RESPONSE OF NON HEATED PLASTIC COVERED GREENHOUSE TOMATOES DURING THE COOL SEASON AND UNDER TWO DIFFERENT NATURAL VENTILATION METHODS

High air relative humidity is a major problem in non-heated tomato greenhouses in Portugal owing to the favourable conditions for botrytis development. An experiment was carried out to test the effect of permanent night ventilation on tomato growth and yield, and on the incidence of Botrytis cinerea, by comparing the behaviour of a tomato crop planted in two similar non-heated plastic greenhouses: Night closed greenhouse (NCG) with the windows opened in the morning and closed in the afternoon; Night opened greenhouse (NOG) with the windows kept opened day and night until the end of the experiment.

Permanent ventilation slightly decreased air temperature integral and had a clear effect on the reduction of the periods with air relative humidity above 85%. There were no differences on the number of flowers, number of fruits, average fruit size, and tomato fruit yield between NCG and NOG. The number of fruits with botrytis was 10–12% of total tomato fruits in NCG and only 1% in NOG. Night ventilation proved to be an interesting means of controlling botrytis on tomato without affecting plant growth and yield, under mild-winter climates when non-heated greenhouses are used.