Differential response of photosynthesis in greenhouse- and field-ecotypes of tomato to long-term chilling under low light.

Three greenhouse- and four field-ecotype varieties of domestic tomato (Lycopersicon esculentum) were compared for the sensitivity of their photosynthetic apparatus to chilling under low light intensity. After chilling at 12/7 degrees C under 100 micromolm(-2)s(-1) of light for 10 days, they were allowed to recover at 25/18 degrees C and 600 micromolm(-2)s(-1) of light for 10 days. For both pre-chilling and recovered plants, greenhouse-ecotype varieties did not necessarily show higher net CO(2) assimilation rate (A), quantum yield of electron transport at PSII (Phi(PSII)) and photochemical quenching (q(P)) than field-ecotype varieties. However for the post-chilling period, greenhouse-ecotype varieties, exhibited higher A, and Phi(PSII) values than field-ecotype varieties. The difference in Phi(PSII) was found to be largely due to q(P). The absence of ecotypic differences in pre-chilling plants indicates that the trait was not expressed constitutively, but relied mainly on adaptation/acclimation mechanisms. Greenhouse-ecotype varieties were able to adapt to low temperature and low light more quickly, and then exhibited higher A, Phi(PSII), q(P) values and greater re-growth capacity after chilling than field-ecotype varieties. Plant re-growth capacity after chilling was highly correlated with Phi(PSII) and q(P) measured in chilled plants, suggesting the usefulness of Phi(PSII) and q(P) measured at low temperature after defined chilling stresses as screening indexes for chilling tolerance in breeding programs.