Studies On The Pathogens Of Flower Rot Of Loquat In Chongqing

According to diseases investigation and pathogens identification on loquat in Chongqing,the results showed there were two kinds of flower rot diseases,five fungal diseases occurrence on leaf and two sorts of fungal diseases on fruit.The paper studied the biological characters of flower rot diseases the Eriobotrya japonica in Chongqing.Meanwhile,the relationship between disease occurrence and leaf diseases,loquat variety,humidity,climate,management and other factors also were researched respectively.The results show that two kinds of loquat flower rot in Chongqing were dry rot type (Pestalotiopsis eriobotrifolia)and wet rot type(Botrytis cinerea).Five kinds of diseases occurred on leaf.They were rust:loquat anthracnose(Colletotrichum acutatum),loquat annulus spot (Pestalotiopsis funerea),loquat grey spot(Pestalotiopsis eriobotryfolia),and loquat round spot (Phyllosticta eriobotryae),loquat leaf withered(Phoma eriobotryae).The results of fruit disease were rust:loquat anthracnose(Colletotrichum acutatum)and loquat grey spot(Pestalotiopsis eriobotryfolia).The relationships between occurrence regularity of loquat flower rot and leaf spot disease, loquat variety,humidity,climate,and management were studied.The results showed,although Eriobotrya japonica normally occurred in plant areas in Chongqing,there was great difference in disease severity.In severe leaf disease fields flower rot was much heavier.Some pests,oribatid mites and peach borer were found in wilting and rotting flowers,where the prevalence of disease was related the transmission by pests.When it concerned to variety,Dawuxing and Longquanyihao were more susceptible to flower rot,of which flower cluster rotting most and average incidence rate were 64.6%.When humidity concerned,it could promote the occurrence degree when giving the same variety.In addition,the orchard hold a short tree age,strong tree vigor,fine ventilation condition and drainage situation,took a low incidence rate of loquat flower rot.The two kinds of loquat flower rot in Chongqing were dry rot type(P.eriobotrifolia)and wet rot type(Botrytis cinerea).The symptom of dry rot type was,after surface of floral axis became brown,the spot extended to the whole bud and the parts from browned axis to flower were shrinkage and withered.When the flowers fell down,receptacle appeared black spots,which were acervulus of pathogen,proved by microscopic examination.The symptom of wet rot type was the issue of floral axis became soft rot,flowers were infected,and several petals became brown,shrank and rotted.In addition,the grey sporophores of the fungus might appear when humidity increased,which were the conidiophore and the conidium observed under microscopic examination.The biological test showed that P.eriobotrifolia could utilize sucrose and xylose very well, utilize lactose and maltose,while starch was used poorly.In addition,the pathogens grew quickly and formed more spores on aspartic acid and potassium nitrate than other nitrogen source.The optimal condition was at 25℃and pH6.04.Enough light could accelerate the production of spores. In several culture mediums,on PA,the mycelia were wooly and aerial mycelium was abundant.The capacity of Producing spores was highest on PSA,while on OAA and CAA poorly.The temperature 25℃was the best optimum for the conidia germination.When RH=100%,the germination rate of conidia was best.The biological test showed that B.cinerea could utilize sucrose and xylose very well,utilize lactose and maltose,while starch was used poorly.In addition,the pathogens grew quickly and formed more spores on ammonium sulfate and potassium nitrate than other nitrogen source.The optimal condition was at 20℃and pH4.96.The light was against the production of spores.The temperatures above 25℃were beneficial to form sclerotium.In several culture mediums,especially on PSA,the mycelia were wooly and aerial mycelium was abundant.The capacity of producing spores was highest on PA medium.Both on Czapek and OAA,B.cinerea grew poorly.The temperature 20℃was the best optimum for the conidia germination.When RH=100%,the germination rate of conidia was best.Till now,there are few studies in the flower rots of loquat in China.The paper first systematically reported the pathogen P.eriobotrifolia and B.cinerea causing flower rot of loquat, which provides an important theoretic reference for the disease control.