Seventeen strains of extra-slowly growing (ESG) soybean rhizobia isolated from root nodules of Glycine soja and GZycime max growing in five provinces (Liaoning, Heilongjiang, Shanxi, Hubei, and Anhui) in the People's Republic (of China were compared with 48 reference strains belonging to the genera Bradyrhizobium, Rhizobiurn, and Agrobacterium by performing a numerical analysis of 191 phenotypic features. Our results showed that all of the ESG strains examined clustered closely in the genus Bradyrhizobium but were separated from Bradyrhizobium japonicum at the species level and that they could be differentiated from Rhizobium and Agrobacterium species at the genus level. On the basis of the results of our numerical taxonomy analysis, a genomic DNA G+C content analysis, DNA-DNA hybridization experiments, a partial 16s rRNA sequence analysis, a serological analysis, an N and C content analysis, and an N/C ratio analysis of members of the three groups of soybean rhizobia, we propose the name Bradyrhizobium Ziaoningense sp. nov. for the ESG strains; the type strain of this species is strain 2281.Bradyrhizobium japonicum (formerly Rhizobium japonicum) was recognized as the sole symbiont of soybeans for a long time, until Keyser et al. (13) (25). So far, the following three groups of soybean symbionts have been identified: the fast-growing soybean rhizobia, the slowly growing soybean rhizobia, and the ESG soybean rhizobia. These groups differ significantly in their physiological and biochemical properties, generation times, serological characteristics (25,26), G + C contents, levels of DNA homology (16), arid partial 16s rRNA sequences.The slowly growing soybean rhizobia were transferred from the genus Rhizobium to the single species of the genus Bradyrhizobium, B. japonicum, by Jordan (10, 11). Later, the new species Bradyrhizobium elkanii was described by Kuykendall et al. (14). The fast-growing soybean rhizobia were placed in one species of the genus Rhizobium, Rhizobium fiedii, by Scholla and Elkan (19), and in 1988 Chen et al. described the new genus Sinorhizobium, which contained two species, Sinorhizobium fredii and Sinorhizobium xinjiangensis (la). In 1992 Jarvis et al. performed a phylogenetic study in which they used partial 16s rRNA sequencing and concluded that classification of the fast-growing soybean rhizobia in a separate genus was not justified and that the name R. fredii should be retained (8).In order to determine the taxonomic position of the ESG rhizobia, we studied ESG strains and reference strains by performing a numerical analysis, a serological typing analysis, a G + C content analysis, a DNA-DNA hybridization analysis, and a 16s rRNA sequence analysis. On the basis of the results of this study and previously published data from an N and C content analysis, we propose the name Bradyrhizobium liaoningense for the ESG strains.* Corresponding author. Fax: 86-10-2174142. 706 MATERIALS AND METHODSStrains. The bacterial strains used in this study are listed in Table 1. The purity of the strains was...

The objective of this study was to investigate the root growth compensatory effects and cotton yield under drought stress. The results indicate that the root dry weight, boll weight, and cotton yield increased in both the drought-resistant cultivar (CCRI-45) and the drought-sensitive cultivar (CCRI-60). Compensation effects were exhibited under the three-day drought stress treatment at a soil relative water content (SRWC) of 60% and 45% during the seedling stage, and flowering and boll-forming stage over two years. The yield of the drought-resistant cultivar (CCRI-45) was higher than the control, however, following the six-day 45% SRWC drought treatments, the yield of the drought-sensitive cultivar (CCRI-60) was lower than the control. The soluble sugar content, proline content, superoxide dismutase (SOD) activity, and peroxidase (POD) activity of the roots increased under drought stress and then decreased after re-watering, although the values remained higher than those of the controls for a short period. These physiological measures may represent stress reactions and thus may not indicate factors that result in compensation effects. However, catalase (CAT) activity and gibberellic acid (GA) content of the roots decreased under drought stress. After re-watering, the CAT activity and the GA content increased and were significantly higher than those of the controls under the six-day 60% SRWC and 45% SRWC drought treatments. The abscisic acid (ABA) content of the roots increased under drought stress. After re-watering, the ABA content decreased to a lower level under the three and six-day 60% SRWC and 45% SRWC drought treatments than in the controls. According to an analysis of various indicators, the interaction between ABA and GA signals may play an important role in root growth compensatory effects. In summary, the results demonstrate that moderate drought stress is beneficial to root growth and yield. This conclusion is of great significance to improving our understanding of the maximum utilization of limited water resources.

