Screening Of Biocontrol Strains And The Biocontrol Efficacy Of Apple Tree Valsa Canker

Based on many years research of our laboratory,this paper carried out the study on screening of biocontrol strains and field control towards the Apple Tree Valsa Canker.The strain SL01 which had a better control efficacy was screened from the fermentation broths and filtrate of 9 strains of biocontrol agents by inhibiting the mycelial growth,the spore germination test,twigs lesion expansion test towards the target pathogen;The identification of SL01 was ensured via the morphological characteristics,the physiological and biochemical characteristics and 16s rDNA sequence analysis.The fermentation condition of SL01 has optimized by single factor and orthogonal test;Then the strain SL01 was applied in field condition.The main results are as follows:It can be found that the fermentation broth and fermentation filtrate of the 9 biocontrol strains shows different inhibiting effect to the Valsa mali through the mycelial growth experiment.Among them,the fermentation broth and fermentation filtrate of SL01 showed the best inhibitory effect,reaching at 64.2%and 42.5%respectively.Under the condition of liquid culture,the fermentation filtrate of SL01、SF6、SF and F46 still have inhibitory effect when diluted to 20,50,100 times.The inhibitory effect of SL01 is the most excellent when diluted to 100 times,reaching 55.9%.Continuous antibacterial test showed that the growth speed of mycelium of Valsa mali declined significantly after the antifungal substance had been moved away,especially when inhibited by SL01.After observed in microscope,the mycelium became yellow,shorter and misshapen.Spore germination test showed that the fermentation filtrate of the 9 biocontrol agents can inhibit the spore germination of Valsa mali to different degree,and inhibitory effect of SL01 is still the best one,reaching 69.5%.What’s more,the spore affected by SL01 turn to abnormal compared to the control group although they all imbibed.The twigs lesion control test found that the lesion areas treated by fermentation broths of 9 strains were significantly different compared with control,the lesions of treatment group were inhibited in different degree after 5d,and the inhibition ratio of SL01 reaches 67%,After 10 days the inhibitory effect is not that well.It could be certain that SL01 is a member of Streptomyces longissimus via the morphological characteristics,the physiological and biochemical characteristics and 16s rDNA sequence analysis.The antimicrobial substances of SL01 had optimized under the flask condition,it is as follows:millet 2%,yeast powder 1%,MgSO40.15%，under the condition of 28℃ pH=7,inoculation 2%,capacity 50mL/250ml and 180rpm.After optimization of fermentation conditions of strain SL01,the antagonistic activity was significantly advanced,the lesion area of twigs and apples were inhibited obviously after treated with the bacterial suspension of SL01,control effect reached 90.0%,the average control effect of twigs treated by fermentation filtrate was 66.0%and the control effect of apple treated by the fermentation filtrate of SLOlwas 92.5%.The field experiment,in the prevention trials treated with SL01 agent,the prevention effect is 48.6%,in the lesion treatment trials by SL01 agent,the control effect was 100%via treated by SL01 agent after scraping lesion,the control effect was 58.3%via treated by SL01 agent after crossed the lesion.