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

Abstract

Passionfruit plants (Passiflora edulis f. edulis × P. edulis f. flavicarpa cultivar ‘E-23’) were grown under various periods of full sun and shade, but with some of the plants receiving similar amounts of total shortwave radiation. Low irradiance treatments, i.e. 90% shade; 1 week full sun:3 weeks 90% shade; 50% shade; alternate weeks of full sun and 90% shade; and 3 weeks full sun:1 week 90% shade, generally increased vine extension and reduced plant dry weight and floral bud and open flower number compared with full sun or alternate weeks of full sun and 50% shade. The effects of shading on growth and flowering were generally stronger with shorter periods of heavy shade (90%) than with longer periods of intermediate shade (50%), when the average irradiances during the experiment were similar (16.5 and 15.4 MJ m−2 day−1 and 11.2 and 10.0 MJ m−2 day−1).

The concentrations of most nutrients were significantly higher from full-sun plants only with 90% shade or 1 week full sun:3 weeks 90% shade. The levels of most nutrients were in the range considered to be optimum for passionfruit in subtropical Queensland. The only exceptions were leaf N, Mg and Cu, which were low in all treatments. Values for full-sun and shaded plants generally fell into the same category in the standard table. The only exception was leaf B which was low in full-sun vines.

It was concluded that intermittent periods of heavy shade have residual effects on growth and flowering during periods of full sun. Short periods of heavy shade for as little as 1 out of 4 weeks can reduce flowering and potential yield significantly. These results suggest that increases in plant density which lead to inter-vine shading will decrease flowering and fruit set.