 1 h. Bradyrhizobium japonicum strain UMR161 inoculant was grown in YEM broth (Graham, 1963) for 8 d at 28°C, diluted in sterile water, and added to pots 24 h prior to planting at a rate providing 105 rhizobia per gram of potting mixture. Soybean seed was surface-sterilized in ethanol–sodium hypochlorite (Vincent, 1970), then rinsed repeatedly in sterile water. For each cultivar, 30 pots were seeded with 10 seeds per pot. These were thinned to two seedlings per pot after emergence. Plants were grown in a greenhouse with a 16-h photoperiod and 26 and 21°C day and night temperatures, respectively, and were watered alternately with sterile water and sterile low N plant nutrient solution (McDermott and Graham, 1990). In each experiment, except that on cultivar variation in nodule histology, three replicate plants per cultivar were harvested each week for 9 wk, beginning 10 DAE. This corresponded with the period from nodule initiation and development to nodule senescence. Analysis of variance of the data was computed as a two-factor (cultivar and harvest date) randomized complete block using the General Linear Models (GLM) Procedure within SAS version 6.03 (SAS Institute, 1992).
Crown Nodulation and Dinitrogen (Acetylene) Fixation
Crown nodulation and N2 (C2H2) fixation was determined for 11 Maturity Group I soybean cultivars (Alpha, Archer, Bert, Chippewa, Hardin, Hodgson 78, Kasota, Kato, Leslie, Northrup King S-1990, and Parker) from 10 to 59 DAE. At each harvest, the root system was cleaned, rinsed, and blotted dry. Then attached crown nodules (defined as nodules found on the first 4-cm taproot segment, including the first 4 cm of corresponding lateral roots) were assayed for C2H2 reduction (Dart et al., 1975). Gas samples were analyzed on a Varian 3700 gas chromatograph equipped with an electronic gas integrator (Varian Assoc., Sunnyvale, CA). Nodules were then picked and weighed fresh; shoots were dried at 70°C for 72 h and then weighed.
Accumulation of Glyceollin I in Crown Nodules
Crown-nodule glyceollin I accumulation was determined for the same 11 cultivars, plus the hypernodulating genotype Nod 1-3 (generously provided by Dr. J.E. Harper, USDA-ARS, University of Illinois) from 10 to 59 DAE. At each harvest, crown nodules were picked and then immediately frozen and ground in liquid N2. Two hundred milligrams of the resulting powder was extracted at 4°C overnight in 500 µL 5:1 (v/v) acetonitrile–0.1 M HCl, then centrifuged and the supernatant dried in a speed vacuum at 40°C. Samples were suspended in methanol, and passed through a 0.2-µm nylon acrodisc filter (Gelman Sciences, Ann Arbor, MI), with 50 µL then injected into a Hewlett Packard 1090 HPLC (Waldbronn, FRG) system with a 287-nm scanning UV detector and a Phenomenex Maxil 5 C18 (Torrance, CA) reverse-phase analytical column (4.6 by 250 mm). Glyceollin I was separated by linear gradient elution for 25 min in methanol–water (300–1000 g kg-1) at a flow rate of 1 mL min-1. Glyceollin I concentration was then determined against a standard curve constructed using purified glyceollin I (generously provided by Dr. Renee Kosslak, Iowa State University).
Accumulation of Coumestrol, Daidzein, and Genistein in Crown Nodules
When cultivar differences in crown nodule deterioration and glyceollin I levels were detected, the accumulation of other metabolites associated with the phenylpropanoid pathway was also examined. This experiment considered four cultivars (Chippewa, Alpha, Hardin, and Hodgson 78) that differed in onset of nodule senescence and glyceollin I accumulation, plus the supernodulating line Nod 1-3, with harvests made 10 to 59 DAE. Crown nodules were again frozen in N2 and ground. Isoflavonoids were extracted by homogenizing 200 mg of powdered tissue in 10 volumes cold acetone followed by 10 volumes 1:1 (v/v) acetone–methanol for 24 h at 4°C. The samples were centrifuged, dried, resuspended, filtered, and analyzed by HPLC as above. The isoflavonoids coumestrol, daidzein, and genistein were quantified from the retention times and detector response to internal standards.
