Greenhouse crops have quite some flexibility in growing at different temperatures, but the marketable yield will be higher when optimal temperatures are applied. It needs a long experience with a particular crop to find the ultimate optimal values, but as a general guideline a tomato crop grows well at an average diurnal temperature around 17 °C in poor light conditions (DL smaller than 10 mol PAR/(m2 day)) and at an average temperature around 22 °C in abundant light conditions (DL above 25 mol PAR/(m2 day)).
As light is abundant in Saudi Arabia, the general guideline suggests to grow tomatoes with preferably a diurnal mean temperature between 20 and 220C. Experience from past years shows that the crops indeed perform well under these conditions, but there was often still a notable loss of marketable yield due to Blossom End Rot (BER). The plant physiological background of the occurrence of BER is still not clear, but it is related to stress and climate conditions do have an effect. As lower temperatures are likely to result in a decreased stress level, lowering the temperatures might reduce the occurrence of BER. As this will increase the marketable yield, the additional costs of lowering the temperature might be outweighed by better benefits. To test this hypothesis the performance of a number of tomato varieties was observed in a one year tomato cultivation cycle in two temperature regimes.
