Nodule Distribution on Roots of Field-Grown Soybeans in Subsurface ...

Published January, 1982

153

NOTES

NODULE DISTRIBUTION ON ROOTS OF FIELD-GROWN SOYBEANS IN SUBSURFACE 1SOIL HORIZONS

Table 1. Sites of nodule sampling. Site

Year Soil

Aurora,NY

1979 Limaloam (fine--loamy, mixed, mesic glossoboric hapludalfs) 1980 Limaloam 1980 MunsonSandyLoam (coarse--silty over clayey, mixed nonacid, mesic haplaquepts) 1980 Cossayuna gravelly loam {inactivel 1979Dunkirksiltloam (fine--silty, mixed mesic glossoboric hapludalfsl 1980 Darien Gravelly SiltLoam (fine--loamy, mixed mesic aeric ochraqualfs)

V. Grubinger, R. Zobel, J. Vendelandand 2P. Cortes

ABSTRACT Although muchresearch has been carried out on nodulationandnitrogen fixation of soybeans[Glycine max (L.) Merr.], the majority of field studies have centered on nodules whichhave developedwithin the Ap soil horizon. This research provides evidence demonstrating that nodulation does occur to 1 m depth. Additional index words: Glycine max, Nodulation, Nitrogenfixation, Rhizobotany.

S

TUDIESOf the rooting habits of soybean have indicated that a great deal of variability exists due to differences among cultivars and their environment. Cultivars have been shown to differ in morphological characteristics (Mitchell and Russell, 1971, Raper and Barber, 1970a), and differing root-shoot relations have been elicited by varying water availability (Sivakumar et al., 1977, Mayakiet al., 1976). Nutrient adsorption by roots varied between at least two cultivars (Raper and Barber, 1970b), and plant spacing had an effect on root system development (Bohm, 1977). Interest in the process of symbiotic nitrogen fixation, and root nodules as the site of fixation, has increased the attention paid to soybean roots. However, few investigations have focused on the distribution of nodules on these roots. Bhaduri and Sen (1968) observed that the distribution patterns of nodules varied among Phaseolus species. Tendencies toward only tap root nodulation, or toward diffuse nodulation on tap and lateral roots were noted, as well as intermediate patterns. Only a single soybean cultivar was examined in their study. The effect of interplant competition and seasonal development on soybean nodules was studied by Weil and Ohlrogge (1975). Three cultivars were utilized, and cores of 15-cm depth were taken. Such limiting of investigation to the Ap horizon is not uncommonin nodulation and nitrogen fixation research efforts (Hardy et al., 1968; Thibodeau and Jaworski, 1975). Our laboratory has collected in situ data on root and nodulation characteristics (Zobel, 1980) and rates nitrogen fixation potential by acetylene reduction (Denison, 1979). However, these investigations have been restricted to the Ap horizon because of the mechanical obstruction posed by soils of glacial origin, and the difficulty of manipulating roots without causing damage when working with large volumes of soil. It seems reasonable to assume that descriptions of root characteristics and activities in the surface layers of the profile are quite useful, and may well be representative of the entire root system for purposes of comparison. Of course, it is only prudent to ascertain if indeed this is the case. For this reason, we conducted a preliminary field study to determine the variability

