Rooting Products and Cutting Timing for Peppermint (Mentha piperita L.) Radication

Transcription

1 Rooting Products and Cutting Timing for Peppermint (Mentha piperita L.) Radication S. Nicola, J. Hoeberechts, E. Fontana AGROSELVITER, Vegetable Crops & Medicinal and Aromatic Plants, Università degli Studi di Torino, Grugliasco, Italy. Keywords: Auxins, medicinal and aromatic plants, organic farming, root length. Abstract Peppermint is native to Europe and has become both cultivated and naturalised in many countries, including the USA, India, China, Italy, France and Hungary. As a hybrid, peppermint seldom produces seeds that will germinate. As a consequence, the plant is propagated mostly from its vegetative parts, such as green shoots and underground stolons. Cuttings are one of the most important means of plant propagation. The aim of this research was to evaluate propagation by cuttings on peppermint, testing natural rooting hormones for organic farming and synthetic auxins with different application procedures to increase rooting. The experiments started on October 1 and ended on May 2, leading to 12 runs, which were done every two weeks. Treatments consisted of 7 commercial rooting products, one of which applied in two ways, leading to 8 product treatments, plus an untreated control. Trays were located on a bench provided with mist irrigation system. Starting three weeks after each cutting, 4 weekly samplings took place to evaluate rooting degree, measuring the longest root length. The experimental design consisted of a completely randomised design with rooting products as a factor (9 levels: 8 products plus control) with 4 repetitions. The use of rooting products had a positive effect on root system differentiation and development of peppermint. Six weeks after cutting the longest root was about 6 mm long. Thirty-six days after cutting the longest root of cuttings treated with rooting products was significantly longer (15 mm) than the longest root of untreated cuttings. No differences were found between cuttings treated with rooting products of synthetic origin and those treated with rooting products registered for organic farming. Throughout the seasons, rooting products did not show any particularly different behaviour, but using rooting products has been necessary to guarantee the rooting of cuttings for earlier transplanting. INTRODUCTION The genus Mentha (Labiatae) is composed of 19 geographically widespread and 13 named hybrids (Chambers and Hummer, 1994). Peppermint, M. x piperita, is native to Europe and is both cultivated and naturalised in many countries, including the USA, India, China, Italy, France and Hungary. The mint essential oil is considered industrially important (Lawrence, 1985; Tucker, 1992). Peppermint oil is one of the most popular and widely used essential oils, mostly because of its main components, menthol and menthone (Gul, 1994). There are no up-to-date statistics on the mint cultivation and mint oil production in different countries. The USA and India are now the major sources of mint, with China the third largest producer (Stevens, 5). According to a summary report published on the web, in 1 the USA harvested about 37, ha (Anonymous, 2). The area cultivated for Mentha spp. in India is estimated at about 125, ha (Anonymous, 5). India is also one of the largest mint oil producers (Aflatuni, 5; Stevens, 5), exporting about 8,5 tons of oil in 2-3 (Aflatuni, 5), and producing about 15,-, tons of mint oil and exporting 3, tons (Anonymous, 5) in 5. A significant part of India s production is also exported in the form of various derivative products of mint oil, such as menthol. In the north of Italy (Piedmont Region) peppermint is cultivated on about 326 ha (Nicola et al., 3; 4b) and is an important produce of geographical origin. Proc. I st IC on Labiatae Eds.: B. Ruffoni et al. Acta Hort. 723, ISHS 6 297