Expression of Phenylalanine Ammonia Lyase and Chalcone Synthase Genes in Crown Nodules
The cultivars Chippewa, Alpha, Hardin, Hodgson 78, and the genotype Nod 1-3 were also compared for differences in PAL and CHS gene expression 10 to 59 DAE. Crown nodules were frozen and ground as above, then 1 g of powdered nodule tissue was used to extract RNA (De Vries et al., 1988). The dot-blot technique (Sambrook et al., 1989) was used to detect differences in nodule expression of PAL and CHS genes. Eight micrograms of RNA was applied to a nitrocellulose membrane, baked for 2 h at 80°C, and then prehybridized for 2 h at 42°C. Soybean nodule-specific cDNA probes for PAL and CHS (generously provided by Dr. Sengupta-Gopalan, NM) were 32P labeled according to the Rediprime DNA protocol (Amersham, Arlington Heights, IL) to an activity of 1.9 x 109 disintegrations min-1 µg-1. Hybridization was performed overnight at 42°C, and then transcript abundance was quantified by direct counting of hybridized 32P by AMBIS 4000 radioanalytic image analysis, with 8 µg of 18S rRNA and 8 mg of leaf RNA included in each analysis as the negative and positive controls, respectively. Duplicate samples were used in all comparisons.
Soluble Protein, Protease Activity and Leghemoglobin Content of Crown Nodules
The cultivars Chippewa, Alpha, Hardin, and Hodgson 78, which differed in onset of nodule senescence and in level of glyceollin I accumulation, were also contrasted for changes in soluble protein, protease activity, and leghemoglobin content of crown nodules from 10 to 59 DAE. Two hundred and fifty milligrams of crown nodules were homogenized at 4°C in 1 mL of ß-mercaptoethanol extraction buffer, pH 6.8, containing ethylene glycol, sucrose, and phenylmethyl sulfonyl fluoride (Jessen et al., 1987, 1988). Cell debris was removed by centrifugation, and the supernatant placed on ice and immediately used to estimate nodule soluble protein, protease activity, and leghemoglobin content. Nodule soluble protein was determined using the Micro BCA Protein Assay Reagent (Pierce, Rockford, IL), with BSA as a standard. Protease activity was determined using azocasein as substrate (Vance et al., 1979) and expressed as change in absorbance (400 nm) mg protein-1 h-1. Leghemoglobin content was determined using the ELISA dot-blot procedure of Vance and Gantt (1992), with purified soybean leghemoglobin a (generously provided by Dr. R. Klucas, Lincoln, NE) as a standard. Samples were quantified by densitometry using the AMBIS radioanalytic imaging system (Scanalytics, Billerica, MA).
Polyamine Accumulation in Crown Nodules
Levels of cadaverine, putrescine, spermidine, and spermine in the crown nodules of Chippewa and Hardin also were evaluated from 10 to 59 DAE. One hundred milligrams of crown nodules were homogenized in 1 mL of 0.8 M perchloric acid at 4°C, then the samples centrifuged to remove cell debris. Supernatants were amended with 400 µL of dansyl chloride in acetone (15 g L-1), and incubated at 60°C for 1 h. Excess dansyl chloride was removed by the addition of proline; then dansylated polyamines were extracted with 500 µL of toluene (Smith, 1991). Polyamine standards were dansylated separately and used in the quantitative analysis. Dansylated polyamines were separated by thin-layer chromatography on 250-µm silica gel 60A K6F plates (Whatman, Clifton, NJ), with 10 µL of the toluene extract loaded in each lane and with 5:4 (v/v) cyclohexane–ethyl acetate as solvent. Polyamines were visualized under UV light and the spots removed. They were eluted in ethyl acetate and quantified by fluorescence at 350-nm excitation and 495-nm emission.
