Study On The Isolation And Identification Of Black Spot Of Tagetes Erecta In Beijing Area

Tagetes erecta is an annual plant,and also is the main raw material of lutein,which played a vital role in treating macula lutea retinae,improving the immune capability,taking effect on anti-aging.Alternaria has abundant species,which is widely spread distribute in the world,most of megaspore can infect plant.A great loss is produced every year in agriculture.The black spot disease was the main disease on reducing marigold production,from 2012 to 2015,the yield was seriously reduced and a great serious losses was produced.Considering that the issue existed in Beijing area where chrysanthemum demonstration,the urgent affair is pathogen identification and find the pathogen species from our view.The study material was collected from five area in Beijing,including Yanqing County,Daxing district,Mentougou district,Shunyi District,Zhangjiakou,from 2012 to 2014.The polygenic phylogeny tree was constructed with ITS?gpd?Alt a1 and conidia morphology index was acquired,thus we can identify the pathogen.The results indicated that:(1)The condition of cultivation and induced sporulation is: PDA culture medium,25? in the dark,after about a week,the isolation were turned on MA culture medium,25? and 6 hour light from 17:00 pm to 23:00 was needed to induce spores.(2)From the polygenic phylogeny tree,the single spore morphological characteristics of first group shows(65~140)×(15~42)?m in size,the number of transverse septum are 0 to 7,and the number of vertical septum are 3 to 8,the beak length are(7~110)×(3~10)?m.The sporulation pattern are described as,conidia chains are up-right,brownness,unbranched or nearly unbranched,most of are consist of 7 to 10 conidia,the conidia is obovoid or oblong.This is extremely similar to the standard strain of Alternaria tagetica on morphological characteristics.(3)From the polygenic phylogeny tree,the first group are 40 samples in total,accounting for 57.14 percent of the three years,the standard strain of Alternaria tagetica was in this group,thus Alternaria tagetica was the dominant species in the pathogen of marigold black spot disease.(4)The dominant species Alternaria tagetica has strong stability.From the tree,there is no obvious correlation between growing time,growing area and dominant species,which illustrates that dominant species were homogeneous distribution and it's no connection to growing time.In future work,we can study the regularity of infection based on the physiological property of Alternaria tagetica,and then directing the fungicide selection experiments,providing theoretical foundation for the screening disease-resistant varieties.