|Authors: ||S. Wada, B.M. Reed|
|Keywords: ||ammonium, micropropagation, mineral nutrition, nitrate, Pyrus, response surface design|
A major problem limiting in vitro germplasm collections is that many species or cultivars have suboptimal growth on standard growth media.
A series of studies determined that increased amounts of mesos components (CaCl2, MgSO4, KH2PO4) and changes in the nitrogen (N) were required for producing high quality shoots for five pear genotypes.
Many species required unique combinations of N ions (NO3- and NH4+) and total N for optimal growth.
To make these results applicable to germplasm collections, this study evaluated 16 genotypes from five species maintained at the USDA-ARS National Clonal Germplasm Repository in Corvallis Oregon.
Growth responses were determined for quality rating, multiplication, shoot length and leaf characters.
Four patterns of N requirements were observed for shoots grown on increased mesos nutrients.
Most of the pears responded well to NH4+ at moderate concentrations (~20 mM) and NO3- at low to moderate concentrations (20-40 mM). Pyrus communis cultivars 'Horner 51', 'NY 10353', 'OH×F 87R'O, 'Pyrodwarf', 'bileen Gift' and 'Winter Nelis'; P. pyrifolia 'Scion SzuMi'; and P. ussuriensis 'Hang Pa Li' grew well on these concentrations when combined with increased mesos (1.5-2.0×). Five genotypes responded best on moderate to high NH4+ and low NO3- concentrations (P. communis 'Bartlett' and 'Luscious'; a P. pyrifolia wild selection and 'Seuri Li'; and P. ussuriensis 'Harbin'). High concentrations of both N ions were required for P. koehnei and P. pyrifolia 'Hosui', while only P. cordata grew best with high NH4+ and any level of NO3-. It is now possible to culture the entire range of pear genotypes by using a combination of ≥1.5× mesos and one or more of these four N formulations.
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