SALINITY EFFECTS ON THE XYLEM VESSELS IN TOMATO FRUIT AMONG CULTIVARSWITH DIFFERENT SUSCEPTIBILITIES TO BLOSSOM-END ROT

The number and size of xylem vessels in the vascular bundles at the pr oximal and distal positions of both pericarp and placental tissues of tomato fruit were measured in three cultivars with different susceptib ilities to blossom-end rot grown at two salinity levels. While the tot al number of vascular bundles in the pericarp is greater than in the p lacenta, the average bundle size in the distal pericarp is larger than that in the distal placenta. Salinity reduced the total bundle area i n the distal tissue more in the susceptible cultivars, i.e. Calypso an d Spectra than in the less susceptible cultivar, Counter. Both the num ber and size of xylem vessels in the bundles of proximal placenta tiss ue were greater than in the proximal pericarp, while the reverse was t rue 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 sa linity in the placenta of the susceptible cultivars. As the number and the size of xylem vessels in the bundles of the distal placenta of 'S pectra' at high salinity was the lowest of the three cultivars, the xy lem transport of Ca in this tissue may also be the lowest.