Rhizosphere Microorganisms and Their Effect on Fruit Quality - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 369

Such changes influence the biosynthesis and deposition of carotenoids in chromoplasts the
degree of which determines the intensity of color development, the metabolism of sugars
and acids involved in flavor, and modifications to the structure and composition of the cell
walls affecting fruit texture (Hobson and Grierson, 1993). Thus, ripening influences sensory
attributes of fruit quality, such as flavor, appearance (shape, size, and color), and texture.
The main cause that reduces fruit quality is an excessive softening that influences
shipping, storage, and market value (Giovannoni, 2001). Therefore, textural quality is one
of the most important fruit properties to take into account along the production chain.
It has been shown that AMF inoculation has a positive effect on texture; for example,
bulbs of onion plants inoculated with Glomus versiforme are firmer than those inoculated
with Glomus intraradices (Charron et al., 2001), which may be due to an increase in cell
wall calcium content. In tomato, fruits of plants inoculated with G. fasciculatum showed
a penetration force 1.2 times higher than those in noninoculated plants, when evaluated
by a puncture test at different ripening stages, indicating that AMF improve fruit texture
(Mena-Violante et al., 2003). Not only plant inoculation with AMF enhances tomato fruit
texture, but also the use of PGPR. Tomatoes from plants inoculated with B. subtilis were
firmer than those from noninoculated plants (Mena-Violante and Olalde-Portugal, 2007).
It is well known that the modifications of the structure and composition of the cell
walls affect fruit texture (Hobson and Grierson, 1993). These changes are due to the ex-
pression of genes, such as 1-aminocyclopropane-1-carboxylate synthase gene (ACS) and
1-aminocyclopropane-1-carboxylate oxidase gene (ACO), involved in the ethylene biosyn-
thesis (Yang and Hoffman, 1984), and polygalacturonase gene (PG) related to cell wall
breakdown (DellaPena et al., 1986), among others. Thus, to look more closely at the my-
corrhizal effect on the fruit, mRNA levels of PG and ACO were examined. A decrease in
the abundance of the transcripts of the both genes was observed when compared to that in
fruits of noninoculated plants (Mena-Violante et al., 2003).
All these results have revealed that the symbioses between microorganisms and plants
seem to be more complex than it was suspected. Given the role of PGPR and AMF influ-
encing crop quality, the question arises how quality can be enhanced. Further investigation
should be conducted to understand the basis of the variation in the quality of horticultural
products, in order to improve prediction of commodity behavior and ensuring high quality.
17.5 Conclusions
Due to a greater health consciousness among the public, an increasing demand for high-
quality products necessitates the development of novel technologies using mycorrhizal
organisms for enhancing produce quality and shelf life to satisfy the consumers. Moreover,
because of current public concerns about the environment, more attention is now being given
to the organic production of fruits and vegetables in response to the growing goal to reduce
nitrogen and phosphate fertilization levels in agriculture. Alteration of product character-
istics due to preharvest factors strongly determines postharvest quality and the consumer
satisfaction. The results presented here show changes of quality attributes with respect to
preharvest biotic factors such the inoculation of plant roots with PGPR or AMF. Using
such information, new strategies and technologies such as the use of biofertilizers could
be applied to agricultural practices to improve product quality and build environmentally
friendly agrosystems.