Causal Agent Of Tobacco Gray Mould In Shaanxi Province And Control Effectiveness Of Trametes Versicolor Olysaccharides On The Disease

Tobacco (Nicotiana tabacum L.)is an important economic crop in China, occupies animportant position in the national economy. However, various kinds of tobacco diseasesfrequently occur each year due to climate change, geographical distribution, the system offarming and cultivation, tobacco varieties. An unknown disease has broken out and caused agreat lost on tobacco production in Luonan(N110.14E34.09, altitude950m), Shaanxi, Chinain2011. This disease mainly took place in the late growth stage of the tobacco, large area ofgray-brown lesions appeared on the lower leaves of infested tobacco plants, part of the lesioncan be extended to more than half of the blade，the lesion surface covered with thick layer ofpale gray mold. When the weather was nice, those lesions became dry and brittle, some oflesions even forming large perforation on leaf blade which rendered diseased tobacco loseharvested value. The average incidence rate of the disease was40.8%, Causing seriousdamage to the local tobacco production.Based on morphological characters and molecular data, the pathogenic fungus of anunknown tobacco disease in Shaanxi Province in2011was identified. The suspectedpathogen was isolated from diseased leaves of tobacco plants, and after pathogenicity testsand re-isolation of the pathogen, the strain LJL007was determined to be responsible for thedisease. The strain LJL007was identified as Botrytis cinerea Per., whose teleomorph isBotryotinia fuckeliana on basis of morphological and cultural characters. We found that thesequences of the isolate LJL007(Accession no.: HM17900) was100%identical to that of B.fuckeliana (Accession no.: HM849615)by analyzing sequences of the ITS regions ofribosomal DNA, further confirming that the pathogen was Botrytis cinerea Per..The colony of strain LJL007on PDA is offwhite and taupe in the rear, The conidiophoresare clustered, slender, Light brown,147-310×12.8-18.7μm, conidiophores’ trunk is diaphragm,the conidiophores top is branching, trunk and branches showing changes in the large acuteangle. Conidia are oval and colorless,10-12μm×7.5-10μm, conidia cluster at top of branchesof conidiophores looks like“grape”. The Trametes versicolor polysaccharides is a water-soluble polysaccharide extracted fromthe T. versicolor fungus, with a function of immune regulation. This test attempts to explore T.versicolor polysaccharides’preventive effect on tobacco gray mould which caused by B.cinerea.The T. versicolor polysaccharides has better protective effect on tobacco gray mould ingreenhouse experiment. Preventive effect of T. versicolor polysaccharides in3,5,7d, were33.27%,39.24%and56.29%, respectively, which significantly higher than effect of otherthree agents(namely0.5%lentinan AS,0.5%oligosaccharins AS,10%difenoconazole WDG).In the field experiment, T. versicolor polysaccharides showed a maximum value of52.3%preventive effect on the tobacco gray mould. However, the therapeutic effect of Trametesversicolor polysaccharides on gray mould was not satisfactory (this is only36.24%) ingreenhouse experiments. Meanwhile, T. versicolor polysaccharides cannot inhibit themycelium growth and spore germination of B. cinerea in vitro. Chitinase, β-1,3-glucanase andphenylalanine ammonia lyase (PAL) activity has significantly increased after5dadministration of T. versicolor polysaccharides, Chitinase, β-1,3-glucanase and phenylalanineammonia lyase (PAL) activitiese peak were increased by56.89%,429.83%and46.21%,respectively. We speculate that T. versicolor polysaccharides may induce defense enzymes intobacco plant to form resistance to gray mold.