Studies On Etiology And Control Of Fusarium Wilt On Coleus Forskohlii

Coleus forskohlii,which was imported from botany institute of Kunming,Yunnan province by FuRen FuRen Pharmaceutical co.,Ltd,was grown in Tongcheng Country, Hubei province in recent years.It is well-known for its antitumor,blood-depressed, heart-strenghened and antiphlogistic activities.As the times of planting increases, Fusarium wilt disease occurred more seriously and caused 100%yield losses in some diseased fields.The outbreak of this disease led to the shortage of supplied medicine material,and then affected the exploitation of Coleus forskohlii.Since now,no paper was reported about this disease in China.The purpose of the current research was to indentify the causal agent of Coleus forskohlii wilt disease in China,to test the biological characteristics of the pathogen,and to determine the control techniques of this disease.The results were reported as followed:Fusarium sp.was isolated from diseased rhizome of Coleus forskohlii in nursery of Tongcheng country of Hubei province and pathogenicity was tested by inoculating conidia suspension and crude toxin of Fusarium sp.onto root of healthy plants.The inoculated plant appeared leaf wilt and rhizome became brown and rotten.Fusarium sp. was determined to be the pathogen of Coleus forskohlii wilt disease.According to morphological observation,the colonies of pathogen turned dark purple after 5days on PDA,and hyphe were colorless,septate and branch.Bottle-neck conidiogenous cells were produced on aerial hypha laterally.Macroconidia were 20.1×51.7～1.5×6.0μm, and typical mild sickle-shaped curve.Terminal and basal cells of macroconidia were beak and feet shaped,respectively.Microconidia were 6.1×14.6～1.5×4.0μm,oval or elliptical,and at most one septa.Many chlamydospores,which were apical or lateral, single,spheroidal,wall-rough and 7～10μm diameter,were produced on PDA after 10 days of incubation.Comparion with sequence of ITS1-5.8SrDNA-ITS4 in GenBank showed 100%of identity with Fusarium oxysporum.The pathogen was identified as Fusarium oxysporum based on morphological characteristics and sequence analysis of rDNA-ITS. Biological characteristic indicated that the pathogen can grow and produce spores on PDA medium with or without light illumination,12h light and darkness alternation was the most suitable condition for the growth of mycelia,darkness faciliatated the germination of microspore.The range of temperature for mycelia growth was 15-35℃, 25℃was the optimal temperature for mycelia growth and conidia germination.The favorable pH value for mycelia growth was 3-10,with the optimal pH6-7.The pH value range for the geimination of conidia is 4-10,with the optimal pH6.Among the tested carbon and nitrogen sources in Czapek liquid medium,glactose and ammonium were the most favorable for mycelia growth.Galactose and calcium nitrate were the best medium for sporulation.The lethal temperature for mycelia and conidia was 60℃, 10min and 65℃,10 min,respectively.Inhibition of mycelia growth of F.oxysporum by six fundicides was assayed on amended PDA medium.8%pyrimidine nucleotide antibiotic WP had the highest inhibitory effect with the 50%effective concentration(EC₅₀) at 1.1619ug/ml whereas 65%amobam WP had the lowest mycelial inhibition with EC₅₀ values of 56.2914 ug/ml.Field trials for disease control indicated that soil and seed treated with fungicides respectively or concurrently had control efficacy againt Fusarium wilt of Coleus forskohlii.The significant effect was observed with 98%Dazomet WP of 51.79%efficacy,and 2.5%celest SD of 44.47%,which was used as soil and seed treatment,respectively.Application of both soil and seed treatments was effective in controlling Fusarium wilt,treatments of 98%Dazomet WP and 0.36%matrine combination and 98%Dazomet WP and 2.5%celest SD combination had the highest efficiacy at 63.89%and 60.27%disease suppression,respectively.Root treatments with biocontrol agent or fungicides indicated that the efficacy of Trichoderma harzianum (Th-B) and 8%pyrimidine nucleotide antibiotic WP was better with 68.81%and 59.84%,respectively.