Response of Soybean Plants to High Root Temperature as Affected by Plant Cultivar and Rhizobium Strain1

Abstract

AbstractThis study examined the effect of high root temperatures on nodulation, dinitrogen fixation, and growth of five soybean [Glycine max (L.) Merr.] cultivars associated with either of two Rhizobium japonicum strains of contrasting temperature tolerances.In each of three greenhouse experiments, soybeans growing in pots containing vermiculite were submitted to root temperatures of 28, 33, and 37 C or 28, 33, and 35 C by submerging the pots in thermostatically controlled water baths. In the first experiment, cvs. ‘Hutton’ and ‘Ransom’ were inoculated with either strain USDA 110 or 587, while in the second experiment the same strains were used to inoculate cvs. ‘Gasoy‐17’ and ‘Bragg.’ In a third experiment cvs. Bragg, Gasoy‐17, ‘Lee,’ and Ransom were grown in association with strain 587. Plants were harvested 34 days after germination.The superiority in high temperature tolerance of strain 587 over USDA 110, found in earlier work with cv. Lee, was confirmed for cvs. Gasoy‐17, Hutton, and Ransom. Results with cultivar Bragg were inconsistent for the two experiments in which that genotype was included.The results indicate that soybean genotype influences the response of the symbiotic system to high root temperatures. Gasoy‐17 and Lee appeared to be more tolerant to high root temperature than the other cultivars. That characteristic was enhanced when Gasoy‐17 was associated with the tolerant strain 587. Selection of soybean cultivars with tolerance to high root temperature in symbiotic association with R. japonicum appears to be a feasible alternative to overcome high soil temperature stress and needs to be done in conjunction with strain selection.