- CHILLING INJURY IN TOMATO FRUIT 245
fruit, downregulation of gene expression is possibly a function of the
chilling duration to which fruit are exposed. Rugkong et al. (2011)
found that tomatoes stored at 3◦C for 4 weeks showed reduced expres-
sion ofPSY1andCRTISOcompared to tomatoes at harvest. Expres-
sion of these genes increased after fruit were transferred to 20◦Cfol-
lowing 1 week at 3◦C. When fruit were stored for 2 weeks, they
showed increased expression of these genes during ripening at 20◦C
but the expression was lower than in fruit stored for 1 week. Sim-
ilarly, downregulation inGGPPS2expression was observed with a
longer chilling period. These results agree with the idea that for a short
duration at low temperature tomatoes may be able to develop red color
whereas for exposure to chilling temperatures for a longer duration
they may fail to do so and instead show uneven blotchiness or yellow
coloration.
A phenotype that shows uneven blotchy red coloration during normal
ripening has also been reported, although the cause of blotchy ripen-
ing is not clearly understood (J. Giovanonni, personal communication).
Blotchy areas are usually confined to the outer pericarp walls, but locu-
lar walls can also be affected in extreme cases (Yahia and Brecht 2012).
Some preharvest factors including low light intensity, cool tempera-
tures, high soil moisture, high nitrogen, and low potassium or combi-
nations of these factors, are thought to contribute to blotchy ripening
(Yahia and Brecht 2012). Blotchy areas of fruit walls contain less organic
acids, dry matter, soluble solids, and starch than in normal fruit (Adams
et al. 1978), indicating some kind of disrupted metabolism. Molecular
studies suggest that over-expression of a fruit ripening booster (FRB)
gene, an auxin response factor, caused accelerated and patchy ripen-
ing (Breitel 2012). Downregulation ofDR12(developmentally regulated
clones), another auxin-response-factor homolog, in tomato resulted in
a pleiotropic phenotype including dark green and blotchy ripening
fruit (Jones et al. 2002). While upregulation of some genes may cause
a blotchy phenotype, it remains unclear whether blotchy uneven ripen-
ing induced by chilling damage is related to expression of those genes.
Blotchy ripening caused byFRBappeared to have quite sharp bound-
aries between green and red tissues (Breitel 2012), unlike CI where the
color was more diffuse with patches ranging from yellow to red on fruit
surfaces.
Overall, when tomato fruit is exposed to low temperature for a cer-
tain period of time, the fruit exhibits abnormal color development. Fac-
tors inducing blotchy color development may include modification of
organelles such as chloroplasts or the inhibition of enzyme activities
in the biosynthetic pathway to lycopene or degradation of chlorophyll,