Isolation And Identification Of Phytophthorc Capsici In Sichuan Province;the Relationship Of Root Exudates With Resistance To Phytophthora Capsici In Peppers

Phytophthora blight in capsicum plants is a worldwide soil-borne disease results from the infection of Phytophthora capsici L.which seriously influence pepper production.This study is to isolate and identify P.capsici strains from Miyi,Chongzou,and Neijiang three major production areas of Sichuan province.A blight-resistant variety ’Xinshu 215’ and susceptible variety ’Erjintiao’ were then used as experimental materials in artificial inoculation by P.capsici strain NJ-5.The differences in root exudates between the two cultivars were thoroughly investigated.The root exudates were collected from hydroponics,were extracted by liquid phase extraction,and were further identified using a GC-MS.These studies provide us better understanding about the interaction of pepper root exudates and P.capsici in the infection.The main results are as follows:1.The colony morphology of the isolates from different areas was basically the same with white and radial plaque but not the growth rate.The isolated colonies were observed under a microscope vision to identify their hyphae,zoospores and zoosporangium.As a result,a total of 12P.capsici strains were identified which were further confirmed by determining the length of PCR fragment amplified by RNA transcribed spacer(ITS)primers.After optimization,the condition for P.capsici preservation in slant culture medium should be under 16℃ in 5mL medium and by this way the strain can be stored as long as 60d.After optimization,the best way to discriminate the resistance to P.capsici in peppers was following:make zoospore on PDA under 24h-illumination for 6d without any interval;inoculate by 5×104 zoospore per mL at 25℃ when the pepper seedlings were at 6-leaf stage.2.The nutrient solution was collected after the hydroponic plants growing for 50d.As a result of GC-MS identification,there were 50 substances in 9 categories including hydrocarbons,acids,aldehydes,alcohols,esters,benzene,phenols,amines,and heterocyclic compounds.In these root exudates,the most common ones were esters,followed by alkanes.In details,the root exudates from ’Xinshu 215’ contained 29 substances in 9 categories,while those from ’Erjintiao’ contained 24 substances in 8 categories.Moreover,peppers show different root exudates in hydroponic and soil.3.Soluble sugar and protein content in root exudates may be related to disease resistance.After the inoculation,the soluble sugar content was negatively correlated with disease resistance while the soluble protein content was negatively correlated with the resistance of pepper.By using GC-MS to discriminate the root exudates between blight-resistant ’Xinshu 215f and susceptible ’Erjintiao’,I found aldehydes and ketones was negatively correlated with the disease resistance.Azulene,octadecane and heneicosane may have positive correlation with resistance of pepper varieties but Naphthalene,2-methyl-,1(3H)-Isobenzofuranone,3-butylidene-and Butylated Hydroxytoluene were negative correlated with pepper resistance.