Studies based on X-ray photographs were conducted to predict the morphology of tomato (Lycopersicon esculentum Mill.) seedlings at transplanting stage. Currently, seed-lot quality of tomato seeds for growing commercial transplants is determined with grow-out tests in the greenhouse because the standard germination test fails to predict the percentage of normal or usable transplants (UTs). These grow-out tests, however, are difficult to standardize. An X-ray evaluation procedure is presented as an alternative. X-ray images nondestructively provide information on embryo size and morphology and the amount of endosperm and the area of free space. These parameters correlate well with the morphology of 14-day old seedlings. Cotyledon morphology has the highest correlation with the percentage of UTs. A test based on the evaluation of X-ray images, classifying the cotyledon morphology and seed free space, predicts the percentage of UTs more accurately than the currently used germination test. A second method based on an equation that uses the probabilities of all X-ray categories proportionally predicts the percentage of UTs of primed seeds more accurately than the first method. Selecting individual seeds based on X-ray images has the potential to raise the percentage of UTs of seed lots. On the average, the percentage of UTs of control seeds was 22% higher after hand selection based on X-ray evaluation. Primed seeds gave 12% higher results. Hence, X-ray analysis can predict seedling performance and enable the selection of high-quality seeds.

Morphological changes in tomato (Lycopersicon esculentum Mill. cv. Moneymaker) seed during osmopriming and imbibition (‘hydropriming’) were followed using X-ray photographs. Embryo, endosperm and free space areas were measured. Both osmopriming and hydropriming resulted in free space development (+ 8.1% and + 10.8% of the whole seed planar area, respectively), almost all at the cost of the endosperm area. Planar dimensions of whole seeds were relatively constant and the dimension perpendicular to the planar surface, the thickness, could account for the volume increase of primed seeds reported in the literature. In dead seeds, only a small amount of free space developed while the planar area of the seed remained the same. In the imbibing viable seeds no deterioration of endosperm could be detected until the moment of root protrusion.Seeds which were osmoprimed directly after harvest, i.e. in the fresh state, did not showthe induction of any free space, while free space developed normally after dehydration and a second priming treatment. Apparently, a dehydration step prior to the priming treatments is required for the development of free space in osmo- or hydroprimed seed.X-ray photographs of hydroprimed seeds showed that the radicle tip adhered tightly to theendosperm cap. This results in various forms of damage to the root tips upon redrying. Priming did not introduce cotyledon abnormalities.

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