Cultivar Variation in Nodule Histology
Because the cultivars Chippewa and Hardin appeared to differ in several traits related to nodule senescence, a histological comparison of crown nodules from each was also undertaken. At each sampling date, 60 crown nodules from each cultivar were harvested, and fixed in 5:5:90 (v/v/v) formaldehyde–propionic acid–ethanol (700 g kg-1) in water. Nodules were postfixed with the same solution under atmospheric pressure for 12 h and then washed twice with 700 g kg-1 ethanol. Fixed nodules were dehydrated in an increasing ethanol series (700, 850, 950, and 1000 g kg-1 in water), then embedded in paraplast melted in tertiary-butyl alcohol. Sections 9 µm thick were cut with a michrotome, placed on poly L-lysine-treated slides, deparaffinized with graded xylene, and then rehydrated in a decreasing alcohol series. Nodule sections were stained with 0.5 g kg-1 toluidine blue in 6.7 mM benzoic acid, rinsed, and mounted. Stained sections were examined and photographed under bright field at 200x magnification using an HFX-II microscope (Nikon Inc., Melville, NY).
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Results
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Our goals in this study were first to identify soybean cultivars that differed in time to onset of crown nodule senescence and to examine contrasting genotypes for differences in secondary traits that might be used in the further study of additional genotypes or breeding populations.
Differences in crown nodule mass plant-1 for the 11 cultivars tested are shown in Table 1
. Crown nodule mass in Hardin and Hodgson 78 was significantly greater than for the other cultivars from 45 to 66 DAE. In these cultivars, crown nodulation peaked 52 DAE.
In most cultivars, crown nodule SNA (measured using the acetylene reduction assay), was greatest 31 to 38 DAE, with significant decline in activity thereafter (data not shown). Specific nodule activity in Hodgson 78 also peaked 31 DAE, although a secondary peak of activity was noted 52 DAE. Maximum SNA in Hardin occurred 45 DAE. Profiles of crown nodule SNA for the cultivars compared in other aspects of this study (Hardin, Hodgson 78, Chippewa, and Alpha) are shown in Fig. 1
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Fig. 1 Profiles of specific nodule activity for crown nodules of the soybean cultivars Alpha, Chippewa, Hardin, and Hodgson 78 from 10 to 66 d after emergence following inoculation with Bradyrhizobium japonicum strain UMR161. Nodule activity is measured as acetylene reduction to ethylene. Each point is the mean of three replicates, with vertical bars representing ± standard error
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Glyceollin I accumulation was evident in crown nodules of all cultivars except Hardin and Hodgson 78 at 10 DAE and increased steadily thereafter (data not shown). Mean values for crown nodule glyceollin I accumulation (excluding Hardin and Hodgson 78) rose from 43.1 mg g-1 fresh weight 10 DAE to 673.8 mg g-1 fresh weight nodules 38 DAE. By 45 DAE, glyceollin I concentrations in the nodules of several cultivars had begun to fall, and subsequently declined rapidly. An exception was the hypernodulating genotype Nod 1-3, which accumulated 892.6 µg glyceollin I g-1 fresh weight 52 DAE. By contrast, Hardin and Hodgson 78 showed surprisingly low glyceollin I concentrations throughout, with values often three orders of magnitude lower than those for Nod 1-3. Differences in level of glyceollin I accumulation by crown nodules of the contrasting cultivars Hardin, Hodgson78, Chippewa, and Alpha are shown in Table 2
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Table 2 Influence of harvest date on glyceollin I levels in the crown nodules of selected Maturity Group I soybean cultivars
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Glyceollin I is produced in response to infection by a number of soybean pathogens, but is usually only transiently expressed in young nodules (Werner et al., 1985; Estabrook and Sengupta-Gopalan, 1991). Because of this we examined nodules of Chippewa, Alpha, Nod 1-3, Hardin, and Hodgson 78 for evidence of other differences in phenylpropanoid synthesis, including PAL and CHS gene expression, and production of the nod-gene inducers daidzein, genistein, and coumestrol. Transcript abundance for PAL genes, as evidenced by radioanalytic image analysis, was greater in Chippewa, Alpha, and Nod 1-3 than in Hardin and Hodgson 78 (Fig. 2A)
, while differences in CHS gene expression were similar to those obtained with PAL, but not as clear cut (Fig. 2B). Nodule coumestrol and daidzein levels were greatest in the hypernodulating Nod 1-3, but from 17 to 38 DAE were statistically greater in Hardin and Hodgson 78 than in Alpha and Chippewa (data not shown) There were no consistent differences among the four cultivars studied in genistein accumulation.
