Thats a very good question . I strongly feel, these endophytic bacteria continue to reside inside the plant , since they are more comfortable inside the plant than residing in soil.

Many factors affect PGPR effect expression in soil, such competitive (bacteria compete with the indigenous microflora for space and resources), antagonism effect, physico-chimical propreties of soil, inoculum density, method and moment of inoculation, Crop-specific (Certain bacteria do best in specific with certain crops), etc.

Read this Paper Article Transmission of Bacterial Endophytes

Hi Wai Wai Mom,

Very good question.

We should know that there are two types of endophytes and this depends on their life cycle. the obligatory endophytes are those that remain within their plant host throughout their life cycle without leaving it. this kind is the most unknow and the most difficult to study because it very hard to isolate them as they are biotrophic microorganisms (they live depending on life cells). Besides, there are the non-obligatory endophytes that can live both outside and outside their plant host. their life cycle is between the plant and the soil. their behaviors depending on which stage of the life cycle they live. the most studied example is the Rhizobium and azospirillum species: both can play the role of endophytes and PGP Bacteria.

Please find attached an article discussing Rhizobium as PGPR.

I hope this brought some Ideas.

Good luck

Endophytic bacteria enter into the plant tissues from soil/ soil application or through Seed treatment. It secrets enzymes that degrade the cell wall of pathogens and secrets growth hormone for enhancing the growth of plants and make them resistant to diseases.

Endophytic bacteria return to soil from plants or roots it secrets siderophores which is essential for absorption of iron from soil even at lower concentrations. Iron is essential for metabolic activities of plants. Growth hormone also secreted by them.

Las bacterias endófiticas retornarían al suelo en el momento que se realice la incorporación del material vegetal después de la cosecha al suelo, o por la perdida de raíces de las plantas al retirarlas del cultivo. Posteriormente, de encontrar nuevamente un huesped compatible se produciría el endófitismo.

Las bacterias endófitas son habitantes del suelo pero una ves que entran dentro del tejido vegetal viven bien de las secresiones de las plantas sin causarles daños, pueden regresar nuevamente al suelo cuando los restos del tejido son incorporados al suelo. hay algunas esperiencias con hongos endofitos que actuan como represor de ataques de hongos patógenos cuando logran ingresar primero al tejido vegetal

Role and Functions of Endophytes depend on the following; (1). how competitive the endophytes are that able to compete with diverse indigenous microflora for space and other limited resources in soil. (2). antagonism effect to diverse microorganisms in the soil (3)physico-chemical propreties of soil (e.g. soil pH) i, (4) Inoculum density, (5) methods and movements of inoculation and (6).Crop-specificity.