Preliminary Pathogen Identification And Investigation Occurring Regulation On Bacterial Black Spot Disease Of Magnolia Denudata

Magnolia denudata Desr. is one of the important landscape species in our country, which widely cultivated throughout the urban and rural areas. In 2011, Magnolia denudata Desr. black spot disease was first discovered in Taian city of Shandong province, which caused tree early defoliation, and even to 80% when disease was very serious. In this paper, the distribution, damage, symptoms, pathogen classification,morphological characteristics, physiological and biochemical and disease occurring regulation in the field were studied. The results were showedas follows:Black spot of Magnolia denudate was occurred in some places of Taian city From 2011 to 2014 continuous survey, both in the north and south campuses of Shandong Agricultural University, but the most serious was in north campus, only sporadically occurred in south campus. In 2013, the disease was the most serious, which could reach to over 50-80 disease spots in one leaf. Some disease spots could combine into a large spot and caused the leaves died and the early defoliation, in 2014, the disease damaged some less than other years. At the early stage, the disease spot was small, round, and appeared in any part of the leaf. With the extension of disease spot, a wide halo was appeared around the disease spot. a single spot was round and black. when disease was seriously occurred, multiple disease spots connected together and formed into an irregular black spot, diseased leaves gradually was become yellow and finally fell off.The separation, purification and culture characteristics, Gram’s staining, colony morphology,16s rDNA gene sequence, pathogenicity determination and Koch’s postulation of the pathogen weie analyzed, the pathogen was identified by Bacillus subtilis.The overwintering site, dynamic and varieties susceptibility of disease were investigated, the result showed that the bud was mainly overwintering places the bark and leaves were secondly. According to a survey in 2014, disease started from mid-may, peaks in June to August, gradually reduce in September and stoped in October. Different varities showed different resistance,the Magnolia denudata Desr.was the most susceptible,the Michelia champaca L, and Magnolia grandflora were resistant...