Clonal propagation of a selected historical gene pool of evergreen
azaleas
M. Caser, F. Merlo, V. Scariot
Department of Agronomy, Forest and Land Management, Turin University; e-mail
[email protected]; tel +39 011 6708935; fax +39 011 6708798
Keywords: breeding, cuttings, Rhododendron spp., selection
Abstract
Many exotic plants were introduced in Italy during the 19th century.
Particularly, a significant gene pool of evergreen azaleas was set up in public and
private gardens. To conserve and exploit these genetic resources, the present study
investigated the responses of 104 genotypes (50 Japonica, 50 Indica and 4 Amoena
type) to clonal multiplication. Growth aptitude, height/diameter ratio (H/D),
roundness index, number of branches per plant, and branch length were analyzed.
Vegetative propagation allowed to obtain numerous plants (54 plants/genotype) with
uniform characteristics. Elevated variability in growth responses between genotypes
within group was shown, even if differences between local horticultural groups were
found. Amoena genotypes showed the highest number of branches (10.9), and the
lowest roundness index (0.96), opposite to Indica genotypes (number of branches =
6.29; roundness index = 1.03). Both groups resulted higher (Indica 33.7 cm and
Amoena 34.4 cm) than Japonica (32.2 cm). The Principal Component Analysis
distributed specimens without a precise clustering. In general, genotypes were
mainly separated by the HD ratio (eigen vectors= -0.220) and the branch length
factors (eigen vectors= 0.198). The wide variability observed in this historical gene
pool suggests the possibility to find genetic resources with interesting traits to be
used in future breeding programs, for improving morphological characteristics or
abiotic stress tolerance.
INTRODUCTION
Many azaleas were introduced in Italy during the 19th century, and are still present
in public and historical private gardens. This gene pool is locally sorted into three groups
according to the phenotype: (1) Indica, including plants characterized by large flowers,
(2) Amoena, formed by azaleas with very small, purple flowers, and (3) Japonica, a
morphologically intermediate group (Scariot et al., 2006a; Fig. 1). However, at present
only a few or unique specimens are alive. These genotypes are the potential reservoir of
adaptive traits since they were established in a non-native area.
In order to safeguard and exploit this historical germplasm, propagation and
conservation in catalogue-fields are needed. Rhododendrons can be propagated by seeds,
layering, grafting, and tissue culture but there is extreme variability within and among
species and cultivars (Nawrocka-Grzeskowiak and Grzeskowiak, 2003). So, normally, the
azalea assortment is multiplied by cuttings.
The breeding of woody ornamentals calls for considerable investments of
resources over long periods. The outlay can be minimized by a co-operative testing. By
conducting trials with different genotypes, researchers and breeders can test the plant
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adaptability and contribute towards the results of other scientists, specifically by
screening and widening the gene pool for further breeding. This research was started to
obtain and share such information (Scariot et al., 2010). In the present study we report
responses of 104 azalea genotypes to clonal multiplication.
MATERIAL AND METHODS
Plant material
A total of 104 azalea genotypes (50 Indica, 4 Amoena and 50 Japonica) were
previously selected in historical parks and gardens and multiplied (Scariot et al., 2006a;
Tab. 1). For the present study, ten plants per each genotype, two years old, uniform in
size and shape, were clonally propagated by cutting , potted in peat:perlite (60:40)
substrate, and cultivated in a greenhouse with the basal temperature of 20°C and air
humidity of 85%. In order to prevent infections, cuttings were previously treated with an
antibacterial solution (ossichinoline 5 g L-1). No treatments with growth regulators were
applied.
Observation and statistics
After eight months of cultivation, the following parameters were evaluated:
growth aptitude, height/diameter ratio (H/D), roundness index (p2/4n*A*1.064,
p=perimeter, n=pi and A=area; Meijon et al., 2009), number of branches per plant, and
branch length (lenght from the base to the top of the cutting, cm; Meijon et al., 2009). The
variability present within and among each group was described by means of the one
factor ANOVA, and the distribution of variability was shown using a Principal
Component Analyses (PCA). Both statistical analyses were performed using the SPSS
statistical package (version 17.0; SPSS Inc., Chicago).
