Study On Angelica Black Spot Caused By Phyllosticta Angelicae

Angelica black spot is considered as a new and destructive disease of Angelica Dahurica in Sichuan in recent years.On this paper,first and systematically studied on the symptoms of the disease,the identification,biological characteristics and infection process of the pathogen,and the disease occurrence.The main results are as follows.1.Symptom and pathogen identification of Angelica black spotAngelica black spot mainly appears on the leaves,sometimes also on petioles and stalks.The ealy appearance of its symptom is small watery spots,spots gradually expand, with the central changing into colourless and the edge having remained dark.The typical leaf spot is dark brown,nearly round,in diameter of 3～15mm.On petiole or stalk,the symptom is dark brown strip spot.According to the symptom,cultivating characters,espencilly the shape and size of pycnidium and conidia,the pathogen of Angelica black spot was identified as Phyllosticta angelicae Saccardo.2.Biological characteristics of Phyllosticta angelicaeResults showed that the temperature and pH value rage for mycelium growth and sporulation was 5～35℃,pH3～11,with the optimum at 25℃,pH 5,6.All kinds of carbon sources could be effectively used by the pathogen,and the most suitable nitrogen sources was nitrates.It could grow and sporulate well on host juice medium and light treatment. Conidia were able to germinate in 10～35℃,pH 3～10 and humidity of RH≥95%,the maximum rate of spore germination was in 25℃,pH6 and water.In suitable condition, germination of conidia started within 4 hours and the percentage of germination reached above 90%after 24 hours.The lethal temperature of mycelium and conidia was 46℃and 53℃,respectively.3.Infection process and conditions of Phyllosticta angelicaeAfter inoculation,conidia of P.angelicae began to germinate within 12 hours.Then, from 24 to 48 hours,the pathogen started to penetrate into host.The pathogen was able to penetrate host through two paths such as stomata and epidermis,with the infection structure of appressorium and hypha,and the way of directly penetrating into epidermis was the major way on the leaves positive.The infection of Angelica dahurica by Phyllosticta angelicae could be occured at 15 to 28℃,and the optimum temperature was 20℃.At 20℃and 25℃,the incubation period was the same shortest(5 days).The optimum wetness period rage for infecting leaf of Angelica dahurica by the pathogen was 48 to 72 hours,with the incubation period of 5 days and 4 days.Phyllosticta angelicae infected the basal leaves firstly,then spreaded to the upper leaves.Old leaves were more conducive to the infection.4.Disease occurrence of Angelica black spotThe diseased leaves on the seed plants and residue of infected leaves in the field were the primary infectious source.When the pathogen encountered high humidity,the conidia were released from conidiocarp,then transmitted by rain as reinfection sources.By the mycelium and pycnidia in the residue of diseased plants and infected seed plants were the overwintering and oversummering methods of the pathogenic fungi.Results from the two years investigation in the fielde showed that,in Sichuan Angelica black spot cannot be found on Angelica dahurica seedlings;the disease first appeared in early March and with a peak in June,while the highest percentages of diseased plant and leaf were up to 100%,74.51%respectively,and the highest disease index was 37.04.Thereafter,with the cessation of Angelica dahurica growth,the disease degree began to slow down and the development of the disease stopped.