Short Communication

Effect of different concentrations of Indole acetic acid (IAA) in the in vitro rooting of Dahlia sp.

Liudmila Jiménez-Mariña^{1  *} 

Milvia Fonseca-Arias¹ 

Aida García-Alcántara¹ 

Sucel Infante-Fonseca¹ 

Joel Vázquez-Rodríguez¹ 

¹Departamento Genética y Ecofisiología Vegetal. Instituto de Investigaciones Agropecuarias "Jorge Dimitrov", carretera Bayamo - Manzanillo km 16½, Gaveta Postal 2140, Bayamo, Granma. Cuba

ABSTRACT

In the present work, different concentrations of indole acetic acid (AIA) and its effect on the rooting of Dahlia sp cultivated in vitro were studied. Nodal explants from seedlings obtained in vitro were cultured in a modified MS culture medium in a semi-solid state, supplemented with 0; 0,1; 0,5; and 1 mg L^-1 of indole acetic acid (IAA). The variables evaluated were: appearance of the root, number of roots/sprout, length of the root and rooted seedlings. At 30 days was observe in the concentration 0,5 mg L^-1 on highest number of roots (3,9), length (3,76 cm) and rooted explants (87,5 %). The results show that AIA influenced the in vitro rooting of nodal explants of Dahlia sp.

Keys words: auxin; radical system; explants; cut flower

INTRODUCTION

Micropropagation is an attractive alternative for mass multiplication of cultivars by increasing multiplication coefficients and obtaining plant material, since it allows obtaining plants free of diseases ¹. In addition, it favors the commercial propagation on a large scale and the rapid introduction to the market of species and varieties of plants of great ornamental value ².

The genus Dahlia is made up of 35 species, all native to Mexico, of which only four are the genetic basis. This cut flower has very special characteristics that place it abroad as one of the most beautiful flowers and it is the only plant that has the highest number of varieties among all plant species ^3-6.

In vitro cultivation techniques in Dahlia are important tools for germplasm conservation, genetic improvement and seed production. Although it is true that important advances have been made in this area ^7,8, there are few specific studies related to in vitro propagation.

Growth regulators in culture media allow the targeting of tissue morphogenesis and the modification of physiological responses under in vitro conditions. Within these compounds are auxins, whose effects are related to apical dominance and induction of rhizogenic processes in plants and promote growth by means of cellular elongation mechanisms. The most commonly used auxins are indole acetic acid (AIA), indole butyric acid (AIB) and naphthaleneacetic acid (ANA) ⁹.

It has been established that AIA has a significant effect by promoting a greater length of shoots and roots. The function is to induce growth by means of a rapid stimulation of synthesis of the cell wall components of growing cells ¹⁰. Several studies indicate a positive correlation between endogenous levels of AIA in seedlings and the number of adventitious roots produced by plantlets ^11,12.

The aforementioned motivated to determine different concentrations of IAA and its effect in the in vitro rooting of nodal segments of Dahlia sp.

MATERIALS AND METHODS

The research was carried out in the Plant Biotechnology Laboratory of the "Jorge Dimitrov" Agricultural Research Institute, Bayamo, Granma, during the period from September to December 2015.

Vegetal material

The plant material used for the rooting were nodal segments of Dahlia sp with a size of 1.5 cm previously cultivated in MS salts medium, 100 mg L^-1 myo-inositol, thiamine 1 mg L^-1, 1 mg L^-1 of gibberellic acid, 7 g of Agar E, 30 g L^-1 of sucrose from the multiplication phase, which was completed two months after the start of this subculture.

Culture conditions

For in vitro rooting, the semisolid culture medium, consisting of the salts proposed by Murashige and Skoog (MS) ¹³ at half the concentration of salts (50 %), complete micronutrients, 100 mg L^-1 myo- inositol, thiamin 1 mg L^-1, Agar E and 30 g L^-1 sucrose. The treatments consisted of different concentrations of AIA, as shown below in Table 1.

Table 1 Concentrations of indole acetic acid (AIA) used for the in vitro rooting of nodal segments of Dahlia sp. 

Treatments	Concentratiopns of AIA (mg L^-1)
1	Control
2	0,1
3	0,5
4	1

The pH of the solutions of the culture media was adjusted to 5.7 before sterilization.

Glass flasks with a diameter of 5 cm and a height of 8 cm were used, with a capacity of approximately 250 mL, in which 25 mL of the elaborated medium were dispensed. Subsequently, they were sterilized in a vertical autoclave for 20 minutes at 1.2 kgf cm.

Five explants were used per vial and 50 per treatment.

The explants were placed in a growth chamber with sunlight at a temperature of 26 ± 2 °C and with a flux density of photosynthetic photons (DFFF) with an average of 45 umol m^-2 S^-1.

The indicators to be evaluated at 30 days of culture were:

• Root apparition (days): it was recorded at the beginning and completion of appearance of the roots by visual observation, to determine percent.

