Considerable efforts toward understanding the ecology and management of PGPR
have been directed, yet their development as inoculants remains a considerable
challenge. The rhizospheric community is highly complex, comprises of a myriad
of organisms interacting in various ways, acting upon each other and reacting to the
external environment. Several isolates of Bacillus spp. have been developed as
BCAs of plant pests and pathogens. However, to be used as successful BCAs a
greater understanding of their ecology is desired. In this context, greater knowledge
of the diversity, distribution, and physiology of Gram-positive species will be
helpful for identification of new strains compatible with the cropping systems.
Paramount to success of PGPR is a need to better understand the ecology of
rhizobacteria either indigenous or introduced within the rhizosphere. Exploration
and identification of traits involved in the ability of certain bacteria to establishthemselves into the rhizosphere at levels sufficient to exert effects on plant growth,
effectively compete with the indigenous microflora, cooperatively interact with
other beneficial members of rhizospheric biota, and understand the mechanisms
(signaling, growth promotory actions, disease suppression etc.) that occur between
plants and bacteria are also required.
Clearly, the taxonomic and physiological diversity of Bacillus spp. appears
capable of reducing the disease incidence or severity but also indicates that much
remains to be done on the mechanisms by which these bacteria promote plant
growth. The molecular mechanisms involved in the root colonization are under
study nowadays and advancement in the molecular and genomic tools offers new
possibilities for improving the selection, characterization, and management of
biological control. Development of proteomics and functional genomics will be
helpful to determine and follow expression of crucial genes of BCAs during mass
production, formulation, and application. Transformation of BCAs by inserting
genes that improve the tolerance of antagonists to abiotic stresses, such as increased
tolerance or resistance to cold, heat, drought, high salinity, heavy metal rich soils,
or acidic soils, etc., could be another exciting and challenging task and may provide
with better opportunities to implement the concept of biocontrol in the field under
the dynamic natural environments