THE SUSCEPTIBILITY OF MODERN TOMATO CULTIVARS TO BLOSSOM-END ROT IN RELATION TO SALINITY

Three cultivars, Counter, Calypso and Spectra, were grown in NFT at a range of salinities (electrical conductivities of 5, 10 and 15 mS cm-1) in two successive crops during the year. The incidence of blossom-end rot (BER) in 'Calypso' and 'Spectra' was substantially higher than in 'Counter' at all salinities. In the early crop, 'Calypso' had the highest incidence of BER at 10 mS cm-1, of which the proportion of international BER was greater than in 'Spectra'. In the late crop, 'Spectra' had a higher incidence of BER than 'Calypso,' and a higher proportion of external BER. In the early crop, the incidence of BER in both cultivars grown at 10 mS cm-1 was higher than those at 15 mS cm-1, mainly due to an exceptionally high incidence of internal BER. In the late crop, however, the reverse was true. 'Counter', which is not susceptible to BER, had a higher shoot dry weight than the two BER susceptible cultivars. Nevertheless, 'Calypso' and 'Spectra' set more fruit in the lower and upper trusses respectively. A high incidence of BER was related to a high number of fruit set in the susceptible cultivars. Both the Ca content and the daily rate of Ca accumulation in the fruit were reduced by salinity, but no differences between cultivars were observed. The distal placenta and locular tissues had the lowest Ca content in the whole fruit and appeared to be the site of the earliest symptoms of BER. The interaction between cultivar and salinity affecting the Ca content of these tissues was not significant. The causes of susceptibility to BER in tomato are discussed.