Tree seed performance has benefited considerably from the development of controlled methods to overcome dormancy. Traditionally tree seeds have often been stratified outdoors. Depending on the types of dormancy, stratification starts before or during summer and continues during winter, or it starts before winter. Seeds become ready to germinate during winter, and they may start to germinate before sowing. Reducing the water content of the seeds during pre-treatment can prevent this premature germination. If premature germination is prevented, treatments at slightly reduced and controlled moisture content (MC) can be prolonged. As a result, percentage, rate, and uniformity of germination increase. Moreover germination proceeds over a wider range of seedbed conditions. So far, controlled MC treatment has been developed for about 20 species, both broad leaved and conifers

Derkx, M.P.M.

English

Wageningen Yield 

200 Combined Proceedings International Plant Propagators' Society, Vblume 56,2006 
Liquid Sorting and Film Coating: Techniques for Improving 
Tree Seed Performance® 
M.P.M. Derkx 
Applied Plant Research, Flower Bulbs, Nursery Stock and Fruit Section , P.O. Box 85,2160 AB, 
Lisse, The Netherlands 
Email: ria.derkx@wur.nl 
INTRODUCTION 
Tree seed performance has benefited considerably from the development of con­
trolled methods to overcome dormancy. Traditionally tree seeds have often been 
stratified outdoors. Depending on the types of dormancy, stratification starts before 
or during summer and continues during winter, or it starts before winter. Seeds 
become ready to germinate during winter, and they may start to germinate before 
sowing. Reducing the water content of the seeds during pre-treatment can prevent 
this premature germination. 
If premature germination is prevented, treatments at slightly reduced and con­
trolled moisture content (MC) can be prolonged. As a result, percentage, rate, and 
uniformity of germination increase. Moreover germination proceeds over a wider 
range of seedbed conditions. So far, controlled MC treatment has been developed 
for about 20 species, both broad leaved and conifers. 
Seed quality is often a limiting factor in tree seeds, which are often collected from 
the ground. The prevention of premature germination during controlled MC treat­
ment leads to new possibilities for seed enhancement techniques, including liquid 
sorting and film coating. Both techniques have been proven successful in agricul­
tural and horticultural seeds. Liquid sorting is a technique that aims to remove 
poor quality seeds by sorting on specific gravity. Temperature and water potential 
can be controlled to provide conditions which are optimal for the species. Film coat­
ing with fungicides aims to protect the seed against soil-borne diseases, thereby 
increasing the percentage of usable plants. 
The aim of the present study was to investigate effects of liquid sorting and film 
coating with fungicides in some tree species. 
MATERIALS AND METHODS 
Dormancy Breaking. To overcome dormancy, seeds were pre-treated in a con­
trolled way. Cold pre-treatment at 3 °C occurred at controlled MC without medium 
in plastic bags. Warm pre-treatment of fully hydrated seeds was in a sphagnum 
peat and sand (1:1, v/v) mixture in plastic boxes. Three volume parts of medium 
were mixed with one volume part of seeds. Moisture content of Larix kaempferi 
seeds was not controlled, as premature germination is not possible during the rela­
tively short cold pre-treatment of this species. Pre-treatments of the different spe"-~~~ 
cies are shown in Table 1. 
Germination and Sowing Conditions. Four replicates of 50 seeds were sown 
in plastic boxes or Petri dishes on one layer of wet thick paper or wet filter paper. 
Germination of L. kaempferi was tested at 15 °C. Germination of the other species 
in the liquid sorting experiments was tested at 10 °C. Germination in the film 
coating experiments was determined at 17 °C. Germination tests were finished 
Liquid Sorting and Film Coating: Techniques for improving Tree Seed Performance 201 
Table 1. Treatments to overcome dormancy in the different species. 
Species Pre-treatment 
Acer palmatum 12 w 3 °C, 37% MC 
Acer pseudoplatanus 15 w 3 °C, 46% MC 
Carpinus betulus 6 w 20 °C in sphagnum peat/sand followed by 16 w 3 °C, 
28% MC 
Crataegus monogyna 10 w 25 °C in sphagnum peat/sand followed by 24 w 3 °C, 
22% MC 
Fagus sylvatica 20 w 3 °C, 30% MC 
Larix kaempferi 10 or 6 w 3 °C, fully hydrated 
Prunus avium 8 w 20 °C in sphagnum peat/sand followed by 18 w 3 °C, 
28% MC (liquid sorting) 
Or 2 w 20 °C, 6 w 3 °C, 2 w 20 °C, 2 w 3 °C, 2 w 20 °C, 14 w 
3 °C, 28% MC (film coating) 
Tilia cordata 8 w 20 °C in sphagnum peat/sand followed by 24 w 3 °C, 
43% MC 
Note: Abbreviations: w = weeks, MC = moisture content. 
after 4 weeks. Field emergence was determined at an experimental field or at 
commercial nurseries. 
Liquid Sorting. In the first experiment seeds were sorted either before or after 
dormancy breaking; in the second experiment seeds were only sorted before dor­
mancy breaking. Before liquid sorting, using liquids with different specific densi­
ties, air was removed from the seeds. 
