Rhizobium population dynamics in the pea rhizosphere of rhizobial inoculant strain applied in different formulations

Abstract

The effect of inoculant formulation on the population dynamics of rhizobia in the pea rhizosphere was investigated using a streptomycin-resistant mutant of Rhizobium leguminosarum bv. viceae NITRAGIN128C56G (128C56G strR). The isolate was formulated into liquid, peat powder, and granular peat carriers, and was tested on pea at field sites near Saskatoon, Saskatchewan, and Beaverlodge, Alberta, in 1996 and 1997. The liquid and peat powder formulations were applied to seed while the granular inoculant was applied to soil. In three out of four site years, population dynamics were similar among formulations: an initial decline or lag period lasting 2-5 days followed by an increase to approximately 10(5) colony-forming units (CFU)/seedling by 14-28 days after planting (DAP) and, where sampled, a continuing increase from 10(7) to 10(8) CFU/plant at 63 DAP. In these same site years, nodule number (not determined at Beaverlodge in 1997) and nodule occupancy at 60 days were not significantly different among formulations. In contrast, soil populations of 128C56G strR from the liquid formulation declined to near zero by 28 DAP at Beaverlodge in 1996, when soil moisture was excessive in spring because of high rainfall. Populations increased in this treatment after this time, but remained significantly lower than the populations of the other two formulations throughout the sampling period. Pea seed yields were not significantly different among treatments in either year at Beaverlodge, but were significantly higher with granular inoculant than the noninoculated control in Saskatoon. Within inoculated treatments at Saskatoon, there were no significant differences in grain yield.

The origins of uncooperative rhizobia

“…Rhizobia that do not form nodules might avoid post infection sanctions by exploiting host resources that exist on or near roots, and bypassing infection entirely (Denison and Kiers 2004). Rhizobia can reproduce actively in soil and proliferate in the rhizospheres of some plants (Brockwell et al 1987, Hagen et al 1997, Hynes et al 2001, Del Papa et al 2003, Duodu et al 2005), so the formation of nodules on legumes is only one potential life history for these bacteria (Denison and Kiers 2004, Duodu et al 2005). In fact, non‐symbiotic rhizobial strains have been found to predominate numerically over symbiotic rhizobia when their abundances were directly compared (Segovia et al 1991, Sullivan et al 1996, Pongsilp et al 2002).…”

Performance of Rhizobial Inoculant Formulations in the Field

“…In experiments where granular inoculants out‐perform other formulations, enhanced performance likely is related, in part, to increased numbers of rhizobia at seeding and/or reduced mortality rates once applied to the soils (2). Hynes et al (8) studied rhizobial population dynamics in the rhizosphere of field pea inoculated with different formulations. Although little difference was detected at three of four study sites, at one site soil rhizobial populations from a liquid formulation declined to near zero within 28 days of seeding whereas populations from powdered peat and granular formulations were maintained.…”

Contrasting Rhizobium inoculation requirements of zero-tannin faba bean and narrow-leafed lupin in western Canada

“…nodulation compared with peat when applied to lupin (Brockwell et al 1980), chickpea (Gan et al 2005) or field peas (Hynes et al 2001). Granular inoculants tend to outperform seed-inoculants in unfavourable soil conditions, e.g., acid soils, drought, low temperature or excessive moisture (Rice et al 2000;Hynes et al 2001), otherwise there is little difference between inoculant formulations.…”

“…Granular inoculants tend to outperform seed-inoculants in unfavourable soil conditions, e.g., acid soils, drought, low temperature or excessive moisture (Rice et al 2000;Hynes et al 2001), otherwise there is little difference between inoculant formulations.…”