Protocols for Micropropagation of Woody Trees and Fruits

PROPAGATION OF MONGOLIAN CHERRY AND NANKING CHERRY
2.2.7. Dormancy Factor and Hardening
Poor winter survival of rooted cuttings is a common problem when shoot extension
growth ceases following rooting. Harris (1976) observed that softwood cuttings of a
Saskatoon berry (Amelanchier alnifolia Nutt.) behave in this fashion. He also noted
(Harris, 1980) that in vitro – rooted Saskatoon plantlets cease growth and loose their
leaves right after transplantation to the greenhouse bench. Furthermore, we observed
that sometimes plantlets in culture tend to loose leaves and stop growth even during
the rooting period before transferring them to the greenhouse (Pruski et al., 1990,
1991). We have made similar observations with the Mongolian and Nanking
cherries, although the dormancy symptoms were not that severe as with Saskatoon
berry cultures.
Rooting in non-sterile conditions helps significantly in solving the dormancy
problem since the ex vitro rooted plantlets do not require acclimatization to greenhouse
conditions. However, some of the newly ex vitro rooted Mongolian and
Nanking cherry plantlets can still show dormancy symptoms. Changes in levels of
plant growth regulators are correlated with the onset of bud dormancy. Investigation
of endogenous levels of PGRs in a number of plants showed a decrease in growth
promoters, gibberellins and cytokinins, and an increase of the growth inhibitor, the
abscisic acid (ABA) during the development of dormancy. With the breaking of
dormancy, the activity of growth promoters increases. Experiments with exogenously
applied PGRs have shown that dormancy in many species can be overcome by the
use of both cytokinins and gibberellins (Forshey, 1982; Pruski et al., 1990, 2000).
With Mongolian and Nanking cherry, a single foliar application (spray) of gibberellic
acid (GA3) at 200 ppm was beneficial in breaking dormancy of newly ex vitro rooted
(6 weeks-old) plantlets (Pruski unpublished). The effect is noticeable within 48 h
after application; terminal buds in newly rooted plantlets that were showing dormancy
symptoms start to open. The rooted plants can be grown in rootrainers until field
transplant or can be transplanted to larger pots for the container production. The peat
moss/perlite (1:1 v/v) mixture or a commercial Promix is usually used for growing
the transplants.
2.2.8. Field Testing
The newly rooted plants were grown for 10–12 weeks under standard greenhouse
conditions 24/20°C day/night temperature. This growing period seems to be sufficient,
since size of plants after 10 weeks is adequate (15–25 cm) and such plants could be
even be directly transplanted to the field.
There are many reports that a short acclimatization period of 5–10 days under
shade, prior to field planting greatly improves transplant survival in the field (Harris,
1980; Struve & Lineberger, 1985; Pruski et al., 1990; Murai & Harada, 1997). Our
data showed that the 10-day outdoor acclimatization period in the lath-house with
50% shade, enhanced field-transplant survival of Mongolian cherry transplants from
89.5% to 98% (data for Nanking cherry unavailable) (Table 5).
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