2 The vegetative propagation is widely preferred to seeding propagation because seed germination of medicinal and aromatic plants (MAP) is sometimes lower than 5%, and seed selection programs are lacking. Mints are mainly propagated by vegetative reproduction rather than by seeds. Only some mints, such as M. arvensis L., M. pulegonium L. and M. spicata, are propagated by seed (Galambosi, 1995). According to Hornok (1992), peppermint, as a hybrid, seldom produces seeds that germinate. For this reason, propagation is used only with vegetative parts such as green shoots, underground stolons, and rooty turions. The vegetative propagation is used when seed germination is very low. Enhancing cutting propagation techniques are recommended to standardise plantation quality. Increasing demand for organic farming techniques also requires further research to match the needs for organic nursery material. The aims of the present research were to evaluate the propagation by cutting on peppermint (Mentha x piperita L.), testing rooting products registered for organic farming and rooting products of synthetic origin to increase rooting, and to evaluate the difference on rooting among the tested products. MATERIALS AND METHODS The experimental trials were done in a greenhouse at the Experimental Center of the Faculty of Agriculture of the University of Turin (Carmagnola, TO, Italy, N; 7 65 E), where cuttings were produced every 2 weeks. The experiments started on 16 th October 1 and ended on 3 th April 2, leading to 12 runs. At each experiment 14-cell plastic trays were filled with a medium specific for aromatic plants ( Steckmedium, Klasmann-Deilmann GmbH, Geeste-Groβ Hesepe, Germany), a mix of peat moss and perlite, with ph ranging from 5 to 6, composed by 3% d.m. organic carbon of biological origin,.4% organic nitrogen, and 5% organic matter. The medium was well pressed in the cells and wetted with water until saturation. Portions of stem about 8-mm long with lateral buds were cut from disease-free stock plants. About one third of the leaf surface of each cutting was removed to limit the transpiration. Cuttings were treated and immediately planted into holes punched into the medium. Treatments considered were 7 commercial rooting products, already tested in other experiments (Nicola et al., 4a; 5). Rooting Products Registered for Organic Farming, rprof (Cytokin, Radix ), and Rooting Products of Synthetic Origin, rpso (Germon, Naftal, Kendal, Radifarm, Stimolante 66f ), plus an untreated control were compared. According to the application procedures, cuttings were either soaked in the solution for the requested time (Naftal and Cytokin ), or sprayed with the solution until medium saturation (Cytokin, Stimolante 66f, Kendal, Radifarm and Radix ), or dusted in the powder product (Germon ). One product (Cytokin ) was applied in two ways, leading to 8 product treatments. Trays were located on a bench provided with mist irrigation system; irrigation management varied throughout the year according to cutting needs. Four weekly samplings (22, 29, 36 and 43 days after cutting, DAC) were used to evaluate rooting degree starting three weeks after each cutting. The roots of 4 cuttings for each treatment and cutting period were carefully washed in water to eliminate the growing medium. The length of the longest root was measured. The treatments were arranged according to a completely randomized design with rooting products as a factor (9 levels: 8 products plus control) with 4 repetitions. Data were submitted to the analysis of variance and to preplaned orthogonal contrasts for each run and for pooled runs. Orthogonal contrasts considered for the longest root length were: 1) rooting products vs control, 2) rprof vs rpso, 3) Cytokin vs Radix, 4) Products based on NAA (rpnaa) vs Products based on fertilizers (rpfertilizer). RESULTS AND DISCUSSION Rooting of peppermint cuttings was significantly affected by treatments at 22, 36 and 43 DAC in terms of the longest root length (data not shown). Orthogonal contrasts were considered for each sampling with twelve-run pooled cuttings. Results of the 298

3 contrasts indicated that the development of the longest root was favoured by applying rooting products (Table 1). Root length increased with rooting product application versus the control and this difference increased over time. Consequently, rooting products produced rooted plants ready for transplanting earlier than the control products, reducing nursery period. Rooting products always guaranteed the rooting at each run, while this was not assured by the control (Fig. 1). For example, at the second, the sixth and the tenth run, control cuttings did not root even at 43 DAC. Seasonal variation in rooting promotion is very common in plants, but the optimal time for rooting must be established individually for each species (Howard, 1996). Karawyia et al. (1977) found that autumn cutting in North Africa gave lesser yields of Mentha x piperita and Mentha spicata herbs and their oil was of lower quality. Our experiments indicated that overall cuttings prepared in autumn gave poor root growth in general, producing shorter root lengths than in winter or spring, regardless of rooting product application (Fig. 1). This confirmed that autumn is not the perfect season to produce mint cuttings in the Mediterranean areas. The success of mint propagation by cutting is linked to season, but also may be related to the physiological status of the stock plant. Mother plants tend to decline their vigor with autumn approaching (data not shown). The orthogonal contrast between cuttings treated with rprof vs rpso was not significant throughout the 12 cutting runs (Table 1). However, in autumn when the season was not favourable, the products registered for organic farming gave better results (Fig. 1). Growers adopting organic farming have potential products to use for mint production and all growers may choose rprof with a low environmental impact. Among the products registered for organic farming, no statistically significant difference was observed between Cytokin and Radix except in the 1 st sampling, at 22 DAC (Table 1). The rooting action of Radix on cuttings was faster than Cytokin rooting action, allowing the longest root to reach 4.8 mm in 22 days, which was the highest value among the treatments. Then, Cytokin allowed the roots to fill the gap; similar results were obtained in thyme cuttings (Nicola et al., 4a). Throughout the seasons, Cytokin and Radix did not show any particular different behaviour compared with the general trend of the rooting products (Fig. 1). Auxin treatments are a common practice to induce rooting in reluctant species as well as to promote rooting in spontaneous rooting species (Kracke and Cristofori, 1983; Eliasson and Areblad, 1984). Other products, such as biostimulants, are recently used to enhance plant growth and quality, and are basically based on fertilizer elements (Sarli and Marzi, 3). The contrast between products base on NAA (Stimolante 66F, Germon, Naftal ) and products based on fertilizer (Kendal and Radifarm ) was not statistically significant (Table 1). The cuttings treated by the former products slightly produced longer roots than cuttings treated by the latter products, even if the difference was not statistically significant. Throughout the seasons neither type of products highlighted an outstanding performance compared with the general trend of all the products used (Fig. 1). Overall results indicated that fertilizers with rooting action, such as Kendal and Radifarm could also be used for cutting in order to stimulate the plant activity. Similar results were obtained in thyme and sage cuttings (Nicola et al., 4a, 5). The research conducted on peppermint was part of a series of trials involving different aromatic species, all of which confirmed that using rooting products is necessary to guarantee the rooting of cuttings and earlier transplanting (Rizzo, 2; Nicola et al., 4a; 5). In general, peppermint cuttings produced longer roots than other aromatic species, such as thyme, sage and rosemary. Growers may choose the rooting product apart from the season and the product class. Further research should continue to understand the effect of rooting products on peppermint quality in terms of aromatic compounds synthesis since the importance of peppermint essential oil. ACKNOWLEDGEMENTS Thanks to Riccardo Rizzo for his MSc work and Giuseppe Piovano, Mario 299

