News Update on Soybean Seedling: Feb 2021

Fungi associated with soybean seedling disease in Iowa.

Surveys were conducted over a 2-year period to identify fungi associated with soyabean seedling disease in Iowa, USA. Fungi were isolated from diseased soyabean seedlings collected from 52 and 66 locations in 1993 and 1994, respectively. The percentages of major fungal taxa isolated from soyabean seedlings in the 2 years were Rhizoctonia solani 27.5% in 1993 and 27.3% in 1994; Fusarium spp., 11.9% in 1993 and 13.7% in 1994; and Pythium spp. and Phytophthora sojae, cumulatively 60.5% in 1993 and 31.7 and 24.3% in 1994, respectively. Other isolated fungi were the seed decay pathogen Phomopsis longicolla, and the nonpathogenic Rhizopus stolonifer and Trichoderma viride. Species of Fusarium and Pythium were identified as F. acuminatum [Gibberella acuminata], F. equiseti, F. oxysporum, P. aphanidermatum, P. irregulare, P. myriotylum, P. sylvaticum, P. ultimum var. sporangiiferum and P. ultimum var. ultimum. Repeated tests of pathogenicity confirmed that Pythium spp., Phytophthora sojae and R. solani were the major causal fungi associated with the seedling disease complex of soyabeans in Iowa. [1]

Flavonoid and Isoflavonoid Distribution in Developing Soybean Seedling Tissues and in Seed and Root Exudates

The distribution of flavonoids, isoflavonoids, and their conjugates in developing soybean (Glycine max L.) seedling organs and in root and seed exudates has been examined. Conjugates of the isoflavones daidzein and genistein are major metabolites in all embryonic organs within the dry seed and in seedling roots, hypocotyl, and cotyledon tissues at all times after germination. Primary leaf tissues undergo a programmed shift from isoflavonoid to flavonoid metabolism 3 days after germination and become largely predominated by glycosides of the flavonols kampferol, quercetin, and isorhamnetin by 5 days. Cotyledons contain relatively constant and very high levels of conjugates of both daidzein and genistein. Hypocotyl tissues contain a third unidentified compound, P19.3, also present in multiple conjugated forms. Conjugates of daidzein, genistein, and P19.3 are at their highest levels in the hypocotyl hook and fall off progressively down the hypocotyl. These isoflavones also undergo a programmed and dramatic decrease between 2 and 4 days in the hypocotyl hook. All root sections are predominated by daidzein and its conjugates, particularly in the root tip, where they reach the highest levels in the seedling. Light has a pronounced effect on the distribution of the isoflavones; in the dark, isoflavone levels in the root tips are greatly reduced, while those in the cotyledons are higher. Finally, the conjugates of daidzein and genistein and several unidentified aromatic metabolites are selectively excreted into root and seed exudates. Analysis of seed exudates suggests that this is a continuous, but saturable event. [2]

Electrical conductivity of the seed soaking solution and soybean seedling emergence

Vigor of soybean [Glycine max (L.) Merrill] seeds can be evaluated by measuring the electrical conductivity (EC) of the seed soaking solution, which has shown a satisfactory relationship with field seedling emergence, but has not had aproper definition of range yet. This work studies the relationship between EC and soybean seedling emergence both in the field and laboratory conditions, using twenty two seed lots. Seed water content, standard germination and vigor (EC, accelerated aging and cold tests) were evaluated under laboratory conditions using –0.03; –0.20; –0.40 and –0.60 MPa matric potentials, and field seedling emergence was also observed. There was direct relationship between EC and field seedling emergence (FE). Under laboratory conditions, a decreasing relationship was found between EC and FE as water content in the substrate decreased. Relationships between these two parameters were also found when –0.03; –0.20 and –0.40 MPa matric potentials were used. EC tests can be used successfully to evaluate soybean seed vigor and identify lots with higher or lower field emergence potential. [3]

Analysis of Seed Vigor Responses in Soybean to Invasive Silver Carp (Hypophthalmichthys molitrix) Protein Hydrolysate Treatments

Aim: To produce fish protein hydrolysates (FPH) from invasive silver carp (Hypophthalmichthys molitrix) under controlled hydrolysis conditions, and to examine the effects of FPH on seed vigor, using standard vigor tests.

