Future trends

Even though the results already available are very promising there is a long road in front of us for improvement. The examples discussed in this section are technically simple and in many cases they were providing only ‘proof of principle’. Almost all of those examples were ‘world firsts’ demonstrating the feasibility of gene inactivation by antisense techniques, ethylene biosynthesis inhibition by gene knockout, artificial endogenous enhancement of plant hormone levels and so on (Grbic and Bleecker, 1995; Hamilon et al., 1990; Oeller et al., 1991). Most of those experiments were not even designed to produce commercially useful crop varieties but to perform basic research on the roles of ethylene in fruit ripening, different hydrolases in fruit softening, cytokinins in leaf senescence, etc. Therefore we have to judge them for what they are; scientific experiments. Commercial applications will need a lot of refinement that will be possible only as a result of extensive basic research.

There are several constraints to the production of commercially viable crops engineered to provide better post-harvest characteristics.

• More basic research. There is a lack of understanding of the fundamental biochemical, cellular and molecular processes that take place in harvested tissues. Even though our knowledge is advancing at a very rapid pace we still need more research. Companies are too eager to cash in on the new technologies and many new products are being developed without a full understanding of the metabolical processes taking place and we are running the risk of developing products with unintended but potentially adverse agronomic characteristics. This problem is accentuated by recent government attitudes, reducing funds for basic research and pushing universities and government-funded institutions towards applied research that might generate full cost recovery.
• New genes. As our fundamental knowledge advances we will discover new genes that will allow better and more refined control of post-harvest processes. Instead of interfering with the whole ripening process we might decide to target very specific processes, such as the kinetics of sugar accumulation or fruit colour development. New genes are urgently needed to confer resistance to different post-harvest pathogens.
• More advanced technical tools. There is an urgent need for new developmentally regulated promoters that will allow the precise expression of genes in very specific tissues and developmental situations. Inducible promoters are also needed with cheap and easy means of induction in order artificially to turn genes on and off asrequired. More reliable gene knock out techniques such as homologous recombination need to be developed (although some promising resultsare already available in model systems). New, simpler and faster transformation systems are also needed.

The next generation of horticultural crops will need to target improvements that benefit consumers rather than producers. Longer shelf life is an obvious target but a complex objective. A longer-lasting fruit will need to ripen more slowly but at the sametime be protected against pathogens that very effectively attackripe fruits andwill also need to maintain not only its visual appeal but the ideal levels of proteins, vitamins, sugars and aroma.

Metabolic engineering will allow usto increase the nutritional value of fruits and vegetables by adding new components that are normally lacking in the traditional varieties. A good example is the recently developed ‘Golden Rice’ that has been enhanced with high levels of protein A (Ye et al., 2000). This new product has an enormous potential to alleviate the important problem of vitamin A deficiency in developing countries in which rice is the main component of the daily diet.

Biotechnology is emerging as a powerful tool for plant improvement. Althoughin its initial stages, the potential of applying biotechnology to enhance the agronomical and nutritional characteristics of crops is immense. We are seeing only the tip of the ice berg and we are bound to see huge developments in the next ten years.