Allelopathy Of Chinese Onion Root Exudates On Cucumber And Its Application

Cucumber (Cucumis sativus L.) is major crop cultivated in plastic greenhouses. A serious disease of cucumber, fusarium wilt (Fusarium oxysporum f. sp. cucumerinum) has become a common rhizosphere soil-borne disease worldwide. The incidence of fusarium wilt increases significantly with continuous cropping of cucumber and severely reduces the cucumber yield.In this study, cucumber and 12 Chinese onion accessions from Heilongjing province were taken as expermental materials. It was investigated the allelopathy of Chinese onion root exudates, and allelopathic potential of Chinese onion root exudates on cucumber;isolation and identification of allelochemicals in Chinese onion root exudates by GC-MS; proteins related to allelopathy by 2-D electrophoresis; soil nutrients, soil enzymes, soil microorganism number, and the cucumber rhizosphere soil microbial ecological condition by PCR-DGGE technique after Chinese onion root exudates and intercropping with Chinese onion treatments. The objective of this research was to establish a procedure to decrease crop infection and increase yield by using root exudates and intercropping cultivation systems and to provide technical support and a theoretical basis for screening Chinese onion accessions suitable for interplanting with cucumber.The main experimental results were as follows:1. After treatment with the different concentration of root exudates, it stimulated the growth of cucumber radicles, shoot, radicle fresh weight and shoot fresh weight. 10 ml plant-1 had the best stimulation effects. Among the 12 onion accessions, the L06 root exudate showed the highest allelopathic activity, and L04 showed the lowest allelopathic activity.2. Chinese onion root exudates of different concentration had the inhibition effects to germination of F. oxysporum f. sp. cucumerinum spores and mycelial growth. 10 ml plant-1 had the best inhibitory effects. And the high allelopathic potential L06 had strong inhibitory effects.3. Allelochemicals in Chinese onion root exudates were formic acid, butyrate, propionic acid, pentanoic acid, hydroxy acid, benzoic acid, phenylacetic acid, phthalic acid, and disulfide. The percentage content of benzoic acid in L06 was higher than that in L04.4. Cucumber yield was increased and plant disease decreased by intercropping with high allelopathic potential Chinese onion L06.5. The expression level of 47 protein spots were significantly different (±more than 2 folds) by single crop, intercropping treatments and also between accessions from pH4 to pH7. The high expressed protein spots were detected by matrix-assisted laser desorption ionization time-of -flight mass spectrometry (MALDI-TOF MS), and analyzed in retrieval database. According to the peptide mass fingerprints, there were 20 differiential protein spots between Chinese onion L04 and L06 5% proteins related with glucose metabolism; 5% proteins related with nucleic acid metabolism; 15% proteins related with energy conversion; 30% proteins related with signal transduction; 25% proteins related with protein metabolism; 15% proteins related with secondary metabolism; and 9% proteins were unknown proteins. Compare to Chinese onion L04, the express of Ferulic acid 5-hydroxylase in L06 was lower. With intercropping treatment, there were identified 31 differiential protein spots. Those proteins were related with allelopathy. 6% proteins related with glucose metabolism; 6% proteins related with nucleic acid metabolism; 13% proteins related with energy conversion; 10% proteins related with signal transduction; 23% proteins related with protein metabolism; 29% proteins related with secondary metabolism; and 9% proteins were unknown proteins. Besides for shikimate pathway or Shu different diene pathway, allelochemicals were also produced by phenylpropane pathway.6 With Chinese onion exudates treatments, EC value decreased, pH value increased, contents of soil available phosphorus, available K, and organic matter increased in cucumber seedling rhzisphere soil. The activity of soil urease, invertase, catalase and peroxidase increased. The soil bacteria, actinomycets number increased and fungi, Fusarium decreased. There were 3 bacteria population: Actinobacteria, Proteobacteria, and Anaerolineaceae. Compare to L04, Anaerolineaceae was only found with L06 Chinese onion root exudates treated. The yield per plant increased, plant disease decreased. 10 ml plant-1 high allelopathic potential of Chinese onion L06 had the best effects. High concentration, high allelopathic potential of Chinese onion root exudates improved the cucumber rhizosphere soil microbial ecological condition.7. With Chinese onion intercropping treatments, of cucumber rhizosphere soil, soil EC value decreased, pH value increased; contents of soil available phosphorus, available K increased; no changes of organic matter and alkali-hydrolyzable nitrogen. The activity of soil urease, invertase, and catalase increased, and peroxidase decreased. Bacterial community diversity increased. There were 2 common bacteria populations:Actinobacteria and Proteobacteria. Compare to L06, Rhodospirillales and Acidobacteria Gp10 was only found with L06 Chinese onion root exudates treated. There were 3 differential bateria populations: Actinobacteria, Proteobacteria, and Anaerolineaceae. Only the growth of cucumber seedling was increased by intercropping with Chinese onion. Intercropping with the high allelopathic potential of Chinese onion improved the cucumber rhizosphere soil microbial ecological condition.In general, with Chinese onion root exudates and intercropping treatments, it was increased of soil nutrient; the activity of hydrogen peroxidase, saccharase, and urease; and the number of bacteria and actinomycets, but decreased the number of fungi and Fusarium in rhizosphere soil of cucumber. And also, bacterial community diversity increased. For such better rhizosphere nutrient environment, cucumber disease decreased and cucumber yield was increased.