| Rhizosphere was firstly termed by Lorenz Hilter, a Germany scientist, in 1904, to describe the soil micro-environment around plant roots. Plants, soils and microorganisms interacted intensively in the rhizosphere, resulting in great variation in physical, chemical and biological characteristics compared to non-rhizosphere soil. It is necessary to point out that rhizosphere differs in the amounts, actives and community structures of microorganisms from non-rhizosphere one, which influences plant nutrient absorption, soil nutrient bioavailability and soil-borne diseases occurrence.Ralstonia solanacearum, which exists in rhizosphere soils, was the pathogen of tobacco bacterial wilt. The disease severely harmed the tobacco growth in the world, especially in Southwest China. Guizhou was an important tobacco producing province in China, widespread yellow earths, the main zonal soils. The occurrence of tobacco bacterial wilt was, however, high in the yellow earths, which reduced largely tobacco yields. The present experiment was carried out to reveal the occurrence mechanism of tobacco bacterial wilt in order to obtain some information on the theories and practices of ecological pathology and sustainable tobacco production in Guizhou.Three typical and representative tobacco cultivated soils were selected from Guizhou province for experiment, which were yellow earths derived from sandstone, yellow rendzina from limestone and neutral purplish soils from mudstone, respectively. In the stages of rosette, budding and mature during tobacco period, rhizosphere soils were sampled from fields for studying microorganisms. The objectives were to offer fundamental data and theory for (i) controlling tobacco bacterial wilt, (ii) understanding nutrient convert in rhizosphere and (iii) scientific field managements. Following were results obtained:1 . The amount of microorganisms in tobacco rhizosphere varied in the sequence: bacteria (109-1010 CFU.g-1 dry soil) > actinomycetes (107-108 CFU.g-1 dry soil) > fungi (104-106 CFU.g-1 dry soil). In addition, the amount of rhizosphere bacteria and actinomycetes differed among soil types in accordance with yellow earth > yellow rendzina > neutral purplish soil. Moreover, Significant differences of rhizosphere bacteria and actinomycetes were found between yellow earth and neutral purplish soil (p<0.05). Even though no significant variation of fungal amount was observed among three soils, there still existed the tendency: i.e. neutral purplish soils>yellow earths>yellow rendzina.2.The amount of rhizosphere microorganisms changed with growth periods of tobacco. The bacteria were the lowest in rosette stage and then increased till budding. Thereafter, they decreased gradually. But actinomycetes and fungi showed the tendency that increased from rosette stage to mature.3.Bacteria changed most obviously compared to actinomycetes and fungi in the rhizosphere of tobacco. The number of rhizosphere microorganisms varied among soils. The bacteriaand fungi in rhizosphere of tobacco fluctuated greatly in yellow rendzina, while actinomycetes in yellow earths. Bacteria, actinomycetes and fungi changed least in neutral purplish soil compared to other two soils.4.The microorganisms in the rhizosphere of tobacco were rich in populations, 165 bacteria, 123 actinomycetes and 100 fungi were isolated, among which genus of 331 strains was identified.. They were 14 genuses of bacteria, 11 genuses of fungi and 8 groups in Streptomyces of actinomycetes. 57 strains couldn't be identified.5.Dominant populations of bacteria, actinomycetes and fungi showed similarly in tobacco rhizosphere in three soils. 11 of 19 dominant bacteria strains were Pseudomonans, 11 of 14 dominant fungi strains Penicillium and all dominant actinomycetes strains Streptomyces. Additionally, some differences were detected in dominant strains of bacteria and actinomycetes in tobacco rhizosphere soils. Bacillus and Aemmonas, the dominant populations, were found only in neutral purplish soils. Alcaligenes wer...
|
PDF Full Text Request