Background: There is an urgent need to discover biocontrol agents to control bacterial wilt. This study reports on a new lipopeptide-producing biocontrol strain FJAT-46737 and explores its lipopeptidic compounds, and this study investigates the antagonistic effects of these compounds. Results: Based on a whole genome sequence analysis, the new strain FJAT-46737 was identified as Bacillus velezensis, and seven gene clusters responsible for the synthesis of bioactive secondary metabolites in FJAT-46737 were predicted. The antimicrobial results demonstrated that FJAT-46737 exhibited broad-spectrum antimicrobial activities in vitro against three bacteria and three fungi. Pot experiments showed that the control efficiencies for tomato bacterial wilt of the whole cultures, the 2-fold diluted supernatants and the crude lipopeptide of FJAT-46737 were 66.2%, 82.0%, and 96.2%, respectively. The above results suggested that one of the antagonistic mechanisms of FJAT-46737 was the secretion of lipopeptides consisting of iturins, fengycins and surfactins. The crude lipopeptides had significant antagonistic activities against several pathogens (including Ralstonia solanacearum, Escherichia coli and Fusarium oxysporum) and fengycins were the major antibacterial components of the lipopeptides against R. solanacearum in vitro. Furthermore, the rich organic nitrogen sources (especially yeast extracts) in the media promoted the production of fengycin and surfactin by FJAT-46737. The secretion of these two lipopeptides was related to temperature fluctuations, with the fengycin content decreasing by 96.6% and the surfactins content increasing by 59.9% from 20°C to 40°C. The optimal temperature for lipopeptide production by FJAT-46737 varied between 20°C and 25°C. Conclusions: The B. velezensis strain FJAT-46737 and its secreted lipopeptides could be used as new sources of potential biocontrol agents against several plant pathogens, and especially the bacterial wilt pathogen R. solanacearum.

Chloroplast is a crucial organelle for plant photosynthesis and maintaining normal life activities in higher plants. Although some genes related to chloroplast development and pigment synthesis have been identified or cloned in rice, little is known about the relationship between these genes and abiotic stress response. In this study, we identified a novel mutant white stripe leaf 12 (wsl12) affecting pigment synthesis, chloroplast development and abiotic stress response in rice. The mutant phenotype was obvious at seeding and tillering stages and in response to the temperature change. Genetic analysis of reciprocal crosses between wsl12 and wild-type plants showed that wsl12 was a recessive mutant in a single nuclear locus. Map-based cloning revealed that the WSL12 locus encoded OsNDPK2, one of the three nucleoside diphosphate kinases (OsNDPKs). WSL12 expressed in all tested tissues, while it highly expressed in leaves and young tissues. The WSL12 protein localized to the chloroplast. The wsl12 mutant showed higher superoxide anion level and enhanced sensitivity to abscisic acid (ABA) and salinity. The transcription pattern of many genes involved in chlorophyll biosynthesis, ABA synthesis, light signaling pathway, reactive oxygen species-scavenging pathway and the other two OsNDPKs was altered in the wsl12 mutant. These results indicate that the OsNDPK2 encoded by WSL12 plays an important role in chloroplast development and chlorophyll biosynthesis by regulating the expression levels of related genes. In addition, WSL12 also affects the response to abiotic stress, such as ABA and salinity in rice, and is beneficial to molecular breeding of stress tolerance.Electronic supplementary materialThe online version of this article (doi:10.1007/s11032-016-0479-6) contains supplementary material, which is available to authorized users.