Temperature and Endogenous Factors Cause Seasonal Patterns in Rooting by Stem Fragments of the Invasive Giant Reed,Arundo donax(Poaceae)

The effects of upright and plagiotropic stem orientation, temperature, and season on the regeneration of Arundo donax (giant reed) from stem fragments were studied for a period of more than 1 yr. In a temperature‐controlled experiment (16/8 h at 28°/16°C), successful regeneration (30%–80%) occurred from stem fragments with lengths ranging from 1 through 10 cm, even if split lengthwise, but only when the axillary bud was present and intact. Seasonal patterns in regeneration were observed in experiments in an unheated greenhouse with 0%–20% regeneration in the winter and 90%–100% regeneration in summer. During spring, fragments from plagiotropic, or hanging, stems showed 30%–40% regeneration under the temperature‐controlled conditions, while only 0%–10% of fragments from upright stems completed regeneration by rooting. Regeneration success and speed increased toward summer for both plagiotropic and upright stems, with 80%–90% and 80% regeneration rates, respectively. Exogenous indole‐3‐acetic acid (IAA) increased rooting by upright stem fragments in spring to 30%–40%. The seasonal pattern of endogenous IAA in the new stems that grew from fragments of plagiotropic and upright stems was similar to the regeneration patterns but displayed a 4–6‐wk lag period. Distribution of stem fragments could lead to the establishment of new A. donax stands.