| Abstract |
The main purpose of this guidebook is to assist in the identification of diseases and of pathogens causing diseases in cereal crops. It is not intended as an authoritative text on diseases, nor does it provide any new information on diseases or diagnostic techniques. Its primary audience includes breeders, agronomists, and young scientists-in training, especially in developing nations, who are responsible for identifying and recording trial data, screening segregating populations for disease resistance, and verifying the disease reactions of various types of plant material in their programs. At many of the research stations in developing countries, the responsibility for recording disease reactions and making selections belongs to breeders, production agronomists, and their assistants. Most of them are familiar with conspicuous diseases, such as the rusts, smuts and mildews, and feel confident that the data they report are reliable. Their confidence tends to fade, however, when faced with the need to identify foot rots, head blights and leaf blights. This guidebook is intended to help cereal crops researchers improve their knowledge and increase their confidence in dealing with the plant diseases they encounter. The diseases affecting bread wheat, durum wheat, barley, oats and triticale provide the main focus of this guidebook. Triticale is now emerging as a commercial food and feed crop in some countries and production appears destined to increase. Because it is a relatively new crop, published information on the reaction of triticale to specific diseases is meager at this time. Important observations by CIMMYT personnel and national program cooperators regarding diseases associated with triticale are included here. The scope of this guidebook is limited to the use of simple techniques helpful in identifying some of the most common causal organisms of cereal crop diseases and associated saprophytes. It is recognized that many pathogens, such as those causing foot rots and viral diseases, require more elaborate techniques for accurate diagnosis. There are many excellent books available to those who wish to delve deeper into the study of plant diseases. As a start, the Compendium of Wheat Diseases (1977) and the Compendium of Barley Diseases (1982), published by the American Phytopathological Society are especially recommended. In an effort to minimize the confusion that currently exists in the taxonomy of fungi, bacteria and viruses, the most commonly used generic and species names are used in this publication. The perfect or sexual stage is footnoted and discussed in those instances where it serves as an important stage in the initiation, recognition or spread of the disease. Considerable variability exists in nature among microorganisms, just as among higher plants. In the past, there has been a tendency among mycologists to give species status to minor morphological variants or forms that are pathogenic on different host species. Greater awareness among scientists of the natural variation that exists among all life forms has led to the establishment of fewer species groups. This trend is appreciated by many biological scientists outside the realm of taxonomy. |
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