Aurora,NY Chazy,NY

Valatie, NY Varna,NY

Varna,NY

Methodof sampling trench to I m

spadeto 0.5m spadeto0.5m

spadeto0.5m spadeto I m

trench to1.2rn

amongsoybeans in their root nodule distribution, with specific regard to the proportion of total nodules located beneath the Ap horizon. METHODS Different cultivars of soybean [Glycine max (L.) Merr.] were grownat five sites throughout NewYorkState representingdifferent soils (Table1). All sites received224kg/ha 36-24-24 fertilizer, and were treated with 4.7 l/ha of Lasso (alachlor) and 0.84 kg/ha of Sencor (metribuzin) as emergentherbicides. At two of these sites, a back-hoe was used to excavate trenches exceeding 1 m in depth. The trenches ran approximatelyperpendicular to the plant rows, and weresituated so as to include several rows of a minimum of three cultivars. The 1979 Varna experimentwas designed as a drought experiment. The cultivars were covered with a polyethylene-track mounted-canopywhenthere was a threat of rain, and kept uncovered the remainder of the time. Sprinkler irrigation was provided for untreated/control plants as determinedby soil moistureand leaf water potential measurements(Vendeland, 1980). At the other three sites, small pits were dugmanuallyfor brief observations of nodule location. The trench-profile method of root system examination (Bohm, 1979; Schuurmanand Goedewaagen,1971), perhaps the most appropriate for the study of actual root framework (Bohmet al., 1977), was employedin the trench studies. smoothvertical surface of the soil profile at the base of the plant, stage R1-R3(Fehr &Caviness, 1971), to be examined was prepared. Using a herbicide sprayer filled with water, and a hand-held wand, approximately 5 cmof the vertical face of the profile was washedaway. A woodenframe, 1 m × 60 cm and sectioned into squares, 10 cmon a side, with white string was then centered belowthe plant. Noduleswere counted and a few, selected at random, split open to determine their internal color. Rednodules were assumedto be actively fixin~ nitrogen. ~ USDA-ARS and Dep. of Agronomy1023 Bradfield Hall, Cornell Univ., Ithaca, NY14853. Date received 12 Feb. 1981. 2Research assistant, Dep. of Agronomy, Cornell Univ.; research geneticist, USDA-ARS, and assistant professor, Dep. of Agronomy and Plant Breeding, Cornell Univ.; former research assistant, Dep. Agronomy, Cornell Univ.; and research assistant, Dep. of Agronomy, Cornell Univ. 3Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the USDAand does not imply its approval to the exclusion of other products that mayalso be suitable.

CROP SCIENCE, VOL. 22, JANUARY-FEBRUARY 1982

154

Table 2. Nodule distribution within the soil profile from Varna, NY, 1979. Nodule distribution depth, cm Cultivar

Treatment

0-10

10-20

20-30

30-40

40-50

Wilkin

Control Drought Control Drought

7 ±3 t 7±1

5± 1 2±1

3 ±4 5±8

4 ± 7 5 ±8

9± 12 1±1

17 ± 14 2± 1

1±1

15 ±6

5±5

7 ±4

1 ±2 10 ± 1

12 ± 17

50-100

Total

Nodules below 20 cm

28 ± 27 20 ± 1

57 55

35 ±4 44 ± 27

49 84

%

SRF 150

8 ±11

t Mean, plant"' ± S.D. Table 3. Nodule distribution within the soil profile from Varna, NY, 1980.

Cultivar

Nodule distribution depth, cm

No. of plants

Plant height

0-10

10-20

20-30

30-40

40-50

50-100

Total

below 20 cm

5 4 4

1.2 0.6 1.2

61 ±3t 35 ±5 21 ± 10

19 ±4 22 ± 11

10 ±3 16 ± 10 5 ±2

3 ±2 3± 1 1 ±2

Oil 2 ± 2 0

1± 2 0 0

94 ± 34 78 ± 26

15 27 15

%

Gnome Wilkin Chippewa 64

14 ± 5

41 ±8

1

t Values are means, plant" ± SD.

RESULTS AND DISCUSSION The actual proportion of nodules located beneath the Ap horizon ranged from about 10 % to over 50 %, depending on variety, soil, and environmental conditions (Table 2 to 4). Nodules at depths of 20 cm or greater were frequently observed at all six sites. Infrequently, nodules were seen at depths approaching 1 m. Prior disturbance of the soil enhances nodulation at greater depths, as nodules were more abundant deep in the profile in the one instance where tile drains were present (Table 4, 'Ilsoy'). During the summer of 1979 plants subjected to artificial drought conditions during the course of another experiment at Varna were examined (Table 2). In one cultivar, water-stressed plants tended to have agreater depth of nodulation, though this may have been an indirect effect of root exploration to greater depths in response to the water deficit in the upper portion of the soil profile (data not presented). Differences in the lateral distribution of nodules were not calculated, since wide row spacing may be required to minimize reported (Bohm, 1977) intermingling of lateral roots. During the 1980 season two cultivars ('Wilkin' and 'Beechwood') were sampled from yield trials at three locations, Aurora, Chazy and Valatie. Both cultivars had nodules below the Ap horizon at all three sites (data not shown). Further studies are needed to determine specifically which environmental factors influence nodule distribution, and to determine how significant the contribution of fixed nitrogen is from subsoil nodules. The effect of planting density on nodule distribution also warrants further investigation. Weil and Ohlrogge (1975) have calculated that nodule volume per plant, the percentage of red nodules, and specific nodule activity all increased as a result of thinning. They speculated that reduced canopy competition increased the photosynthate available for nodule maintainance, and it is possible that increased depth of nodulation would also result.