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Fig. 2 Expression of phenylalanine ammonia lyase (Fig. 2A) and chalcone synthase (Fig. 2B) in crown nodules of the soybean cultivars Alpha, Chippewa, Hardin, Hodgson 78, and Nod 1-3 from 10 to 59 d after emergence following inoculation with Bradyrhizobium japonicum strain UMR161
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The content of soluble protein in crown nodules of Chippewa and Alpha was numerically greater than for Hardin and Hodgson78 at each harvest from 10 to 59 DAE, but differences were significant (
= 0.05) only at the 10 and 17 DAE harvests (data not shown). Pazdernik et al. (1996) also noted early nodulation and high levels of nodule soluble protein in Chippewa. Protease activity of crown nodules of these four cultivars 10 to 59 DAE is shown in Fig. 3
. Protease activity increased in all cultivars 24 to 31 DAE, with levels in Chippewa and Alpha greater than those for Hardin and Hodgson 78 from 24 to 59 DAE. Increase in the protease activity of nodules was paralleled by a decline in leghaemoglobin content beginning 31 DAE (Fig. 4)
. The decline for Chippewa and Alpha was greater than that for Hardin and Hodgson.
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Fig. 3 Protease activity in crown nodules of the soybean cultivars Alpha, Chippewa, Hardin, and Hodgson 78 from 10 to 59 d after emergence (DAE). Bars with the same letter at each DAE are not significantly different using Duncan's multiple range test ( = 0.05)
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Fig. 4 Leghemoglobin content of crown nodules of the soybean cultivars Alpha, Chippewa, Hardin, and Hodgson 78 from 10 to 59 d after emergence (DAE). Bars with the same letter at each DAE are not significantly different using Duncan's multiple range test ( = 0.05)
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Of the polyamines evaluated, only putrescine and spermidine were detected in crown nodules of Chippewa and Hardin, the amounts of each being greater in Chippewa than in Hardin at all harvests (Fig. 5A and 5B)
. Polyamines can exert an antibiotic effect on rhizobia (Osawa and Tsuji, 1992), so their more rapid accumulation in Chippewa could perhaps contribute to the earlier onset of nodule senescence.
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Fig. 5 Levels of (A) putrescine and (B) spermidine in the crown nodules of Chippewa and Hardin soybeans, from 10 to 59 d after emergence (DAE). Bars with the same letter at each DAE are not significantly different using Duncan's multiple range test ( = 0.05)
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There were significant changes in the morphology of crown nodules from Chippewa harvested 38 DAE (Fig. 6B)
and 45 DAE (Fig. 6D), a period of time that corresponded with significant decline in SNA (see Fig. 1). At the later harvest, cells in the central nodule tissue showed significant lysis, cells infected with bradyrhizobia were no longer evident, and only the vascular bundles conserved their structure. Morphological changes in crown nodules of Hardin were less dramatic (Fig. 6A and 6C), and while the central tissue had begun to senesce, much of the rest of the nodule remained unaltered.
