59-05-032 Proceeding

59 Proceedings of the Princess Maha Chakri Sirindhorn Congress Figure 2 Effect of heat stress on chlorophyll fluorescence parameters in 4 lettuce cultivars. (a) PSII operating efficiency ( Φ PSII). (b) Maximum quantum efficiency of PSII (Fv/Fm). (c) Minimal fluorescence in a dark-adapted state (Fo) (d) Maximal fluorescence in a dark-adapted state (Fm). Values are means ± SE (n = 4). Different letters indicate a significant difference (P < 0.05) Figure 3 Effect of heat stress on fresh (a) and dry weight (b) of 4 lettuce cultivars. Values are means ± SE (n = 4). Different letters indicate a significant difference (P < 0.05).