Table 4. Number of nodules above and below a 15 cm deep Ap horizon at Aurora, 1979. Cultivar Manchuria Williams Lincoln A. K. (Harrow) IlsoyJ Guelph Wells T-85

Number above 15 cm

Number below 15 cm

Total number

21t 36 30 14 23 64 3 60

13

34 48 60 26

12 30 12 21 64 18 44

44 128

21 104

%

below 15 cm 38 25 50 46 48 50 86 42

T Average of two plants. t Ilsoy grew over a drain tile which was buried to 1 meter. Nodules were found at the 1 meter depth. A dramatic increase in soil density below 50 to 60 cm prevented nodulation and, in general, root growth of other cultivars below this depth.

The results presented in this paper indicate that nodules may be present on field-grown soybean roots at depths greater than previously demonstrated. It appears that depth of nodulation may differ among cultivars and among soil types. Environmental factors such as water availability within the profile may also be important in determining nodule distribution.

155

NOTES 8. Mayaki, W. C., I. D. Teare, and L. R. Stone. 1976. Top and root growth of irrigated and non-irrigated soybeans. Crop Sci. 16:92-94. 9. Mitchell, R. L., and W. J. Russell. 1971. Root development and rooting patterns of soybean [Glycine max (L.) Merr.] evaluated under field conditions. Agron. J. 63:313-316. 10. Raper, C. D., and S. A. Barber. 1970a. Rooting systems of soybeans. I. Differences in root morphology among varieties. Agron.: J. 62:581-584. 11. ——— ——, and —————. 1970b. Rooting systems of soybean. II. Physiological effectiveness as nutrient absorption surfaces. Agron. J. 62:585-588. 12. Schuurman, J. J., and M. A. J. Goedewaagen. 1971. Methods for the examination of root systems and roots. Center for Agricultural Publishing and Documentation, Wageningen. 13. Sivakumar, M. V. K., H. M. Taylor, and R. H. Shaw. 1977. Top and root relations of field grown soybeans. Agron. J. 69: 470-473. 14. Thibodeau, P. S., and E. G. Jaworski. 1975. Patterns of nitrogen utilization in the soybean. Planta. 127:133-147. 15. Vendeland, J. 1980. A field evaluation of the plastochron index. M.S. Thesis, Cornell Univ., Ithaca, New York. 16. Well, R. R., and A. J. Ohlrogge. 1975. Seasonal development of, and the effect of interplant competition on, soybean nodules. Agron. J. 67:487-490. 17. Zobel, R. W. 1980. Rhizogenetics of soybean, p. 73-87. In F. T. Corbin (ed.) World soybean research conference II: proceedings. Westview Press, Boulder, Colo.

NEW SOURCES OF RESISTANCE TO SEED TRANSMISSION OF SOYBEAN MOSAIC VIRUS IN SOYBEANS1 G. H. Bowers, Jr., and Robert M. Goodman2 ABSTRACT The purpose of this study was to identify resistance to seed transmission of soybean mosaic virus (SMV) among soybean [Glycine max (L.) Merrill] germplasm lines that were previously ignored because of their high incidences of seed coat mottling. Twelve germplasm lines from Maturity Croups II and III were identified as sources of resistance to seed transmission of the Illinois severe isolate of SMV. These lines can be used to develop cultivars for areas where SMV is a problem and seed transmission serves as the principal source of primary inoculum. In addition, resistance to seed transmission could be incorporated into soybean lines grown for seed production, thereby eliminating or simplifying the efforts required to produce virus-free material. Additional index words: Glycine max (L.) Merrill, Plant introduction, Virus infection.

