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Resume' of cassava study for Jamaica, July 12, 1954

In order that any group of plants useful to man may be most fruitful, it is essential to utilize the most productive plants of that group. Often plants are maintained merely because of some preference of an emotional nature, not for reason of most productivity.

It is impossible to make a wise choice of plants for a particular purpose unless a thorough knowledge of all clones, varieties, or species of the group under consideration is available. It is possible, with a thorough classification, to proceed with the process of selection for any purpose, whether for studies of an agronomic nature or for hybridization to produce combinations of useful characteristics or other such studies.

To provide a basis for such activities as mentioned above, an effort is being made to classify all the variants of cassava, (Manihot utilissima). The method of classification is essentially one of morphology, comparing structures of the variants to determine relationships amongst them, but the biochemical information of carbohydrate, protein and fat content are also valuable in such work. Although stem, leaf and root colors can be useful in certain cases, it is more important to base a classification on more stable characteristics such as type of branching, height of plant, shape of leaf, number of lobes of leaf, root shape and size; size shape and number of leaf bases or scars on stems, etc. No characteristic must be overlooked, no matter how insignificant it may seem, for these structures are our best indicators of the gene complement of the plants.

Although morphological rather than color characteristics are most important in classification, it is still important to record the information as to colors of various parts. These will sometimes give some preliminary indication of relationship, and it is essential that these observations must be recorded at the time of observation in the field. If not recorded at the moment all other data are collected, but memory is relied upon to give this information at a later date, the data as to colors of parts, maturity of fruit or other part is very liable to error.

In order that permanent records of the variants be kept, a system of photography and herbarium specimens of each variant must be employed. The type of specimen made (what parts to include in the specimen) and the kind of photographs to be made must be determined by an intense study of the whole group under study. No two groups (other than closely related groups) will have the same requirements to provide the soundest data for classification. This can be accomplished best by constant observation in the field, and cannot be expected to be done in a very short period. The value of "museum" plots in such a study cannot be over-estimated; these provide a constant source of new information.

These considerations apply to my study of cassava. They are of equal value in the study of any particular group. It is a valuable technique if employed consistently and competently.