Bradyrhizobium japonicum Survival in and Soybean Inoculation with Fluid Gels

Abstract

The utilization of gels, which are used for fluid drilling of seeds, as carriers of Bradyrhizobiumjaponicum for soybean (Glycine max (L.) Merr.) inoculation was studied. Gels of various chemical composition (magnesium silicate, potassium acrylate-acrylamide, grafted starch, and hydroxyethyl cellulose) were used, although the hydroxyethyl cellulose gels were more extensively investigated. Gel inocula were prepared by mixing gel powder with liquid cultures of B. japonicum (2% [wt/vol]). The population of B. japonicum USDA 110 did not change in each gel type during 8 days of incubation at 28°C. These fluid gels were prepared with late-exponential-growth-phase cells that were washed and suspended in physiological saline. Mid-exponentialgrowth-phase B. japonicum USDA 110, 123, and 138 grew in cellulose gels prepared with yeast extractmannitol broth as well as or better than in yeast extract-mannitol broth alone for the first 10 days at 28°C. Populations in these cellulose gels after 35 days were as large as when the gels had originally been prepared, and survival occurred for at least 70 days. Soybeans grown in sand in the greenhouse had greater nodule numbers, nodule weights, and top weights with gel inoculants compared with a peat inoculant. In soil containing 103 indigenous B. japonicum per g of soil, inoculation resulted in increased soybean nodule numbers, nodule weights, and top weights, but only nodule numbers were greater with gel than with peat inoculation. The gel-treated seeds carried 102 to 103 more bacteria per seed (107 to 108) than did the peat-treated seeds.

Effect of trehalose on survival of Bradyrhizobium japonicum during desiccation

“…In addition, slow re-hydration of desiccated bacteria improves survival (Kosanke et al 1992). The effectiveness of gels in delivering viable bacteria to the soil is consistent with desiccation being the major cause of cell death (Jawson et al 1989). Studies on membrane permeability of rhizobia subject to desiccation indicate that damage to the cytoplasmic membrane may be the main cause of death (Bushby and Marshall 1977b).…”

“…1992). The effectiveness of gels in delivering viable bacteria to the soil is consistent with desiccation being the major cause of cell death (Jawson et al. 1989).…”

“…9% maltose (w/v) Vincent et al 1962] or the beneficial effect of the addition is not significant. Other strategies for improving delivery of high numbers of viable bacteria include massive inoculant doses (Dunigan et al 1983), use of nutrient-added granules (Fouilleux et al 1996), and preparation of inoculants such as silicate, acrylamide, starch, or cellulose gels (Jawson et al 1989).…”

“…1983), use of nutrient‐added granules (Fouilleux et al. 1996), and preparation of inoculants such as silicate, acrylamide, starch, or cellulose gels (Jawson et al. 1989).…”

Production and survival during storage of spray‐dried Bradyrhizobium japonicum cell concentrates

“…However, the feasibility of utilizing freeze-dried Rhizobium as commercial inoculants has been recently reported (Jauhri 1989). Moreover, dried inocula could be combined with the promising oil carrier (Peterson and Kremer 1989) or with the fluid gels process (Jawson et al 1989) in order to increase tolerance against high temperatures.…”