Phytopathology. 2003 Sep;93(9):1173-81. doi: 10.1094/PHYTO.2003.93.9.1173.
ABSTRACT Determining the population density of the spinach wilt pathogen Fusarium oxysporum f. sp. spinaciae in soil with conventional Fusarium-selective media is quite difficult because nonpathogenic strains of F. oxysporum also grow on those media and are indistinguishable from the pathogen. Therefore, a nitrate-nonutilizing (nit) mutant of the pathogen and corresponding selective media were tested in an experimental approach to determine the population density of the pathogen. Colony forming units of the pathogen were countable after soil-dilution plating onto nit mutant-selective media MMCPA, CMP, and CGMBP. Colony forming units of wild-type Fusarium spp. were countable using a wildtype Fusarium-selective medium, GMBP. By combining nit mutant- and wild-type-selective media, the population densities of pathogenic and nonpathogenic F. oxysporum in the same soil could be measured selectively. This method was useful in studying population dynamics of the pathogen after different soil treatments. Soil disinfested with hot water or chloropicrin was amended with the nit mutant pathogen, and subsequent changes in population densities of the pathogen were compared with those in nontreated field soil. The pathogen rapidly proliferated in disinfested soil and wilt developed faster than in nontreated soil. When a nonpathogenic isolate of F. oxysporum was added at high density to sterilized soil prior to the pathogen, growth of the pathogen was greatly suppressed. Nonpathogenic F. oxysporum could not, however, reduce the density of preexisting pathogen.
摘要 使用常规的镰刀菌选择性培养基来测定土壤中菠菜枯萎病病原菌尖孢镰刀菌（Fusarium oxysporum f. sp. spinaciae）的种群密度是相当困难的，因为非致病性的尖孢镰刀菌菌株也会在这些培养基上生长，且与病原菌无法区分。因此，本实验采用一种硝酸盐非利用（nit）突变体的病原菌及其相应的选择性培养基来测定病原菌的种群密度。通过在 MMCPA、CMP 和 CGMBP 等 nit 突变体选择性培养基上进行土壤稀释平板计数，可以计数病原菌的菌落形成单位。使用野生型镰刀菌选择性培养基 GMBP 可以计数野生型尖孢镰刀菌的菌落形成单位。通过结合 nit 突变体和野生型选择性培养基，可以选择性地测定同一土壤中致病性和非致病性 F. oxysporum 的种群密度。该方法在研究不同土壤处理后病原菌的种群动态时非常有用。用热水或氯化苦消毒的土壤中添加 nit 突变体病原菌，随后比较病原菌种群密度的变化与未处理田间土壤的变化。病原菌在消毒土壤中迅速增殖，枯萎病的发展速度比未处理土壤更快。当将高浓度的非致病性 F. oxysporum 分离物添加到病原菌之前的灭菌土壤中时，病原菌的生长受到了极大的抑制。然而，非致病性的 F. oxysporum 不能降低已存在的病原菌的密度。
