1985 Volume 53 Issue 4 Pages 419-426
Using 3-year-old wase satsuma mandarin (Citrus unshiu Marc.) trees grafted on trifoliate orange (Poncirus trifoliata Raf. ), 8-month-old natsumikan (Citrus natsu-daidai Hayata) seedings, and 6-month-old avocado (Persea americana Mill.) seedings, the effect of low root temperatures on cold hardiness was examined in relation to whole-plant water status, changes in carbohydrate and proline concentrations, and endogenous hormone activities in plant parts.
Transpiration and leaf water potential in all species were reduced at low root temperatures (5° and 13°C), leaf water potential being most markedly affected at the lower temperature.
Total sugars and proline in the leaves, stems, and roots accumulated while starch was reduced at low root temperatures.
Cold hardiness in all species was greatly augmented at 5°C root temperature compared to 13°C and the control.
Endogenous gibberellin and cytokinin activities in the roots (trifoliate orange) of wase satsuma mandarin were increased when exposed to 5°C root temperature.
In conclusion, in both citrus species and avocado lowering root temperature restricts water uptake and then induces cold hardening together with accumulation of sugars and proline in the plant tissues.