Temperature Effects on Bradyrhizobium spp. Growth and Symbiotic Effectiveness with Pigeonpea and Cowpea

ABSTRACT

Temperature is a limiting factor on legume-Bradyrhizobium symbiosis of subtropical plants in the temperate region. Twelve strains of Bradyrhizobium spp. that nodulate pigeonpea [Cajanus cajan (L.) Millsp], and cowpea [Vigna unguiculata (L.) Walp], were evaluated for tolerance to three temperature regimes (20°C/10°C, 30°C/20°C, and 38°C/25°C day/night temperature) by determining their growth following exposure to the regimes. The five most temperature-tolerant strains were further evaluated for symbiotic effectiveness with pigeonpea and cowpea under controlled temperatures. These strains were USDA 3278, USDA 3362, USDA 3364, USDA 3458, and USDA 3472. Plant heights of both crops were generally independent of Bradyrhizobium strains and were dependent mainly on temperature regimes. Plant heights were the shortest at the lowest temperature. At the lowest temperature regime, biological nitrogen (N) fixation by pigeonpea was almost completely inhibited. Cowpea genotype IT82E-16 inoculated with USDA 3458 formed the most effective symbiosis. The 30°C/20°C temperature regime was optimum for effective symbiotic association in both crops, and also for Bradyrhizobium survival.

Keywords:

• Cajanus cajan
• nitrogenase activity
• nitrogen fixation
• temperature
• Vigna unguiculata

ACKNOWLEDGMENTS

The support of the USDA-CSREES Research Capacity Building Grants, No. 91388146261, in funding this project and the collaboration of the USDA-ARS agency are greatly appreciated. Mention of product names does not imply endorsement by the U.S. Department of Agriculture, Lincoln University, or University of Missouri over other products not mentioned.

Notes

^Z Tests any two means in the columns for the direct microscopic counts of bacterial cells.

^Y Tests any two means in the columns for the viable cell counts of bacteria strains.

^Z Tests any two means in rows and columns for pigeonpea.

^Y Tests any two means in rows and columns for cowpea.

^Z Tests any two means in rows and columns for pigeonpea.

^Y Tests any two means in rows and columns for cowpea.

^Z 0 = No nodule.

^Y Tests any two means in rows and columns for pigeonpea.

^X Tests any two means in rows and columns for cowpeas.

^Z No nitrogenase activity.

^Y Tests any two means in rows and columns for pigeonpea.

^X Tests any two means in rows and columns for cowpea.