Chikelu Mba

An EST resource for cassava and other species of Euphorbiaceae.

Cassava (Manihot esculenta) is a major food staple for nearly 600 million people in Africa, Asia, and Latin America. Major losses in yield result from biotic and abiotic stresses that include diseases such as Cassava Mosaic Disease (CMD) and Cassava Bacterial Blight (CBB), drought, and acid soils. Additional losses also occur from deterioration during the post-harvest storage of roots. To help cassava breeders overcome these obstacles, the scientific community has turned to modern genomics approaches to identify key genetic characteristics associated with resistance to these yield-limiting factors. One approach for developing a genomics program requires the development of ESTs (expressed sequence tags). To date, nearly 23000 ESTs have been developed from various cassava tissues, and genotypes. Preliminary analysis indicates existing EST resources contain at least 6000–7000 unigenes. Data presented in this report indicate that the cassava ESTs will be a valuable resource for the study of genetic diversity, stress resistance, and growth and development, not only in cassava, but also other members of the Euphorbiaceae family.

Use of AFLP Markers in Surveys of Plant Diversity

The collection of the available range of genetic variation in a gene pool, usually made of the cultivated species and their undomesticated relatives, is referred to as a germplasm collection. Increasingly, discriminator data generated using molecular genetic markers are either complementing or completely replacing those from morphological characters (known as descriptors) in surveys of genetic diversity. In addition to highlighting the state of knowledge on the specific applications of amplified fragment length polymorphisms (AFLPs) in surveys of plant genetic diversity, an attempt at a brief description and comparison of the different marker systems in use has also been made in this chapter. We have also attempted a description of the AFLP marker technology, its strengths and weaknesses, methodologies for generating reliable AFLP data, available resources (hardware, software, consumables); the kinds of questions for which AFLP data provide valid answers; and data management options. This chapter also highlights salient considerations that would guide decisions on the adoption of molecular marker assays.