Department of Plant Pathology, University of Florida, Apopka, FL 32703, USA.
Phytopathology. 2012 Feb;102(2):185-94. doi: 10.1094/PHYTO-05-11-0145.
Ralstonia solanacearum causes bacterial wilt on a wide range of plant hosts. Most strains of R. solanacearum are nonpathogenic below 20°C; however, Race 3 Biovar 2 (R3B2) strains are classified as quarantine pathogens because of their ability to infect crops, cause disease, and survive in temperate climates. We have identified race 1 biovar 1 Phylotype IIB Sequevar 4 strains present in Florida which were able to infect and produce wilt symptoms on potato and tomato at 18°C. Moreover they infected tomato plants at rates similar to strains belonging to R3B2. We determined that strains naturally nonpathogenic at 18°C were able to multiply, move in planta, and cause partial wilt when inoculated directly into the stem, suggesting that low temperature affects virulence of strains differently at early stages of infection. Bacterial growth in vitro was delayed at low temperatures, however it was not attenuated. Twitching motility observed on growing colonies was attenuated in nonpathogenic strains at 18°C, while not affected in the cool virulent ones. Using pilQ as a marker to evaluate the relative expression of the twitching activity of R. solanacearum strains, we confirmed that cool virulent strains maintained a similar level of pilQ expression at both temperatures, while in nonpathogenic strains pilQ was downregulated at 18°C.
青枯雷尔氏菌可引起广泛植物宿主的细菌性萎蔫病。大多数青枯雷尔氏菌菌株在 20°C 以下是非致病性的；然而，由于其能够感染作物、引起疾病和在温带气候下存活，Race 3 Biovar 2 (R3B2) 菌株被归类为检疫病原体。我们已经在佛罗里达州发现了存在于其中的 1 型生物型 1 phylotype IIB Sequevar 4 菌株，这些菌株能够在 18°C 下感染和引起马铃薯和番茄的萎蔫症状。此外，它们感染番茄的速度与属于 R3B2 的菌株相似。我们确定在 18°C 下自然非致病性的菌株能够增殖、在植物体内移动并引起部分萎蔫，这表明低温在感染早期对菌株的毒力有不同的影响。细菌在体外的生长在低温下延迟，但不会减弱。在非致病性菌株中，在 18°C 时观察到的游动运动减弱，而在凉爽的毒力菌株中则不受影响。使用 pilQ 作为标记来评估青枯雷尔氏菌菌株的游动活性的相对表达，我们证实凉爽的毒力菌株在这两个温度下都保持了相似水平的 pilQ 表达，而在非致病性菌株中，pilQ 在 18°C 时下调。
