THE EFFECT OF CUTTING DATES, TEMPERATURE AND DIFFERENT ROOTING STIMULATORS ON THE ROOTING OF CUTTINGS OF AUBRIETA CULTORUM

Ewa Chojnowska

ABSTRACT

The effects of cuttings harvesting date, rooting temperature and hormone powder on rooting of Aubrieta cultorum cuttings were investigated. The percentage of rooted cuttings varied depending on rooting dates. In the summer (July 6 and August 17) 98% and 98.6% of cuttings formed adventitious roots. In the autumn (September 28 and November 9) 100% of cuttings formed adventitious roots. However, there were big differences in number of roots per cutting and root system quality depending on a date, temperature and rooting powder applied. The cuttings formed root system of the best quality with the highest number of roots, when they were prepared on September 28 and treated with Ukorzeniacz A (0.3% IBA, 0.1% Benomyl and 1% Captan). Cuttings treated with Ukorzeniacz B (0.2% NAA, 2.5% Benomyl and 1% Captan) and Ukorzeniacz AB (0.3% NAA, 0.05% IBA, 2% Benomyl and 1% Captan) had lower number of roots and lower quality but higher than control cuttings. Temperature 10°C was better than 15&de

Key words: Aubrieta cultorum, cuttings, rooting dates, IBA, NAA, temperature..

INTRODUCTION

Many species of perennials are vegetatively propagated by cuttings. It is a relatively cheap, simple and fast method of propagation. However, there are a lot of species that are considered hard to root and require long time to produce saleable plants.

Differences in rootability of cuttings are due to anatomical, physiological, biochemical and environmental factors. Individual variation within the same species in rooting ability is highly significant [3, 4, 7]. The physiological processes of root initiation are very complex and are influenced by many factors. No single factor but a specific constellation of factors (promoters and inhibitors) and interaction between them determine the rootability of cuttings.

It is well known that rooting of cuttings depends on a large number of external and internal factors – not only on the age of the stock plant and time of year when the cuttings are taken, but also on a genotype of the stock plant [11, 1, 16]. Adventitious rooting of cuttings may be controlled also by biological, physiological and morphological factors. Problems with root regeneration are due to environmental rooting conditions (such as rooting media, light, temperature, humidity and nutrition) before, during and after the cutting is stuck [5, 15]. Optimal rooting conditions may change if one or more of the factors affecting rooting processes are changed. Root initiation and development is an effect of the interaction of many factors. The influence of these factors on rooting of Aubrieta cultorum cuttings is not well understood.

Auxins are the most important substances regulating root regeneration. Application of natural and synthetic auxins as well as different hormone combinations speeds the cuttings through the callusing stage, and then they produce more roots faster [10, 2]. Certain hard to root species have been successfully rooted after treatment with high concentrations of growth hormones, but sometimes high auxin concetrations have been detrimental as well. Auxin talcum powder mixtures often contain more than one auxin and may also contain a fungicide, which protects newly formed roots from fungal attack.

Rooting response of species and cultivars can vary and factors limiting rooting ability must be determined empirically. A temperature increase around the cuttings can decrease the relative humidity, may also increase respiration rates, which may deplete carbohydrate reserves and retard the rooting processes. The timing is one of the more critical factors for successful rooting [4, 17]. In Poland a typical period for preparing cuttings of Aubrieta cultorum is autumn [12]. However, it is not clear if rooting ability of this species depends mainly on temperature, or on complex relationships between factors affecting rooting process.

The aim of this research was to study the main factors affecting rooting process in Aubrieta cultorum cuttings, i.e., time of cuttings collection, rooting temperature and root promoting substances and their effect on root number and quality.

MATERIALS AND METHODS

The Aubrieta cultorum ‘Red Carpet’softwood cuttings were made from the shoots of mother plants growing in the field of Institute of Pomology and Floriculture in Skierniewice (field stock plants). The cuttings (4 cm long) were taken on July 6, August 17, September 28, and November 9. The basal parts of cuttings were stripped of foliage and dipped into a rooting hormone powder. Three kinds of commercial hormone powders were used: Ukorzeniacz A, Ukorzeniacz B, Ukorzeniacz AB. The Ukorzeniacz A is used for difficult to root green and semi hardwood cuttings and contains 0.3% IBA, 0,1% Benomyl and 1% Captan. Ukorzeniacz B is used for rooting green (softwood) cuttings and contains 0.2% NAA, 2.5% Benomyl and 1% Captan. Ukorzeniacz AB is used for difficult to root semi hardwood or hardwood cuttings and contains 0.3% NAA, 0.05% IBA, 2% Benomyl and 1% Captan. After treatment, the cuttings were lightly tapped off to remove any excess powder and immediately inserted into the rooting medium. Cutti ngs were stuck into preformed holes in a moistened rooting medium which consisted of pure (100%) peat moss. The rooting medium was gently firmed around each cutting after insertion. Plastic boxes 30×50×8 cm were used for rooting and they were placed under polyethylene tunnels in growth chambers in the air temperatures 10 and 15°C under artificial light (200 mol×m^-2×s^-1 PAR). Captan was applied once a week to protect cuttings from fungal attack.

After six weeks of the rooting process root system quality was evaluated according to 5-grade scale and the number of roots per cutting was determined. The experimental design applied was factorial design with following factors: time of cutting, temperature of rooting and rooting substances. Five replicates (20 cuttings in each) per experimental treatment were used. The results obtained were subjected to analysis of variance and Duncan’s multiple range test was used at the 5% level of significance.

