Effect of Salinity on Nodule Formation by Soybean

Abstract

A split-root growth system was employed to evaluate the effect of NaCl on nodule formation by soybean (Glycine max L. Meff. cv Davis). By applying the salinity stress and rhizobial inoculum to only one-half the root system, the effects of salinity on shoot growth were eliminted in the nodulation process. Rhizobium colonization of inoculated root surfaces was not affected by the salt treatments (0.0, 26.6, 53.2, and 79.9 millimolar NaCI). While shoot dry weight remained unaffected by the treatments, total shoot N declined from 1.26 grams N per pot at 0.0 millimolar NaCI to 0.44 grams N per pot at 79.9 millimolar NaCl. The concentration of N in the shoot decreased from 3.75% N (0.0 millimolar NaCI) to 1.26% N at 79.9 millimolar NaC. The decrease in shoot N was attributed to a sharp reduction in nodule number and dry weight. Nodule number and weight were reduced by approximately 50% at 26.6 millimolar NaCl, and by more than 90% at 53.2 and 79.9 millimolar NaO. Nodule development, as evidenced by the average weight of a nodule, was not as greatly affected by salt as was nodule number. Total nitrogenase activity (C2H2 reduction) decreased proportionally in relation to nodule number and dry weight. Specific nitrogenase activity, however, was less affected by salinity and was not depressed signficantly ntil 79.9 milimolar NaCI. In a second experiment, isolates of Rhizobium japonicum from nodules formed at 79.9 millimolar NaC did not increase nodulation of roots under salt stress compared to nodule isolates from normal media (0.0 millimolar NaCl). Salt was applied (53.2 millimolar NaC) to half root systems at 0, 4, 12, and 96 hours from inoculation in a third experiment. By delaying the application of salt for 12 hours, an increase in nodule number, nodule weight, and shoot N was observed.Nodule formation in the 12-and 96-hour treatments was, however, lower than the control. The early steps in nodule initiation are, therefore, extremely sensitive to even low concentrations of NaCl. The sensitivity is not related to rhizobial survival and is probably due to the salt sensitivity of root infection sites.Rhizobium growth and survival are generally more tolerant in vitro to high osmotic pressures than are their respective host legumes (8,15, 17). Tu (22), however, observed reduced colonization of soybean root surfaces by Rhizobium japonicum when plants were grown in salinized culture medium.Legumes grown in saline environments exhibit reduced yield potential and reduced numbers and weight of root nodules (1,14,15, 22, 24). There were, however, serious limitations in the above studies for evaluating the effects of salinity on the early stages of nodule formation. With the exception of the work of Lakshmi et al. (14), inoculation of seedlings with Rhizobium preceded the salinization of the rooting medium. It is likely that in these studies some critical steps of rhizobial attachment and infection thread formation could have occurred before the introduction of the salt stress. In the study of Lakshmi et aL, (14) plant...

Conserved salt tolerance quantitative trait locus (QTL) in wild and cultivated soybeans

“…It has been estimated that 20% of the irrigated land in the world is presently affected by salinity (Yamaguchi and Blumwald 2005). Salt stress is reported to inhibit soybean germination and plant growth (Abel andMacKenzie 1964, Wang andShannon 1999), nodule formation (Singleton and Bohlool 1984), and seed yield (Parker et al 1983). Chloride is a major toxic element in soybean salt stress (Abel andMacKenzie 1964, Parker et al 1983).…”

Salinity Tolerance of Super-Nodulating Soybean Genotype En-b0-1

“…Saline conditions hamper germination, growth (Abel and Mackenzie, 1964;Wang and Shannon, 1999), and nodule formation (Singleton and Bohlool, 1984) in soybean, resulting in significant reductions in seed yield (Parker et al, 1983;Yang and Blanchar, 1993). Studies comparing genetically diverse cultivars have found significant differences in salt tolerance (Parker et al, 1983;Yang and Blanchar, 1993;Lee et al, 2008;Tuncturk et al, 2008;Ghassemi-Golezani et al, 2009;Hakeem et al, 2012;Karim et al, 2012;Mannan et al, 2012).…”

A Study on the Effect of the Rhizobacterium, Bacillus sp. SH1RP8 and Potassium Family Polymers on the Crop Growth under Saline

“…토양생태계의 염류화 현상은 건조 지역에서 빈번하게 발생 하며, 지구온난화에 의해 수분 증발량이 증가되어 전세계 지 표면의 10%가 이미 염류화가 진행되었다 [1]. 염분이 토양에 존재할 경우 대부분 식물의 생장을 저해하고 염에 민감한 식 물인 콩과 식물의 경우는 고농도의 Cl -에 의해 잎의 황백화 와 광합성 저해로 생장이 억제된다 [2].…”