Vol. 81 No: 2

Title:
The influence of root zone temperature on growth and flavour precursors in Allium cepa L.

Authors:
TIMOTHY W. COOLONG and WILLIAM M. RANDLE

pp: 199-204

Abstract:
The effects of changing root zone temperature (RZT) while maintaining a constant foliar temperature were tested. ´Granex 33` onions (Allium cepa L.) were grown at RZTs of 12°C (± 3.0°C), 21°C (± 0.5°C) (control), or 34°C (± 0.7°C) while maintaining the air temperature at 21°C (± 0.5°C). Plants were harvested at maturity and bulbs evaluated for their growth and flavour characteristics. Bulb fresh weight was highest at an RZT of 21°C and lowest for plants grown at other RZTs. Total bulb-S was no different for the 12°C and 21°C treatments, but was significantly lower for bulbs grown at an RZT of 34°C. Bulb soluble solids contents and total pyruvic acid (pungency) levels responded similarly, increasing between 12°C and 21°C, and falling in the 34°C treatment. Concentrations of trans-S- 1-propenyl-L-cysteine sulphoxide, and two peptide intermediates, 2-carboxypropyl glutathione and γ-glutamyl propenyl cysteine sulphoxide were highest at 21°C, and lowest at 34°C. The adverse affect of the high RZT (34°C) treatment was significant, leading to short, highly-branched roots and was clearly detrimental to the growth and development of onion plants, as well as reducing sulphur allocation to the flavour biosynthetic pathway.

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