Introduction
Pearl millet [Pennisetum glaucum (L.) R.Br.] has traditionally
been an important grain, forage, and stover crop primarily in
the arid and subtropical regions of many developing countries.
As pearl millet cultivation expands into nontraditional areas
in temperate and developed countries, production constraints from
diseases are assuming greater importance. Dissemination of accurate
information on diseases of the crop has not kept pace with the
increased interest in pearl millet as a viable crop in nontraditional
areas.
The literature concerning pearl millet diseases is often confused
and contradictory. Many treatises on pathology are composed of
information on diseases of "millet," which is a broad
category of any number of small-seeded grasses. Millets include
pearl millet (Pennisetum glaucum); proso, browntop, or
broomcorn millet (Panicum miliaceum); little millet (P.
sumatrense); foxtail millet (Setaria italica); finger
millet or ragi (Eleusine coracana); teff (Eragrostis
tef); fonio (Digitaria spp.); guinea millet (Brachiaria
deflexa); barnyard or japanese millet (Echinochloa crus-galli);
jungle rice millet (E. colonum); kodo millet (Paspalum
scrobiculatum); and Job’s tears (Coix lacryma-jobi).
Many diseases of the different millets are quite host-specific,
particularly those caused by obligate parasites. Compounding the
difficulty of identifying diseases of pearl millet, it is not
unusual for a pathogen to be attributed as the cause of a disease
on "Pennisetum" without a specific host designation.
Considerable diversity exists within the genus Pennisetum,
which consists of over 100 species having chromosomes numbers
in multiples of x=5, 7, 8, or 9 (Oliver
1934).
In addition, pearl millet itself has undergone several changes
in nomenclature, which can also lead to some confusion. Throughout
the literature it is variously referred to as P. glaucum, P.
typhoides, P. americanum, or other names depending on the
accepted nomenclature at the time. It is also known by several
different common names including cumbu, bajra, and cattail millet.
Because of all these variables, attempts to identify the diseases
of "millet" without strict differentiation of the host
have resulted in sometimes confused and misinformed quarantine
and regulatory policies. This bulletin was written in an attempt
to provide some scientific clarity for use in making policy decisions.
Most of the following information was derived from the published
scientific literature. When possible, I examined the original
publications rather than relying on conclusions and information
attributed to earlier scientists by others in more recent publications.
Because of the purpose of this document, descriptions of pathogen
characteristics and the diseases they cause are necessarily brief.
For positive identification of pathogens, reference to the appropriate
citations is advised. Designated host ranges can be inconsistent
among pathogens. Cross-inoculation studies have not been performed
with most of these pathogens, and host specificity and strain
specificity are difficult to determine from the literature. Common
names of additional hosts were sometimes used instead of binomial
nomenclature, and some binomial nomenclature has been changed
since publication of the original works. Geographic distributions
may vary depending on whether the pathogen has been observed on
pearl millet or on other hosts. The accuracy of the geographic
distribution on all hosts depends on the degree of host-pathogen
specificity, which, as addressed above, is not well defined for
most of these pathogens. For the most part, information on seed
transmission of diseases does not exist. Seed infection is well
documented for several pathogens; however, transmission to the
seedling has not often been demonstrated. Despite these problems,
some important attributes of known pathogens can be summarized
(table 1).
Various regulatory agencies have been concerned about some
diseases that are not well documented in the literature. These
putative pathogens and their actual role in causing diseases of
pearl millet are sometimes vague but are discussed in an attempt
to address these concerns where questions of thoroughness may
arise.
United States
Department of Agriculture
Agricultural
Research Service
The material on this page is in the public
domain.
Original posting: June 5, 1999.
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