Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2006
Publication Date: 12/1/2006
Citation: Marsh, L.E., Baptiste, R., Marsh, D.B., Trinklein, D., Kremer, R.J. 2006. Temperature effects on bradyrhizobium spp. growth and symbiotic effectiveness with pigeonpea and cowpea. Journal of Plant Nutrition. 29(3):331-346.
Interpretive Summary: Optimum production of food grain legumes can efficiently provide essential protein that is often limiting in the human diet in many parts of world. Nearly all of the 20 or more species of food legumes form a symbiotic association with bacteria (rhizobia) that infect the roots and form specific growths (nodules) where atmospheric nitrogen is eventually converted to plant protein. The efficiency of this process, known as biological nitrogen fixation, is often considerably reduced because adverse environmental conditions suppress the activity of the rhizobia involved in the association. The adverse conditions include low soil moisture, high soil temperatures, and poor soil fertility. Because many of the food legumes are grown in tropical climates, we examined the potential for selecting specific rhizobia able to withstand high temperatures and continue to efficiently provide nitrogen to cowpea and pigeonpea, two major food legumes widely grown in tropical and subtropical regions of the world. Different strains of rhizobia able to infect both legumes were grown alone in culture media over a range of temperatures that simulated conditions encountered in soils and were also grown with the legume plants to determine the effect of temperature on nodulation, nitrogen fixation, and plant growth. Of the 12 strains examined, only a few could grow at the high day/night temperature of 38C/25C (100F/78F) but most grew readily at 30C/20C (88F/69F). However, optimum nitrogen fixation and plant growth resulted with only three of the rhizobia infecting the plants at 30C/20C. The results suggest that strains very effective in nitrogen fixation can be selected and combined with legumes (via a process known as inoculation) to assure optimum plant growth and protein production. The information presented in this paper also provides a practical guideline for screening rhizobia and the nitrogen-fixing symbiosis for temperature tolerance in the development of effective inoculants for food legumes. These potential applications are useful to agronomists, legume geneticists, scientists in the seed and inoculant industry, crop farmers, and personnel involved in agricultural programs in developing countries where strategies for improving quality of food production is essential.
Technical 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.