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This document is a report on the proceedings of an Expert Consultation on Biodeterioration of Cassava held at FAO Headquarters, Rome from 11 to 13 December 1991. The meeting was sponsored by FAO and cosponsored by the Rockefeller Foundation. It provided a forum for scientists to review the biochemistry associated with post-harvest deterioration of the cassava crop and to explore the possibility of applying modern molecular biology to develop varieties with superior storability.
Cassava is a major subsistence crop for over 500 million people in developing countries. However, the rapid deterioration of fresh cassava roots after harvest is a severe problem to producers, consumers and marketers irrespective of the scale of operation. The roots begin to deteriorate as quickly as 24 hours after harvest and most cultivars deteriorate within two to three days. This situation is due to physiological deterioration which leads to substantial quantitative and qualitative post-harvest losses of the roots causing high production, processing and marketing risks.
Current post-harvest management practices used to extend the storage life of cassava roots were reviewed and were considered either technically or economically unsuitable for most marketing needs. Although the mechanism involved in post-harvest deterioration has yet to be adequately elucidated, it was felt that the problem could be resolved considering that, when the crop is left unharvested, the roots could be "stored" on the plant successfully without deterioration for over one year.
The genetic variability for post-harvest deterioration was reviewed and it was found that the evaluation method used was considered insufficiently precise to critically assess the trait. It was considered necessary to define and develop a screening assay to quantify post-harvest physiological deterioration in the available germplasm collection to determine genetic variability and stability.
Conventional breeding was considered as a possibility using recurrent selection methods. However, tremendous efforts would be required for incorporating the trait into different cultivars without altering the characteristics of the parent genotypes.
Genetic manipulation using molecular techniques was considered most appropriate in resolving the problem. Nevertheless, there is no information available on genes involved in the biochemical pathways that are associated with physiological deterioration in cassava. However, because of their implication in the process of post-harvest deterioration, the genes and gene products associated with the synthesis and degradation of phenylpropanoids were considered principal targets for study and manipulation.
Many of the phenylpropanoids associated with wound-induced responses have been isolated and characterized from various plants. These genes could be used to isolate the corresponding genes from cassava. These studies could then provide an insight into the deterioration process and would assist in developing strategies for genetic manipulation approaches. The introduction into cassava of discrete gene constructs by genetic manipulation offers the unique advantage of adding new traits to elite genotypes without altering other desired characteristics. It was envisaged that FAO would collaborate with appropriate institutions to facilitate a comprehensive initiative in this research area.
FAO considers that the review process and interpretation on the problem of post-harvest deterioration of cassava by the experts at the consultation merits publication as a proceedings in that it is the only document that deals with an indepth analysis of this important area.
H. de Haen
This document resulted from an Expert Consultation on the Biodeterioration of Cassava organized by E.A. Kueneman, Senior Officer and W.B. Charles, Root Crop Officer, Field Food crops Group (FFCG), Plant Production and Protection Division (AGP).
The proceedings were prepared under an author's contract with Dr J.E. Wenham, National Research Institute, UK, with technical support from the FFCG, Crop and Grassland Service, AGP.
The organizers and author would like to express gratitude to all those who participated in the meeting and in particular to Drs Richard Jefferson, Carlos Inglesias, Clair Hershey, Jorge Mayer and Mr Ulrich Kleih for their substantial contribution during the preparatory phase of the publication.
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