Agriculture Reference
In-Depth Information
13
Genetic Diversity of Tropical Fruit
National Bureau of Plant Genetic Resources, Pusa Campus,
New Delhi, India
13.1 Introduction
13.2 Diversity in Climacteric and Non-
climacteric Fruit Ripening
Botanically, a true fruit is a mature ovary;
however, other fl ower and infl orescence
parts also form a part of the fruit in some
taxa. There is a vast diversity of fruits in
angiosperms. Fruits are classifi ed based on
their morphology and development: simple
(fruit from a single ovary); accessory (fruit
from inferior ovary); aggregate (fruit from
several separate ovaries); and multiple
(fruit from several independent fl owers).
Simple fruits can be dry or fl eshy and
result from the ripening of a simple or
compound ovary with only one pistil. Dry
fruits may be dehiscent (opening to
discharge seeds) or indehiscent (not
opening to discharge seeds). Ecological
parameters and the habitat of a plant play
an important part in the fate of a fruit,
facilitating the reproductive mechanism,
dissemination of seeds and eventually
propagation of the species.
Ripening is the fi nal stage of fruit
development and makes the fruit com-
mercially important and brings about
changes in cell-wall structure, ultra-
structure and texture, the conversion of
starch to sugars, alterations in pigment
biosynthesis and accumulation, and
heightened levels of fl avour and aromatic
volatiles (Giovannoni, 2001; White, 2002).
Fruit are classifi ed as climacteric or non-
climacteric on the basis of respiration and
ethylene evolution patterns (Table 13.1) as
described by Hiwasa-Tanase and Ezura
(Chapter 1, this volume). The molecular
distinctions underlying climacteric versus
non-climacteric ripening are poorly
understood. Nevertheless, it seems likely
that, at least in instances of the same or
closely related species with examples of
both climacteric and non-climacteric types,
non-climacteric phenotypes may represent
mutations in ethylene synthesis or
signalling as opposed to more complex
distinctions. Crossing of a non-climacteric
melon with a climacteric one indicated
that the climacteric character is genetically
dominant and conferred by two duplicated
loci. However, other experiments made by
crossing two non-climacteric melons have
generated climacteric fruit, indicating that
different and complex genetic regulation
exists for the climacteric character.
13.3 Fruit Diversity in Tropical Fruits
There is a vast diversity of tropical fruits in
Asia, America and Africa. Tropical fruit
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