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Fig. 6 Cytology of crown nodules of Chippewa and Hardin soybeans 38 and 45 DAE at 200x magnification. Transverse sections of nodules from (A) Hardin and (B) Chippewa 38 d after emergence (DAE). Longitudinal sections of nodules from (C) Hardin and (D) Chippewa 45 DAE. Sections stained with toluidine blue. Outer cortex (OC), nodule endodermis (NE), inner cortex (IC), infected cells (INC), uninfected cells (UIC) and vascular bundles (VB)
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Discussion
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There is increasing evidence for genetic variation in nodulation and N2 fixation in soybean (Neuhausen et al., 1988; Sinclair et al., 1991; Pazdernik et al., 1996) and for moderate heritability in this trait (Ronis et al., 1981; Greder et al., 1986; Herridge et al., 1994; Pazdernik et al., 1997a). At the field level, improvement can be made simply by selection among plants grown in soils low in N (Coale et al., 1985; Cregan and Yaklich, 1986; Pazdernik et al., 1997a). However, N2 fixation is generally regarded as a quantitative trait, and progress could be more rapid if the parents used in breeding programs differed in the traits each contributed to overall N2 fixation. Pazdernik et al. (1996) sought to extend the period of active N2 fixation in soybean through selection for lines demonstrating early nodulation and N2 fixation. This study also sought to extend the period of active fixation, but through the identification of genotypes in which nodule senescence was delayed. We emphasized crown nodulation because soybeans in the American Midwest bear a heterogeneous population of nodules, with those formed near the crown of the plant more likely to contain superior inoculant rhizobia (McDermott and Graham, 1989; Wadisirisuk et al., 1989). Selection of crown nodules also ensures that the nodules are of uniform age, limiting confounding effects from later-formed lateral-root nodules.
Among the varieties evaluated, only Hardin and Hodgson 78 maintained active crown nodulation until 52 DAE and showed strong SNA postflowering. Delay in nodule senescence in these cultivars was associated with lower levels of glyceollin I, putrescine, and spermidine; reduced PAL and CHS gene expression; and lower protease activity than in nodules of equivalent age in the other cultivars tested. Of these traits, the differences in glyceollin I and spermidine levels were of a magnitude sufficient to suggest that these traits might be used in a preliminary screening of additional germplasm or breeding populations.
Accumulation of glyceollin I has been shown in several studies in which host and rhizobia were incompatible (Werner et al., 1985; Karr et al., 1992; Werner et al., 1994), but no previous study has shown that cultivar differences in nodule senescence might be related to accumulation of glyceollin I. Both glyceollin I and polyamines have been reported to have an antibiotic effect on B. japonicum in culture medium (Parniske et al., 1991; Osawa and Tsuji, 1992), so it is not unlikely that high levels of these compounds might affect nodule function and nitrogenase activity. Similarly, high protease activity could promote both early decline in the leghemoglobin content of nodules, and the degradation of infected cells. It is interesting to note that nodules of the hypernodulating genotype Nod 1-3, which exhibited low nitrogenase activity in the studies of Pazdernik et al. (1996), had both high levels of glyceollin I and elevated PAL gene expression during most developmental stages.
If the delayed senescence of crown nodules demonstrated in this study contributes to enhanced N accumulation, growth, and yield in Hardin and Hodgson 78, these varieties should have value in breeding for enhanced N2 fixation in soybean. Studies to examine differences in these traits under field conditions are warranted, as are further studies to identify molecular markers associated with each trait. The impact of delayed crown nodule senescence on secondary nodulation in soybean is also deserving of study.
A multiple-trait recurrent selection breeding program, such as that mounted by Barnes et al. (1984) in alfalfa (Medicago sativa L.), seems appropriate for the improvement of nodulation and N fixation in soybean. For Maturity Group I, parental sources could include lines with the capacity for early nodulation and N2 fixation (Chippewa or PI438068; Pazdernik et al., 1997a, 1997b), lines that are efficient in N translocation to the developing seed (`Parker' or `Agassiz'; Pazdernik et al., 1997b), and Hardin or Hodgson 78 from the present study. Such a program might also need to include cultivars with the ability for N2 fixation in the presence of moderate levels of combined N (e.g., `Mendota'; S.G. Wagner, 1993, personal communication).
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NOTES
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The research was supported by a fellowship from the Consejo Nacional de Ciencias y Tecnologia (CONACYT, Mexico) to D. Espinosa-Victoria and by a grant from the Minnesota Soybean Research and Promotion Council. Journal series no. 991250079 of the Univ. of Minnesota Agric. Exp. Stn.
