Biotechnological Approaches to Enhancing Tropical Fruit Quality - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 373

Chapter 18
Biotechnological Approaches to
Enhancing Tropical Fruit Quality
Miguel Angel G omez Lim
18.1 Introduction
Most fleshy fruits exhibit a high metabolic activity when compared to other plant-derived
foods such as seeds. This metabolic activity continues during postharvest storage and makes
most fruit highly perishable commodities with short shelf life. It is estimated that around
50% of all fresh fruits and vegetables are lost due to such spoilage, but the exact figure
is difficult to determine (FAO, 2006). Fruit quality parameters such as deficiency in flavor
and aroma development, reduced shelf life, rapid softening and spoilage, sensitivity to low
temperatures, and increased susceptibility to pathogen infection are all a consequence of
postharvest deterioration and are major constraints to the availability of fruits. Postharvest
problems have been partially solved for many commercial crops (particularly those of
temperate climate) by harvesting them at the mature or green stage or by applying various
physical and chemical treatments to the ripe fruits and storing them at low temperatures
or in controlled atmospheres. However, many fruits, particularly tropical fruits, cannot be
handled successfully using these methods. Many tropical fruits harvested at full maturity
do not store well, but if harvested at the immature stage, they fail to ripen adequately. In
addition, they are very susceptible to low temperatures. Tropical fruits are important in the
diet of people in less developed countries, and are increasingly important as exports from
many of these countries.
Genetic improvement of tropical fruit crops has a range of objectives, including genera-
tion of cultivars with (a) tolerance of biotic and abiotic stresses, with reduced size and altered
shape (apical dominance) to increase orchard plant density, lower harvesting and pruning
costs, shorten the unproductive period, and improve availability of radiation at the canopy,
(b) simultaneous ripening for mechanical harvesting, (c) reduced juvenility period, and
(d) higher nutritional value (sugar, oil, vitamins, flavonoids, etc.) to improve the organolep-
tic qualities and shelf life of fruits.
Conventional breeding of perennial tropical fruit cultivars has been limited by their
long juvenile period (up to 20 years), low fertility, high levels of heterozygosity, various
levels of ploidy, polyembryony, complex intraspecific incompatibility relationships, and
severe inbreeding depression (Gomez Lim and Litz, 2004). Genetic diversity within many
tropical fruit crop species is unexplored, and most cultivars are either seedlings from un-
controlled pollinations or dooryard selections. The production of many tropical fruit crops
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