RESULTS AND DISCUSSION
Vegetative propagation allowed to obtain numerous plants with uniform
characteristics (mean = 54 plants/genotype). The results show high differences in growth
responses among genotypes within group, but differences between groups were also
found, confirming their local horticultural classification. As demonstrated in Table 2,
Amoena genotypes showed the highest number of branches (10.9), and the lowest
roundness index (0.96), opposite to Indica genotypes (number of branches = 6.29;
roundness index = 1.03). Both groups resulted higher (33.7 and 34.4 cm for Indica and
Amoena) than Japonica (32.2 cm), which showed a more compact growing form.
Moreover, this last group showed intermediate values of a number of branches (7.7) and
roundness (1.00), and the lowest length of branches (17.4 cm).
With the purpose to describe the relationships between all the analyzed genotypes,
a PCA based on the collected morphological data was computed. On the basis of the
eigenvector values for traits along the first two components, the attributes responsible for
a maximum separation were (with values in parentheses) the H/D ratio (-0.220) and the
branch length factors (0.198). The first two components accounted for 39.55 % of the
total variance and were used to visualize a scatter plot (Fig. 2). The specimens were
distributed without a precise clustering. However, all the Amoena were clustered very
closely to the medium values of PC1 and PC2. Some Indica and Japonica were set more
apart in two small groups (the first for low values of PC1 and the second for high).
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At the end of the experiment, with the aim to conserve this historical germplasm, a
total of 3400 plants were planted in six catalogue-fields located in the Lake Maggiore
area (North-West Italy).
CONCLUSIONS
Morphological and growth aptitude differences found within and among groups
revealed a wide phenotypic and cultivation variability (Scariot et al., 2006b). A molecular
fingerprinting approach, previously applied, already highlighted the genetic diversity and
relationships among genotypes (Scariot et al., 2007). Together, all these information
could be useful for both germplasm safeguarding and breeding programs, especially
aiming at improving abiotic stress tolerance.
Literature Cited
Meijon M., Rodriguez R., Canal M.J. and Feito I. 2009. Improvement of compacteness
and floral quality in azalea by means of application of plant growth regulators. Sci
Hortic 119:196-176.
Nawrocka-Grzeskowiak U. and Grzeskowiak W. 2003. Rooting of azalea shoot cuttings
depending on the degree of lignification. Dendrobiology 49:53-56.
Scariot V., Remotti D. and Merlo F. 2006a. Le Azalee Sempreverdi del Lago Maggiore.
Supplemento al n. 50 dei ‘Quaderni della Regione Piemonte – Agricoltura’. 334 p.(
Scariot V., Handa T. and De Riek J. 2006b. Morphological characteristics and AFLP
markers for classifying an Italian genepool of evergreen azaleas. Acta Hort. 714:221225.
Scariot V., Handa T. and De Riek J. 2007. A contribution to the classification of
evergreen azalea cultivars located in the Lake Maggiore area (Italy) by means of
AFLP markers. Euphytica 158:47-66.
Scariot V., Merlo F. and Larcher F. 2010. Cutting propagation of an old Italian gene pool
of evergreen azaleas. Acta Hort. 885:331-336.
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Tables
Table 1. Identification code (ID), cultivar name, and local horticultural group of 104
studied azaleas.