Received for publication July 27, 1998.
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REFERENCES
|
|---|
- Barnes D.K., Heichel G.H., Vance C.P., Ellis W.R. A multiple-trait breeding program for improving the symbiosis for N2 fixation between Medicago sativa L. and Rhizobium meliloti. Plant Soil 1984;82:303-314.
- Coale F.J., Meisinger J.J., Wiebold W.J. Effects of plant breeding and selection on yields and nitrogen fixation in soybean under two soil nitrogen regimes. Plant Soil 1985;86:357-367.
- Cregan P.B., Yaklich R.W. Dry matter and nitrogen accumulation and partitioning in selected soybean genotypes of different derivation. Theor. Appl. Genet. 1986;72:782-786.
- Dart, P.N.J., J.M. Day, and D. Harris. 1975. Assay for nitrogenase activity by acetylene reduction. p. 85–100. Rothamsted Experimental Station, Harpenden, Herts, England.
- DeVries S., Hoge H., Bisseling T. Isolation of total and polysomal RNA from plant tissues. In: Galvin S.B., Schilperoot R.A., eds. Plant molecular biology manual. Dordrecht, the Netherlands: Kluwer Academic Publ, 1988:6 Chapter B.
- Dobereiner J., Urquiaga S., Boddey R.M. Alternatives for nitrogen nutrition of crops in tropical agriculture. Fert. Res. 1995;42:339-346.
- Estabrook E.M., Sengupta-Gopalan C. Differential expression of phenylalanine ammonia-lyase and chalcone synthase during soybean nodule development. Plant Cell 1991;3:299-308.[Abstract/Free Full Text]
- Graham P.H. Antibiotic sensitivities of the root nodule bacteria. Aust. J. Biol. Sci. 1963;16:557-560.
- Greder R.R., Orf J.H., Lambert J.W. Heritabilities and associations of nodule mass and recovery of Bradyrhizobium japonicum serogroup USDA 110 in soybean. Crop Sci. 1986;26:33-37.
- Ham G.E. Interaction of Glycine max and Rhizobium japonicum. In: Summerfield R.J., Bunting A.H., eds. Advances in legume science. Kew, UK: Royal Botanic Gardens, 1978:289-296.
- Herridge D.F., Rupela O.P., Serraj R., Beck D.P. Screening techniques and improved biological nitrogen fixation in cool season food legumes. Euphytica 1994;73:95-108.
- Jessen D.L., Barnes D.K., Vance C.P. Bidirectional selection in alfalfa for activity of nodule nitrogen and carbon-assimilating enzymes. Crop Sci. 1988;28:18-22.
- Jessen D.L., Barnes D.K., Vance C.P., Heichel G.H. Variation for activity of nodule nitrogen and carbon assimilating enzymes in alfalfa. Crop Sci. 1987;27:627-631.[Abstract/Free Full Text]
- Karr D.B., Emerich D.W., Karr A.L. Accumulation of the phytoalexin, glyceollin, in root nodules of soybean formed by effective and ineffective strains of Bradyrhizobium japonicum. J. Chem. Ecol. 1992;18:997-1008.
- McDermott T.R., Graham P.H. Bradyrhizobium japonicum inoculant mobility, nodule occupancy, and acetylene reduction in the soybean root system. Appl. Environ. Microbiol. 1989;55:2493-2498.[Abstract/Free Full Text]
- McDermott T.R., Graham P.H. Competitive ability and efficiency in nodule formation of strains of Bradyrhizobium japonicum. Appl. Environ. Microbiol. 1990;56:3035-3039.[Abstract/Free Full Text]
- Neuhausen S.L., Graham P.H., Orf J.H. Genetic variation for dinitrogen fixation in soybean of Maturity Group 00 and 0. Crop Sci. 1988;28:769-772.[Abstract/Free Full Text]
- Osawa T., Tsuji T. Inhibition of growth of Bradyrhizobium japonicum bacteroid by spermidine and spermine in yeast extract. Soil Sci. Plant Nutr. 1992;38:375-379.
