Variation Of Rhizosphere Microalgae-ecology In The Tobacco Field Which Is Susceptible To Black Shank And Its Effects On The Quality Of Flue-cured Tobacco

In order to clarify the soil microbial ecology variation trend and its effects on the quality of flue-cured tobacco in fields that were sensitive to black shank,this research has studied the indexes of yellow,purple and red soil nutrient,soil enzyme activity,soil microbial number and its diversity.Roasted tobacco leaf indexes of regular chemistry,neutral aroma components and tobacco sensory quality were also studied with tobacco leaves harvested from susceptible and insusceptible(Health fields)to black shank fields with one of yellow,purple and red soil types.From this research we found that:1)Compared with health tobacco fields with yellow,purple and red soil,the pH increased slightly while the contents of rapid available potassium,rapid available phosphorus and available nitrogen decreased in those susceptible to black shank fields.With tobacco growing the organic content in those susceptible to black shank tobacco fields showed little change while those health fields showed significant change.2)The activity of urease,catalase and sucrase first increased and then decreased with the extension of the growth period of tobacco plant,during rosette stage and vigorous growing stage the activity level reached the highest point.Soil enzyme activity was low in those susceptible tobacco fields compared to the health fields.3)With the extension of the gro-wth period,the number of oil bacteria and fungi raised first and then dropped,but the number of actinomycetes increased gradually.In those susceptible to black shank fields,the number of oil bacteria and actinomycetes dropped,while fungi number raised.4)We have studied the diversities of bacteria and fungi with the method of metagenomics,the results showed that the diversity of bacteria and its richness in those susceptible to black shank fields were less than those health fields,but fungi diversity and its ricliness were more than those health ones.In phylum level,the species of dominant bacterial community in the susceptible to black shank fields and the health fields were the same,but the portion of dominant bacterial community between these two kinds of tobacco fields were different.In the genus level,however,there were big differences in the variety of bacterial and fungi dominant communities and their proportions between the susceptible to black shank fields and the health fields.5)The content of potassium,reducing sugar and total sugar in each part of the tobacco leaf from the susceptible to black shank fields decreased at different degrees compared with the health fields.Soil in the susceptible to black shank fields could raise the content of total nitrogen and nicotine in upper leaves,but the ratio of potassium to chlorine and the ratio of sugar to nicotine in each part of the leaf decreased,thus to deteriorate the coordination of tobacco quality and reduced its availability.6)After measuring the neutral aroma component in upper leaves we found that compared with those harvested from the health fields,the content of neutral aroma component in the leaves from fields that were susceptible to black shank decreased at different degrees.In the yellow soil type,the significant difference in aroma components between susceptible to black shank fields and the health fields mainly were maillard reaction products and aromatic amino acid degradation products.In the purple soil type,the contents of maillard reaction products and class cypress alkanes degradation products in upper leaves and neophytadiene content in middle leaves were significant different between tobaccos planted in the health fields and those in the susceptible to black shank fields.In the red soil type,the significant differences between tobaccos planted in the health fields and the susceptible to black shank fields mainly were neophytadiene content and carotenoids content of the upper leaves.7)Sensory evaluation of smoke revealed that oil in those susceptible to black shank fields had negative effects on the sensory qualities such as smoking aroma quality,aroma quantity,smoke density,smoke impact,remaining taste and irritancy.The marks of these sensory quality evaluation indexes were lower than those planted in the health fields.