Australian Daisies - Germination Requirements

David Murray

This article has been reproduced from the April 1995 issue of Native Plants for New South Wales, newsletter of the Australian Plants Society (NSW).




Rhodanthe chlorocephala ssp rosea   
Rhodanthe chlorocephala ssp rosea.
Photo: Australian Daisy Study Group
  

Australian daisies are potentially very popular as ornamental pot plants. To help realise their full potential, a systematic evaluation of seed germination requirements was needed, as well as other information on vegetative propagation and flowering requirements.

In 1992, the Australian Flora Foundation provided a grant to help Dr K.V.Sharman and Dr R.M.Dowling at the Queensland Department of Primary Industries, Redlands Research Station, study the germination requirements of more than 20 species. They later secured further funding from HRDC (Horticultural Research and Development Corporation) to study flowering requirements.

Selection of Species

Because of the drought, a planned field trip to western Queensland to collect seed of species of interest was not undertaken. Instead, seed was obtained from commercial suppliers and volunteer donors from the Australian Daisy Study Group.

Germination Tests

   Chrysocephalum apiculatum
   Chrysocephalum apiculatum
     
   Schoenia filifolia subsp. subulifolia
   Schoenia filifolia subsp. subulifolia
     
   Lawrencella rosea
   Lawrencella rosea
Photos: Australian Daisy Study Group

The seed to be tested was first stored at room temperature for a minimum of 6 months, to eliminate any possible dormancy due to a requirement for a period of 'after-ripening'. Between three and six species were included in each germination trial, there being five trials altogether. Tests were carried out using 9 cm Petri dishes lined with filter papers. For each species evaluated, the treatments were:

  • intact seed incubated with water,
  • scarified seed (pierced with dissecting needles) incubated with water, and
  • intact seed incubated with gibberellic acid (GA3) at 500 mg per litre.

The fungicide Thiram (0.2 %) was included in both the water and the GA3 solution, dispensed at 5 ml per dish. For each treatment, there were five replicate dishes, each containing 15 seeds. The dishes were placed under ambient conditions with either a light/dark cycle, or continuous darkness (achieved by wrapping in alfoil).

The seeds of one species, Chrysocephalum apiculatum, were too small to scarify without damaging the embryo, hence this treatment was omitted. As the seeds were not dormant (see below), the absence of this treatment did not matter.

Emergence of the radicle was taken to indicate germination. Seeds that had germinated were counted every 3 days for 30 days, or at day 15 only for the dark treatments. At the end of the assessment period, ungerminated seeds were dissected, and those that contained partially formed or no embryos were scored as non-viable. Germination was then expressed on a viable seed basis.

Non-dormant species

Five species showed no dormancy and were not stimulated by light: Brachyscome latisquaemea, Podolepis gracilis, Rhodanthe chlorocephala subsp. rosea (syn. Helipterum roseum), Rhodanthe humboldtiana (syn. Helipterum humboldtianum), and Schoenia filifolia subsp. subulifolia (syn. Helichrysum subulifolium).

Four more showed no dormancy and were stimulated by light, although light was not an absolute requirement for germination: Brachyscome iberidifolia, Chrysocephalum apiculatum, Hyalosperma glutinosum subsp. venustum (syn. Helipterum venustum), and Watsia acuminata.

Dormant species

One species, Lawrencella rosea (syn. Helichrysum lindleyii) showed complete dormancy, overcome by scarification. Another two species showed complete dormancy, overcome by GA3: Chrysocephalum podolepidium and Leucochrysum molle (syn. Helipterum molle).

Altogether, nine other species showed partial dormancy. For two of these, Rhodanthe chlorocephala subsp. chlorocephala (syn. Helipterum chlorocephalum) and Rhodanthe manglesii (syn. Helipterum manglesii), scarification alone was sufficient to promote germination; and for one, Leucochrysum stipitatum (syn. Helipterum stipitatum) either scarification or GA3was effective.

   Rhodanthe manglesii
   Rhodanthe manglesii
Photo: Australian Daisy Study Group

The remaining six species all responded to GA3: Leucochrysum fitzgibbonii (syn. Helipterum fitzgibbonii), Myriocephalus stuartii, Podolepis jaceoides, Rhodanthe moschata (syn. Helipterum moschata), Rhodanthe polygalifolia (syn. Helipterum polygalifolium), and Rhodanthe stricta (syn. Helipterum stricta).

Failure to germinate

Seeds failed to germinate for one species under all circumstances: Erymophyllum ramosum subsp. involucratum (syn. Helipterum involucratum) .

Conclusion Regarding Depth of Planting

As a general rule those species with seeds responding to a light stimulus should be sown on the soil surface, with all others sown beneath a shallow cover.

Future Dormancy Assessment

Dr Sharman and Dr Dowling concluded that it would be worthwhile to test responses to a higher temperature during seed storage. Of interest also are observations from the Kirstenbosch Botanic Garden in South Africa showing that the compounds extracted from bushfire smoke have the ability to overcome dormancy in a variety of species, including the former genus Helichrysum (as reported in The Australian Garden Journal, 1995).

Horticultural Potential

A panel of seventeen retailers and wholesalers recently judged the horticultural potential of more than 40 species and varieties cultivated at Redlands Research Station ("Year round production of Australian daisies as flowering potplants"). Species were preferred on the basis that they had compact upright growth (less than 35 cm tall), and produced numerous small flowers, or several distinctive showy blooms.

The top nine, in rank order, were:

  1. Rhodanthe manglesii
  2. Rhodanthe floribunda
  3. Schoenia filifolia subsp. subulifolia
  4. Brachyscome halophila
  5. Lawrencella davenportii
  1. Schoenia cassiniana
  2. Hyalosperma cotula
  3. Lawrencella rosea
  4. Hyalosperma glutinosum subsp. venustum

It is gratifying that four of the top nine species, including those ranked first and third, had been included in this germination study.



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