Review on Autotoxicity of Watermelon

As a special form of allelopathy, autotoxicity is common in cucurbits, and it is one of main factors inducing： continuous cropping obstacles. Therefore, the autotoxicity research has both theoretical and practical significance on overcoming continuous cropping obstacles. In this review, commencing on the concept of autotoxicity, research results of autotoxicity in watermelon in recent years were summarized. The significance of researches on autotoxicity in watermelon, watermelon root exudate and its autotoxicity, and the autotoxicity of watermelon stubble and the mechanisms were explained. Meanwhile, some questions needed to be further studied.

Advances of Allelopathic Autotoxicity in Rehmannia glutinosa L.

Allelopathic autotoxicity occurs when a plant releases toxic chemical substances into the environment which inhibits development and growth of the same plant species.Rehmannia glutinosa L.( R.glutinosa ) is one of the most common traditional Chinese medicines,whose productivity and quality,however,are seriously impacted by consecutive monoculture obstacle.Allelopathic autotoxicity is one reason for consecutive monoculture obstacle.In this paper,we reviewed the categories of allelochemicals,the methods of allelochemicals identification,and the mechanisms of allelopathic autotoxicity,which provides clues for further study of the molecular mechanisms of allelopathic autotoxicity and consecutive monoculture obstacle.

Effect of Autotoxicity and Soil Microbes in Continuous Cropping Soil on Angelica sinensis Seedling Growth and Rhizosphere Soil Microbial Population

Objective To study the effect of autotoxicity and the co-effect of autotoxicity and soil microbes from continuous cropping soil on Angelica sinensis growth, root yield and content of essential oils, and soilmicrobalpopulation. Methods The pot experiments were conducted upon A. sinensis seedlings in continuous cropping soil. At the different growth stages, we determined the seedlings in growth parameters, root yield, content of essential oils, ethanol extract, and cultivable microbial populations in rhizosphere soil. Results A. sinensis seedlings were significantly inhibited in growth, root yield and quality. Compared with the control, the composition and structure of soil microbes were changed and the diversity indexes of bacteria functional groups were reduced in rhizosphere soil ofA. sinensis. A. sinensiscropping problems were more seriously after the treatment with combination of autotoxicity and soil microbes than with autotoxicity alone. Conclusion The autotoxicityand soil microbes from continuous cropping soil of A. sinensis could cause the continuous cropping obstacle together.

Developmental Characteristics and Cinnamic Acid Resistance of Root Border Cells in Cucumber and Figleaf Gourd Seedlings

Root border cells （RBCs） originate from the root tip epidermis and surround the root apices. In this study, we evaluated the developmental characteristics and the roles of RBCs in protection of root apices of cucumber and ifgleaf gourd seedlings from CA toxicity. The formation of RBCs and the emergence of the root tip occurred almost simultaneously in root apices of cucumber and ifgleaf gourd seedlings. CA ranging from 0 to 0.25 mol L-1 inhibited root elongation and decreased root cell viability in the root tip, moreover the inhibitory effects of CA were more signiifcant in the CA-sensitive cucumber than in the CA-tolerant ifgleaf gourd. Removal of RBCs from root tips led to more severe CA induced inhibition of root elongation and decline in root cell viability. Increasing CA levels and treatment time decreased the relative viability of attached and detached RBCs. CA also induced a thicker mucilage layer surrounding attached RBCs of both species. Additionally, a signiifcantly higher relative cell viability of attached RBCs and thicker mucilage layers were observed in ifgleaf gourd. These results suggest that RBCs play an important role in protecting root tips from CA toxicity.

Screening and Application of Phthalic Acid Degrading Bacteria

O-phthalic acid is a kind of important pollutant, which accumulates in the environment with the extensive use of plastics and other products. Meanwhile, phthalic acid is one of the high content of allelopathic autotoxic substances secreted by tobacco. The accumulation of phthalic acid in soil is an important cause of tobacco continuous cropping effect. In order to degrade phthalic acid accumulated in environment, the barrier effect of tobacco continuous cropping caused by phthalic acid accumulation in soil can be removed. A strain capable of degrading phthalic acid was isolated from sludge of sewage treatment plant and compared with 16 s DNA. The homology between this strain and Enterobacter sp. is 99%. The optimum growth conditions are as follows: pH7 at 30°C, 500 mg/L of o-phthalic acid, inoculation concentration ≥ 1.2% and its highest degradation rate of o-phthalic acid is 74%. The results of pot experiment showed that the degradation efficiency of o-phthalic acid in soil was about 40%, which alleviated the inhibitory effect of o-phthalic acid accumulation on tobacco growth.