RA 00110.pdf - OAR@ICRISAT

Role and Utilization of Microbial Associations to
Facilitate Pearl Millet Growth.
D . H . Hubbell 2
Abstract
Plants growing in a natural soil environment respond to prevailing chemical, physical, and biological
factors unique to that soil. The importance of root-microbe associations that enhance plant growth is
becoming increasingly apparent. This enhancement occurs with a wide variety of microbes in diverse
agronomic situations. Some of these beneficial associations, such as Rhizobium-legume, nitrogen-fixing
symbioses and mycorrhizal associations, have been recognized and agronomically exploited for many
years. The unique requirements which must be met to insure the successful establishment and function of
these associations are briefly reviewed. Other root-microbe associations are beneficial but the nature and
extent of the relationships are often much less obvious in terms of their structure and/or function. These
latter associations vary in direct proportion to the variability of their soil environments, which is enormous.
Soil factors can be controlled only within meager limits. The existing root-microbe associations, therefore,
are generally recalcitrant to agronomic exploitation through manipulation of soil or microbial factors.
Technology cannot at present supply requirements which have not been met naturally through evolution.
However, modern plant genetics research may, in the future, provide or enhance specific plant rhizosphere
environments which will select for ubiquitous, indigenous soil microbes with the inherent ability to form
growth-enhancing root associations.
1. Professor, Department of Soil Science, University of Florida, Gainesville, Florida 32611, USA.
ICRISAT (International Crops Research Institute for the Semi-Arid Tropics). 1987. Proceedings of the International Pearl Millet
Workshop, 7-11 April 1986, ICRISAT Center, India. Patancheru, A.P. 502324, India: ICRISAT.
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