Effects of Chilling on the Length and Number of Epidermal Cells in Petioles of Strawberry Plants during the Rest Period.

Abstract

On 1 November, 1989, resting strawberry plants of 'Nyoho', 'Hokowase', and 'Morioka 16' (low, medium, and high chill-requiring cultivars for the breaking of the resting state, respectively) were kept at 4°/3°C (day/night), under a 12-hr photoperiod for 0, 18, and 37 days (chilling treatment), and then transferred to a growth chamber maintained at 24°/20°C (day/night) under a 12-hr photoperiod (forcing treatment).When 'Nyoho' strawberry plants received no chilling (unchilled control treatment), final petiole length and leaf area increased at higher leaf positions than did those of lower leaf position. However, such an increase was not distinct in the other 2 cultivars.When the plants were chilled, the petiole length, the mean epidermal cell length of a petiole (petiolar cell length), and the leaf area of plants increased significantly, reaching maximum between the 3rd to 6th leaf which emerged during the subsequent forcing period, and then decreased at higher leaf positions. However, the number of epidermal cells per petiole length (number of petiolar cells) increased at higher leaf positions, irrespective of cultivars and duration of chilling.Petioles of chilled plants were longer than those of unchilled plants, irrespective of leaf positions, because the former had longer cells than those of the latter. The contribution in petiole length by cell division was greater at higher than at lower leaf positions.Leaves which differentiated after the plants were chilled had petioles which were longer than those at the same position on unchilled plants.