atmospheric nitrogen (N) by way of a relationship with Frankia bacteria, which colonize root nodules ( Stibolt, 1978 ). Such N-fixing species can survive, and often thrive, in N-poor soils in the wild ( Paschke, 1997 ); in cultivated situations, they can add
hyperplastic lesions on inoculated grapefruit leaves. All studies used bacteria no more than two transfers from the stock culture. AMPs were tested at concentrations of 0, 0.03, 0.1, 0.3, 1, 3, 10, and 30 μM. Assays were performed in 96-well plates with lids
used as with and without bacteria controls. All wells then received 25 μL of the 1 × 10 8 CFU/mL Aac described previously with the exception of the “without-bacteria” control wells, which received 25 μL sPBS. Plates were covered and placed on a rotary
agents of HLB, Candidatus Liberibacter spp., are fastidious, phloem-inhabiting Gram-negative bacteria ( Garnier et al., 1984 ; Tyler et al., 2009 ), which are difficult to obtain in pure culture ( Davis et al., 2008 ; Sechler et al., 2009 ). Three
, acetohydroxy acid synthase [also known as acetolactate synthase (ALS)] is inhibited by valine and leucine and 2-isopropylmalate synthase is inhibited by leucine. *The gene is found in bacteria but not in plants. Hydrogens in carbon–hydrogen bonds are not shown
Frost-sensitive plant species have a limited ability to tolerate ice formation in their tissues. Most plants can supercool below 0°C and avoid ice formation. Discrepancies exist about the role of intrinsic and extrinsic ice-nucleating agents in initiating ice formation in plants. Previous research has demonstrated the ability of infrared video thermography to directly observe and record the freezing process in plants (Wisniewski et al., 1997. Plant Physiol. 113:4378–4397). In the present study, the ability of droplets of a suspension of the ice-nucleating-active (Ice+) bacterium, Pseudomonas syringae, and droplets of deionized water, to induce ice formation in bean plants was compared. The activity of these agents were also compared to intrinsic ice formation in dry plants. Results indicated that the presence of the Ice+ bacteria in droplets ranging from 0.5–4.0 μL always induced freezing at a warmer temperature than droplets of deionized water alone (no bacteria) or intrinsic nucleators in dry plants. When droplets of Ice+ bacteria were allowed to dry, they were no longer effective but were active again upon rewetting. Droplets of water would often supercool below temperatures at which ice formation was initiated by intrinsic agents. When a silicon grease barrier was placed between the droplets of Ice+ bacteria and the leaf surface, the bacteria were no longer capable of inducing ice formation in the plant, despite the droplets being frozen on the plant surface. This indicates that ice crystals must penetrate the cuticle in order to induce freezing of the plant.
Abstract
Common blight in beans (Phaseolus vulgaris L.), incited by Xanthomonas campestris pv. phaseoli (Smith) Dye, is a serious seedborne disease in various parts of the world. We tried to detect possible differences in seed infection and transmission of bacteria in selected bean cultivars/lines. Dry seeds, flower buds (24 to 36 hr before anthesis), small pods (2 to 3 days old), and green seeds of individual plants of Bac-6, ‘Venezuela 44% ‘Pompadour Checà’ dry beans, and of dry seed of Great Northern (GN) ‘Tara’ were examined for possible internal infection after inoculating the seeds, seedlings, and plants with common blight bacterium at various sites. Inoculation of the pedicels of the flower buds and small pods resulted in transmission of the bacteria through the vascular tissue of the pod to the seeds, causing internal infection without any external symptoms shown either by the pods or seeds. Bac-6 was resistant to seed infection, and ‘Venezuela 44’ was most susceptible, followed by ‘Pompadour Checà’ and GN ‘Tara’. Planting infected seeds did not result in a systemic transmission of the bacteria in the vascular tissue of the plants to the seeds. Infected leaves were likely to be the main source for the external infection of pods, which could lead to internal and/or external seed infection. Breeding for resistance to seed infection and transmission of bacteria should aid the control of this disease. A useful technique for assessing internal infection of seeds with the bacteria was developed.
Our objectives were to test whether Maackia amurensis Rupr. & Maxim. nodulates and fixes N and to characterize the N-fixing bacteria effective with this host. Soil samples were collected near diverse legume trees at arboreta and public gardens in the United States, Canada, and China. Seedlings of M. amurensis were grown for 6 weeks in a low-N, sterile medium and inoculated with soil samples. At harvest, nodules were found on the lateral and upper portions of root systems. Bacteria were isolated from nodules and subculture. Roots of seedlings inoculated with all 11 of these isolates nodulated and freed N, confirming that the isolates were rhizobial bacteria. Growth of isolates in axenic culture generally was poor when single sources of C were provided. Generation times of the isolates ranged from 6 to 10 hours, and all isolates raised the pH of culture media. Isolates were highly resistant to several antibiotics, showed no 6-phosphogluconate dehydrogenase (6PGD) or β-galactosidase activity, and were highly sensitive to NaCl. These results provide the first evidence that M. amurensis has the capacity to form N-fixing symbioses with rhizobial bacteria and indicate that the bacteria are Bradyrhizobium sp.
The postharvest longevity of fresh-cut flowers is often limited by the accumulation of bacteria in vase water and flower stems. Aqueous chlorine dioxide is a strong biocide with potential application for sanitizing cut flower solutions. We evaluated the potential of chlorine dioxide to prevent the build-up of bacteria in vase water and extend the longevity of cut Matthiola incana `Ruby Red', Gypsophila paniculata `Crystal' and Gerbera jamesonii `Monarch' flowers. Fresh-cut flower stems were placed into sterile vases containing deionized water and either 0.0 or 2 μL·L–1 chlorine dioxide. Flower vase life was then judged at 21 ± 0.5 °C and 40% to 60% relative humidity. Inclusion of 2 μL·L–1 chlorine dioxide in vase water extended the longevity of Matthiola, Gypsophila and Gerbera flowers by 2.2, 3.5, and 3.4 days, respectively, relative to control flowers (i.e., 0 μL·L–1). Treatment with 2 μL·L–1 chlorine dioxide reduced the build-up of aerobic bacteria in vase water for 6 to 9 days of vase life. For example, addition of 2 μL·L–1 chlorine dioxide to Gerbera vase water reduced the number of bacteria that grew by 2.4- to 2.8-fold, as compared to control flower water. These results confirm the practical value of chlorine dioxide treatments to reduce the accumulation of bacteria in vase water and extend the display life of cut flowers.
, 71, 107, and 142 postinoculation. In plants of all three cultivars ( Table 1 ), bacteria were not isolated from leaves 1, 3, and 5 above the inoculation site 36 d postinoculation or from leaves 7, 8, and 9 at 107 d postinoculation. When leaves 2, 4