Film Coating with Fungicides. Different film coatings with fungicides were ap­
plied after dormancy breaking. The fungicides used were a combination of fosetyl-
aluminium (Aliette, 3 or 6 g-kg"1 seed) and iprodione (Rovral Aquaflo, 3 or 6 mlkg"1 
seed); and a combination of propamocarb hydrochloride (Previcur, 6 or 12 ml kf1 
seed) and thiophonate-methyl (Topsin M) (4 or 8 ml kg1 seed). In Fagus sylvatica 
these fungicides were also applied individually. 
RESULTS 
Liquid Sorting. Germination often correlated with the specific density of the 
seeds (Fig. 1). In general, low-density fractions showed the poorest germina­
tion. Sometimes, the heaviest fraction showed poor germination too. By remov­
ing these fractions the performance of a seed lot can be improved. In most spe­
cies liquid sorting was successful before and after dormancy breaking (data not 
shown). In Prunus avium and Crataegus monogyna, liquid sorting after dor­
mancy breaking was disturbed by loose fruit parts. In 2005 complete fruits of 
Acer pseudoplatanus were sorted. Sorting in water allowed removal of the light­
est fraction. However, this fraction still showed 70% germination (Fig. 1). In 2006 
de-winged and winged fruits of A. pseudoplatanus were sorted. Results were 
comparable (Table 2). In contrast to 2005 liquids with a specific density higher 
than 1 were required to remove the heaviest fraction in A. pseudoplatanus, 
which showed poorer germination than the lighter fractions (data not shown). 
202 Combined Proceedings International Plant Propagators' Society, Volume 56,2006 
CmMfumMd« Pn««»«n 
Figure 1. The effect of liquid sorting on germination of seeds of Crataegus monogyna, Prunus 
avium, Acer pseudoplatanus, Carpinus betulus, and Larix kaempferi. Before (Crataegus) 
or after (other species) dormancy breaking as indicated in Table 1 seeds were divided in 
different density fractions, c = nonsorted control. C. monogyna: 1 > 1.300, 2 = 1.260 - 1.300, 
3 = 1.175 - 1.260, 4 < 1.175; P. avium: 1 > 1.220, 2 = 1.200 - 1.220, 3 = 1.155 - 1.200, 
4 = 1.100 - 1.155; A. pseudoplatanus: 1 > 1.060, 2 = 1.000 - 1.060, 3 < 1.000; C. betulus: 
1 > 1.225, 2 = 1.190 - 1.225, 3 < 1.190; L. kaempferi: 1 > 1.110, 2 = 1.075 - 1.110, 3 = 1.025 -
1.075, 4 < 1.025. Germination of all fractions was tested at 15 °C (Larix) or 10 °C 
(other species). 
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Liquid Sorting and Film Coating: Techniques tor Improving Tree Seed Performance 203 
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204 Combined Proceedings International Plant Propagators' Society, Volume 56,2006 
Table 2 shows that the benefit of liquid sorting on laboratory germination differs 
from seed lot to seed lot. 
Some seed lots were sown outdoors. The results in Table 2 show that liquid sorting 
improved field performance in several seed lots. In 2006 field performance of A pseu-
doplatanus did not benefit from liquid sorting, whereas laboratory germination did. 
Film Coating With Fungicides. The combination of Aliette and Rovral Aquaflo 
and that of Previcur and Topsin M had no phytotoxic effect on seeds of A. palmatum 
and Tilia cordata. On P. avium phytotoxic effects were found in laboratory tests, on 
Fagus sylvatica phytotoxic effects were seen both in laboratory and field emergence 
tests. Single fungicides also produced phytotoxic effects in laboratory tests of F. 
sylvatica. 
In the field only Aliette was phytotoxic. Positive effects of Previcur on reduction of 
damping-off were seen in F. sylvatica; positive effects also resulted from both tested 
combinations on A. palmatum (data not shown). In general, there were only low lev­
els of damping-off on the untreated plots in our trials, so it was not possible to draw 
final conclusions about the effectiveness of the film coatings against damping-off. 
Prunus avium seeds with a film coating of Aliette and Rovral Aquaflo were also 
sown at two nurseries. In one nursery film-coated seeds gave significantly better 
field emergence (Table 3). Only a few seedlings showed damping-off. 
Table 3. The effect of a film coating with Aliette (6 g kg-1 seed) and Rovral Aquaflo (6 mlkg1 
seed) on laboratory germination and field emergence of Prunus avium seeds. 
Laboratory Field emergence Damping-off 
Treatment germination Nursery 1 Nursery 2 Nursery 2 
Control 89 53 49 6 
Film coating 90 52 73 1 
DISCUSSION 
Liquid sorting resulted in seed fractions with different specific densities (Fig. 1). By 
removing fractions with poor germination, the performance of a seed lot can be sig­
nificantly improved (Fig. 1, Table 2). The benefit of liquid sorting varied from seed 
lot to seed lot and depended on the initial quality of the seed lot and the dormancy-
breaking pretreatment. 
A safe film coating with fungicides has been developed for A. palmatum, P. avi­
um, and T. cordata, but not yet for F. sylvatica. So far, few conclusions can be drawn 
about the effectiveness against damping-off. In one nursery, field performance of 
film-coated seeds of P. avium was better than that of control seeds (Table 3). Fur­
ther research is required to develop a safe film coating for F. sylvatica and to con­
firm effects against damping-off. 


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