BREEDING EGGPLANT (SOLANUMMELONGENA) FOR PROTECTED CULTIVATIONS: VARIETAL DIFFERENCES LINKED TO THE WATER STATUS OF THE PLANTS

Winter and spring cultivation of aubergines under glass can only develop if cultivars are produced which are adapted to this particular environment (low light intensity). Under these conditions the plants usually show excessive vegetative growth accompanied by flower shedding before or after anthesis.

We first established that, in a period of short days, cultivars from humid temperate regions (e.g. Japan) set their fruits much better than those from a dry climate (Mediterranean type) or from the tropics (e.g.S.Asia). The reverse was thrue in summer in the open, when the water demand was high.

We have therefore shown that the fruiting of all these cultivars can be improved by cultural practices which reduce the root system or diminish the water supply to the plant.

These facts lead us to suppose that the low potential evapotranspiration in the greenhouse can be responsible for too high a water potential in the plants, unfavourable to CO₂ assimilation (hydropassive stomatal closure).

We have shown that specific transpiration was highest in the cultivars best adapted to greenhouse culture. This phenomenon can be observed in many diverse conditions, in entire plants or in leaves cut when ETP is between 0.5 and 3 mm per day.

Fruiting does not take place when the dry matter content of standard leaves is less than 16–17% or when the water deficit of the same leaves is less than 3%.

The selection of varieties suitable for greenhouse culture could be directed to genotypes with a reduced root system and a high specific transpiration.