ID
29
30
32
33
34
35
60
61
62
63
64
66
67
68
69
71
73
74
75
77
78
79
80
82
84
85
88
89
90
91
92
94
95
204
205
206
207
210
211
213
218
226
227
235
240
248
251
254
255
276
70
76
Cultivar
'Rosa Pastello Cavadini'
'Ester Cavadini'
'Camilla Bianchi'
'Universiadi Torino 2007'
'Arianna Follis'
'Franca Ciampi'
'Lavinia Borromeo Elkann'
'Maria Ratti'
'Laura Zegna'
'Carla Ferrero'
'Paolo Pejrone'
'Vito Ratti'
'Agnese Pallavicino'
'Oomurasaki'
'Jennifer Isacco'
'Luisa Pallavicino'
'Mara Zini'
'Rosmini Antonio'
'Katia Zini'
'Ester della Valle di Casanova'
'Sofia Browne'
'79 UNITO'
'Akebono'
'Villa San Remigio'
'84 UNITO'
'Silvio della Valle di Casanova'
'Capitano Neil Mc.Eacharn'
'89 UNITO'
'Conte Alessandro Orsetti'
'Gerda Weissensteiner'
'Akebono'
'94 UNITO'
'Gabriella Paruzzi'
'Carlo Contini'
'Giuseppe Mazzola'
'Principe Pietro Troubetzkoy'
'Antonella Confortola'
'Paralimpiadi Torino 2006'
'211 UNITO'
'Alessandro Pirotta'
'Carmine Emilia'
'Pescherino'
'Ghetta Bruno'
'235 UNITO'
'San Rocco'
'Grazia Castelli'
'251 UNITO'
'Colomè'
'255 UNITO'
'Isola Madre'
'70 UNITO'
'76 UNITO'
Group
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Indica
Amoena
Amoena
4
ID
86
208
1
2
3
4
5
12
13
14
15
17
18
19
20
21
22
23
24
25
26
27
52
53
55
56
57
58
203
212
217
219
222
225
228
231
232
233
236
239
242
245
246
256
268
269
271
273
274
279
280
281
Cultivar
'86 UNITO'
'208 UNITO'
'Mergozzo'
'Moederdag'
'Suna'
'Intra'
'Bèe'
'Verbania'
'13 UNITO'
'Premeno'
'15 UNITO'
'Laveno'
'18 UNITO'
'Cannobbio'
'Meina'
'Caldè'
'Isabella Cavadini'
'Luigi Cavadini'
'Cinzia Cavadini'
'Giulia Cavadini'
'Eugenio Cavadini'
'Lina Cavadini'
'Rosa Doppio Cavadini'
'Rosa Confetto Cavadini'
'Alba Rosa Cavadini'
'Rosa Salmone Cavadini'
'Rosa Intenso Cavadini'
'Fior di Pesco Cavadini'
'Neve Cavadini'
'Sabine Valbusa'
'Carmine Paola'
'219 UNITO'
'Carmine Pierina'
'Hawanaky Fuji'
'Alsides Ferrari da Barbè'
'231 UNITO'
'Mario Carmine'
'Cannero Riviera'
'La Grotta'
'239 UNITO'
'Gardanina'
'245 UNITO'
'Ronc de Gira'
'256 UNITO'
'268 UNITO'
'Perla del Verbano'
'Daila Dameno'
'273 UNITO'
'Elena Accati'
'La Coletta'
'280 UNITO'
'Stella del Verbano'
Group
Amoena
Amoena
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Japonica
Table 2. Mean values of height (cm), height/diameter ratio (H/D), number of branches,
roundness, and length of branches (cm) observed in 104 studied genotypes, sorted in the
three local horticultural groups.
No. of
Length of
Roundness
branches
branches
Indica
33.7 b*
1.2
6.3 a
1.03 c
20.4 b
Amoena
34.4 b
1.2
10.9 c
0.96 a
17.8 ab
Japonica
32.2 a
1.1
7.7 b
1.00 b
17.4 a
P
*
ns
**
**
**
Means followed by the same letter do not differ significantly at P < 0.05, according to REGW-F test (* = P
< 0.05, ** = P < 0.001, ns = non-significant).
Group
Height
H/D
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Figures
Figure 1. Particulars (from left to right) of Rhododendron ‘Arianna Follis’ (Indica),
Rhododendron ‘86 UNITO’ (Amoena), and Rhododendron ‘Cannobbio’ (Japonica).
Figure 2. Scatter diagram of 104 Rhododendron accessions obtained from performing
the Principal Component Analysis (PCA) on morphological characteristics. The first two
components explain 39.55% of the total variation.
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