Partial defoliation and runner removal affect runnering, fruiting, leaf photosynthesis and root growth in ‘Toyonoka’ strawberries for subtropical winter production

Removing runners and old leaves are two major routine and labor consuming tasks in winter strawberry (Fragaria × {ptananassa} Duch.) production in subtropics. However, the potential negative effects of defoliation has not been evaluated. We studied the effects of partial defoliation and runner removal on plant growth, leaf photosynthesis (Pn), and yield in field-grown or potted strawberry plants (‘Toyonoka’). The treatments were consisted of partial defoliation by removing leaves older than 45 days (PD), removing all runners (DR), PD + DR, and the control (CK). Treatments were applied weekly from mid-November until early March. DR promoted yield and number of fruits for the first harvest cycle but not for the second harvest cycle. Multiple linear regressions indicated that leaf area had greater overall effects on runnering and fruit traits than the existence of runners. The leaf Pn was not responsive to DR but a transient increase in Pn was consistently detected on the remaining leaf after each PD treatment. The compensatory increase in Pn was only detectable within 1 days after each PD treatment, indicating that the actual compensation for partial loss of functioning leaf area may be negligible. Crown dry weight was less affected by canopy manipulation than growth and dry weight of roots. Our results indicated that yield of strawberry in Taiwan’s subtropical climate can be improved by removing runners while maintaining a greater leaf area with less severe defoliation.