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 matteo.caser@unito.it; 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 the 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 out 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 taking 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 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 S AND METHODS Plant material s
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 (how?), potted in peat:perlite (60:40) substrate, and cultivated in a greenhouse with the basal temperature of 20°C and air humidity of at 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; what is it?Meijon et al., 2009), number of branches per
plant, and branch branch length (what is 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 univariate 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 R results show ed high differences in growth responses among genotypes within group, but differences between groups were also found, confirming their local horticultural classification. As demonstrated reported in Table 2, Amoena genotypes showed the highest number of branches (10.9), and the lowest roundness index (0.96), opposite to the 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. Anyway However, all the Amoena were clustered very closely d for 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).
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 to at improving e 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.( in Italien with English abstract??)
Scariot V., Handa T. and De Riek J. 2006b. Morphological characteristics and AFLP markers for classifying an Italian genepool of evergreen azaleas. Acta Hort. 714:221-225.
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.
Tables
Table 1. Identification code (ID), cultivar name, and local horticultural group of the 104 studied azaleas.
ID Cultivar Group ID Cultivar Group
29 'Rosa Pastello Cavadini' Indica 86 '86 UNITO' Amoena 30 'Ester Cavadini' Indica 208 '208 UNITO' Amoena 32 'Camilla Bianchi' Indica 1 'Mergozzo' Japonica 33 'Universiadi Torino 2007' Indica 2 'Moederdag' Japonica 34 'Arianna Follis' Indica 3 'Suna' Japonica 35 'Franca Ciampi' Indica 4 'Intra' Japonica 60 'Lavinia Borromeo Elkann' Indica 5 'Bèe' Japonica 61 'Maria Ratti' Indica 12 'Verbania' Japonica 62 'Laura Zegna' Indica 13 '13 UNITO' Japonica 63 'Carla Ferrero' Indica 14 'Premeno' Japonica 64 'Paolo Pejrone' Indica 15 '15 UNITO' Japonica 66 'Vito Ratti' Indica 17 'Laveno' Japonica 67 'Agnese Pallavicino' Indica 18 '18 UNITO' Japonica 68 'Oomurasaki' Indica 19 'Cannobbio' Japonica 69 'Jennifer Isacco' Indica 20 'Meina' Japonica 71 'Luisa Pallavicino' Indica 21 'Caldè' Japonica 73 'Mara Zini' Indica 22 'Isabella Cavadini' Japonica 74 'Rosmini Antonio' Indica 23 'Luigi Cavadini' Japonica 75 'Katia Zini' Indica 24 'Cinzia Cavadini' Japonica 77 'Ester della Valle di Casanova' Indica 25 'Giulia Cavadini' Japonica 78 'Sofia Browne' Indica 26 'Eugenio Cavadini' Japonica 79 '79 UNITO' Indica 27 'Lina Cavadini' Japonica 80 'Akebono' Indica 52 'Rosa Doppio Cavadini' Japonica 82 'Villa San Remigio' Indica 53 'Rosa Confetto Cavadini' Japonica 84 '84 UNITO' Indica 55 'Alba Rosa Cavadini' Japonica 85 'Silvio della Valle di Casanova' Indica 56 'Rosa Salmone Cavadini' Japonica 88 'Capitano Neil Mc.Eacharn' Indica 57 'Rosa Intenso Cavadini' Japonica 89 '89 UNITO' Indica 58 'Fior di Pesco Cavadini' Japonica 90 'Conte Alessandro Orsetti' Indica 203 'Neve Cavadini' Japonica 91 'Gerda Weissensteiner' Indica 212 'Sabine Valbusa' Japonica 92 'Akebono' Indica 217 'Carmine Paola' Japonica 94 '94 UNITO' Indica 219 '219 UNITO' Japonica 95 'Gabriella Paruzzi' Indica 222 'Carmine Pierina' Japonica 204 'Carlo Contini' Indica 225 'Hawanaky Fuji' Japonica 205 'Giuseppe Mazzola' Indica 228 'Alsides Ferrari da Barbè' Japonica 206 'Principe Pietro Troubetzkoy' Indica 231 '231 UNITO' Japonica 207 'Antonella Confortola' Indica 232 'Mario Carmine' Japonica 210 'Paralimpiadi Torino 2006' Indica 233 'Cannero Riviera' Japonica 211 '211 UNITO' Indica 236 'La Grotta' Japonica 213 'Alessandro Pirotta' Indica 239 '239 UNITO' Japonica 218 'Carmine Emilia' Indica 242 'Gardanina' Japonica 226 'Pescherino' Indica 245 '245 UNITO' Japonica 227 'Ghetta Bruno' Indica 246 'Ronc de Gira' Japonica 235 '235 UNITO' Indica 256 '256 UNITO' Japonica 240 'San Rocco' Indica 268 '268 UNITO' Japonica 248 'Grazia Castelli' Indica 269 'Perla del Verbano' Japonica 251 '251 UNITO' Indica 271 'Daila Dameno' Japonica 254 'Colomè' Indica 273 '273 UNITO' Japonica 255 '255 UNITO' Indica 274 'Elena Accati' Japonica 276 'Isola Madre' Indica 279 'La Coletta' Japonica 70 '70 UNITO' Amoena 280 '280 UNITO' Japonica 76 '76 UNITO' Amoena 281 'Stella del Verbano' Japonica
Table 2. Mean values of height (cm), height/diameter ratio (H/D), number of branches,
roundness, and length of branches (cm) observed in the 104 studied genotypes, sorted in the three local horticultural groups.
Group Height H/D No. of branches Roundness Length of 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).
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 the 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.
