The Effect of Different Levels of Indole-3-butyric Acid (IBA) and Naphthaleneacetic acid (NAA) on the Rooting of Pear Stem Cutting

Introduction Pears have a high nutritional and economic value worldwide. One of the major problem in growing pear cultivars is their late fertility on seed bases. To solve this problem, using asexual propagation methods can lead to the production of root trees. Cuttings are commonly used for proliferation either softwood, semi-hardwood or hardwood. Clonal propagation is considered proper in rapid propagation of shrubs and trees species. Adventitious root formation in stem cuttings is a crucial physiological process for vegetative propagation of many plant species. Rooting ability of tree species through stem cuttings is affected by several factors particularly plant growth regulators. Rooting of pear stem cuttings is time consuming. Auxin is effective in stimulating root formation on cuttings. The most widely used auxins in rooting of stem cuttings are indole-3-butyric acid (IBA) and naphtaleneacetic acid (NAA). Of these two auxins, IBA is the most widely used root promoting chemical, because it is nontoxic over a wide range of concentrations. Applied concentration is an important factor. Typically, a concentration of 2000 to 4000 ppm will result in good rooting for most shrubs and trees.Materials and Methods In this experiment, pear (Pyrus communis) was used as mother plants. Stem cuttings were used as plant materials in this experiment. The effect of different levels of indolebutyric acid (IBA) and naphthalene acetic acid (NAA) was studied on the rooting of pears in a factorial experiment based on a randomized complete block design with 16 treatments and 4 replications. The experimental treatments included IBA and NAA at the rates of 0, 1000, 2000 or 4000 mg L-1. Rooting percentage, rooting time, root number, root length, root volume, plant height, leaf number and fresh and dry weights of cuttings were measured after about 130 days.Results and Discussion The results showed that the highest rooting (3.56 per seedling) was observed in cuttings treated with 4000 mg L-1 IBA. Also, the highest root number was obtained from the treatment of 1000 mg L-1 NAA and 2000 mg L-1 IBA with an average number of 0.16 roots per plant. According to the means comparison for the simple effect of IBA on the rooting time, the highest rooting time was related to the application of 4000 mg L-1 IBA.  The results revealed that plants treated with 4000 mg L-1 NAA and 2000 mg L-1 IBA grew the longest roots. Also, ANOVA showed that among the applied factors, only the simple effect of IBA was significant on root volume. Means comparison for the simple effect of IBA on root volume showed that the highest was related to the application of 2000 mg L-1 IBA. According to the means comparison for the interactive effect of IBA × NAA on cutting fresh weight, the highest fresh weight was, on average, 8.36 g in plants treated with 4000 mg L-1 NAA and 2000 mg L-1 IBA. As well, means comparison the effect of IBA × NAA on cutting dry weight showed that the highest dry weight was 15.9 g related to the application of 4000 mg L-1 NAA × 2000 mg L-1 IBA. It was also observed that 2000 mg L-1 NAA × 1000 mg L-1 IBA was related to the longest cutting with an average length of 2.82 cm. Finally, plants treated with 4000 mg L-1 NAA and 2000 mg L-1 IBA produced the highest number of leaves (15.9 g, on average). One of the effective factors in the success of vegetative propagation of plants with stem cuttings, especially woody plants with hard-rooting stems, is the production of more roots in a short time. Plant growth regulators, including auxins, play an important role in this regard. The effect of auxins on the percentage and number of roots produced on stem cuttings has been shown by many researchers on various plants, including plants with hard-rooting cuttings particularly in trees. The most widely used auxins in this regard are IBA and NAA, respectively. The individual or combined effect of auxins for successful rooting depends on a number of factors, including plant type, cuttings type, cuttings size, cuttings age, and the time of year the cuttings were removed. In the present study, the combined effect of IBA and NAA had the greatest effect on most of the measured traits.