Spermosphere Effect

Spermosphere Effect

	Spermosphere Effect When a seed is sown in soil, certain interactions take place between the seed-borne microflora (due to the secretion of certain chemicals by the seed) and the soil-borne microflora which influence the quality of the spermosphere at that condition. When the seed is pre-treated with a fungicide or with any other biological agent, this influences such interactions to a great extent, as for example, the fungicide may totally alter the seed microflora (by inhibiting some fungal flora and increasing some other bacterial flora). This could also influence the nature of microflora that is about to colonise the root (rhizosphere) once the radical emerges out of the seed. Thus by manipulating the spermosphere, one changes the rhizosphere also.
When a seed carrying a natural or altered (by manipulating) load of microbes is sown, certain microbes are activated and others are suppressed. Usually, the microbes that are artificially loaded onto the seed are more dominant flora of the seed and this enables the scientists to beneficially alter the spermosphere of a particular seed, as in Rhizobium, Azotobacter and Azospirillum coated seeds. These organisms get established on the root surface of the germinating seed and benefit the plant (by fixing nitrogen directly into the roots).
Along with spermosphere microflora, the soil-borne flora may also get activated and compete with the former (for nutrition and space). The qualities of chemicals excreted by the germinating seed decides the final quality and quantity of the microflora around the seed. Usually microbes move from the spermosphere to the rhizosphere within three days. Various chemical treatments of the seed (organo-mercurial pesticides) definitely change the rhizosphere micro flora of the seedling thus indicating the plant-root-microbes interactions in the soil through the seed.
When the seed is internally or externally infected by certain pathogenic microorganisms (smut spores), this definitely alters the quality and quantity of the spermosphere and rhizosphere microflora (again through competition). When such a suspected seed is pre-treated with plant protection chemicals, the competition is eliminated (since the pathogen gets killed) and hence the seed gets coated with harmless microbes.
	When the seed is pre-treated with organic manure (cow dung) where the seed gets coated with saprophytes present in the manure there is competition between pathogens and non-pathogens (saprophytes present in the organic manure) and depending on the efficiency of one group, one is suppressed and gets eliminated. For example, a seed-borne pathogen of cotton Xanthomonas campestris pv malvacearum is controlled when the seed is pretreated with cow dung slurry containing a lot of saprophytes

To understand the effect better, we can take this example. When a seed infected with a pathogen is sown in unsterile and sterile soil, there is intense spermospheric effect (enough to suppress the pathogen) in the former whereas in the latter case, pathogen becomes highly virulent (since there is no competition by other organisms)

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