1966 Volume 35 Issue 2 Pages 106-110
To clarify the mechanism of frost hardening on citrus trees, the relation between frost hardiness and contents of sugars, starch and nitrogen compounds in leaves was studied with Satsuma orange trees. Eighteen young orange trees grafted on trifoliate root stocks were used in this experiment. They were cultured in the green house during the beginning of June, 1963 to the end of October, 1964. Three plots were settled on October 31, 1964; that is“Keeping warm”- kept in the green house-, “Non-treatment”-kept in the out-door field (110 hours at below 0°C)-, and“Chilling”-kept in the cold chamber at the temperature of -1 to 0°C for 400 hours from November 6 to December 27 and then moved in the out-door field untill next January 23 (460 hours in totals at below 0°C). Samples were collected from each plot on December 28 or 29, 1964, for quantitative analysis of carbohydrates and nitrogen, for microscopic examination of intercellular starch contents, and for determination of osmotic concentration in leaves and stems.
After the determination, it was found that contents of glucose and osmotic concentrations in leaves on a trees of“Chilling”plot were highest, that of“non-treatment”plot was next, and that of“keeping warm”plot was lowest. On the contrary, the contents of starch in leaves on a tree of“chilling”plot were lowest and so on.
Trees of all plots were met and frozen with the low temperature of -5.0 to -7.5°C for 9.5 hours on January 24, 1965, to confirm the effect of pretreatments on frost hardening. As a result, a comparable difference was found among the plots; that is, 95 to 100 percent of trees on“keeping warm”plot were frozen, 85 to 100 percent of trees on“nontreatment”plot, and 30 to 50 percent of trees on“chilling”plot were frozen.
