Productivity and fruit quality of Vaccinium corymbosum cv. Elliott under photo-selective shading nets

The productivity and development of northern highbush blueberry plants (Vaccinum corymbosum L. cv. Elliott) was examined under photo-selective nets of different colors (black, red and white) and shade intensities (25%, 50% and 75%) in Michigan-USA over two growing seasons. Photoselective nets influenced the photosynthetic active radiation (PAR) transmitted through the canopy, with white nets allowing significantly higher radiation to penetrate than red and black nets at all shade levels. After one year of treatment, the rate of flower bud development decreased linearly as % PAR increased, but the total number of flower buds per cane and terminal shoots increased gradually as light levels increased, reaching an asymptote at 50% PAR. The percentage of mature fruit on a particular date was higher in the control plants and decreased as the % PAR was reduced. The harvest delay was maximum at the lowest light level (20%) and decreased exponentially with increasing % PAR. Fruit soluble solids increased linearly (r2 = 0.86; P < 0.0001) and fruit water content decreased linearly (r2 = 0.88; P < 0.0001) as % PAR increased. Fruit yield showed a positive, curvilinear relationship with % PAR and reached an asymptote at 50% PAR. The interaction between color and shade was not significant. However, fruit quality (fruit weight, soluble solid and firmness) showed significant color × shade and color × harvest time (fruit weight, soluble solids and titratable acidity) interactions. Our results indicate that placing red and white nets over mature plants at intermediate shade levels (40–60% PAR) provide a harvest delay without detrimental effects on return bloom, yield or fruit quality.

► The rate of flower bud opening decreased linearly as % PAR increased.
► Mature fruit on a particular dates were higher in the control plants and decreased as the % PAR was reduced.
► The maximum harvest delay was 13 days.