Growth and survival of root-nodule bacteria in legume inoculants stored at high temperatures

• Published in: Soil biology & biochemistry 1995, Vol.27 (4), p.707-712
• Main Authors: Roughley, R.J., Simanungkalit, R.D.M., Gemell, L.G., Hartley, E.J., Cain, P.
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Bradyrhizobium; Economic plant physiology; Fundamental and applied biological sciences. Psychology; Glycine max; Rhizobium; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...)
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/0038-0717(95)98652-5

The maximum temperatures to which legume inoculants were exposed when despatched to five destinations in Australia (36–39°C) and nine in Indonesia (29–42°C) were used to define experimental storage conditions to study survival of root-nodule bacteria in peat culture. Cultures of three strains of Bradyrhizobium and two strains of Rhizobium were prepared in sterilised peat at a moisture potential of −log 10 4.5 Pa and incubated at 25°C for 14 days. They were then stored at either 25, 30, 35 or 40°C for 28 days. There was no significant effect of temperature in the first 5 days. By day 7, the numbers of the clover strain declined significantly at temperatures between 30 and 40°C and those of the medic, lupin and both soybean strains at 40°C. Numbers of all strains exceeded log 10 8.3 g −1 peat when stored at 35°C for 28 days; the two strains for soybeans exceeded log 10 9.0 g −1. Although when stored at 40°C for 2 weeks, the numbers of the five strains declined, they all multiplied rapidly when returned to 25°C. This response was repeated when the same packets were subjected to this regimen a second time. After a third cycle, recovery when returned to 25°C was slower than before but numbers still exceeded log 10 7.6 g −1 peat. Storage at 40°C for 42 days did not affect the infectivity of the strains. These results indicate that peat-based cultures may be distributed with safety in the tropics from a centralised production centre. Regional reincubation at a favourable temperature (25°C) for growth is recommended when temperatures inside the packaging are likely to have exceeded 35°C for 7 days.