Measurement of chlorophyll fluorescence as a heat stress indicator in tomato: Laboratory and greenhouse comparisons

Chlorophyll fluorescence was measured under both laboratory and greenhouse conditions in an effort to develop a quick, reliable, and inexpensive labor atory procedure capable of predicting heat stress experienced by tomato (Ly copersicon esculentum Mill.) under greenhouse conditions. The laboratory te sts consisted of measurements of the ratio of variable to maximal chlorophy ll nuorescence (F-v/F-m) performed on leaf discs taken from whole tomato le aves and placed on a temperature controlled plate. Comparisons were made wi th greenhouse measurements of the same parameter conducted on intact leaves of whole plants exposed to different temperature treatments imposed by man ipulation of the aerial environment of the greenhouse. Dark adaption period s ranging from 15 min to all day in the greenhouse and temperature exposure periods ranging from 5 min to 60 min in the laboratory were compared to fi nd the best correlation between the two tests. Best agreement was obtained with 60 min treatment times in the laboratory and 60 min dark adaption peri ods in the greenhouse. F-v/F-m decreased quadratically with increasing leaf temperature in a similar fashion in both tests, suggesting that the labora tory approach can adequately predict plant response to greenhouse heat stre ss.