Agriculture Reference
In-Depth Information
2
Tomatoes
Elhadi M. Yahia and Jeffrey K. Brecht
INTRODUCTION
Worldwide importance
The cultivated tomato that was carried by Spanish
explorers from Mexico to Europe in the early sixteenth
century was a rough-skinned, small-fruited type, and the
earliest written account of it in Europe by Matthiolus in
1544 describes a round, yellow fruit (Gould 1992). The
tomato slowly gained favour over succeeding centuries,
but by the eighteenth century breeding of new cultivars in
Europe was well underway. Tomatoes are now one of the
leading horticultural crops worldwide in terms of value
and amount consumed. The FAO reports world production
of tomatoes in 2009 as 152 956 115 tonnes, with China,
the United States, India, Turkey, Egypt and Italy the top
six producers, respectively (FAOSTAT 2009). In the
United States more than 80% of the tomatoes grown are
consumed as processed tomato products (USDA ERS
2006). The fresh fruit is very sensitive to improper
handling, storage and shipping conditions, and therefore
proper pre-harvest and post-harvest handling are critical
for high product quality, a prerequisite to successful
marketing (Yahia
et al
. 2005).
Origin
The wild tomato,
Solanum lycopersicum
L., is native from
the coastal plain to the foothills of the Andes of western
South America, centred in Peru and extending north to
central Ecuador and south to northern Chile (Peralta
et al
.
2005). It was later distributed by indigenous peoples into
what are now Mexico, Colombia, Bolivia and other South
American countries (Rick & Holle 1990). Currently, this
species is known only from cultivation and escapes and is
grown worldwide from sea level to 4000 meters. A number
of other related species are also found in the same area
of South America, several of which, such as
S. pennellii
,
S. cheesmaniae
and
S. pimpinellifolium
, are able to cross-
pollinate with
S. lycopersicum
(Stevens & Rick 1986).
Types of tomatoes
The tomato fruit is a berry consisting of two to several
carpels with seeds borne on placental stalks within locules
and surrounded by the locular gel, all contained within a
fleshy pericarp (Figures 2.1 and 2.2). Modern commercial
tomato types for fresh and processed use are mostly red
and include a variety of different fruit types from small,
'cherry' and 'grape' tomatoes so named due to their
similarity in size and shape to those fruits, to large, round
tomatoes, pear-shaped tomatoes and oblong 'roma' or
'plum' tomatoes. Tomato varieties are bred specifically for
consumption as either fresh tomatoes or processed tomato
products. Processing requires varieties that contain higher
dry matter content than varieties for the fresh market.
POST-HARVEST PHYSIOLOGY
AND FRUIT QUALITY
Ethylene and fruit ripening
Tomato fruit show a climacteric pattern of respiration,
and therefore ripening can be initiated before or after
harvest. Ethylene plays an important role in the ripening
of tomatoes (Andrews 1995; Lelievre
et al
. 1997). Ethylene
