Identification Of Race Of Phytophthora Nicotianae And Biological Control Of Tobacco Black Shank By Actinomyces In Sichuan Province

Tobacco black shank,caused by Phytophthora nicotianae,causes serious damage to cultivated tobacco including flue-cured tobacco,air-cured tobacco,sun-cured tobacco,burley tobacco and oriental tobacco in many parts of China.Identification of physiological race of P. nicotianae can provide an important reference to tobacco varieties arrangement and control of tobacco black shank in Sichuan Province.Actinomyces has immense biocontrol potential to many pathogens.Up to now,many actinomyces isolates have been used to control plant diseases.Using actinomyces to control tobacco black shank is a valuable measure that can avoid chemical pollution and pathogen resistance to fungicides.108 samples of tobacco blank shank were brought from the main planting tobacco areas of Sichuan.74 P.nicotianae isolates were obtained from these disease samples through isolating the samples by tissue isolation method and medulla plate method.The physiologic races were determined by using identification of TTZ color and differential host.According to the differential host,21 isolates were identified to race 0,in proportion of 28.38%,53 isolates s were identified to race 1,in proportion of 71.62%.Both Race 0 and Race 1 existed in all tobacco planting areas of Sichuan,and their distributions were different.However,Race 1 was predominant race type.239 actinomyces strains were isolated from 29 soil samples.Among them,48 isolates showed antagonistic effects against P.nicotianae through plate dual culture,in proportion of 20.1%.Based on the characteristics of morphology and physiology-biochemistry,the antagonists were identified as Streptomyces(47 strains,97.92%) and Nocardia(1 strain).Streptomyces was the dominant genera including Griseofuscus,Albosporus,Lavendulae,Globisporus,Griseorubroviolaceus, Aureus,Roseosporus.Griseofuscus is in proportion of 41.67%and its average inhibition percentage was 54.73%,Albosporus is in proportion of 27.08%and its average inhibition percentage was 46.64%.The highest average inhibition percentage was Lavendulae,61.83%.The fermentation culture conditions of 4 actinomycetes strains were optimized through determining antagonism against P.nicotianae under different days,different pH,and different temperature. Strain A20-8 showed its strong inhibition activity through fermentating 4 days,the initative pH7～8, 28℃.A27-12 was fermentated 8d,pH8,24-28℃.A30-19 was fermentated 4d to 8d,pH8,24℃.A36-15 was fermentated 8d,pH 8,28℃.The results of greenhouse test showed that the 4 actinomycetes had different control effects on curing tobacco blank shank.The strain A30-19 had the best effect,which was 78.79%.And it had no significant difference with 58%Metalaxyl and Mancozeb WP 800 times.Control effect of strain A36-15,A27-12,A20-8 were 67.95%,57.41%, 50.46%,respectively.