Abstract
June-bearing strawberry plants (Fragaria xananassa, cv. Toyonoka) were grown in a greenhouse kept at 25 0/20 °C (day/night) and a 15-hr photoperiod (forcing) under one of the following treatments : 1) all unfolded leaves (OL) were removed at the onset of forcing (DOL), 2) all leaves which unfolded during the forcing period (NL) were removed as they emerged (DNL), 3) both OL and NL were removed (DAL), and 4) undefoliated control. Changes in the carbohydrate levels were determined in the roots and leaves on days 0, 21 (full bloom for the primary truss), and 63 (picking date for the primary truss).
1) Petiole length of the first two NL was shorter in DOL than it was in undefoliated control. On the other hand, leaf area did not differ significantly between the treatments, irrespective of leaf positions.
2) Dry weight of fruit on primary truss (total weight of 7 fruit) on day 21 was greater in DNL than it was in undefoliated control. However, the weight on day 63 did not differ significantly among the treatments.
3) In DAL, fruit of the primary truss grew normally during the first 21 days of forcing. However, when stipules and sepals were removed and peduncles were shaded on day 21, all plants died within a week.
4) Reducing sugar, sucrose, and starch levels of roots decreased rapidly during the first 21 days of forcing, they decreased slightly thereafter, irrespective of the treatments. Starch level on day 63 was lower in defoliated plants than it was in undefoliated control.
5) The present study reveals that the stored reserve carbohydrates in the strawberry roots are consumed during the early phases of plant growth after forcing.
