The effect of water supply of seedlings cultivated in different substratesand rasing systems on the bio-morphological and plant-physiological parameters of lettuce

Wood fiber substrates perform well for lettuce seedlings production in spee dling trays compared to standard commercially used press pots as well as gr owing media on peat base. Wood fibers contain a high air volume to allow hi gher levels of water tension without danger of water saturation in the subs trate. For optimum growth they require a "high" matric potential. For culti vation of lettuce seedlings irrigation pulses at phi = -30 to -50 hPa are r ecommended in ebb and flood cultivation systems. This will provide good roo ting and the least amount of proline, an indicator for plant stress. Accumulation of proline in lettuce seedlings could only be proved under con ditions of visible stress symptoms. Not only water tension, but also the su bstrates in raising systems influence the free content of proline. At phi = -200 hPa proline in lettuce seedlings cultivated in a peat based press pot s were ca. 40 % lower compare to seedlings in a wood fiber substrate in spe edling trays. The difference in proline content between well-watered and st ressed seedlings was smaller than with tomato transplants. Also, the correl ation between proline content of lettuce seedlings and critical water tensi on for irrigation pulses was lower than with tomato transplant. The lettuce plants performed well after transplanting and no differences de rived from seedling-treatments were recorded.