Acclimatizing micropropagated black cherry by comparison with half‐sib seedlings

Abstract

Black cherry (Prunus serotina Ehrh.) plantlets were cultured in vitro, transferred to potting mixture and evaluated for 8 weeks for acclimatization to a varying, but controlled environment. Whole plantlet growth and water relations were monitored and compared to seedlings of comparable size of the same maternal genotype grown under different conditions, but given the same pretest environment. At one week ex vitro. gravimetrically determined leaf conductance of plantlets was high, but became closer to that of seedlings in both magnitude and diurnal pattern as acclimatization progressed. By 8 weeks, leaf conductance of plantlets was nearly identical to that of seedlings, but the xylem water potential of the plantlets was significantly less. Logarithmic regressions of shoot vs root dry weight indicated that seedlings were allocating twice as much dry matter to shoot than to root growth compared to 4‐ and 8‐week plantlets. Over the same period, stomatal densities of both seedlings and plantlets decreased and stomatal pore lengths increased. Multiple adventitious roots of plantlets emerged from a single site just below the root collar whereas secondary or lateral roots of seedlings originated acropetally along the central root axis. Leaf conductance of plantlets at 8 weeks was similar to that of seedlings indicating satisfactory acclimatization. The larger relative root growth rate of plantlets compared to the shoot, however, was associated with lower stem xylem water potential. The anomaly may be a consequence of the method of in vitro root formation. Plantlet growth rates were lower than growth rates of seedlings and their leaf area was correspondingly less.