ISHS Acta Horticulturae 287: II International Symposium on Protected Cultivation of Vegetables in Mild Winter Climates
EFFECTS OF STRESSFUL AND UNSTRESSFUL LOW TEMPERATURE ON VEGETABLE CROPS: MORPHOLOGICAL AND PHYSIOLOGICAL ASPECTS |
| Author: | T. Franco |
| Abstract:
The mediterranean area is a typically warm one with mild winter and rain distributed around the year. This makes it possible to grow fruit crops such as citrus, olive and fig, and some vegetables such as tomato, pepper, eggplant, melon, any time of the year using very simple shelters in the coldest period. Tomatoes hold the first place among vegetable crops grown in these countries either in or out of season crops. Peppers, cucumbers and melons are the highest temperature demanding plants, therefore they can be grown only in a certain warm area using a skillful calendar of cultivation or more sophisticated greenhouses. In the mediterranean area light is not, in general, a limiting factor, except sometimes in winter. On the contrary, despite the mild climate, a wide day-night temperature excursion occurs especially in winter or early in the spring. This induces physiological and morphological modifications and affects the productivity of plants. Temperature strongly influences plant growth, and its conditioning largerly increases the management costs of greenhouse crops; therefore the control of this environmental factor should be carefully evaluated through technical devices or cropping cycle. As far as I am aware, today we have very sophisticated greenhouses where all the climatic parameters can be easily controlled. However these modern technologies are generally justified when high income-crops are grown. On the contrary, low income-crops, such as vegetables, require simple shelters and cropping strategies for energy saving. For these reasons vegetable crops are mainly cultivated in the southern mild area. Greenhouse crops often suffer from abiotic stresses such as temperature, light, humidity, which are scarcely maintained at the optimal level. Any change of these climatic factors may induce a different plant reaction according to the intensity of variation. From a biological point of view, stress can be defined as "an environmental factor capable of inducing potentially injuriousstrain in plants" (Levitt, 1972). The first effects of a stress (drought, flooding, cold, heat) on plants is the reduction or the cease of growth, followed by severe injury and even death, according to the intensity and duration of the stress. On the other hand, as far as crop plants are concerned, biological stresses can be ineffective on productivity (yield or net income) and, in some cases, may enhance it. Therefore, from an agronomic point of view, these external factors may be defined "unstressful". Talking about low temperature stress on vegetable crops grown in the mediterranean area, we refer mainly to the range of temperature usually indicated as chilling (0–10 °C). These conditions are in fact | |
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