RESULTS

Rooting ability of cuttings depended on the date they were harvested (tab. 1). However, in all dates investigated, percentage of rooted cuttings was very high (98-100%). Other factors studied, i.e., temperature of rooting and hormone powder applied, had no significant effect on percentage of rooted cuttings (data not shown).

All factors investigated (date, temperature of rooting process and rooting hormone powder) had highly significant effect on number of roots produced by cuttings. There was observed a highly significant effect of interaction between date of cutting and hormone powder applied (tab. 2). The highest number of roots was produced by cuttings harvested on September 28 and treated with Ukorzeniacz A (20.6 roots/cutting). Cuttings obtained on November 9 and treated with the same rooting powder (Ukorzeniacz A) formed slightly lower number of roots (19.0). Generally, in each date the highest number of roots was obtained after treatment of cuttings with Ukorzeniacz A (tab. 2) and the lowest number of roots was obtained for control plants (8.3 to 11.3 roots/plant depending on the cuttings’ harvest date). The average number of roots obtained at 10°C was higher than at 15°C (14.4 compared to 12.3 regardless of other factors). However, interaction of all factors investigated, i.e., cuttings harvesting date, rooting temperature and hormone powder was statistically significant. The differences in number of adventitious roots between temperatures 10°C and 15°C were lower for experimental combinations in which effect of hormones applied to cuttings was relatively high i.e. for Ukorzeniacz A applied in all dates of cuttings’ harvest and for Ukorzeniacz B and AB applied in September and November (fig. 1).

Similarly to number of roots, quality of root system also depended on all investigated factors, which were highly significant. Additionally, interactions of first and second order between studied factors were highly significant. The highest quality was obtained for cuttings harvested on September 28 (3.1) and the lowest (2.4) for July 6 (tab. 3). Temperature 10°C was better than 15°C (cuttings quality – 3.0 and 2.5 respectively). However, if regarded interactions between cuttings harvesting date and hormone powder applied, the highest cuttings’ quality (3.6) was obtained for cuttings harvested on September 28 and treated with Ukorzeniacz A (tab. 3).

Generally, lower temperature (10°C) during rooting process gave better quality of root system after six weeks. Effect of temperature on cuttings root system quality was lower for combinations, that provided the highest rooting and quality of cuttings, i.e., cuttings treated with Ukorzeniacz A in all dates investigated and cuttings treated with Ukorzeniacz B and AB at September 28 and November 9 (fig. 2).

DISCUSSION

The results obtained in the presented experiments showed that rooting ability depends highly on a date of cuttings’ harvest. Percentage of cuttings with adventitious roots differed slightly but significantly (from 98% to 100%). However, number of roots per cuttings and root system quality showed big differences among cutings’ harvesting dates. Seasonal changes in rooting have been observed for many years [15]. This indicates that the physiological status of the stock plant at the time the cuttings are excised is of great importance for the rooting process. It seems to be related to seasonal variation in temperature, irradiance level and photoperiod. The rooting ability of herbaceous cuttings fluctuates during the season even if they are taken from stock plants grown in greenhouses. Our results are in agreement with those presented for Aubrieta cultorum by Grunert [8] and Hellwig [12]. They stated that optimal period of taking cuttings is autumn, when the basal parts of shoots are wel l hardened. In the experiments presented by Jarocka and Hetman [13] rooting percentage was relatively low, but optimal period for rooting was also in September.

Temperatures in the rooting medium and ambient glasshause air temperatures are very important factors influencing rooting. Strong influence on root formation have also temperatures during stock plants growth. Cuttings taken from stock plants grown at very low temperatures (3-4°C) had more roots than those grown at higher ambient temperature [15]. Better rooting of cuttings taken on September or November may confirm those results. The cuttings of Aubrieta cultorum rooted better when propagated at low temperatures (10°C compared with 15°C). For some species poor rooting appeared to be associated with cuttings health. High temperatures favor fungal disease, the cuttings rooting in low temperatures exhibited a greater resistance to disease [5]. Other studies [14] have suggested that rooting was best at lower temperatures, probably because respiration rates were reduced. In contrast to these results Carpenter [6] found that rooting of the cultivars of evergreen azaleas was best and mo st rapid at 24°C with progressive delays and declining root development at 21, 18 and 15°C.

Root initiation is dependent on the presence of auxin whether endogenous or artificially applied [9]. Additional naturally occurring and a synthetic auxin has been reported to stimulate rooting in cuttings [2]. In our experiments rooting powder containing 0.3% IBA (Ukorzeniacz A) was better than powder containing NAA (0.2%) or mixture IBA and NAA (0.05% and 0.3%) (Ukorzeniacz B and AB, respectively). These data confirmed previously reported observations on many species that IBA is more effective in rooting process than NAA [2].

CONCLUSIONS

1. Rooting powder containing 0.3% IBA (Ukorzeniacz A) was most effective in rooting of Aubrieta cultorum cuttings. It induced the highest number of adventitious roots and gave the highest quality of rooted cuttings in all collection dates.

2. Cuttings of Aubrieta cultorum harvested on September 28 and rooted for six weeks had the highest number of roots and the best quality, irrespective of other factors investigated.

3. Temperature 10°C was more effective than 15°C in rooting Aubrieta cultorum cuttings. However, the effect of temperature was not statistically significant if other factors (date of cuttings harvest and rooting powder applied) were optimal.

4. The best root system and the highest quality had cuttings of Aubrieta cultorum harvested on 28 September, treated with Ukorzeniacz A (0.3% IBA, 0.1% Benomyl and 1% Captan) and rooted at 10°C.

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