Methodology: Soybeans were treated with FPH hydrolyzed for 1, 5.5 and 10 hrs with papain (FPH-Pa), pepsin (FPH-P) and trypsin (FPH-T), respectively. Overall vigor tests (accelerated aging and warm and cold germination dry weight, height, total phenolics and guaiacol peroxidase assessment-GuPx) were compared to a distilled-water control over a 12-day germination period.

Results: Seeds treated with FPH-P and FPH-Pa at 1 hr (23% degree of hydrolysis) elicited the greatest growth responses. FPH-Pa at 1 hr increased (P=0.05) weight (1.38 g) and height (53 mm) compared to water control (1.25 g and 46.8 mm, respectively). FPH-Pa at 1 hr also had the highest GuPx values, which are indicative of lignification. FPH-Pa appeared to stimulate lignification and thus enhance weight and height of the seedling. FPH-P elicited the greatest phenolic response, with the highest total phenolic content on day 4 (1.27 mg GAE/g FW) and day 12 (1.43 mg GAE/g FW) compared to water control (0.59 mg GAE/g FW on day 4, 1.10 mg GAE/ g FW on day 8). Higher phenolic content may have protected against oxidation during accelerated aging vigor test, resulting in higher germination rates (53.8% germination) for soybeans primed with FPH-P at 1 h compared to water controls (32.2% germination). Most FPH treatments increased germination under warm conditions, compared to water control. GuPx values overall were higher in FPH-treated soybeans.

Conclusion: Results suggest that the use of FPH produced with the enzymes papain and pepsin at 1 hour of hydrolysis are comprised of free amino acids and peptides that are beneficial to the stimulation of the proline-linked pentose phosphate pathway, which enhanced the vigor parameters measured. [4]

Phosphorus Application and Rhizobia Inoculation on Growth and Yield of Soybean (Glycine max L. Merrill)

An experiment was conducted in the major and minor cropping seasons of 2012 and 2013 under field conditions at Bolgatanga Polytechnic, to study the effect of phosphorus fertilizer and Rhizobia inoculation on growth and yield of soybean using randomized complete block design and three replications. The treatments studied were:  Soybean + phosphorus fertilizer + Rhizobia inoculation (+P/+I), Soybean + phosphorus fertilizer only (+P/-I), Soybean inoculated with Rhizobia (-P/+I) and the control-Soybean only (-P/-I). Results indicated that Phosphorus fertilizer application is required for shoot growth, pod and seed yield. Nodulation and root growth were significantly increased by Phosphorus + Rhizobia inoculation (+P/+I) but P fertilizer only did not enhance root growth. Dry matter accumulation was highest between onset of flowering and Podding. Grain yield was again highest for Rhizobia inoculation plus Phosphorus fertilizer (+P/+I) and Phosphorus fertilizer only (+P/-I) recording 7.61 t/ha and 7.30 t/ha respectively whiles Rhizobia inoculation only (-P/+I) and the control (-P/-I) produced the lowest grain yield (4.41 t/ha) and (3.80 t/ha) respectively. [5]

Reference

[1] Rizvi, S.S.A. and Yang, X.B., 1996. Fungi associated with soybean seedling disease in Iowa. Plant disease, 80(1), pp.57-60.

[2] Graham, T.L., 1991. Flavonoid and isoflavonoid distribution in developing soybean seedling tissues and in seed and root exudates. Plant physiology, 95(2), pp.594-603.

[3] Vieira, R.D., Scappa Neto, A., Bittencourt, S.R.M.D. and Panobianco, M., 2004. Electrical conductivity of the seed soaking solution and soybean seedling emergence. Scientia Agricola, 61(2), pp.164-168.

[4] Thomson, S. P., Liceaga, A. M., Applegate, B. M. and Martyn, R. D. (2014) “Analysis of Seed Vigor Responses in Soybean to Invasive Silver Carp (Hypophthalmichthys molitrix) Protein Hydrolysate Treatments”, Journal of Experimental Agriculture International, 5(3), pp. 178-191. doi: 10.9734/AJEA/2015/13087.

[5] M. Akpalu, M., Siewobr, H., Oppong-Sekyere, D. and E. Akpalu, S. (2014) “Phosphorus Application and Rhizobia Inoculation on Growth and Yield of Soybean (Glycine max L. Merrill)”, Journal of Experimental Agriculture International, 4(6), pp. 674-685. doi: 10.9734/AJEA/2014/7110.

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