Department of Life and Environmental Science, Hangzhou Normal University, Hangzhou 310036, China.
Phytopathology. 2012 Apr;102(4):413-20. doi: 10.1094/PHYTO-07-11-0189.
Previously, oscillations in beet seedling damping-off by Pythium ultimum, measured as area under the disease progress curve (AUDPC), were demonstrated after incorporation of organic materials into organic and conventional soils. These periodic fluctuations of P. ultimum infections were cross-correlated with oscillations of copiotrophic CFU at lags of 2 to 4 days. For this article, we investigated whether bacterial communities and microbial activities fluctuated after a disturbance from incorporation of organic materials, and whether these fluctuations were linked to the short-term oscillations in AUDPC of beet seedling damping-off and bacterial populations (CFU) in soil. Soil microbial communities studied by polymerase chain reaction-DGGE analysis of 16S DNA after isolation of total DNA from soil and microbial activities measured as CO(2) emission rates were monitored daily for 14 days after addition of grass-clover (GC) or composted manure (CM) into organic versus conventional soils. Similar to our previous findings, AUDPC and density of copiotrophic bacteria oscillated with time. Fluctuations in species richness (S), Shannon diversity index (H), and individual amplicons on DGGE gels were also detected. Oscillations in AUDPC were positively cross-correlated with copiotrophic CFU in all soils. Oscillations in AUDPC were also positively cross-correlated with 19 to 35% of the high-intensity DNA fragments in soils amended with GC but only 2 to 3% of these fragments in CM-amended soils. AUDPC values were negatively cross-correlated with 13 to 17% of the amplicons with low average intensities in CM-amended soils, which were not correlated with densities of copiotrophic CFU. CO(2) emission rates had remarkable variations in the initial 7 days after either of the soil amendments but were not associated with daily changes in AUDPC. The results suggest that infection by P. ultimum is hampered by competition from culturable copiotrophic bacteria and some high-intensity DGGE amplicons, because AUDPC is cross-correlated with these variables at lags of 1 to 4 days. However, negative cross-correlations with low-intensity DNA fragments indicate that P. ultimum infection could also be suppressed by antagonistic bacteria with low densities that may be nonculturable species, especially in CM amended soil. The organic soil generally had lower AUDPC values, higher bacterial diversity, and negative cross-correlations between AUDPC and low-intensity DNA fragments (after CM amendment), indicating that specific bacteria that do not attain high densities may contribute to P. ultimum suppression in organic soils.
先前，在将有机物质掺入有机和常规土壤后，已证明由终极腐霉引起的甜菜幼苗猝倒病的振荡（以病害进展曲线下的面积（AUDPC）表示）。这些终极腐霉感染的周期性波动与富营养型 CFU 的波动相关，滞后 2 至 4 天。在本文中，我们研究了在掺入有机物质后，细菌群落和微生物活性是否会发生波动，以及这些波动是否与甜菜幼苗猝倒 AUDPC 和土壤中细菌种群（CFU）的短期波动有关。通过从土壤中分离总 DNA 后对 16S DNA 进行聚合酶链反应-DGGE 分析来研究土壤微生物群落，并监测添加草皮-三叶草（GC）或堆肥粪肥（CM）后 14 天内的微生物活性每日 CO2 排放率。与我们之前的发现类似，AUDPC 和富营养型细菌的密度随时间波动。还检测到物种丰富度（S），香农多样性指数（H）和 DGGE 凝胶上的单个扩增子的波动。在所有土壤中，AUDPC 的波动与富营养型 CFU 呈正相关。在添加 GC 的土壤中，AUDPC 的波动也与 19 至 35％的高强度 DNA 片段呈正相关，但在添加 CM 的土壤中仅为 2 至 3％。在添加 CM 的土壤中，AUDPC 值与低平均强度的 13 至 17％的扩增子呈负相关，这些扩增子与富营养型 CFU 密度无关。在添加任何一种土壤调节剂后的最初 7 天内，CO2 排放率均有明显变化，但与 AUDPC 的每日变化无关。结果表明，终极腐霉的感染受到可培养富营养型细菌和某些高强度 DGGE 扩增子的竞争的阻碍，因为 AUDPC 在 1 至 4 天的滞后时间与这些变量呈正相关。但是，与低强度 DNA 片段的负相关表明，P. ultimum 的感染也可能被密度较低的拮抗菌抑制，尤其是在添加 CM 的土壤中，这些拮抗菌可能是非培养物种。有机土壤通常具有较低的 AUDPC 值，较高的细菌多样性以及 AUDPC 与低强度 DNA 片段之间的负相关关系（在添加 CM 后），这表明在有机土壤中，密度不高的特定细菌可能有助于抑制 P. ultimum。
