Isolation And Identification From Pecan Scab And Screening Of Fungicides Of Fusicladium Effusum

Carya illinoinensis（Wangenh.）K.Koch is a deciduous tree of the genus Pickory in Walnut family,commonly known as"pecan fruit".Pecan is tall,thick branches and leaves.It is an excellent garden greening and ornamental tree.It has been introduced and planted in more than 20 countries all over the world.It is one of the world famous dry fruit and oil tree species.In recent years,pecan industry has developed rapidly,and 14 provinces（municipalities directly under the central government）in China have introduced and cultivated pecan.With the expansion of planting area and the diversification of introduced varieties,the occurrence of diseases and insect pests on pecan has become more and more serious,causing great economic losses.At present,there are few researches on pecan scab in China,in order to master the disease characteristics,pathogenic bacteria,growth characteristics and control methods of pecan scab,this paper studied pecan scab mainly from the following two aspects:1.Combining morphology and molecular biology methods to isolate and identify the pathogen of pecan scab and use mycelium growth rate method to study the biological characteristics of Fusicladium effusum;2.Mycelium growth rate method and spore germination method were used to do screening of pathogen of Fusicladium effusum.The main research contents are follows:1.38 cases of leaf and fruit samples of 7 varieties of pecans were collected from different sites,including Gaochun,Liuhe,Jintan,and Quanjiao,etc.in September 2019.117 isolates were obtained by traditional single spore separation method.Among them,72 isolates were preliminarily identified as Fusicladium effusum by morphological identification,25 were Cladosporium spp.,12 were Alternaria spp.and 8 were others.The Fusicladium effusum was olive-colored on the PDA,and brown in the later period,with pigmentation and dark green in color.The mycelium are dense,branched,septic,dark brown,the apex sporogenic site is extended in a coaxial form,the conidia are marked with spore marks after shedding,the conidia are light olive to brown,pear-shaped,smooth surface,the base truncated.The 72isolates were identified by MLSA,and the homology with Fusicladium effusum LSEM1156was 99.46%by BLAST analysis in NCBI,which was consistent with morphology.Studies have shown that Fusicladium effusum is the pathogen of pecan scab.The study on the biological characteristics of pecan scab was mainly to treat the growth environment of mycelia,set different light,temperature and p H values.It was found that under different light treatment,the mycelia grew best in darkness for 24 h.Under different temperature treatment,25℃was the best for mycelia growth.Under different p H values,mycelia from 6 to 6.5 all grew well.2.Fusicladium effusum laboratory medicament screening through laboratory toxicity measurement,the method of mycelium growth rate and spore germination method was used to screen 7 kinds of fungicides,including benziothiazolinone,difenoconazole,azoxystrobin,tebuconazole,propiconazole,potassium phosphite and aluminum triethylphosphate.Five fungicides were screened to inhibit the growth of pecans scab.The inhibiting effect of difenecycloazole on mycelial growth and spore germination was the best.The lowest EC₅₀ of inhibiting mycelial growth was 0.0729 mg/L and the lowest EC₅₀of inhibiting spore germination was 0.0473 mg/L.Among the other 4 fungicides,inhibitory effect on mycelium growth shows:benziothiazolinone,tebuconazole and propiconazole had the best inhibitory effect on mycelial growth of PQ-05,with EC₅₀ of 0.3169 mg/L,0.5366 mg/L and 0.194 mg/L,respectively.The inhibitory effect of azoxystrobin on mycelial growth of WG-1 was the best,with EC₅₀ of 0.9506 mg/L.Inhibitory effect on spore germination shows:benziothiazolinone and propiconazole had the best inhibitory effect on conidial germination of PQ-05,with EC₅₀of 0.0602 mg/L and 0.0568 mg/L,respectively.Tebuconazole had the best inhibitory effect on spore germination of WG-1,with EC50 of 0.2227 mg/L.Azoxystrobin had the best inhibitory effect on spore germination of SJ-1-04,with EC₅₀ of 0.3872 mg/L.The difference of the same fungicide to each strain was significant（P<0.05）,and the difference of the bacteriostatic effect of five agents to the same strain was significant（P<0.05）.All the five fungicides could control pecan scab and effectively reduce the loss.