Identification And Biological Effects Of Root Exudates Of Continuous Cropping Potato

Soil-borne diseases and autotoxicity of root exudates were important factors of continuous cropping obstacles. Pot and field experiments were conducted to determine the possible mechanism of potato continuous cropping obstacles from autotoxicity and relationship of root exudates to soil-borne pathogenic microorganism. The potato root exudates of rotation(RP) and continuous cropping for 5 years(CP4) were collected by in-situ and in-vitro elution collection method in root-box at the seedling and squaring stage. The chemicals in root exudates were identified by GC-MS. The toxicity of the exudates and chemicals in root exudates to potato plants were detected by biological detection in a pot experiment, and the relationship of root exudates to soil-borne pathogenic microorganisms were studied preliminarily. The main research results were as follows:1. The potato root exudates of rotation(RP) and continuous cropping for 5 years(CP4) were collected by in-situ collection with Self-made root box at the seedling and squaring stage, the chemicals in root exudates were identified by GC-MS. The results showed that: the main components in potato root exudates were Glucides, acids, amines, alcohols, esters and pyrimidine. Glucide was the highest in the root exudates, followed by organic acids, but the acid contents in CP4 was higher than that in RP. The relative content of palmitic acid in CP4 was 0.94% and 1.4%, and dibutyl phthalate were both 0.15% in in CP4. However, the relative content of palmitic acid in RP was only 0.15% and 0.2%, and dibutyl phthalate was not identified in RP.2. The potato root exudates of rotation(RP) and continuous cropping for 5 years(CP4) were collected by the in-vitro elution collection in field experiment at the seedling,squaring and florescence stage. The chemicals in root exudates were identified by GC-MS. The results showed that: The main components of patota root exudates were the same as the in-situ collection with Self-made root box. The chemicals were glucide, organic acids, amines, alcohols, esters, and pyrimidines in both RP and CP4 treatments. Glucides and acids were dominating components. Dibutyl Phthalate was found to exist in root exudates of CP4. The relative content at seedling, squaring and florescence stages were 0.16%, 0.21% and 0.24%, respectively. Palmitic Acid was also tested in root exudates of CP4, and the relative content at three stages were 0.34%, 1.12% and 0.47%. Palmitic Acid can be found in RP, but only appeared in two potato growth stages with low content of 0.56% at squaring and 0.24% at florescence stage. Potato root secreted much more root exudates at squaring stage, which was the suitable period for collection of potato root exudates.3.Quantitative analysis of palmitic acid in root exudates of RP- CP4 showed that: The main components in potato root exudates of RP- CP4 were Glucides, acids, amines, alcohols, esters and pyrimidine, but the content of chemicals were different in RP-CP4. Palmitic acid was identified in all RP-CP4. Relative contents were 0.55%, 0.87%, 1.24%, 1.05% and 0.95%, respectively. The concentration of palmitic acid were 7.12mg/l, 7.39 mg/l, 9.46 mg/l, 8.38 mg/l and 8.02 mg/l. Dibutyl phthalate were not identified. Palmitic acid in root exudates content was relatively high and stable, whilst Dibutyl phthalate was unstable and varied at inter annual.4. The results of biological detection of root exudates from RP-CP4 indicates that, palmitic acid and dibutyl phthalate on potato root exudates inhibited the plant height, fresh weight of shoot and root fresh weight, total root length, root surface area, root volume and root tip number. The inhibition expression were CP4>CP3>CP2>CP1>RP. The inhibition of palmitic acid and dibutyl phthalate to potato growth showed obvious concentration effects, but did not show the superimposed effects. Inhibitory effect of palmitic acid was 100mg/L>50 mg/L>10 mg/L>5 mg/L.5. Effect of root exudates from continuous cropping years(RP-CP4) and different concentrations of palmitic acid on anti-reverse enzyme of potato seedling showed that: The SOD, POD activity and MDA content increased. However, CAT activity decreased with the continuous cropping years increasing. Different concentration of palmitic acid significantly increased the contents of SOD, POD activity and MDA content, and significantly decreased CAT activity. Therefore, the potato root exudates caused membrane lipid peroxidation of potato plants. This change might be attributed to palmitic acid from the potato root exudates.6. Effect of root exudates from continuous cropping years(RP-CP4) and different concentrations of palmitic acid on the growth of Rhizoctonia solani showed that: Potato root exudates promoted the growth of R. solani. The colony diameter and mycelia fresh weight of R. solani was highest in CP2 and lowest in RP. No significant differences were observed between CP1, CP3 and CP4. Palmitic acid could promote the growth of R. solani. The colony diameter and mycelia fresh weight of R. solani increased firstly and then decreased along with the increase of the concentration of palmitic acid. The colony diameter and mycelia fresh weight of R. solani was highest at 10mg/L. Therefore, the potato root exudates could promote the growth of R. solani, and this promoting effect was related to palmitic acid from the potato root exudates.In conclusion, the potato root exudates have autotoxicity with palmitic acid being the main autotoxins. Promotion of potato root exudates to Rhizoctonia solani growth exacerbated the continuous croppingobstacle. In-situ collection and in-vitro elution collection are both suitable method for potato root exudates with squaring stage being the most suitable period.