Cultivating tomato under water and saline stress

Although the effect of water stress and saline stress have been widely studied in tomato plants growing under semi-arid environments, little is known about the interactive effects of the nitrogen supplied during episodes of water stress or about the effect of the application of amino acids in tomato cultivated using saline water. Losses due to blossom-end rot (BER) are common in the tomato plantations where waters with a high salt content are used. It seems that BER (Figure 1) is related not only with one factor but by interactions between water availability, salinity and nutrient ratios in the root zone, air humidity, and inadequate xylem tissue development in the fruit when the plant is exposed to increased salinity. The appearance of BER is related to a decrease in the absorption and translocation of calcium (Ca), due, among other factors, to excessive salinity in the soil solution. The incidence of this disorder is greater as the Ca content in the solution decreases. However, BER is common in highly saline conditions even when the Ca needs of the plants are totally provided for, and the application of Ca at the beginning of cultivation (Franco et al., 1994) or the increasing of the level of irrigation (Franco et al., 1999) do not completely eliminate the disorder. On the other hand, products containing amino acids and low molecular weight peptides, called protein hydrolysates, used to complement fertilisation with mineral elements to regulate the plant water balance, have been effective in order to correct BER. Amino acids can play an important role in the osmotic adjustment of the plant in saline cultivation conditions. Proline, particularly, has been mentioned as cytosolute in the adaptation of some plants to osmotic stress (García et al., 2006). The aim of the four studies summarised in this paper was to study the effects of mineral nutrition and the amino acids inclusion in irrigation solutions on the cultivation of tomato under water and saline stress