Submitted to: Advances in Endophytic Research
Publication Type: Book / Chapter
Publication Acceptance Date: March 7, 2013
Publication Date: January 1, 2014
Citation: Bacon, C.W., Hinton, D.M. 2014. Microbial endophytes: future challenges. In: Verma, V.C., Gange, A.C., editors. Advances in Endophytic Research. XXIII edition. New Delhi, India: Springer. p. 441-451. Interpretive Summary: Endophytic microorganisms are those that dwell within plants and confer some positive benefits. Such benefits include disease suppression, insect resistance, and environment stress relief as drought and temperature tolerances. All plants are naturally infected with endophytes and the tendency not is to dissect these from plants and utilize them both in native host and in agricultural uses in crop plants for biological improvements. Fuel for the use of this group is based on the environmental concerns for the use of highly toxic chemical pesticides. The authors of this paper were invited to review and comment on the present and future status of both bacterial and fungal endophytes as biocontrol agents and other uses of this group of endophytic organisms. The major thrust of this work was to address the concerns that have not been addressed scientifically or politically that are required before advancements and exploitations for endophytes can be fully utilized. In this work we identified and addressed several scientific and political concerns that should be considered during various research activities by scientist universally. Positive research results were acknowledged, questions posed that should further address research on key issues. It was concluded that the use of these organisms is on firm grounds and that their use in the future is secure and their exploitation will be successful.
Technical Abstract: Endophytes are represented by a diverse group of prokaryotic (bacteria or cyanobacteria) or eukaryotic (fungi or parasitic vascular plants) organisms that form life-long associations within tissues of plants. Ecologically, these associations are usually viewed as advantageous although in some instances we also know that there are some disadvantages that may be in the direction of either the plant or the microorganism. Nevertheless, most of the associations are viewed as sources of secondary metabolites capable of serving as novel medicinals and agrichemicals. It is this area that serve to stimulate the large research investigations from all parts of the planet. Since the work demonstrating the production of ruminant deterrents in pasture grasses in 1977, much emphasis has been placed on these and many other microbial endophytes. Still, after several decades of active research involving an international cadre of research scientists, we have not learned the essentials necessary to predict nor maintain associations, but have developed some important hypotheses and most of these have not been tested. Of consequence is the central dogma that these associations are of merit and play an important role in plant defense. Thus, the hypothesis of defensive mutualism serves to drive the thinking of so many endophytic systems. There are however objections to this hypothesis, although poorly supported and not replaced by another rationale for existence. Regardless of the raison d’être, if endophytes are to be used for biotechnological explorations, we must put into place several basic concepts to assist in understanding microbial endophytes that will aid in making intelligent uses of such mutualists. Many attempts have been made at surrogate transformations of endophytic systems with the hope of obtaining specific material for specific areas. However, this is not always the case as some endophytes are mysterious and appear not to effect a change in the host. The manner in which specific endophytes of vast genetic diversity effect host fitness traits is unknown nor how long term or stable are these effects within a population. Are these traits environmentally triggered or are they manifested regardless of the environment? The challenges as we see them are multifaceted. These include an understanding of the genetics nature of fungi, how endophytes communicate and partition themselves within hosts, and how do these biotrophic fungi obtain nutrients, and is nutrient acquisition key to the final effects observed? Are there basic differences between bacterial endophytes and fungal endophytes? What influence the host interactions to produce the desired effects, and how is the stability of the system affected. These and many more future challenges must be defined before we can truly say we have made advances in endophytic research.