Salinity effects on the xylem vessels in tomato fruit among cultivars with different susceptibilities to blossom-end rot

The number and size of xylem vessels in the vascular bundles at the proximal and distal positions of both pericarp and placental tissues of tomato fruit were measured in three cultivars with different susceptibilities to blossom-end rot grown at two salinity levels. While the total number of vascular bundles in the pericarp is greater than in the placenta, the average bundle size in the distal pericarp is larger than that in the distal placenta. Salinity reduced the total bundle area in the distal tissue more in the susceptible cultivars, i.e. Calypso and Spectra than in the less susceptible cultivar, Counter. Both the number and size of xylem vessels in the bundles of proximal placenta tissue were greater than in the proximal pericarp, while the reverse was true in the distal tissue. Salinity reduced the total xylem area in the bundle of the distal tissue significantly, particularly in 'Spectra'. Thus, the total xylem area in the distal layer was reduced more by salinity in the placenta of the susceptible cultivars. As the number and the size of xylem vessels in the bundles of the distal placenta of 'Spectra' at high salinity was the lowest of the three cultivars, the xylem transport of Ca in this tissue may also be the lowest.