Yellow shoulder disorder in tomatoes under natural and controlled conditions
Romero-Aranda, R.1, Fernández-Muñoz, R., López-Casado, G., and J. Cuartero.
Department of Plant Breeding, Estación Experimental La Mayora, Consejo Superior de
Investigaciones Científicas, 29750 Algarrobo-Costa, Málaga, Spain. 1 E-mail: rromero@eelm.csic.es
Yellow shoulder disorder (YSD) of tomato fruit is a yellow or yellow-orange shoulder region
separated from the normal red surface color by a distinct line demarcation (Picha, 1987). Incidence
of YSD is high in greenhouse tomato crop production at southeastern Spain, where marketable-
yield losses caused by YSD can exceed 60 % (López-Casado, 2002). The purpose of the
experiments described here was to clarify the role of high temperature and light as causal agents of
YSD in tomato fruit.
Cultivars ‘Kalohi’, ‘Moneymaker’, and ‘Corbarese Severino’, and commercial F1’s ‘Rambo’,
‘Naomí’, and ‘Josefina’ were used in experiments carried out in a polyethylene greenhouse from
January to June 2004.
In order to separate possible effects of high temperature from those of high solar radiation,
two different artificial heating treatments were applied during wintertime. Firstly, immature green-
fruits were daily applied a hot air flow with a hand-dryer during 2 h around midday until normal red
matured stage was reached in the non-heated fruit area. Fruit surface temperature was measured
with an infrared thermometer. It ranged from 39-48°C on treated fruits and 23-33°C on non-treated
ones. Defective coloration was only observed in treated fruits but it was different from the typical
YSD since it consisted of a clearly defined area of a gray-white color. Secondly, a few plants of the
experiment were moved to a small glasshouse where air temperature at midday was increased to
40°C. Surface temperature of fruits of those plants were similar to that of hand-dryer treated fruits.
Under these low-radiation, high temperature conditions, the ripening process was accelerated but
no YSD or any other color injury was observed.
Experiments were also carried out under natural conditions. At different times of the growing
season, incidence of solar radiation on fruits was modified either by pruning leaves or by covering
fruits with aluminum foil. These treatments were imposed at immature green-fruit stage. Also, the
natural orientation of fruits in the plant was changed placing the style-end of the fruit facing upward.
From end-January to mid-April, 80% of tomatoes from ‘Kalohi’ presented well-defined YSD
symptoms. The YSD area was about 30% of the fruit surface and the border with the red fruit
surface was well defined. At that time, no YSD was observed on fruits of the other five tomato
genotypes. Later, as spring progressed to summer, incidence of YSD in ‘Kalohi’ decreased
meanwhile a significant increase was recorded in most of remaining genotypes. YSD incidence for
the fruit harvested in May was 70%, 58%, 40%, 30%, and 20% in ‘Naomí’, ‘Rambo’, ‘Kalohi’,
‘Corbarese Severino’, and Josefina, respectively. No YSD was recorded in May on ‘Moneymaker’
fruits.
From May to June, YSD incidence under natural greenhouse conditions was higher on fruits
placed on south and west sides of plants rows. YSD was observed on fruits more directly exposed
to solar radiation but also on fruits shaded by foliage. In contrast, no YSD was observed in the fruits
covered with aluminum foil. As a reference, midday surface temperatures in late-June were ca.
46°C for fruits exposed directly to solar radiation and ca. 39°C for fruits both shaded by foliage and
covered with aluminum foil. Fruits whose natural orientation in the plant was
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