4 Gilardi, Gabriele Gariglio, Mauro Gilli and Paolo Gastaldi for their field work. The authors have contributed equally to the research and to the manuscript. Literature Cited Aflatuni, A. 5. The yield and essential oil content of mint (Mentha spp.) in northern ostrobothnia. Academic dissertation Faculty of Science, University of Oulu, Linnanmaa. 5 pp. Anonymous, 2. Pest Management Strategic Plan for Pacific Northwest Mint Production. In: (up-to-date on 25 March 6). Anonymous, 5. MCX launches Mentha oil futures. In: The Financial Express, Wednesday, April 27, 5. In: Content_id=8913 (up-to-date on 31 January 6). Chambers, H.L. and Hummer, K.E Chromosome counts in the Mentha collection at the USDA-ARS national germplasm repository. Taxon. 43: Eliasson, L. and Areblad, K Auxin effect on rooting pea cuttings. Physiol. Plant. 61: Galambosi, B Mauste-ja rohdosyrttien luonnonmukainen viljely. Helsinki: Printing center (Painatuskeskus) ISBN Gul, P Seasonal variation of oil and menthol content in Mentha arvensis Linn. Pakistan Journal of Forestry 44:16-. Hornok, L Peppermint (Mentha piperita L.) in cultivation and processing of medicinal plants. Akademiai Kiado, Budapest. p Howard, B.H Relations between shoot growth and rooting of cuttings in three contrasting species of ornamental shrub. J. Hortic. Sci. 71: Karawyia, M.S., Hifnawy, M.S., El-Hawary, S Effect of nitrogen fertilizers, time of cutting and drying on Mentha piperita and Mentha spicata L. Egypt. J. Pharm. Sci. 18(4):45. Kracke, H. and Cristofori, G Effect of IBA and NAA treatments on the endogenous hormones in grapevine rootstocks hardwood cuttings. Acta Hort. 137: Lawrence, B.M A review of the world production of essential oils (1984). Perfumer & Flavorist 1:1-16. Nicola, S., Saglietti, D., Hoeberechts, J., Fontana, E. 3. La coltivazione di piante officinali in Piemonte: situazione attuale e prospettive. Quaderni della Regione Piemonte, Ambiente 38: Nicola, S., Fontana, E., Hoeberechts, J. 4a. Cultural techniques to optimize the thyme (Thymus vulgaris L.) propagation. Acta Hort. 631: Nicola, S., Hoeberechts, J., Fontana, E., Saglietti, D. 4b. Medicinal and Aromatic Plants in Italy: situation and perspective for the Piedmont Region. Acta Hort. 629: Nicola, S., Hoeberechts, J., Fontana, E., Saglietti, D. 5. Rooting Products and Cutting Timing on Sage (Salvia officinalis L.) Propagation. Acta Hort. 676: Rizzo, R. 2. Effetti dell impiego di radicanti convenzionali e ammessi in agricoltura biologica e dell epoca di taleaggio sulla propagazione per talea di piante officinali. MSc. Thesis, S. Nicola Advisor, Università di Torino, Torino. 19 pp. Sarli, G. and Marzi, V. 3. Valutazione, in vivaio ed in piano campo, di biostimolanti su specie rappresentative dell Italia. Italus Hortus 1(suppl. 4): Stevens, T. 5. Lecture: The Changing World of Mint. In: (up-to-date on 25 March 6). Tucker, A.O The truth about mints. The Herb Companion. 4:

5 Table Table 1. Longest root length in cuttings in 4 samplings (22, 29, 36 and 43 days after cutting, DAC), orthogonal contrasts and P values. Twelve-run pooled cuttings. Figure ) Treatments 22 DAC 29 DAC 36 DAC 43 DAC Control Rooting products Significance (P=) <.1.1 rprof rpso Significance (P=) Cytokin Radix Significance (P=) rpnaa rpfertilizers Significance (P=) Rooting products Control rprof rpso Cytokin Radix rpnaa rpfertilizer Figure 1. Longest root length in cuttings on 43 DAC at each run for each tested contrast. 31