Study On Biological Characteristics And Genetic Diversity Of Paecilomyces Cateniannulatus In A Massion's Pine Plantation Ecosystem

Paecilomyces cateniannulatus,an entomogenous fungus and one of the predominant species of the fungi in a Masson's pine plantation ecosystem,plays an important role on forest pest control.During investigation,collection and isolation in the present study,156 isolates were obtained and their biological characteristics,genetic diversity and niche were studied.1.Colony diameter growth and sporulation of 3 P.cateniannulatus isolates under different temperatures were compared,optimal medium was chosen by screening,and impact of illumination on mycelium growth and sporulation was determined.The result showed that colony growth at 23℃was significantly faster than at the other temperatures. As compared to those on PDA and SDAY,the colony diameter and sporulation on a modified rice-peptone medium were significantly larger.Mg²⁺and K⁺ exerted significant influence on sporulation.Sporulation under 24h illumination was significantly higher than at 4h illumination.Under Oh illumination,colony diameter growth was the biggest and sporulation the poorest.2.In a bioassay for virulence on the pine sawyer,Monochamus alternatus,conidial suspension of 4 P.cateniannulatus isolates were sprayed onto larvae of the sawyer.The result showed that Pc45,Pc130,Pc287 and Pc305 caused a mortality of 75,55,30,and 35%,respectively.Pc45 showed high virulence,with LT₅₀at 11.1 day.3.Ten primers among 20 primers tested were chosen for ISSR,which amplified out clear bands with good repeats.From them,78 bands were resulted,with 46 of them showed polymorphism.The size of the bands amplified were 200-2000bp,with percent polymorphism at 59.0%,and average band number at 7.8 from each primer.By POPGENE analysis,genetic diversity and differentiation coefficient of P.cateniannulatus were obtained.Its general Nei's genetic diversity index(H)was 0.0660,Shannon's information index(I)at 0.1161.Based on collection origin,the isolates were divided into 3 subpopulations,with its total genetic diversity(Ht)at 0.0618,genetic diversity within subpopulation(Hs)at 0.0579.Its gene differentiation coefficient(Gst)at 0.0641,indicating that 6.41%variation existed between subpopulations and 93.59%variation existed within subpopulations.Based on hosts infected,the isolates were divided into 5 subpopulations, with Ht at 0.0595,Hs at 0.0457,and Gst at 0.2316,indicating that 23.16%variation existed between subpopulations and 76.84%variation existed within subpopulations.Based on collection time,the isolates were divided into 12 subpopulations,with Ht at 0.0662,Hs at 0.0592,and Gst at 0.1065,indicating that 10.65%variation existed between subpopulations and 89.35%variation existed within subpopulations.Through above analysis,It was suggested that genetic variation of P.cateniannulatus in Jingtingshan area existed mainly within subpopulations.When 3 subpopulations were divided,the maximum gene flow(Nm)was 7.3005.4.By Nei's method,genetic distances subpopulations were determined.When the isolates were divided into 3 subpopulations based on collection origin,genetic distance was between 0.0043 to 0.0075,with the shortest distance at 0.0043,between airflow and soil.When divided into 5 subpopulations based on host,the distance was between 0.0041 and 0.0495,with the shoetest distance between Coleoptera and Hymenoptera and the longest between Acarina and Mantodea.When divided into 12 subpopulations based on collection time,the distance between 0.0009 and 0.0124,with the shortest between June, 2005 and August,2008,and the longest between March,2005 and July,2005.Their host specificity met the then temperature.5.A clustering analysis on 156 isolates of P.cateniannulatus revealed that the population could be clustered into 5 groups at the genetic distance of 0.08-0.11,with the isolates from the same host tended to meet together.In Group Bâ…¢,however,no isolates came from airflow or soil.6.Host resource niche width,in terms of Levin's measurement index,of P. cateniannulatus was the widest for Group Bâ…¡(2.0870),and narrowest for Group BV (1.1172).Time resource niche width was the widest for Group Bâ…¡(1,1172),narrowest for Group Bâ…¢(2.9412),suggesting that the isolates of Group Bâ…¡has a wide time span and a strong survival ability.Niche overlap index was the highest between Group Bâ… and Group Bâ…¡(0.9855)followed by that for Bâ…£and Bâ… (0.9411),and lowest between Bâ…¡and Bâ…¢(0.7912).Similarity index was the highest between Bâ… and Bâ…¡(1.0582),followed by that between Bâ…£and Bâ…¤(1.0179),and the lowest between Bâ…¡and Bâ…¢(0.8075).Group Bâ…¡with broad niche were highly adaptive in the Masson's pine ecosystem,with high population superiority,and plays an important role in sustainable pest management;on the contrary,the isolates of the groups with narrow niche,like Group Bâ…¢,are poorly adaptive in the plantation ecosystem and will account for smaller and smaller portion in the plantation.