Study On The Biological Characteristics And Pathogenicity Of Pear Black Spot Pathogen Alternaria Spp.

Pear black spot is a serious disease in pear producing areas in China,especially in sand pear producing areas in the south.Previous studies in our laboratory confirmed that the pathogens causing pear black spot in China are Alternaria alternata,A.tenuissima,A.longipes,A.gossypina,A.gaisen and A.arborescens,A.tenuissima is the dominant pathogen.This study further studied the biological characteristics of these six Alternaria species,in order to provide reference basis for the control of black spot in pear producing areas.The main research results are as follows:1.Observation results of culture characteristics.The observation results of the culture characteristics of 19 representative strains of 6 species of Alternaria showed that among the 6 species of Alternaria,A.gaisen had the fastest mycelial growth rate and the most melanin production,while A.gaisen had the slowest mycelial growth rate and the least melanin production.The spore production time of A.gaisen strains were the longest and the spore production were the least.2.Determination results of pathogenicity and host range.The conidia suspension and mycelium block of the above representative strains were inoculated on the isolated leaves of six sand pear varieties（Jinshuisu,Zhaotong Xiaohuang pear,20th century,Jinbi,Jinxin,and Lvyun）.The results showed that the effect of using mycelium block to determine the pathogenicity of pear black spot was significantly better than that of using conidia suspension.The results of mycelium inoculation on six sand pear varieties showed that jinshuisu,Zhaotong Xiaohuang pear and the 20th century were more susceptible to pear black spot than Jinbi,Jinxin and Lvyun.According to the cluster analysis of the lesion size,the pathogenicity of the tested strains can be divided into three kinds:strong,medium and weak.There are obvious differences in the proportion of these three strains among the six species of Alternaria.The results of host range determination showed that the six strains of Alternaria could cause disease in cherry,plum,peach,loquat and kiwi leaves,while the strains of A.gossypina and A.longipes could not cause disease in grape leaves.3.Sensitivity test results of crude toxin and chemical agents.The results of UPLC-MS showed that A.arborescens produced five toxins（AME,ALT,AOH,TEN and Te A）,while A.tenuissima and A.longipes produced four toxins and lacked ALT.The results also showed that the toxin production of the three Alternaria species and the toxin production of different Alternaria arborea strains were significantly different.The EC₅₀ of A.tenuissima strain G-12 against five fungicides（Difenoconazole,Flusilazole,Tebuconazole,Difenoconazole-azoxystrobin and Pyrazoconazole）was determined by mycelium inhibition method.The results showed that the inhibitory effect of Difenoconazole was the best,and the EC₅₀ was 0.02 mg·L^-1.This study identified the differences in culture characteristics and pathogenicity of six species of Alternaria causing pear black spot in China,which laid a research foundation for further exploring the occurrence law of pear black spot and the role of different Alternaria in disease epidemic.