• Number of roots/sprout: by counting the same in each sprout.

• Percentage of rooted seedlings: calculated from the number of rooted shoots of the total.

• Root length (cm): all were measured from the neck to the apex of the root and the average was obtained.

A completely randomized experimental design with three repetitions was used. A multiple comparison test of Duncan's means was applied for the 5 % error probability. All statistical analyses were processed with the Statistica for Windows package, version 10.

RESULTS AND DISCUSSION

Table 2 shows that, treatment with 0.5 mg L^-1 at 30 days has the highest percentage of rooted seedlings with the appearance of small roots from 10 days of culture with significant differences compared to the rest of the treatments. While the treatments with 0 and 0.1 mg L^-1 of AIA did not show significant differences, this can be attributed to the non-presence (control) and low concentration of AIA used. The response of the explants in the presence of 1 mg L^-1 of AIA suggests that it was not adequate to achieve satisfactory results in this species since the development of the roots could be affected by high concentrations of auxins in the culture medium, which together with the endogenous concentrations of the explant, it produces an increase in the concentration of this auxin, which acts at low concentrations, observing a decrease in the values for all the indicators, since the concentration of the hormone is a determinant of growth. This result could be given to a response to the application of auxin to control the excess of free auxin, which may be regulated by the increase in the endogenous concentration of the AIA ¹⁴.

In studies related to the micropropagation of Dahlia variabilis Cav ¹⁵ there was a very wide variation in the rooting capacity of the shoots in a medium with 0.1 mg L^-1 of AIA, where 35.7 1% of rooted seedlings were obtained with an average length of 4.16 cm.

This response was documented in other studies ¹⁶, where the results indicated that the AIA had an effect on the in vitro rooting of G. atter (Hassk.) Kurz and that this auxin stimulated the emission of roots. After 10 days of cultivation, the presence of small roots was observed in all the treatments studied.

Table 2 Effect of the concentration of AIA, in the in vitro rooting phase of explants of Dahlia sp. 

Concentration AIA (mg L^-1)	% of rooted seedlings	Number of roots/shoots	Root apparition (days)	Length of the root (cm)
0	33.3 b	2.5 b	12-33	1.22 b
0,1	40.0 b	2.6 b	12-33	1.55 b
0.5	87.5 a	3.9 a	10-30	3.76 a
1	14.29 c	1.8 c	12-30	0.76 c
EE	0.46	0.26	0.32	0.15

Means in each column with different letters differ p (≤0,05) according to Duncan test

Statistically significant differences were observed between the different treatments for the variable number of roots/shoots. The best performance corresponded to the 0.5 mg L^-1 dose of AIA, with a value of 3.9 that differed from the rest of the treatments; between the control and 0.1 mg L^-1 there were no significant differences. The variable length of the root showed the same behavior as the previous one. It is necessary to highlight that for both cases the treatment of 1 mg L^-1, was the worst behavior since a smaller magnitude was observed for the variables evaluated. It has been studied that auxins or any other type of phytoregulator are physiologically functional when they are found in small quantities, and that a high concentration of these substances exerts a negative effect on plants because their excess, instead of inducing a specific response through part of the plant tissue, produces toxicity in it. In studies conducted, increasing the concentration of AIA from 0.5 mg L^-1 to 1.0 mg L^-1 under the same culture conditions, the development rate of the orchid protocorms (E. elongatum Jacq) was lower ¹⁷.

AIA is precisely the most recommended auxin for most rooting media described in the literature ¹⁸. In this sense, authors such as ^19,20 studied the effect of indole-3-acetic acid (AIA) and achieved rooting in vitro in several species of bamboo, which resulted in an increase in the number of plants with roots emitted (96 %) at 20 days of culture.

However, in Spanish carnation (Dianthus caryophyllus L), the best results were obtained regarding the length of the root when using 0.1 mg L^-1 of AIA with a value of 3.48 cm ²¹.

On the other hand, in in vitro plants of poinsettia (Euphorbia pulcherrima Willd ex Klotzsch), of the hybrids 'Zacatepec 10' and 'Zacatepec 48', the number of roots emitted by plants and the length thereof were affected by the doses of AIA in both hybrids ¹⁸.

In a general way, the results obtained in this experiment indicate the best treatment for the concentration of 0.5 mg L^-1 of AIA, which promoted rooting up to 87.5 %, as well as the number (3.9) and length of the roots (3.76 cm) which could have an effect on the increase of the vigor of the explants and facilitate the direct acclimatization of the plants produced in vitro.

CONCLUSIONS

• The presence of Indole acetic acid (AIA) in the culture medium favored the in vitro rooting of Dahlia sp.

• The concentration of 0.5 mg L^-1 of AIA favored the in vitro growth of nodal segments of Dahlia sp, with 3.9 roots/shoot, 3.76 cm in length and 87.5 % of rooting.

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Received: June 04, 2018; Accepted: January 16, 2019

^* Author for correspondence. [e-mail]