Grafting of Sturt's Desert Pea ('Swainsona formosa') onto various Leguminosae plants under 'in vitro' and 'in vivo' conditions

Abstract

Stuart's Desert Pea (SDP), 'Swainsona formosa', is one of Australia's most admired wild flowers with considerable potential as an ornamental plant becausse of its curiously shaped flowers. However, one of the major problems in growing SDP is that it is sensitive to soil fungi such as 'Phytophthora' and 'Fusarium', which cause sudden death in established plants. Grafting SDP onto rootstocks not susceptible to these fungi could overcome this problem. SDP was grafted onto the following rootstocks; 'Clianthus puniceus', 'Senna artemisioides', 'Acacia' apecies and SDP (as a control). Grafting was conducted under 'in vivo' conditions. Twenty percent of SDP plants grafted onto 'Clianthus puniceus' showed secondary growth and successfully grew to produce flowers. Grafting onto the other rootstocks was not successful. To improve the percentage of success, grafting under 'in vitro' conditions was performed. The rootstocks were grown either in complete darkness or under a 16 hour photoperiod with light intensity of 20 μmol m⁻² s⁻¹. The grafted plants were incubated under a 16 hour photoperiod at temperatures of 20 or 30°C. Nearly 50% of SDP grafted onto SDP and 'Clianthus puniceus' grown under both light and dark conditions showed secondary growth when they were incubated at 20°C. The other treatments and graft combinations showed very low percentages of grafting success. To improve the percentage of success, plant growth regulators were applied at the junction of the graft union. Although 100 ppm IBA increased the percentage secondary growth of SDP grafted onto 'Clianthus puniceus' to 91%, it did not affect the percentage of secondary growth of SDP grafted onto SDP. Twenty ppm BAP and the mixture of 100 ppm IBA and 20 ppm BAP did not affect the percentage of secondary growth of SDP grafted onto both SDP and 'Clianthus puniceus'.