Factors Affecting the Germination Ecology of Pimelea trichostachya and Its Relationship to Field Emergence

Abstract

Pimelea trichostachya Lindl is a little-understood Australian native plant, with irregular field emergence, causing significant poisoning to grazing livestock. The study aims to examine the form of dormancy exhibited by P. trichostachya and determine how key environmental conditions, such as alternating temperature and light conditions, moisture availability, substrate pH and burial depth, affect its germination and emergence. The study concludes that P. trichostachya has a complex dormancy mechanism. This comprises a physical component that can be partly removed by fruit scarification, a metabolic dormancy that can be overcome by gibberellic acid (GA3), and a suspected third mechanism based on a water-soluble germination inhibitor. The results showed that scarified single seeded fruit (hereafter seed) with GA3 treatment gave the highest germination percentage (86 ± 3%) at 25/15 °C, with good germination rates at other temperature regimes. Light exposure stimulated germination, but a significant proportion of seeds still germinated in the dark. The study also found that seeds could germinate under water-limited conditions and a wide range of pH levels (4 to 8). Seedling emergence was inhibited when seeds were buried below 3 cm in soil. Pimelea trichostachya emergence in the field commonly occurs from Autumn to Spring. Understanding its dormancy mechanism and recognizing its triggers for germination will enable better prediction of outbreaks. This can help landholders prepare for emergence and help manage seedbank build-up in pastures and crops.

Poisonous Plants of the Genus Pimelea: A Menace for the Australian Livestock Industry

“…A recent study on the germination ecology of P. trichostachya suggests that it has a complex dormancy mechanism that involves multiple factors. The study identified a physical component of dormancy that can be partially overcome by diaspore scarification, a metabolic dormancy that can be overcome by the application of the plant growth regulator GA 3 , and a suspected third mechanism based on a water-soluble germination inhibitor [25]. These results suggest that P. trichostachya has a sophisticated system for regulating its germination in response to environmental cues and conditions, which can complicate management efforts.…”

“…Freshly shed diaspores would germinate after a period of ageing (possibly promoted by high temperatures) in the soil to breakdown diaspore tissues (e.g., the hard endocarp). Once dormancy is broken, Pimelea diaspores can germinate and form seedlings under a range of environmental and soil conditions [25].…”

“…Mildly acidic soil conditions are preferred, although Pimelea can also grow in more neutral or alkaline soils. Understanding the environmental and soil conditions that are most favorable for Pimelea germination and seedling formation can help to guide the development of effective management strategies that target these specific conditions [25].…”

“…The development of effective IWM strategies for Pimelea species will require a thorough understanding of their biology and ecology [25], as well as careful consideration of the potential impacts of management actions on the environment. Integration of chemicals with different cultural techniques or mechanical approaches is imperative to suppress and manage Pimelea species in a sustainable way [6].…”