Effect of continuous shading on growth, flowering and nutrient uptake of passionfruit

Abstract

Low irradiance (mean total shortwave radiation of 2.1 or 6.3 MJ m −2 day −1 compared to 10.5, 14.6 or 20.9 MJ m −2 day −1) increased shoot elongation and reduced leaf area, plant dry weight, and floral bud and open flower number in the Passiflora edulis f. edulis × P. edulis f. flavicarpa hybrid, E-23. Shading also increased the proportion of stem contributing to plant dry matter and reduced the proportion of root, and altered a range of plant morphological characteristics. The decline in shoot weight at low irradiance was associated with a fall in the total shoot content of most nutrients. The shoot tissue levels of Ca, Mg and Fe rose and those of P fell at lower irradiance. The levels of S and Zn rose as irradiance fell to 14.6 or 10.5 MJ m −2 day −1. The concentration of the other nutrients (N, K, Na, Mn, Cu, B and Al) was not consistently affected by shading. It was concluded that irradiance may be one of the major environmental factors contributing to seasonal fluctuations in passionfruit flowering and fruit set. Potential production was reduced by each reduction in irradiance below full sun. The effect of irradiance on vine development did not appear to involve changes in nutrient uptake.