Diagnosis And Microecological Management Of Citrus Slow Decline Disease

A survey of distribution and damage of the citrus nematode(Tylenchulus semipenetrans)was conducted during October 2005 and March 2008 in Fujian province.T.semipenetrans was distributed in main citrus producing regions of Fujian, including Fuzhou,Ningde,Sanming,Zhangzhou,Quanzhou.50 in total of 67 citrus orchards investigated were infested with the citrus nematode,which infested rate was account for 74.6%.The percentage of infected citrus was from 5.0%to as many as 100%in orchards.The study on mycoflora of T.semipenetrans was carried out.Eight species belonging to six genera were identified from rhizosphere and roots of citrus infected with T.semipenetrans.The dominant fungi were Aspergillus flavus,Fusarium solani and Paecilomycs lilacinus,accounted for 23.8%,18.6%,12.8%of the total isolates respectively.Twelve species belonging to nine genera nematophogous fungi insolated from females of T.semipenetrans were identified.The dominant fungi were Fusarium solani,F.oxysporum and P.lilacinus, accounted for 36.6%,15.4%,9.76%of the total isolates respectively.The results showed that T.semipenetrans suppressed the growth of mycorrhizal fungi Glomus etunicatum.The quantity of the mycelium and vesicles of Glomus etunicatum in roots infected with T.semipenetran was decreased significantly compared with control roots.The study on development and application of bioagent was carried out.P. lilacinus He-5 which have large sporulation quantity,high activity of chitinase and high pathogenicity was screened from eleven isolates of P.lilacinus.A temperature of 20℃-30^℃and pH 5-8 were favorable for the growth of P.lilacinus He-5.P. lilacinus He-5 could endure alkai and salt stresses.The rate of parasitism of P. lilacinus He-5 on embryo eggs of T.semipenetrans was 89.86%in vitro.The microbial agent of P.lilacinus He-5 was developed by diphasic fermentation technology.Strain He-5 sporulated with microcirculation in medium of liquid fermentation.The yield of conidia could reached 12.36×10⁷ spores/mL after 96 h of fermentation in 3%prawn shell powder substrate medium of liquid fermentation. The activity of producing chitinase reached a peak in 5-6 days.A large quantity of spores was produced quickly by controlling temperature and humidity in mass salver solid fermentation.The yield of conidia reached 1.20×10¹⁰spores per mL on the sixth day of fermentation.The conidia powder containing an average of 1.30×10¹⁰spores/g was produced,which germination rate of conidia was 89.86%.Field application of He-5 microbial agent was performed.The result showed that the He-5 microbial agent had a good control effect on T.semipenetrans.The population density of females of T.semipenetrans in treatment group decreased to 44.90%compared to control.The strain He-5 could colonize and grow on rhizosphere of citrus as dominant species,the quantity of conidia of strain He-5 was about 2.60×10⁴ cfu per gram after applied for 10 months.The He-5 microbial agent improved micro-ecological environment and the health of citrus root.