Influence of nighttime electrical conductivity of substrate solution on fruit cracking and blossom-end rot of greenhouse tomato in the tropics

The influence of the electrical conductivity (EC) of the substrate solution during the night, i.e., moderately high EC ("HEC", 3.0 dS m(-1), full solution) and low EC ("LEC", 0.5 dS m(-1), CaCl2 or Ca(NO3)(2) and H3BO3), on the incidences of blossom-end rot (BER) and fruit cracking (FC) in greenhouse tomato (Solanum lycopersicum, L.) was investigated and compared with a control without additional nighttime fertigation (NTF). In three consecutive experiments conducted in Central Thailand between November 2005 and March 2007, additional NTF cycles were applied for 1 h after the regular daytime fertigation (EC 1.5/1.8 dS m(-1), prior to/after the first harvest). In the first experiment (dry season 2005/06), two cultivars with either low (FMTT 260) or high (King Kong 2) susceptibility to BER and FC were used. The total amount of fruits affected by FC or BER was 4- and 10-fold, respectively, higher in King Kong 2, but the relative response to NTF was similar in both cultivars. Therefore, in the following experiments only FMTT 260 was planted. In all experiments, NTF exerted significant effects on the uptake and allocation of water and mineral elements to the fruits and the proportions of fruits affected by BER and FC. The overall proportion of nonmarketable fruits was not significantly reduced, neither through LEC nor HEC because a decrease in BER by LEC and in FC by HEC was counteracted by enhanced FC in LEC and BER in HEC. It is concluded that under the tropical climate conditions of Central Thailand leading to high losses of marketable fruit yield through BER and FC, an integrated approach is required combining an optimized management of the fertigation system and particularly the selection of genotypes highly tolerant of BER and FC.