Postharvest needle abscission responses of balsam fir (Abies balsamea L.) to foliar application of naphthalene acetic acid

Auxins are proven to delay senescence in many horticultural crops postharvest owing to their interactive effects with ethylene activity and/or sensitivity. Therefore, we explored the potential of naphthalene acetic acid (NAA) in delaying the postharvest needle abscission in balsam fir. The experiment followed a 3×4 factorial design with NAA concentrations at 3 levels (0, 0.5 and 50 ppm) and application cycles at 4 levels (1, 14, 28 and 42 days after harvest). Apart from these treatments, an absolute control (AC; no-spray) was also included to mimic household conditions. Foliar application was administered through handheld mist sprayed until the branches were completely soaked with the respective solutions. Fresh needle loss (g day^-1) and daily water consumption (mL g^-1) were monitored for 120 days and the days until 5% needle loss (based on fresh weight) and the cumulative water consumption (CWC) (mL g^-1) were calculated. Data were analysed using Minitab 16. Peak needle abscission occurred around 60 days. NAA application (5 and 50 ppm) delayed abscission at 5% level when compared to 0 ppm (29 days) with one cycle of application, however, when compared to AC (61 days) or with other cycles, this effect was not significant (P>0.05). CWC was higher (25%) in all foliar sprayed treatments (around 2 mL g^-1) when compared to AC (1.87 mL g^-1) with one or two cycles of application. Again, this effect disappeared with repeated applications. We conclude that NAA exhibits limited ability to delay the needle abscission in balsam fir.