I have grown some soybean plants in autocleaved sand with only Farhun medium (Nitrogen free medium) but I have got nodules on plants root. How it is possible? Moreover, I got nodules on some plants which were inoculated with Rhizobia. But I have not got any nodule in 1% agar medium which was inoculated with solution of Rhizobia.
Hi Syed Raju Ali,
You should evaluate a possible contamination in your substrate to discard it possibility.
Regards,
Jorge
Nodulation needs recognition between the host plant and the rhizobial counterpart. If they are not compatible nodulation may not take place. Even if it takes place, the nodules will be non-functional. So check for plant-bacterial compatibility.
Certain Medicago species can develop non-nitrogen fixing structures on their root systems, without Rhizobium (NAR = Nodulation in Absence of Rhizobium). But, it is clear that these structure are non-nitrogen fixing (Truchet et al. 1989)...
Truchet, G., Barker, D. G., Camut, S., de Billy, F., Vasse, J., and Huguet, T. (1989). Alfalfa nodulation in the absence of Rhizobium. Molecular and General Genetics MGG, 219: 65-68.
No, nodules structures formed in soybean roots, if it were analysed and have anatomic characteristics similar to nitrogen fixing nodules, will only be formed in response to rhizobial bacterial cells. It is very common that seeds carry rhizobial cells and if the seed desinfestation process were not carefully done, this rhizobial contaminants will survive, grow on the substrate and infect plant roots. It is also important to make a carefull sterilization of the substrate to avoid rhizobial cells that may survive. Tindalization process (a series of autoclavation steps wih one day interval, repeated for 3 days) may eliminate this possibility.
Your question is really brain exercising . Please make a distinction between functional /active and non-functional/non-active nodules . There is one strain of rhizobia that forms non-effective nodules. There are lot of distinctions between effective and non-effective nodules with respect to both morphology and internal structures. In effective nodules , in bacteriod zone , color of internal tissue is red at young age , which alter turns brown , means not much change with age , in addition to Y-shaped bacteriod and remarkable area covered under nodulation tissue compared compared to non-effective nodules where nodules infected area is much less and bacteriod is spherical or elliptical in shape. Find below an excellent manuscript , how to identify the effective nodules from non-effective nodules.
Wishes..
whatever it is.. you got a response (+/-) from your research (plant microbial interactions)
1. Do you have the reproducible results of your research work ?.
2. then, identify the morphology and biochemical behavior of nodule/tumor
3. Expression may vary but everything is result only..Do the work properly with keen observations
Dear Hani Antoun,
I have autoclaved sand at 121 oC, 15 PSI for 1 and half hour in a conventional autoclave. nutrient media (Farhun) was also autoclaved, I have grown the plants at glass house at 24 oC at light but the control replication and inoculated with rhizobia replications were in a same room.
II agree to Dr. Anoop Kumar explanation. Definitely, there are functional and non-functional nodules. Nonfunctional nodules yield nothing.
Marc's answer is most likely correct. As for the soybean on agar, it may be that soybean roots are sensitive to red light as is Lotus japonicus. See: Suzuki et al. 2011. Proc. Natl. Acad. Sci. USA. 108:16837-16842.
1) As others suggested allready, a control should be made because infection with some Rhizobium bacterium is possible of course. So you should look at presence of bacteria in the nodules. This of course can be done by microscope and by plating a (eventual desinfected) and crushed nodule on a suitable medium. In absence of bacteria you may conclude spontanious nodulation.
2) To obtain nodulation on agar you could shield the root for light . In nature roots grow in darkness. See answer Ann Hirsch.
I would first run a parallel experiment on sand without autoclaving to check for the presence of rhizobia. Even in acid washed sand we got excellent chickpea nodulation. The autoclaved sand should have been plated to see if any rhizobia/agrobacteria persisted. Thirdly the surface sterilized soybean seeds should have been plated to check for presence of any epiphytic bacteria present. Fourthly the nodule should be sliced to see if they contained leghaemoglobin. Finally it also possible that there was aerial transfer of rhizobia/agrobacteria from air/water used for irrigation. Are you sure the conditions were absolutely sterile.? Only at this stage would I look for non-rhizobial mechanisms!
Well, I strongly recommend that your sand should be sterilised wet and well mixed, since sand is a bad heat conductor and most probably the sterilising process is just working in the outside regions of the bag where is packed your sand.
Also, try to apply copper sulphate solution (1 gr for each 10 liter) into your sand to inhibit the nodulation process.
Regards
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