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Effect of rootzone temperature on the growth, photochemical light use efficiency and rootzone ethylene accumulation of recombinant inbred lines of lettuce in a tropical greenhouse

Choong, T. W., He, J., Qin, L., Lee, S. K., Dodd, I. C.
Acta horticulturae 2017 no.1176 pp. 9-16
aeroponics, chlorophyll, crops, electron transfer, energy, ethylene, ethylene production, genotype, greenhouses, heat tolerance, inbred lines, leaf area, lettuce, photochemistry, plant growth, roots, temperature, tropics
Optimising rootzone temperature (RZT) of aeroponically grown crops can prevent the excessive production of ethylene by the roots, which would otherwise limit plant growth. Since energy is required to cool the RZ when a temperate crop (such as, lettuce) is grown in the tropics, this experiment aimed to (1) identify variation in thermotolerance within a population of recombinant inbred lines (RILs) of lettuce, and (2) study the productivity, light use efficiency, and RZ ethylene accumulated of selected RILs. 104 RILs and their parental lines were grown aeroponically in a tropical greenhouse under cool-RZT (C-RZT) of about 25°C and fluctuating ambient-RZT (A-RZT) of 29-36°C, at spray intervals of 5 min. A thermotolerance index was calculated as the ratio of shoot fresh weight (SFW) at C-RZT to A-RZT. A heat-resistant (HR) and heat-sensitive (HS) RIL were then selected and grown, with their parental lines, under the same RZ conditions. SFW and specific leaf area were significantly higher (p‹0.05) in C-RZT, than A-RZT, for all genotypes. There was higher non-photochemical quenching of chlorophyll fluorescence and lower electron transport rate for HS-RIL, under A-RZT than C-RZT. Ethylene concentrations per unit root fresh weight (RFW) were significantly higher at 1400 h than at 1100 h, with the greatest difference in HS-RIL. Consistently, there were much higher concentrations of RZ ethylene accumulated in A-RZT than C-RZT per unit RFW, for all genotypes. Thus, the poorer growth of HS-RIL than HR-RIL at high A-RZT may have resulted from the negative effects of RZ ethylene accumulation.