Cutting propagation of Victorian smoke-bush, Conospermum mitchellii (Proteaceae)

Rooting and death of vegetative tip cuttings of Victorian smokebush, Conospermum mitchellN Meisn., taken from softwood, semi-hardwood and hardwood material, were examined using formUlations of auxins (IBA and NAA) at three air temperatures (20'C/16' C,25'C/20'C and 28'C/23'C ; day/night) . This species was found easy to propagate, particularly if softwood material is used or cuttings are treated with an I SA-based formulation . Formulations containing NAA should be avoided as they result in few rooted cuttings and a high incidence of cutting death. Air temperature had no significant impact on rooting under conditions of high relative humidity and root-zone heating.

The smokebushes, Conospermllm spp., are representatives of the family Proteaceae, sub-family Proteoideae, which has provided floriculture with several we ll -known A frican genera such as Prolea, Leur:ospermuln and Leucadendrol1, as well as the Australian Slirlingia. Most Conospermul11 species occur in Western Australia, and several of the western species are harvested extensively from natural populations for domestic and export use as cut flowe rs (Wrigley & Fagg 1991). The western species are considered difficult to propagate (Sainsbury 1991), and the purpose of thi s research was to assess the amenability to propagation of one of the eastern species.
Victorian smokebush, C. mitchel/ii Meisn., is an eastern species which occurs as an upri ght woody shrub to 2 m in hei ght, producing large attractive terminal corymbs of white or pale cream fl owers, sometimes tinged with blue or lil ac, in late winter and spring. The species is currently being assessed for commercial exploitation as a cut flower (T. Slater, personal communication), and may also have value as an ornamental species or as a rootstock for the western species.
Vegetative tip cutti ngs of C. mitchellii were collected from a large natural stand near Anglesea,Victoria (38 ' 25'S,144' II 'E) in late-November, mid-March and late-May representing softwood, se mi-hardwood and hardwood cuttings respectively. After overnight storage at 4°C, cuttings were trimmed to 80 mm length, leaves were removed from their basal halves, and the stem ends were dipped in treatment solutions for approximately 40 s. Five different solutio ns were assessed: 1) water; 2) a commercial gel containing 3000 mg I" indol e-3-butyric acid (IBA) + macro-and micro-nut rients (Growth Technology, South Fremantie, Western Australia); plus fresh 50% ethanol solutions of 3) 5000 mg I" IBA, 4) 5000 mg 1-' a-naphthaleneacetic acid (NAA), and 5) 3500 mg I" IBA + 1500 mg I'] NAA. A 50% ethanol solution was requ ired for dissolving hi gh doses of IBA, 243 which precipitates at about 30% ethano l containing 40 00 mg I-I lBA (Dawson and King, 1994). Each treated cutti ng was placed individually in a 50 mm wide tube containing a steam-sterilized I: 1 : I coarse sand: perlite: peat mixture. Tubes were placed randomly in moist vermiculite in heated trays which maintained a root zone temperature of 28°C. An automatic misting system controlled by evaporative sensors, and polyethylen e frames reaching I m above cutting height, maintained high re lati ve humidity. The propagating trays were located in glasshouse cells which provided fine control of air temperature under natural illumination. Three air temperature regimes were tested: 20' C1I6' C, 25' C120' C and 28' C/23' C (day/night; 12 h/ 12 h cycle). For every treatment combination, 20 cuttings were used, and the percentage of rooted and dead cuttings for each combination was recorded after 8 weeks. Dead cuttings clearly di splayed stem and leaf necrosis. Cutting type, auxin and air temperature effects on the percentage of rooted or dead cuttings were assessed using 3-way analyses of variance without replication. Where significant differences were detected, Tukey's HSD comparisons were performed.
Rooting percentage and cutti ng mortality were not significantly affected by air temperature, but both were significantly affected by cutting type and by auxin treatment (P < 0.05) ( Table  1). Softwood cuttings were the most amenable to propagation, providing a higher rooting frequency than either semi-hardwood or hardwood cuttings, as well as a lower incidence of cutting death than hardwood cuttings (Tab le 2). The highest rootin g frequencies were also obtained using formulations containing IBA,  except when accompanied by NAA (Table 3). Formulations containing NAA greatly increased cutting mortality.
These results indicate that C. mitchellii is highly amenable to propagation from cuttings, particularly if softwood cuttings are used and the stern ends are dipped in IBA-based formulations. Conventional propagating systems that provide misting and root temperature control appear satisfactory for C. mitchellii propagation over a range of air temperatures. The suitability of softwood in preference to semi-hardwood or hardwood cuttings is consistent with results from a range of Au stralian woody shrubs (Dawso n & King 1994). Formulations containing both IBA and NAA have been recommended for Persoonia propagation (Ellyard 1981a;Carmen 1993) but cuttings of many other Proteaceae, including Grevillea and Banksia, have responded best to IBA treatments (Ellyard 1981 b;Ellyard & Ollerenshaw 1984;Bennell & Barth 1986;Carmen 1993). The results for C. mitchel/ii confinn the finding that some Proteaceae, such as Protea, are susceptible to tissue death following NAA treatments (Gouws et 01. 1990).
The role of chemical fun gic ides and pesticides is currently under closer scrutiny than ever before. As safety standards in developed countries increase and new data all health and environmental hazards become ava il able, more and more products are being withdrawn from the market (Evans 1995) . Current research is concentrati ng on alternat ive contro l methods. This has led to the re-examination and improvement of many old practices and to the development of new methods in co ntrolling plant di seases. It has been reported by Hasset et at. ( 198 7) and Kai el al. ( 1990) that humic substances possess an antimicrobial activity. Humic acid, isolated from domestic sewage, was shown by Hasset e f al. (1987) to have bactericidal activity against Serratia marcescellS Bizio and Staphylococcus allrelfS Rosenberg. No direct reference to the antimicrobial activity of fulvic acid has been reported in the literature (Bosch 1993 ). However, water-soluble extracts, poss ibly fulvic acid, of bark were shown to have antifungal activity on compost (Kai et al. 1990; Hardy & Sivasithamparan 1991).
Alternative uses for the country 's abundant coal reserves and the need to overcome its lack of id entifiable commercially recoverable crude oil reserves has been documented and this encouraged the research fraternity to explore the benefication of coal for other appl ications. This led to the deve lopment of an environmentally friendly, controlled, wet coal oxidation process for the production of non-toxic chemicals that are similar to th e humic acids and fulvic acids found ' naturaily in fertile soils. These