2013 ASHS Annual Conference

Postharvest needle loss in Christmas trees is a complex phenomenon regulated by genetic, environmental, management and postharvest factors affecting physiological processes. Typically, the initial water consumption of a freshly cut Christmas tree is 0.20 mL·g^-1 per day, but follows an exponential decline until a steady state of approximately 0.05 mL·g^-1 per day is reached. It is hypothesized that bacteria growing in standing water of Christmas tree stands inhibits water flux and, ultimately, contributes to poor needle retention. A total of 100 branches were collected and placed in water. Each week ten branches were randomly selected and assessed for percentage of needle loss, water use, xylem pressure potential (XPP), and relative water content (RWC). In addition, the stand water was collected and analyzed for bacterial count and percentage of transmittance at 600 nm wavelength. In general, it was found that water use, RWC, XPP, and transmittance all decreased over time; and the percentage of needle loss and bacterial count increased over time. Bacterial counts were only able to be monitored over the first three weeks, which followed an exponential growth and a logarithmic transformation of this data had a significant (P < 0.001) linear negative relationship with transmittance (R² = 86.0%). Over the duration of the experiment, transmittance had a significant (P < 0.001) positive linear relationship with water use (R² = 62.5%) and XPP (R² = 62.1%). None of the factors studied was directly related to percentage of needle loss, but that was likely due to the fact that no needle loss occurred in the first few weeks. A comparison of the number of days until needle loss commencement and the number of days for water use to reach the steady state of 0.05 mL·g^-1 per day revealed a strong positive linear relationship (R² = 87%). It is suggested that the overall water quality, as indicated by transmittance, is strongly linked to water use. A quick decline in daily water use, due either to poor water quality or other reasons, can promote needle abscission. There is evidence to suggest that bacterial growth in standing water may perhaps be a contributor to the poor water quality and needle retention, postharvest.