Phytopathology. 1999 Nov;89(11):1073-9. doi: 10.1094/PHYTO.1999.89.11.1073.
ABSTRACT Two biological control agents, nonpathogenic Fusarium oxysporum Fo47 and Pseudomonas putida WCS358, were evaluated for suppression of Fusarium wilt of flax grown in nutrient solution and for suppression of the population density and metabolic activity of the causal organism F. oxysporum f. sp. lini strain Foln3GUS on root surfaces. Due to the presence of an introduced gusA reporter gene construct in Foln3GUS, the pathogen expressed beta-glucuronidase activity that was related to its carbon metabolism. At a Fo47 to Foln3GUS inoculum ratio of 100:1, both the population density of the pathogen and the beta-glucuronidase activity on and in flax roots were reduced by the nonpathogenic strain, and Fusarium wilt was suppressed. At a Fo47 to Foln3GUS inoculum ratio of 10:1, Fo47 decreased the severity of Fusarium wilt to a smaller extent and it also reduced beta-glucuronidase activity without reducing the density of Foln3GUS on flax roots. At a nonpathogenic to pathogenic Fusarium strains ratio of 10:1, the addition of P. putida WCS358 further suppressed Fusarium wilt and the density of the pathogen at the root level, whereas a mutant of WCS358 deficient in pseudobactin production had no significant effect. Iron availability to WCS358 on flax roots, assessed by ice-nucleation activity conferred from a transcriptional fusion (pvd-inaZ) of an ice-nucleation reporter gene to an iron-regulated promoter, was sufficiently low to allow pseudobactin production. P. putida WCS358 did not reduce the severity of Fusarium wilt of flax when inoculated without Fo47, and it did not improve disease suppression achieved by high inoculum doses of Fo47 (a Fo47 to Foln3GUS ratio of 100:1). Together, these data provide evidence that (i) suppression of Fusarium wilt of flax by Fo47 is related to reductions in the population density and metabolic activity of the pathogen on the root surface; (ii) WCS358 can enhance the biological control activity of Fo47, but this enhancement depends on the population of Fo47 relative to the pathogen; and (iii) pseudobactin contributes to suppression of Fusarium wilt by the combination of Fo47 and WCS358 on roots in which conditions are conducive to pseudobactin production by the bacterium.
本研究评估了两种生物防治制剂，即不致病的尖孢镰刀菌 Fo47 和假单胞菌 WCS358，以研究其在营养液中对亚麻枯萎病的防治效果，以及对根表病原菌尖孢镰刀菌 f. sp. lini 菌株 Foln3GUS 的种群密度和代谢活性的抑制效果。由于 Foln3GUS 中存在引入的 gusA 报告基因构建体，病原菌表达了与碳代谢相关的β-葡萄糖醛酸酶活性。在 Fo47 与 Foln3GUS 接种物比例为 100:1 时，非致病菌株可降低病原菌的种群密度和β-葡萄糖醛酸酶活性，从而抑制枯萎病的发生。在 Fo47 与 Foln3GUS 接种物比例为 10:1 时，Fo47 在较小程度上减轻了枯萎病的严重程度，同时降低了 Foln3GUS 在亚麻根上的密度，但不降低其β-葡萄糖醛酸酶活性。当非致病尖孢镰刀菌与致病菌株的比例为 10:1 时，添加假单胞菌 WCS358 进一步抑制了根部的枯萎病和病原菌密度，而缺乏假単胞菌素产生能力的 WCS358 突变体则没有显著效果。通过对根表面转录融合体（pvd-inaZ）的冰核活性（来自铁调控启动子的冰核报告基因）评估了 WCS358 对铁的利用，结果表明铁的可用性很低，足以允许假単胞菌素的产生。当 WCS358 单独接种而不接种 Fo47 时，不会减轻亚麻枯萎病的严重程度，也不会改善 Fo47 高接种量（Fo47 与 Foln3GUS 比例为 100:1）所实现的疾病抑制效果。综上所述，这些数据提供了以下证据：（i）Fo47 对亚麻枯萎病的抑制作用与病原菌在根表面的种群密度和代谢活性的降低有关；（ii）WCS358 可以增强 Fo47 的生物防治活性，但这种增强取决于 Fo47 相对于病原菌的种群；（iii）在有利于细菌产生假単胞菌素的条件下，Fo47 和 WCS358 联合使用时，假単胞菌素有助于抑制根际枯萎病。
