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 Jobs 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.
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Original posting: June 5, 1999.