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Effects of light intensity and duration on physiology, productivity, quality and tipburn in lettuce
Author
Ng, Eliz Si Qi
Supervisor
He, Jie
Abstract
This project investigated the impacts of light intensity and duration on physiology, productivity, quality as well as the mechanism(s) leading to leaf tipburn using two lettuce varieties with distinct head morphology - butter head lettuce (Lactuca sativa L. cv. Canasta) and Cos lettuce (L. sativa L. cv. CL - 2741). The lettuce plants were grown under three different light intensities and photoperiods: L1 (250 µmol photon m-2s-1, 20h, daily light integral, DLI = 18 mol m-2 day-1), L2 (250 µmol photon m-2s-1, 12 h, DLI = 10.8 mol m-2 day-1) and L3 (160 µmol photon m-2s-1, 20 h, DLI = 10.8 mol m-2 day-1).
Canasta grown under L1 showed a significantly higher shoot fresh weight (FW), total chlorophyll (Chl), carotenoids (Car), Ribulose-1,5-Bisphosphate Carboxylase Oxygenase (Rubisco) content, total reduced nitrogen (TRN), total soluble protein (TSP) concentrations. Stomatal conductance (gs), transpiration (Tr), internal CO2 (Ci) were not significantly different in Canasta grown under the three different conditions, before the occurrence of tipburn. Only photosynthetic CO2 assimilation rate (A) and light- saturated photosynthetic CO2 assimilation (Asat) were significantly lower in Canasta grown under L3. Although the shoot FW of Cos grown under L1 was the highest, there were no significant differences in most physiological parameters studied, except that plants grown under L3 showed a significantly lower A and Asat. Both varieties grown under L1 had better quality with a lower concentration of NO3- but higher total ascorbic Acid (TASc) and phenol in the leaves. The concentrations of dietary minerals (Mg and Fe) were similar for both varieties regardless of light conditions while K concentration was significantly higher in Canasta under L2 but lowest in Cos under the same condition.
Results from present study also suggested the involvement of different mechanisms in the formation of tipburn for the two varieties. During the maturity stage, Canasta exhibited both inner leaf tipburn and outer leaf marginal necrosis while inner leaf tipburn was prevalent in Cos and outer leaf marginal necrosis was largely absent. Furthermore, marginal necrosis appeared along the entire Canasta leaf while it was confined to only the tip for Cos. The onset of tipburn in Canasta seemed to be initiated by low Ca2+ concentration. On the contrary, Cos grown under the three different light conditions had similar Ca2+ concentration before the onset of tipburn although Cos grown in L1 and L3 showed more severe tipburn compared to L2. Cos contained higher Ca2+ concentrations in both inner and outer leaves compared to Canasta, which may have caused less severe tipburn in this variety. The areas which exhibited tipburn also showed a lower Ca2+ concentration for both varieties. Although the Ca2+ concentration seemed to play a role in tipburn progression, tipburn was not formed due to an absolute Ca2+ concentration as Cos showed a marked higher Ca2+ concentration in tipburn area. By growing both varieties of lettuce under L1 light condition, growers would be able to harvest Canasta within 28 - 35 days and 21 - 28 days for Cos lettuce with high yield and better quality without tipburn.
Canasta grown under L1 showed a significantly higher shoot fresh weight (FW), total chlorophyll (Chl), carotenoids (Car), Ribulose-1,5-Bisphosphate Carboxylase Oxygenase (Rubisco) content, total reduced nitrogen (TRN), total soluble protein (TSP) concentrations. Stomatal conductance (gs), transpiration (Tr), internal CO2 (Ci) were not significantly different in Canasta grown under the three different conditions, before the occurrence of tipburn. Only photosynthetic CO2 assimilation rate (A) and light- saturated photosynthetic CO2 assimilation (Asat) were significantly lower in Canasta grown under L3. Although the shoot FW of Cos grown under L1 was the highest, there were no significant differences in most physiological parameters studied, except that plants grown under L3 showed a significantly lower A and Asat. Both varieties grown under L1 had better quality with a lower concentration of NO3- but higher total ascorbic Acid (TASc) and phenol in the leaves. The concentrations of dietary minerals (Mg and Fe) were similar for both varieties regardless of light conditions while K concentration was significantly higher in Canasta under L2 but lowest in Cos under the same condition.
Results from present study also suggested the involvement of different mechanisms in the formation of tipburn for the two varieties. During the maturity stage, Canasta exhibited both inner leaf tipburn and outer leaf marginal necrosis while inner leaf tipburn was prevalent in Cos and outer leaf marginal necrosis was largely absent. Furthermore, marginal necrosis appeared along the entire Canasta leaf while it was confined to only the tip for Cos. The onset of tipburn in Canasta seemed to be initiated by low Ca2+ concentration. On the contrary, Cos grown under the three different light conditions had similar Ca2+ concentration before the onset of tipburn although Cos grown in L1 and L3 showed more severe tipburn compared to L2. Cos contained higher Ca2+ concentrations in both inner and outer leaves compared to Canasta, which may have caused less severe tipburn in this variety. The areas which exhibited tipburn also showed a lower Ca2+ concentration for both varieties. Although the Ca2+ concentration seemed to play a role in tipburn progression, tipburn was not formed due to an absolute Ca2+ concentration as Cos showed a marked higher Ca2+ concentration in tipburn area. By growing both varieties of lettuce under L1 light condition, growers would be able to harvest Canasta within 28 - 35 days and 21 - 28 days for Cos lettuce with high yield and better quality without tipburn.
Date Issued
2018
Call Number
QK757 Ng
Date Submitted
2018