عنوان مقاله [English]
Introduction Pears have a high nutritional and economic value worldwide. One of the main problems in growing pear cultivars is their late fertility. The use of asexual propagation methods can lead to the production of own rooted trees to solve the problems. Cuttings are commonly used for proliferation either softwood, semi-hardwood or hardwood. Clonal propagation is considered as a suitable method for rapid propagation of shrubs and tree species. Adventitious roots 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 (PGRs). Rooting of pear stem cuttings is hard and time consuming. Auxin is an effective PGR in stimulating root formation on cuttings. The most auxins widely used 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 at high concentrations. Applied concentration is an important factor. Typically, a concentration of 2000 to 4000 ppm will result in proper rooting for most shrubs and trees.
Materials and Methods In this experiment, pear (Pyrus communis cv. ‘Bartlet’) was used as mother plants. Stem cuttings were used as plant materials. The effect of different levels of IBA and NAA was studied on the rooting traits of pear cuttings in a factorial experiment based on a randomized completely block design (R.C.B.D.) 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 applied individually and/or in combination to facilitate rooting of cuttings. 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 of analysis of variance showed that the interaction of IBA and NAA on all measured traits except for root volume was significant. Results showed that the least time (59 days) until start of rooting on cuttings and the highest number of root (16 per cutting) was obtained in cuttings treated with 1000 mg l−1 NAA together with 2000 mg l−1 IBA. There was no significant difference between this treatment and treatment of 4000 mg l−1 NAA together with 2000 mg l−1 IBA with induction of 15.66 roots. Maximum rooting percentage (57.66%) was obtained in cuttings treated with 4000 mg l−1 IBA. The longest root (51 cm per cutting), the highest cutting fresh weight (36.83 g) and dry weight (9.15 g) was observed in treatment of 4000 mg l−1 NAA together with 2000 mg l−1 IBA. Root length (49, 48.60 and 44 cm) was high in stem cuttings treated with 4000 mg l−1 IBA, 1000 mg l−1 NAA together with 2000 mg l−1 IBA and 2000 mg l−1 NAA together with 2000 mg l−1 IBA, respectively. The highest root volume (3.70 cm3 per cutting) was obtained in treatment of 4000 mg l−1 IBA. There was no significant difference between this treatment and treatment of 2000 mg l−1 IBA including 3.30 cm3 root volume per cutting. The largest number of leaf (9.93 per cutting) was observed in cuttings treated with 4000 mg l−1 NAA together with 2000 mg l−1 IBA. Treatment containing 2000 mg l−1 NAA together with 1000 mg l−1 IBA induced the highest plantlet length. Plantlet length (77.66 cm) was high through the use of 4000 mg l−1 NAA together with 2000 mg l−1 IBA. The most widely used auxins in the basal region of stem cuttings for induction and growth of adventitious roots are IBA and NAA. These two PGRs are much superior to the induction of rooting because of their greater chemical stability and their low mobility in the plant. The positive effect of IBA and NAA was shown on root induction in cuttings of many difficult-to-root plants including fruit trees. In the cases of auxin application, great variation was observed among the concentrations, formulations and forms of application of PGRs. Plant type, type, size and age of cutting and time of isolation of cuttings from trees, are also effective in the success or failure of rooting cuttings. Exogenous application of auxins enhances the rooting percentage due to their ability to act in plant tissues located near the region of contact with the PGRs. Therefore, the application of exogenous auxins increases the concentration of endogenous auxins, and the accumulation of them in the basal region of the stem cuttings act as a metabolizing agent and signal to induce rooting. During external contact with the cell, auxins induce changes in the metabolism of enzymes, carbohydrates, DNA, RNA and proteins, and these changes in the rooting zone may inhibit or promote regeneration of adventitious roots, mainly during cell division and differentiation. The success of IBA application is probably due to its low activity and its slow degradation by auxin destroying enzyme. The maximum number of sprouts per cutting with optimum IBA with or without NAA treatments might be ascribed to better root growth which augmented absorption and translocation of nutrients from the soil, which takes an active part in various plant metabolic processes. In the present study, the combined effect of IBA and NAA had the greatest effect on most of the measured traits.
Conclusion: In summary, IBA and NAA significantly improved the adventitious root initiation and growth of pear (Pyrus communis cv. ‘Bartlet’) shoot cuttings. The concentration of 4000 mg l−1 IBA induced the highest percentage of rooting and production of an acceptable number of roots on shoot cuttings. Therefore, the use of this treatment individually is recommended because it stimulates the highest percentage of rooting and is economical for rooting in pear shoot cuttings.