The effect of LED interlighting on yield components in blackberry

MSc-thesis abstract (submitted 4 September 2017): High market price and low availability of local winter and spring production has stimulated production of blackberries in glasshouses in northern latitudes. For this production, light is the main limiting factor for growth and development.
Therefore, our objective was to understand the potential of LED interlighting to improve blackberry fruit yields.

In a glasshouse experiment, three treatments were applied to blackberry plants:
(1) only natural lighting (no SL), (2) two interlighting modules (2IL) or 3) four (4IL) interlighting modules (95% red (667nm) and 5% blue light (554 nm).
The average supplemental light intensity was 27 (2IL) and 52 ╬╝mol m-2 s-1 (4IL). IL was applied for 13 hours from February until April and thereafter was set to follow the natural daylength.

The blackberry plants showed increased vegetative biomass under 2IL and 4IL, although the differences were not significantly different. Compared to no SL, final biomass allocation to the fruits was higher in the 2IL and 4IL.
Fresh fruit yield increased by 79% and 122% with 2IL and 4IL, respectively, compared to no SL.
The quantity of fruiting laterals that successfully elongated after bud break was the primary factor explaining this variation in yield (R2= 0.86; p= 0.00).
Lateral elongation was increased by 51% in the 2IL and 63% in the 4IL treatments.
Additionally, leaves of 4IL showed a 58% higher maximum assimilation rate in March and 47% higher in May, compared to the no SL treatment.

In low light conditions, the quantity of elongated laterals can be a limiting factor for yield, therefore it is concluded that 2 IL is a recommendable supplemental lighting method, further research optimal positioning of additional supplemental lighting within the canopy.

Key words: LED; supplemental light; interlighting; Rubus spp.; blackberry; yield components; budbreak