- Parniske M., Ahlborn B., Werner D. Isoflavonoid-inducible resistance to the phytoalexin glyceollin in soybean rhizobia. J. Bacteriol. 1991;173:3432-3439.[Abstract/Free Full Text]
- Pazdernik D.L., Graham P.H., Orf J.H. Heritability in the early nodulation of F3 and F4 soybean lines. Can. J. Plant Sci. 1997;77:201-205 a.
- Pazdernik D.L., Graham P.H., Orf J.H. Variation in the pattern of nitrogen accumulation and distribution by soybean under N stress. Crop Sci. 1997;37:1482-1486 b.[Abstract/Free Full Text]
- Pazdernik D.L., Graham P.H., Vance C.P., Orf J.H. Host genetic variation in the early nodulation and dinitrogen fixation in soybean. Crop Sci. 1996;36:1102-1107.[Abstract/Free Full Text]
- Pladys D., Vance C.P. Proteolysis during development and senescence of effective and plant gene-controlled ineffective alfalfa nodules. Plant Physiol. 1993;103:379-384.[Abstract]
- Ronis, D., D.J. Sammons, and J.J. Meisinger. 1981. Estimating broad sense heritability of nitrogen fixation in an F2 soybean population. p. 95. In 1981 Agronomy Abstracts. ASA, Madison, WI.
- Sambrook J., Fritsch E.F., Maniatis T. Molecular cloning. New York: A laboratory manual. 2nd ed. Cold Spring Harbor Laboratory Press, 1989.
- SAS Institute. SAS/STAT guide for personal computers, 6th ed Cary, NC: SAS Inst, 1992.
- Sinclair T.R., Soffes A.R., Hinson K., Albretch S.L., Pfahler P.L. Genotypic variation in soybean nodule number and weight. Crop Sci. 1991;31:301-304.[Abstract/Free Full Text]
- Smith M.A. Chromatographic methods for identification and quantitation of polyamines. In: Slocum R.D., Flores H.E., eds. Biochemistry and physiology of polyamines in plants. Boca Raton, FL: CRC Press, 1991:229-242.
- Vance C.P. Legume symbiotic nitrogen fixation: Agronomic aspects. In: Spaink H.P., et al. , ed. The Rhizobiaceae. Dordrecht, the Netherlands: Kluwer Academic, 1998:509-530.
- Vance C.P., Gantt S. Control of nitrogen and carbon metabolism in root nodules. Physiol. Plant. 1992;85:266-274.
- Vance C.P., Heichel G.H., Barnes D.K., Bryan J.M., Johnson L.E. Nitrogen fixation, nodule development, and vegetatve regrowth of alfalfa (Medicago sativa L.) following harvest. Plant Physiol. 1979;64:1-8.[Abstract/Free Full Text]
- Vincent J.M. A manual for practical study of root-nodule bacteria. IBP Handbook 15. Oxford: Blackwell Sci. Publ, 1970.
- Wadisirisuk P., Danso S.K.A., Hardarson G., Bowen G.D. Influence of Bradyrhizobium japonicum location and movement on nodulation and nitrogen fixation in soybeans. Appl. Environ. Microbiol. 1989;55:1711-1716.[Abstract/Free Full Text]
- Werner D., Mellor R.B., Hahn M.G., Grisebach H. Soybean root response to symbiotic infection glyceollin I accumulation in an ineffective type of soybean nodules with an early loss of the peribacteroid membrane. Z. Naturforsch 1985;40c:179-181.
- Werner D., Ahlborn B., Antoun H., Bernard S., Bolanos C., Cooper J.E., Gorge E., Jacobi A., Kalliopi P., Kape R., Katinakis P., Kosch K., Muller P., Parniske M., Schmidt P., Streit W., Wetzel A. Communication and signal exchange in the Rhizobium/Bradyrhizobium–legume system. Endocytob. Cell Res. 1994;10:5-15.
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ABSTRACT
INTRODUCTION
