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

Abstract

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.