Effects of nitrogen and sodium chloride concentration in nutrient solution on passionfruit flowering, vegetative growth, and fruit quality

In passionfruit, excess vegetative growth and high temperature sometimes reduces number of flowers, which is a major limitation of yield. Drought stress was reported to increase flowering, and then mild drought stress via high nitrogen (N) and/or sodium chloride (NaCl) concentrations in nutrient solution on flowering in passionfruit grown in sand culture under high air temperature condition was examined. Cutting-propagated passionfruit was used. From June 21, 1000 mL of nutrient solution containing 50 or 100 mM N and 0, 12.5, or 25.0 mM NaCl was applied twice a week. From July 14 to 28, number of flowers was counted, and artificial pollination was conducted. Vine length, SPAD value, leaf length, leaf mineral concentrations, stomatal conductance, and fruit quality were measured. Interaction between N and NaCl concentration was not observed. With 100 mM N or/and NaCl application, flower number increased. Daily highest air temperature in flowering period were near 35°C or more. It was possible that mild drought stress induced by low osmotic potential in nutrient solution increased number of flowers under high temperature condition. Vine length, leaf length, and SPAD value for 50 mM N were higher than those for 100 mM N, and NaCl did not affect those. Stomatal conductance was not affected by N or NaCl. Leaf N concentration was 6.8 and 8.0% for 50 and 100 mM, respectively. Leaf K concentration was not affected by N or NaCl. Leaf Na concentration was 0.7, 0.8 and 1.4% for 0, 12.5 and 25.0 mM NaCl, respectively. Fruit weight and dimensions decreased with NaCl application. Titratable acidity for 50 mM N was lower than that for 100 mM N.