Persistence and competitiveness of threeBradyrhizobium japonicum inoculant strains in clay loam Nile valley soil

Abstract

The survival and persistence of three B. japonicum inoculant strains USDA 110, USDA 138 and TAL 379 were studied in a clay loam Nile valley soil. The inoculated field plots in the summer of 1985 were sown with soybean again in 1986 season. No inoculation in the season of 1986 was conducted and the plants were left to nodulate with the persisted cells of the inocula strains applied a year before. The soil had no background of B.japonicum, however, some nodules were formed on the control plants due to the carryover of the strains with water circulation and some other agricultural practices.The results indicate the persistence of all applied inoculant strains until the next planting season in 1986 with strain USDA 110 being higher in the rhizosphere of the plants than the other two strains. The population dynamics of the three strains in both growing seasons followed the same trend with maximum rhizosphere colonization at blooming stage. While strain USDA 110 was as high in 1986 season as in 1985 season, the counts of both strains USDA 138 and TAL 379 were much lower in 1986 season.The significant response to inoculation recorded in the 1985 season was extended to the 1986 growing season. Although nodulation and seed yield still differed significantly in 1986 season from the control uninoculated plots, no significant differences were found among the strains or their mixtures.The results of the competition between the strains in the two seasons showed that strain USDA 110 was more competitive than strains USDA 138 and TAL 379. The competition patterns in the second season were not markedly different from those of the first season. The predominance of strain USDA 110 in nodules was not correlated with a numerical advantage of that strain over other strains in the host rhizosphere.

Persistence of twoRhizobium etli inoculant strains in clay and silty loam soils

“…The highest N accumulation in clay soil was found in the treatment previously inoculated with CE3, whereas in silty loam soil the largest N accumulation was found with strain Ph 163. These results are in agreement with those obtained by other investigators, who found that the soybean and lintel rhizobia were able to survive and persist in clay loam soil for three successive seasons after the first inoculation (MOAWAD et al 1988(MOAWAD et al , 1994.…”

“…The strains were able to survive and persist for the whole year in both soil types prevailing in the major bean production areas, and the competition for nodulation is a major limiting factor for the full utilization of the symbiotic advantages of the selected rhizobial strains. This is in agreement with the work conducted by other scientists in the field of Biological Nitrogen Fixation (MOAWAD et al 1988, YOU et al 1998, AGUI-LAR et al 2001, KAOUTHAR et al 2001, LOPEZ-GARCIA et al 2002, SONIA et al 2002. This also shows the need for deeper understanding of competition attributes to find a way to reduce the nodulation by unknown native rhizobia and enhance the formation of plantrhizobia symbiotic systems with promising strains of rhizobia.…”

“…These values are not lower than those obtained with inoculation in the first season, where 56 -60% of nodules on both cultivars were formed from indigenous rhizobia in both soils, whereas native rhizobia occupied 10 -50% of nodules on BRONCO cultivar in clay soil and 40 -60% on GIZA 6 cultivar in the same soil. The ability of other rhizobia to survive and persist in the soils was reported previously (MOAWAD et al 1988).…”

“…The survival and persistence of three R. japonicum strains in clay loam soil was studied by MOAWAD et al (1988). They found that the three-inoculant strains were capable of persisting for a whole year after the first inoculation.…”

Field and genetic analysis of Chinese fast-growing rhizobia

“…The ability of a rhizobial strain to adapt to prevailing soil conditions and to persist into subsequent growing seasons is an important consideration in selecting inocula (Brunei et al, 1988;Moawad et al, 1988). Brockwell et al (1985) used antibioticresistant strains to inoculate a soil free of B. iaponicum.…”