M

ANY important agricultural crops are known to transmit a number of viruses through seeds from infected plants (1, 10). Seed transmission can be epidemiologically important, especially for viruses that are nonpersistently transmitted by aphids and have a narrow host range. Genetic resistance to seed transmission is a possible tool to be used in the control of virus diseases (3). In previous work from our laboratory, we screened 497 soybean lines from Maturity Groups II and III and

400 soybean lines from Maturity Groups VIII, IX, and X for incidence of seed transmission of the Illinois severe isolate of soybean mosaic virus (SMV) (2, 5). Results of these screening trials led to the identification of 15 accessions of Maturity Groups II and III that exhibited no apparent seed transmission and had a low incidence of seed coat mottling in tests with 1,000 seeds produced by SMV-infected plants. An additional 48 soybean lines were identified that exhibited no apparent seed transmission, but that displayed a high incidence of seed coat mottling in tests with 200 seeds produced by SMV-infected plants (2). We have tested further these 48 lines and in this paper report the results of a screening trial that identified 12 lines that exhibited no apparent seed transmission in tests with 1,000 seeds produced by SMV-infected plants. MATERIALS AND METHODS Four replications of 48 lines of Maturity Groups II and III were evaluated in a complete randomized design on 18 May 1978 near Urbana, 111. Each entry was planted in a 91-cm row with 30-cm alleys and 76 cm between rows. Two accessions known to transmit SMV through seeds, PI 86146 and PI 181549, were included to ensure that conditions were favorable for seed transmission. The plants were inoculated with the Illinois severe isolate of SMV (SMV-I1-S) (11) on 14 June 1978. The inoculum was prepared from SMV-I1-S infected soybeans ('Rampage') which had been inoculated in the greenhouse 14 to 21 days previously. Leaves were homogenized in 4 ml of 50 mM sodium phosphate, pH 7.0, per gram of tissue (fresh weight). The inoculum was strained through a double layer of cheesecloth plus one layer of Miracloth, 10 g of 22-jtm (600 mesh) Carborundum were added per liter, and the inoculum was applied to the plants using a Type B Wren airbrush (Binks Manufacturing Company, Franklin Park, 111.) that was supplied air pressure by an air compressor operating at 4.9 kg/cm2 (7). The soybean plants were inoculated by holding the leaves in one hand while applying the inoculum with a distance of 1 to 2 cm between the leaves and the air brush nozzle. The inoculum was frequently agitated to keep the Carborundum in suspension. Symptomless plants were removed 4 weeks after inoculation. The rows were harvested at maturity. A sample of 250 seeds from each row (1,000 seeds/accession) was examined for seed coat mottling and planted in a sandbench. The emerging seedlings were counted and examined for visual symptoms of virus infection. Any seedling exhibiting questionable symptoms was indexed by infectivity (8), or by enzyme-linked immunosorbent assay (ELISA) (4). RESULTS AND DISCUSSION Twelve of the lines tested in 1978 produced all healthy seedlings when 1,000 seeds from SMV-infected plants were planted (Table 1). The nontransmitting 1 Contribution from Dep. of Plant Pathology and International Soybean Program, Univ. of Illinois, Urbana, IL 61801. Research support was from the U.S. Agency for International Development research contracts cm/ta-c-73-19 and TA/-1294 with the Univ. of Illinois International Soybean Program (INTSOY) and from the Illinois Agric. Exp. Stn. Views and interpretations are those of the authors and should not be attributed to USAID or to any individual acting in their behalf. Received 10 April 1981. 2 Former graduate research assistant, present address, Texas A&M Univ. Agric. Res. & Ext. Ctr., Route 7, Box 999, Beaumont, TX 77706; and professor, of Plant Pathology, Univ. of Illinois, Urbana, respectively.