Studies On Pathogens Of Lotus Rhizome During Storage And Coating For Preservation

In this study, pathogens causing lotus rhizome diseases were isolated and identified, the lotus rhizomes were stored at 0-10℃. On that basis, the pathogenic mechanism was studied by the method of selecting the microbe with strong pathogenicity and determining the activity of cell wall degrading enzyme. Then the inhibition of antibacterial agent containing carbendazim and rovral, ozone and negative ion on pathogens in vitro and in vivo was studied. At last, property of sodium alginate film, effects of sodium alginate and in combination with beewax, chitosan alone and in combination with nano-SiOx coatings on the quality of lotus rhizome were studied. The main results were showed as below:1. The pathogens of lotus rhizome diseases during storage were isolated and identified. The identification result was that there were 9 fungi and 5 bacteria. Artificial inoculation test proved that all the 9 fungi and one of the 5 bacteria have the pathogenicity. According to morphological characteristics, three fungi were identified as Penicillium, Alternaria and Cladosporium respectively, the other six were defined as Fusarium, one strain of the Fusarium producing red pigment has the strongest pathogenicity. The pathogenic bacterium was determined as Acinetobacter calcoaceticus-baumannii by VITEK system based on physiological and biochemical reactions.2. Select the Fusarium strain producing red pigment and having the strongest pathogenicity, then study the pathogenic mechanism through the varing of PGM and Cx activity, the result showed that in vitro, PMG activity was increased initially and then decreased until it can not change in the later period, and Cx activity was increasing during the same time, this meant that PMG mainly took effect at the previous period and Cx played an important part at the later stage. In vivo, PMG and Cx activities of lotus rhizome inoculated pathogenic fungus were higher than the control (P<0.05). A conclusion can be drew that cell wall degrading enzyme played a significant part in the period of pathogen causing disease, and which was an important pathogenic factor.3. The inhibition of carbendazim and rovral on pathogenic fungi was studied. The results indicated that carbendazim can effectively retarded the growing of Fusarium strains, the inhibition ratio to M5 was 98.1%, and to M4, M6, M7, M8 and M9 were 100%; inhibition of rovral on Alternaria was the most effective; combination carbendazim and rovral has a synergy action in vitro, except Penicillium whose inhibition ratio was just 61.8%, which can completely inhibited Alternaria, Cladosporium and Fusarium, with the inhibition ratio of 100%. In vivo, carbendazim and rovral in combination with chitosan coating can retarded pathogens invading and rhizome rot, especially at the mid and later stage, inhibition was more effective.4. Ozone and negative ion were produced by ionizing air to study the antibacterial property, pathogenic fungus inoculated on PDA culture medium and lotus rhizome were treated with these two gases. The result was that the inhibition was more effctive when extending the treatment time in vitro, comparing 60min to 30min, the inhibition ratio of ozone was increased by about twofold, and negative ion raised by approximately 2.42 times. In vivo, both of the treatmens can prevent rhizome lognitudinal tissue from rot, but on superficial and transversal expanding of the pathogenic fungus, ozone had a negative impact.5. Property of sodium alginate film was tested firstly, then the effects of sodium alginate and in combination with beewax coatings on quality of lotus rhizome were studied. The results showed that with the solution concentration increasing, film thichness increased, transmittance decreased; both coatings had a certain positive effect, coating treatment can retard weight loss, respiration, sugar consumption and hardness decline, but had a unconspicuous or negative action on L-value and PPO activity.6. Three coating solutions were prepared and the effects of which on quality of lotus rhizome were studied.The formulations were based on chitosan alone, and in combination with nano-SiOx, and nano-SiOx and SnCl2, an uncoated sample as a control, all products were stored at 0-10℃. The results showed that the coating of chitosan in combination with nano-SiOx was the most effective in keeping the quality of lotus rhizones by retarding weight loss, respiration, sugar consumption, color darkening and hardness decrease, while adding SnCl2 to which didn't have a positive influence on the quality of lotus rhizone during storage.7. Make a combination of 1.5% chitosan with 0.5% SiOx and 1% glycerol, then lotus rhizomes were coated with this complex solution and treated with ethanol vapor continuously from 95% ethanol for 15 days at 0-10℃as the coating dried, which was conducted to improve rhizome quality. The results showed that ethanol vapor can prevent microorganism completely from infection, retarded lotus rhizome respiration, but PPO activity was higher and L-value was lower, color of rhizome was darker.