Rooting Response of Hardwood Cuttings of MM111 Apple Clonal Rootstock to Indolebutyric Acid and Rooting Media

MATERIALS AND METHODS

This study was conducted in Khorasan Razavi Natural Resource and Agricultural Research Center, in Mashad, Iran during 2009 and 2010. Hardwood cuttings were collected in February. Treatments consisting of four concentrations of IBA (0, 1500, 2500 and 3500 mg L^-1) and three rooting media (cocopeat, perlite, cocopeat + perlite 1:1 by volume) in a factorial design were applied to stem cuttings. Twenty centimeter-long cuttings were prepared and treated with a commercial fungicide, Captan, by being dipped in a liquid solution for 5 sec. After surface drying, the cuttings were dipped for 10 sec in one of four concentrations of IBA, which was dissolved in a solvent composed of 50% ethanol and 50% distilled water. The control cuttings were treated with distilled water. After treating, the cuttings were planted in cocopeat, perlite, or perlite+cocopeat (1:1 by volume) to a depth such that the third node below the terminal whorl was 1 cm below the surface of the medium. The cuttings were maintained under mist for 45 days on a rooting bench in a greenhouse. The bottom of the rooting bench was heated at 24°C and the temperature and relative humidity in the greenhouse were kept at 21±2°C and 70-80%, respectively.

In the experiment, the percentage of rooting, the number and length of rooted cuttings were measured and the percentage of rooting was calculated (Hartmann et al., 2002).

This experiment had a Completely Randomized Design (CRD) with factorial arrangement in three replications including 15 cuttings per each replicate. Data were analyzed with SPSS (SPSS Inc., Chicago, USA) and means were separated by Duncan’s multiple range test.

RESULTS AND DISCUSSION

Table 1 indicated that media and IBA concentrations has significant effect, while interaction has non significant on rooting percentage. Based on the result, the highest rooting percentage (37.03%) was obtained in the concentration of 2500 mg L^-1 IBA (Table. 2). Our results were close to those of Tajbakhsh et al. (2009). Our finding showed that the exogenously applied IBA and its levels were both very critical in the present experiments to increase the percentage of rooting. IBA may enhance rooting via increase of internal-free IBA, or may synergistically modify the action of IAA or the endogenous synthesis of IAA. IBA can enhance tissue sensitivity to IAA and increase rooting (Vander Krieken et al., 1993).

Rooting media and IBA concentrations significantly affected the number of main roots per cutting (Table 2). More roots were produced in cocopeat + perlite than the other media (p<0.01). All IBA treated cuttings, except those treated in 3500 mg L^-1, gave more roots than the controls (p<0.01). The 2500 mg L^-1 IBA was the best treatment in terms of the main root number and rooting percentage (except the root length) per cutting in all of the media. The results of this experiment were similar to those of Iqbal et al., (1999) who reported that the number of roots are enhanced by increasing the IBA concentration to 3000 mg L^-1.

Table 1:	Analysis of Variance (ANOVA) of survival and rooting percentages of MM111 apple cutting
ns: Not significant. * and ** significant at 5% and 1% levels respectively.

Table 2:	The effect of media, IBA concentration on rooting, root length and number of main root per cutting of apple ‘MM111’
Values followed by the same letter in the same column are not significantly different at the 99% level according to Duncan’s test

The induction of maximum number of roots in the treated cuttings may be due to the fact that cambial activity involved in root initiation is stimulated by growth regulators in many species (Ullah et al., 2005).

Both rooting media and IBA concentrations significantly affected root length (p<0.01) (Table 2). Cuttings in perlite+cocopeat medium had longer roots than they had in other media. IBA treated cuttings, except those treated with 3500 mg L^-1, gave longer roots than control did in all medium types.

The best treatment in terms of rooting length was in 1500 mg L^-1 concentration (10.5 cm). But the best treatment in terms of rooting number was in 2500 mg L^-1 concentration (11.33). This showed that by increasing IBA concentration, root length decreased, but root number increased. Wagner and Oprita (1985) reached the same conclusion in Sweet cherry, they showed that low auxin concentrations cause lower root number but increase its length and high concentration increases the root number and decreases its length. The application of auxin causes the enhancement of ethylene synthesis (Hansen, 1987) which inhibits root length growth (Etri, 1991).

Our findings showed that rooting decreased by increasing IBA concentration (3500 mg L^-1). Our data are consistent with a study suggesting IBA treatment with high concentration reduced rooting percentage in cuttings of MM106 (Sun and Bassuk, 1991). Moreover, Karakurt et al. (2009) reported that the best concentration of IBA for rooting was 1000 mg L^-1 for MM106 apple rootstock but by increasing IBA concentration to 2000 mg L^-1 and 4000 mg L^-1 no rooting occurred.

Our result revealed that rooting was significantly higher in cuttings in cocopeat + perlite medium than other media (p<0.01). Improved rooting in this medium can be due to the improvement of both aeration and water holding capacity (Islam, 2008).

Our experiment showed that the lowest rooting percentage was obtained from cocopeat medium. This might be because of its phenolic compounds which cause phytotoxicity, its high salinity (Ma and Nichols, 2004) and high water holding capacity leading to low aeration (Abad et al., 2002).

In perlite medium, rooting percentage was also low. It seems that it is due to its low water retention capacity. Most of the granular inorganic substrates such as perlite have low water retention capacity (Martyn and Szor, 2001).

This result suggests that cocopeat medium retains more water and less air space than the 100% perlite.

CONCLUSION

In conclusion, the results confirmed the importance of exogenous IBA applications and that choosing the right concentrations of IBA for rooting was of critical importance. The application of IBA with a concentration of 2500 mg L^-1 and cocopeat + perlite medium were found to be the most suitable for rooting of hardwood cuttings of MM111 apple clonal rootstock. However, apart from IBA and rooting media, other factors such as the temperature of rooting media, cutting type and the timing of cutting sampling should be taken into consideration. When this method is compared to other methods of propagation such as grafting and layering, it saves time and is a more economical way of propagation than these alternatives.