Effects of high temperature on survival, symbiotic performance and genomic modifications of bean nodulating Rhizobium strains

Abstract

High temperatures can affect the survival, establishment and symbiotic properties of Rhizobium strains. Bean nodulating Rhizobium strains are considered particularly sensitive because on this strains genetic recombinations and/or deletions occur frequently, thus compromising the use of these bacteria as inoculants. In this study R. tropici and R. leguminosarum bv. phaseoli strains isolated from Cerrado soils were exposed to thermal stress and the strains’ growth, survival and symbiotic relationships as well as alterations in their genotypic and phenotypic characteristics were analyzed. After successive thermal shocks at 45ºC for four hours, survival capacity appeared to be strain-specific, independent of thermo-tolerance and was more apparent in R. tropici strains. Certain R. leguminosarum bv. phaseoli strains had significant alterations in plant dry weight and DNA patterns obtained by AP-PCR method. R. tropici strains (with the exception of FJ2.21) were more stable than R. leguminosarum bv. phaseoli strains because no significant phenotypic alterations were observed following thermal treatments and they maintained their original genotypic pattern after inoculation in plants.

Variability of isolated colonies in bean nodulating Rhizobium strains before and after exposure to high temperature

“…phaseoli strains submitted to high temperature. Furthermore, these results confirm the high genetic instability among the Rhizobium species capable of nodulating bean plants and the greater stability of the R. tropici strains shown by other authors and in our previous works (14). These results allow us to recommend especially the use of strains of R. tropici in the production of commercial inoculants for bean grown in tropical soil.…”

“…Irregular response of bean plants to Rhizobium inoculation has been attributed to, among other factors, low competitive ability, low N 2 fixation efficiency and genetic instability of the symbiont. Several research laboratories have reported genetic instability of Rhizobium strains as one of the causes that compromise relevant characteristics of these organisms in the nitrogen fixation, both in wild-type strains obtained by conventional selection procedures (13,14,17,25,26) and in genetically improved strains (3,29). Rhizobium strains capable of nodulating bean display particular genetic characteristics that favor such instability.…”

Temperature Effects onBradyrhizobiumspp. Growth and Symbiotic Effectiveness with Pigeonpea and Cowpea

“…Temperature affects the legume-Bradyrhizobium symbiosis either directly, by limiting the growth of the microsymbiont and/or indirectly, by regulating the growth of the macrosymbiont (Hashem et al, 1998;Kuykendall et al, 2000). The findings of several other researchers support the regulatory effects of temperature on growth and survival of Bradyrhizobium strains in culture (Ahmad et al, 1981;Boonkerd and Weaver, 1982;Alexander, 1982a, 1982b;Singh and Khurana, 1988;Pinto et al, 1998). However, all reported temperature tolerance variability among Bradyrhizobium and Rhizobium strains.…”

“…Since variability exists among Bradyrhizobium strains and crop genotypes in response to different temperatures (Pinto et al, 1998), it may be possible to identify genotype-strain combinations that can withstand unfavorable temperate limits and are associated with a fair degree of symbiotic efficiency. Such findings will be beneficial to tropical legumes, which experience a wide range of temperatures extending from the low chilling ones of early spring to the higher extremes in summer.…”

Characterization of rhizobia that nodulate Arachis pintoi by RAPD analysis

“…More recently, molecular techniques have been developed to provide reliable information on the diversity of Rhizobium populations in soils (7,10,11). Among these techniques, genomic DNA fingerprinting using random amplification of polymorphic DNA (RAPD) has been shown to be useful to differentiate very closely related strains (4,8,21).…”