Identification Of A New Lettuce Leaf Spot Pathogen And Biocontrol Potential Study Of A Hypovirulence Mycovirus

Lactuca sativa L.is an important vegetable crop in the world.In the winter of2013-2015,there was a widespread serious leaf spot disease on lettuce discovedin Hunan.The field symptom is the water stained necrotic spots,gray-brown,round to oval,diameter2-10 mm.The pathogen of lettuce leaf spot disease was isolated and purified by tissue culture,and through the combination of the morphological analysis and molecular biology,it was identified as Stemphylium vesicarium,we numbered it as SvHN-02.After confrontation culture the SvHN-02 with WS-01(Stemphylium solani),a Weak germ strains with fungal viruses which was obtained earlier in our lab,the mycovirus was found can be horizontally transferred to SvHN-02.1、The strain SvHN-02 which was isolated and purified from the lettuce leaves with leaf spot disease was confirmed by the Koch law.Morphological combines molecular biology to identify it as S.vesicarium.This is the first discoved Lettuce leaf spot disease caused by S.vesicarium.The biological characteristics of SvHN-02 were studied,the fastest rate of growth occur when the pH value is 7,and the optimum growth temperature was 25℃.2、After confrontation culture the SvHN-02 with WS-01(Stemphylium solani),a Weak germ strains with fungal viruses which was obtained earlier in our lab,the mycovirus was found can be horizontally transferred to SvHN-02.3、Comparing the biological traits of SvHN-02 before and after the virus acquisition found that SvHN-02 shows decreased spore production,the mycelium morphological structure distortion,deformity atrophy,the mycelium growth rate slowed down on the medium,the pathogenicity decreased.The results showed that the fungal virus could lead to the declination of host pathogenicity and possess the potential of prevention.4、A partial genome sequence of the mycovirus was obtained.After splicing,the first dsRNA was 3592 bp,encoding an open reading frame of 1180 aa,which contained RdRp domain.Homology comparison of nucleic acid sequences in NCBI database showed that the nucleotide sequence of the virus was the highest among the reported sequences of Alternaria virus AaV-1,76%.Its amino acid sequence was similar to that of the viral AaV-1 amino acid in Alternaria,with a similarity of 85%.This suggests that the fungus is related to the viral AaV-1 reported in alternaria.