Occurrence Regulation Of Sclerotinia Stem Rot Of Oilseed Rape And Genetic Diversity Of Sclerotinia Sclerotiorum In Chongqing

Sclerotinia stem rot,caused by Sclerotinia sclerotiorum,is one of the most important diseases in rapeseed production,which causes serious damage in the Yangtze River Basin and southwest region of China.In this study,the occurrence regulation of S.sclerotiorum in Chongqing City was investigated.In addition,90 isolates of S.sclerotiorum from nine counties of Chongqing City were selected to study their biological characteristics,mycelial compatibility groups,genetic diversity and pathogenicity.This study is aim to clarify the genetic differentiation and epidemics of S.sclerotiorum in Chongqing City and to provide a comprehensive control of sclerotinia stem rot in Chongqing City.The results are as follow:1.The results of investigation on the occurrence regulation of sclerotinia stem rot in two types of oilseed rape field with different crops in Batang Town,Bishan District,Chongqing,showed that the number of apothecium,the diseased leaves rate,the incidence of stems,and the disease index in corn pre-stubble fields were much higher than those in sweet potato pre-stubble field.The apothecia of the corn pre-stubble field began to appear in mid-February.After reaching the peak in early March,it reached its peak again in mid-March.The cumulative number of apothecium was 112.4 per m~2.The disease on leaves began in early March and reached a peak in late March and the diseased leaves rate was 44.93%.The incidence of stems began in late March and reached a peak in late April.The stem incidence rate was 34%and disease index was 18.The apothecia of the sweet potato pre-stubble field began to appear in late February and reached its peak in early March.The cumulative number of apothecium was 12.2 per m~2.The disease on leaves began in mid-March and reached it’s peak in late March and the diseased leaves rate was 2.42%.The incidence of stems began in early April and reached a peak in late April.The stem incidence rate was 6%and disease index was 1.5.The correlation analysis results showed that the weekly average temperature was significantly correlated with the diseased leaves rate,the stem incidence rate,and the disease index.But the weekly rainy days and relative humidity are not correlated with the number of apothecium,the diseased leaves rate,the stem incidence rate and the disease index.2.90 isolates of S.sclerotiorum were collected,purified and identified from infected rapeseed of nine counties in Chongqing City.77 isolates were selected for biological characteristics detection,the results showed that there were significant differences in colony morphology,mycelial growth rate and sclerotia number among different isolates.In terms of colony morphology,the isolates can be divided into two types:rich and sparse,according to the texture of mycelium.According to the distribution of sclerotia,the isolates can be divided into three types:around the edge of the petri dish,scattered in the petri dish and around the center of petri dish to form 1-3 sclerotia bands.The mycelial growth rate ranged from 3.4 mm/d to 52.4 mm/d.The sclerotia number ranged from 3.3 to 27.There was no significant correlation between the mycelial growth rate and the sclerotia production.34 isolates selected from 90 S.sclerotiorum isolates were used for aggressiveness test on detached stalk of rapeseed cultivars Zhongyou 821.The results revealed that the diameter of the lesions ranged from7.2 to 40.2 mm.There was a significant variation among the isolates aggresiveness.The aggresiveness of this isolates were not associate with the mycelial growth rate,sclerotia number,MCGs or SSR haplotypes results.3.Mycelial compatibility groups(MCGs)was conducted between 90 isolates of S.sclerotiorum.The results showed that 47 MCGs were identified in 90 isolates,of which 13 MCGs included at least two isolates.The rest of 34 MCGs contain only one isolate that is compatible with itself.There was an accociation between MCGs and the geographic source of the isolates,but has no significant correlation with the mycelial growth rate and sclerotia production of isolates.4.The genetic diversity of 90 S.sclerotiorum isolates was analyzed by using nine pairs of SSR primers.After excluding a pair of non-polymorphic primers(42-4),the remaining 8 pairs of SSR primers amplified a total of 24 bands.52 microsatellite haplotypes were identified in 90 isolates,and a few haplotypes were found with high frequency,and there was no correlation between microsatellite haplotypes and MCGs.The genetic diversity of 9 populations ranged from 0.1570 to 0.4700.A constructed UPGMA dendrogram based on Nei’s genetic distance,a STRUCTURE analysis and genetic differentiation and gene flow reveal that the genetic composition of the isolates collected in the five counties located in the west of Chongqing are different from those collected in the two east counties.Analysis of linkage disequilibrium indicated primarily clonal reproduction in the isolates from 9 populations.The results of AMOVA analysis show that the genetic variation among the 9populations mainly comes from the isolates in nine populations.The correlation analysis of genetic distance and geographical distance shows that there was some correlation between genetic distance and geographical distance.