Identification Of Colletotrichum Species Associated With Anthracnose Disease Of Trichosanthes Kirilowii Maxim And Their Sensitivity To Three Fungicides

Trichosanthes kirilowii Maxim is a perennial climbing herbaceous plant of Cucurbi-taceae and Trichosanthes.It has high medicinal value and edible value,and is an important special economic crop.It is widely planted in Anhui,Jiangsu and Henan provinces.The main diseases of Trichosanthes kirilowii in China are anthracnose,vineblight,root knot nematode,virus disease,root rot and angular leaf spot.Among them,the anthrax of Trichosanthes kirilowii is one of the most serious diseases in the production of Trichos-anthes kirilowii,which can damage the leaves,stems and fruits,reduce the quality of Trichosanthes kirilowii products,and lead to yield reduction and even harvest.In recent years,with the expansion of the planting range of Trichosanthes kirilowii,the damage area and degree of anthrax in Trichosanthes kirilowii have increased significantly,and the disease symptoms have changed,which seriously affects the yield and product quality of Trichosanthes kirilowii.In this study,Colletotrichum gloeosporioides was identified in the main producingareas of Trichosanthes kirilowii in Anhui Province.The pathogenicity of different Colletotrichum gloeosporioides strains to fruit and leaf of Trichosanthes kirilowii was explored,and the sensitivity of different Colletotrichum gloeosporioides strains to three conventional fungicides was tested.The main research results are as follows:1.Isolation and identification of Colletotrichum gloeosporioides from Trichosa-nthes kirilowiiThe leaves and fruits of Trichosanthes kirilowii with typical anthrax symptoms were collected from different locations in the main producing areas of Trichosanthes kirilowii in Anhui Province.A total of 138 strains of anthrax were isolated by tissue separation method.According to the colony morphology,conidia and appressorium characteristics of the isolated strains on PDA,the obtained strains were divided into four types.Type 1（74strains）:Aeromycetes white and sparse,with a black linear basal hyphae radiating outward from the center.Type 2（46 strains）:aerial hyphae dense,light gray green.Type 3（15strains）:the aerial hyphae are rare,the colonies are pink,and the annular distribution of black particles is produced later.Type 4（3 strains）:Gaseous hyphae dark gray green denser,the distribution of the back from the center to the outside radiation of black line stripes.The representative strains of each type of anthrax were selected,and the molecular biology identification was carried out by using 4-6 groups of primers（ITS,ACT,CAL,CHS-1,TUB2,GAPDH）.The multi-gene development trees were constructed,and the morphological analysis was carried out.The results showed that:Type 1 Colletotrichum liaoningense（ITS,ACT,TUB2,GAPDH）,type 2 and type 4 Colletotrichum fructicola and C.gloeosporioides（ITS,ACT,CAL,CHS-1,TUB2,GAPDH）,type 3 Colletotrichum sojae（ITS,ACT,CHS-1,TUB2,GAPDH）.2.Pathogenicity determinationThe pathogenicity of four Trichosanthes kirilowii Colletotrichum strains on fruit and leaf of Trichosanthes kirilowii was tested by needle inoculation with conidia suspension and mycelium.The results showed that C.fructicola and C.gloeosporioides were pathog-enic in fruits and leaves.C.liaoningense had pathogenicity on Trichosanthes kirilowii fruits,but no obvious symptomson leaves.C.Sojae has no pathogenicity on the fruits and leaves of Trichosanthes kirilowii.3.Sensitivity of Colletotrichum gloeosporioides to three fungicidesIn this study,the sensitivities of mycelia and conidia of Colletotrichum gloeosp-orioides to three fungicides were tested.The results showed that the sensitivity of Colletotrichum gloeosporioides mycelia to difenoconazole was higher than that of chlorot-halonil,and the EC₅₀was 0.6743-7.2286μg/m L,37.6913-357.0656μg/m L and 18.9885-2406.6276μg/m L.The mycelia of Colletotrichum gloeosporioides from Trichosanthes kirilowii had poor sensitivityto azoxystrobin,and there were significant differences in the sensitivity between strains and within strains.Among them,C.fructicola had the lowest sensitivity to azoxystrobin,and had high resistance to azoxystrobin.EC₅₀of the tested strains could not be measured at the highest concentration gradient.C.liaoningense is less sensitive to the drug than C.sojae,EC₅₀were respectively 1694.5589-2406.6276μg/m L,18.9885-903.0699μg/m L and 25.3664-299.6036μg/m L.In addition,the conidia of C.fructicola with strong resistance were sensitive to three fungicides,and azoxystrobin had the strongest inhibitory effect on conidia germination of Colletotrichum gloeosporioides,followed by chlorothalonil,and difenoconazole had weak inhibitory effect,EC₅₀were respectively 0.1349μg/m L,0.2088μg/m L and 1.4791μg/m L.