Regulation of Germination of Seed of Anigozanthos manglesii

Abstract

Germination of seed of Anigozanthos (Haemodoraceae) species is usually low and unreliable which hinders the propagation of sexually generated progeny, impedes plant breeding activities and their use in horticulture. This study was undertaken to investigate the basis of these germination problems. Seeds of cultivated Anigozanthos manglesii D. Don. were shown to possess two mechanisms for regulating seed germination, both of which were external to the embryo. Embryos germinated freely on excision and culture on nutrient agar. This first barrier is a physico-chemical barrier and can be eliminated by a brief treatment with 5 M KOH and less effectively by physical abrasion with 50% H₂SO₄ or 0.7% NaOCl. Release of this barrier was correlated with permeability to fluorescein diacetate (FDA) and this proved to be a more useful indicator of seed viability than 2,3,5-triphenyl tetrazolium chloride (TTC). The other barrier was physiological and could be eliminated by treatment with GA₃ or KNO₃. Treatment of A. viridis Endl., A. humilis Lindley and A. flavidus DC. with KOH or H₂SO₄ with or without GA(3) elicited a small, a nil or negative response showing that mechanisms of control of germination may differ between taxa. Observations on the effects of temperature and duration of storage suggest mechanisms which may be significant in natural systems: moist stratification at 5°C caused reduced germination but sustained viability (as assessed by FDA) while dry seed stored at room temperature, showed increased germination with increasing duration of storage. The chilling response may indicate the capacity to initiate secondary dormancy under unfavourable germination conditions.