Glutathione S-transferase activity facilitates rice tolerance to the barnyard grass root exudate DIMBOA.

BACKGROUND: In paddy fields, the noxious weed barnyard grass secretes 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA) to interfere with rice growth. Rice is unable to synthesize DIMBOA. Rice cultivars with high or low levels of allelopathy may respond differently to DIMBOA. RESULTS: In this study, we found that low concentrations of DIMBOA (≤ 0.06 mM) promoted seedling growth in allelopathic rice PI312777, while DIMBOA (≤ 0.08 mM) had no significant influence on the nonallelopathic rice Lemont. DIMBOA treatment caused changes in the expression of a large number of glutathione S-transferase (GST) proteins, which resulting in enrichment of the glutathione metabolic pathway. This pathway facilitates plant detoxification of heterologous substances. The basal levels of GST activity in Lemont were significantly higher than those in PI312777, while GST activity in PI312777 was slightly induced by increasing DIMBOA concentrations. Overexpression of GST genes (Os09g0367700 and Os01g0949800) in these two cultivars enhanced rice resistance to DIMBOA. CONCLUSIONS: Taken together, our results indicated that different rice accessions with different levels of allelopathy have variable tolerance to DIMBOA. Lemont had higher GST activity, which helped it tolerate DIMBOA, while PI312777 had lower GST activity that was more inducible. The enhancement of GST expression facilitates rice tolerance to DIMBOA toxins from barnyard grass root exudates.

Intercropping with Achyranthes bidentata alleviates Rehmannia glutinosa consecutive monoculture problem by reestablishing rhizosphere microenvironment.

Background: The consecutive monoculture of Rehmannia glutinosa leads to a serious decrease in its production and quality. Previous studies have demonstrated that intercropping altered species diversity and rhizosphere microbial diversity. However, it remained unknown whether the impaired growth of monocultured plants could be restored by enhanced belowground interspecific interactions. Method: In the present research, a continuous cropping facilitator Achyranthes bidentata was intercropped with R. glutinosa under pot conditions, and three different types of root barrier treatments were set, including that complete belowground interaction (N), partial belowground interaction (S), and no belowground interspecies interaction (M), with the aims to investigate belowground interaction and the underlying mechanism of alleviated replanting disease of R. glutinosa by intercropping with A. bidentata. Results: The results showed that the land equivalent ratio (LER) of the two years was 1.17, and the system productivity index (SPI) increased by 16.92 % under S treatment, whereas no significant difference was found in N and M regimes. In the rhizosphere soil, intercropping systems had significantly increased the contents of sugars and malic acid in the soil of R. glutinosa, together with the content of organic matter and the invertase and urease activities. Meanwhile, intercropping increased the community diversity of fungi and bacteria, and the relative abundance of potential beneficial bacteria, such as Bacillus, Nitrospira, and Sphingomonas, despite the pathogenic Fusarium oxysporum was still the dominant genus in the rhizospheric soil of R. glutinosa under various treatments. The results of antagonism experiments and exogenous addition of specific bacteria showed that Bacillus spp. isolated from rhizosphere soil had a significant antagonistic effect on the pathogen of R. glutinosa. Conlusion: Taken together, our study indicated that the R. glutinosa//A. bidentata intercropping systems alleviate the consecutive monoculture problem of R. glutinosa by recruiting beneficial bacteria. The studies we have conducted have a positive effect on sustainable agricultural development.

Effects of different technical substitutions on reducing replant disease of Radix pseudostella-riae and the underlying mechanism.

Radix pseudostellariae is a traditional Chinese medicinical herb, with tuberous roots being used as a medicine. Serious continuous monoculture problems were suffered from process of artificial and intensive cultivation. To explore the effective technical methods to overcome the monoculture problems, the effects of different technical substitution patterns on soil environment remediation, photosynthetic physiology and yield performance of R. pseudostellariae were assessed under continuous cropping system with four technical substitution treatments in the phase between two crops after the newly harvested R. pseudostellariae (first crop): fallow (RP-F-RP), fallow treated with microbial fertilizer (RP-F-BF), water flooding (RP-WF), and water flooding treated with specific microbial fertilizer (RP-WF-BF). Results showed that RP-WF-BF pattern was the single one that could effectively restore R. pseudostellariae yield under two-year monoculture and three-year monoculture to more than 90% and 70% of the newly planted respectively. All the other patterns did not significantly improve R. pseudostellariae yield under two-year monoculture. The contents of polysaccharide and total saponin in R. pseudostellariae under RP-WF-BF treatment were significantly increased by 15.3% and 16.5% compared with those of the newly planted, respectively. The abundance of beneficial microorganisms in the rhizosphere soil of R. pseudostellariae significantly increased. A reverse pattern occurred for pathogens under RP-WF-BF pattern. Moreover, soil nitrogen cycling was improved. The expression of AOB, nosZ and nirK was increased by 931%, 124% and 100% compared with those in the RP-F-RP pattern, respectively. Soil acidification under RP-WF-BF pattern was alleviated. The alleviation of soil biological and abiotic stress enhanced the stability of the antioxidant enzyme system, thereby improving the growth and development of R. pseudostellariae at the seedling and the early expand stages. The chlorophyll content, leaf area index and photosynthesis rate of leaves were increased, with the dry matter translocation improved and accumulation of underground dry matter accelerated, which ultimately increased yield and quality under RP-WF-BF pattern. In this study, the separate water flooding treatment (RP-WF) and microbial fertilizer treatment (RP-F-BF) failed to significantly reduce the continuous cropping obstacles of R. pseudostellariae, while the combination of them could produce a multiplication effect of sustainable strengthening on rhizosphere environment. The findings suggested that effective technical substitution could reduce replant disease of R. pseudostellariae.