Symbiotic effectiveness of Rhizobium meliloti at low root temperature

Abstract

Laboratory, growth chamber and field experiments were conducted to select among 226 isolates of Rhizobium meliloti for the ability to grow, nodulate alfalfa (Medicago sativa L.) and support N2-dependent plant growth between 9 ° and 12 o C. There was wide variation in the abilities of R. meliloti isolates to grow and form nodules at 10 °C. Culture doubling times (td) varied from 1 to 155 h, and the number of nodules formed on alfalfa in growth pouches in 2 weeks varied from 0 to 3.8 nodules per plant. Nodulation occurred at 9 °C, but there was no significant N2-dependent plant growth at this temperature. However, several isolates of R. meliloti had the ability to nodulate alfalfa and produce N2 -dependent growth at root temperatures between 10 o and 12 °C. Six isolates, including strain NRG-34, produced significantly more N2-dependent plant growth at 12 °C root temperature than did 14 other isolates tested. In field experiments, inoculation with strain NRG-34 resulted in greater nodule numbers, nodule weight, proportion of nodules occupied by the inoculant strain and plant weight than did inoculation with a commercial strain (NRG-185). These results permitted selection of a strain with better low-temperature competitive abilities than the currently available commercial strains.

Widespread fitness alignment in the legume–rhizobium symbiosis

“…(2007); NUR88‐89, Nurhayati et al. (1988, 1989); PAN79, Pankhurst & Jones (1979); PAN81, Pankhurst (1981); RICE95, Rice et al. (1995); ROD99, Rodriguez‐Navarro et al.…”

Impact of Harsh Environmental Conditions on Nodule Formation and Dinitrogen Fixation of Legumes

“…This leads to decline in total nitrogen fixation and lower crop yield (Lynch and Smith 1994), and can be at least partially corrected by the addition of genistein (Zhang and Smith 1997; Pan and Smith 1998). It is known, however, that low soil temperatures affect nodule initiation (Cordovilla et al 1999) and function (Rice et al 1995).A greater concen in the tropical zone, but also important during the peak of summer in temperate zones., is excessive soil temperature and its ability to be an important limitation to nodulation and nitrogen fixation (Hungria and franco 1993; Boddey et al 1997; Graham and Vance 2000). Hungria and Vargas (2000) note that maximum soil ternperature in the tropics regularly exceed 40 °C at 5 cm below the soil surface and 50 °C at 1 cm.…”

Alfalfa response to elevated atmospheric CO2 varies with the symbiotic rhizobial strain

“…One week after seeding, seedlings were thinned to 10 plants per pot and the pots were inoculated with 50 ml of Sinorhizobium meliloti suspension containing 10 8 cells of either strain A2 or NRG34. These two strains are used in Canadian commercial inoculants; strain A2 is adapted to survive in soils after freezing (Bordeleau et al 1977) and strain NRG34 is adapted for nodulation and stimulates plant yield at low temperature (Rice et al 1995). The fertilization schedule was as follows: 1 g l −1 week −1 of 8-20-30 for the first 2 weeks, and 1 g l −1 week −1 of 0-52-34 plus micronutrients for the six subsequent weeks.…”