Interior spruce seedlings compared with emblings produced from somatic embryogenesis. II. Stock quality assessment prior to field planting

Abstract

Interior spruce (Piceaglauca (Moench) Voss × Piceaengelmannii Parry) seedlings and emblings produced through somatic embryogenesis tissue culture were removed from frozen storage and tested with a stock quality assessment procedure prior to spring planting. Seedlings, compared with emblings, had greater height as well as shoot and root dry weights. Seedlings and emblings had similar root-collar diameter, buds per total shoot length, and needle primordia in their terminal buds. Seedlings and emblings had similar shoot form (i.e., branch quotient) and balance between their shoot and root system (i.e., plant water balance ratio). Emblings, compared with seedlings, had a lower osmotic potential at turgor loss point and symplastic fraction, plus a higher dry weight fraction and total turgor. Seedlings and emblings had similar osmotic potential at saturation and relative water content at turgor loss point. Seedlings and emblings had similar resistance to water movement through the plant–atmosphere continuum (Rpac) at 22 °C root temperature, though emblings had greater Rpac at 7.5 °C root temperature. Seedlings had greater net photosynthesis (Pn) than emblings over a 14-day period at both 7.5 and 22 °C root temperatures. Seedlings, compared with emblings, had greater root development over a 14-day period at 22 °C root temperature, though they had low and similar root development at 7.5 °C root temperature. Both Pn and needle conductance (gwv) decreased as predawn shoot water potential (Ψpd) declined in seedlings and emblings. Nearly complete stomatal closure occurred at Ψpd less than −1.5 MPa, while similarly low Pn readings (seedlings: −0.01 ± 0.04 μmol•m−2•s−1; emblings: 0.02 + 0.04 μmol•m−2•s−1) occurred between a Ψpd of −1.0 and −2.0 MPa. A performance potential index (PPI), which combines material and performance attributes in a comprehensive characterization of field performance potential, indicated that seedlings had a better PPI under optimum environmental conditions. However, seedlings and emblings had similar PPI under low temperature and drought conditions.