Individual study: Vegetative propagation of three mangrove tree species by cuttings and air layering, Pichavaram, Tamil Nadu, India
Eganathan P., Srinivasa Rao C. & Anand A. (2000) Vegetative propagation of three mangrove tree species by cuttings and air layering. Wetlands Ecology and Management, 8, 281-286
In sub-tropical and tropical mangroves may protect coastlines and provide important estuarine habitats; they are also of great significance in terms of their use for wood and fish produce. Due to natural and anthropogenic pressures, mangrove forests are being destroyed every year and strategies that can expedite the restoration of degraded areas are being investigated.
Rooting of cuttings: Semi-soft wood cuttings (about 30 cm in length; basal diameter 8–15 mm) were collected from secondary mangrove branches. Basal ends were dipped for 5 min in a rooting hormone solution (see below) to a depth of 1 cm. The terminal end was sealed with cow dung to prevent desiccation. Cuttings were planted in polythene bags in a sand:clay (1:1 w/w) substrate and placed in low cost mist chamber (60–90% relative humidity at 28-30ºC, controlled through intermittent spraying with water) for 1 month. Cuttings were then transferred to a field nursery in mangrove forests of Pichavaram, Tamil Nadu, southeast India.
Air layering: Experiments were conducted over 2 years between October to January (the monsoon period coinciding with the flowering season), and between February to April (just after the monsoon). A ring of bark c.2.5 cm width was removed from around the shoot (to be rooted) and covered with rooting medium (1:1 clay: sphagnum moss) which was wrapped in a layer of polythene. The rooting medium was treated with various concentrations and combinations of the auxins: Indole 3 butyric acid (IBA) and naphthalene acetic acid (NAA); it was kept wet by spraying with water once every three days.
Monitoring: Roots were monitored for rooting response. A minimum of 20 samples were used for each treatment in the study. Data were recorded for percent rooting, number of primary roots and root length.
Root initiation was first observed after 6–7 weeks in the majority of shoots, and the cuttings which developed roots were ready for planting out in about 13 weeks.
In both cuttings and air layer experiments, all the three species, responded better to IBA (2,000– 2,500 ppm) over control, NAA or a combination of IBA and NAA: for H. fomes maximum percentage of rooting (64%), average number of roots (8.1) and root length (4.1 cm) was observed when cuttings were treated with 2,500 ppm IBA); I.bijuga also responded best with IBA (2,500 ppm); E. agallocha produced highest rooting response (68%) and number of roots (7.1) with 2,000 ppm IBA.
All air layers showed a rooting response after 6 weeks. Observations at 7 weeks showed rooting response to be maximum with IBA treatment of 2,000 ppm for E.agallocha and I. bijuga, whereas H. fomes responded best with 2,500 ppm IBA. The rooted air layers when separated from the branch were successfully established in the substrate.
Effect of season: Season played an important role in rooting characteristics as a marked seasonal variation was apparent. Maximum rooting was obtained in cuttings and air layers made during October to January. October was found to be the best time for taking cuttings of H.fomes (55%) and E.agallocha (46%), whilst for I.bijuga January planted cuttings had best rooting response (46%). Cuttings planted between July and November showed no signs of sprouting or rooting in any treatments. In all three species air layers made in October showed best rooting response, and average number of roots per cutting was greatest in October.
Conclusions: The authors suggest that this study identifies a cost effective and promising technique for the propagation of these three mangrove species for raising populations in nurseries or directly planting into the field.
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