Pollination biology of Ptilotus axillaris

Summary of final report on the Australian Flora Foundation funded project:

Melinda Perkins and Margaret Johnston
Centre for Native Floriculture, School of Land, Crop and Food Sciences, University of Queensland, Gatton
29 June 2009

Grant Details   Final Report

Ptilotus axillaris (Amaranthaceae) is a little known Australian species purported to have ornamental potential, however previous breeding attempts have had limited success. Aspects of pollination biology and flowering physiology were investigated to ensure future breeding work employs appropriate strategies for efficient seed production. Seven stages of floral development were characterised. Stages that encompassed anther development, maturation and pollen dehiscence were of longer duration in male-fertile genotypes, however the time between anthesis and flower closure was shorter (compared with male-sterile genotypes). On the basis of seed set data, no significant difference in stigma receptivity was detected during the 14 d period between anthesis and flower closure. In vitro pollen germination showed viable pollen was produced 0 to 2 d following anthesis, suggesting that P. axillaris is homogamous. Partial to complete self incompatibility was observed, with ratios of seed set from self-pollinations to that of cross-pollinations (index of self incompatibility) being 0.27 or lower. Cultivation under low temperatures (25/10°C day/night) was shown to promote floral initiation. Flower initiation was delayed by high temperatures (35/20°C day/night) but once visible buds were present, flower development was more rapid at high temperatures. However, if plants are maintained continuously under 35/20°C flowering will be suppressed. Flowering is greatly enhanced at 25/10°C, as is plant form. Plants at anthesis had significantly fewer leaves when maintained under long days (16 h photoperiod) compared with short days (11 h photoperiod), suggesting that P. axillaris may be a facultative long day plant.