Vegetable texture improvements through breeding and genetic engineering

Conventional breeding is based on crossing two cultivars with complementary traits and selecting within the segregating population. The development of improved hybrids using this process is very time-consuming and breeding has therefore concentrated on key agronomic traits. Breeding of vegetables specifically to obtain improved textural properties on processing has not been carried out to any significant extent. Although lead-in times can be dramatically reduced using genetic engineering approaches, the controversy surrounding genetically engineered foods needs to be resolved first. This controversy led to the removal of GM tomato puree from the UK market despite it being of better flavour and consistency, as well as being cheaper, than the non-GM puree. However, GM studies directed towards the development of more precise techniques for the manipulation and expression of transgenes should lead to new cultivars that have enhanced textural attributes being grown under controlled conditions.

Genetic studies are currently being employed to help uncover the genes that encode some of the cell wall-related biosynthetic and hydrolytic enzymes, and structural proteins. The latter have tended to be overlooked in the efforts to understand the functionality of the starches, polysaccharides and phenolic components of plants. For example, the hydroxyproline-rich glycoproteins, or extensins, a family of structural proteins present in plant cell walls, have long been considered to contribute to fruit and vegetable texture. They are essential and integral components of the macromolecular cell wall complex whose close association with sclerenchyma, lignin and fibres suggests that they play a structural role. Research is required to determine whether extensin synthesis leads to a stronger wall, and to see if an alteration of the amount in the plant cell wall affects its strength and rigidity. If it does, it may be possible to alter the properties of plant cell walls by genetically, or otherwise, manipulating the amount and type of extensin that is synthesised in the wall, thereby regulating processes in ripening/maturation in order to improve post-harvest textural characteristics.

The finding of a ferulic acid-specific peroxidase in sweet potato (Leon et al., 2002) could lead to studies with other vegetables designed to enhance the formation of stable diferulate crosslinks. Essential to such studies would be the knowledge gained on the phenylpropanoid pathway in plants.

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