Increasing vegetative growth, yield and seed quantity in tomato by inducing plant vigour at the earliest seedling stage

The complete immersion of very young tomato seedlings just after germination (about 5 days after sowing) into osmotic solutions (-0.5 MPa) generated by the non-permeant compound PEG-6000, during a period of 5 days, promotes vegetative growth during seedling establishment, which can also be reflected in plant vigour, crop yield and seed quantity. In the case study of the indeterminate commercial tomato hybrid Durinta F1, the vegetative biomass of osmoprimed plants at flowering under hydroponic conditions was up to twice as great as the control plants. Similar results have also been obtained with the dwarf determinate cultivar, Micro-Tom. In this case, the early vegetative vigour was also reflected in chlorophyll status and the total and fruit biomass at the end of the life cycle. Moreover, the seeds produced by the osmoprimed plants weighed more than the control ones and the plants obtained from them also showed a higher vigour. In spite of the earliness and relatively short duration of the seedling osmopriming treatments, the adult plants showed differences in the endogenous hormonal content that could help explain the improved vigour. Thus, the leaf concentrations of the growth-promoter and/or antisenescent hormones indolacetic acid and zeatin were 2-4 times higher than in the control plants. However, the concentration of the stress-related hormone ABA, a putative growth inhibitor, was also 8 times greater in the osmoprimed plants. The growth retardant and senescence inductive signal ethylene precursor ACC was reduced.