Molecular identification of Azolla in the Yangtze River Watershed, China

Authors: Madeira, Paul; Dray, F Allen; Tipping, Philip

Submitted to: Aquatic Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2019
Publication Date: 12/1/2019
Citation: Madeira, P.T., Dray Jr, F.A., Tipping, P.W. 2019. Molecular identification of Azolla in the Yangtze River Watershed, China. Aquatic Botany. 159. https://doi.org/10.1016/j.aquabot.2019.103149.
DOI: https://doi.org/10.1016/j.aquabot.2019.103149

Interpretive Summary: Azolla species are small aquatic ferns that live in a symbiotic association with nitrogen fixing blue-green algae. These nitrogen-fixing capabilities have led to the introduction of Azolla as a ‘‘green manure’’ for rice in many countries. In China, Azolla pinnata subsp. asiatica is a native which has long been used for rice culture, however it is a sub-tropical plant. For this reason both Azolla filiculoides and Azolla caroliniana were introduced for climatically temperate rice systems. Often, where Azolla has been introduced it has exhibited invasive tendencies, creating dense surface mats, impeding boating, fishing, recreational activities, and obstructing water-flow systems necessary for agriculture. Exotic Azolla populations, lacking normal natural enemies, may also out-compete native Azollas. Samples were collected from a broad area of the Yangtze River watershed of China during a search for samples of Azolla pinnata, a listed Federal Noxious Weed (USA), discovered in Palm Beach County, Florida in 2007. The samples were sought to identify by molecular taxonomy the subspecies introduced to Florida. This knowledge can inform where to search for biological control insects to control the Florida exotic. Samples were sequenced using two chloroplast sequences and one nuclear sequence, and were identified as Azolla caroliniana. This survey found only Azolla caroliniana in the broad range of the Yangtze watershed sampled, which was unexpected since the literature reports mostly Azolla filiculoides introductions. Azolla caroliniana, introduced for its use in early rice systems, may now predominate due to its intermediate tolerance to both heat and cold, and its high biomass production. In contrast, Azolla pinnata does less well in the cold and Azolla filiculoides does less well in heat.

Technical Abstract: Seven samples were collected from a broad area of the Yangtze River watershed of China during a search for samples of Azolla pinnata asiatica. These samples were intended as molecular references to aid in determining the identity (subspecies) of a new exotic invasion of A. pinnata in Florida, USA. The samples were sequenced using the trnL-trnF and trnG-trnR chloroplast sequences as well as the nuclear ITS1 sequence and were identified by molecular taxonomy, using NCBI, as Azolla caroliniana. The dominance of A. caroliniana in the Yangtze was unexpected given the predominance in the literature historically of Azolla filiculoides introductions. In four of five provinces sampled, cold tolerant Azolla filiculoides and A. caroliniana would be expected competitively to dominate A. pinnata due to biological advantages during over-wintering and early spring growth. A. caroliniana’s predominance over A. filiculoides may be due to its use in early rice systems, its intermediate tolerance to both heat and cold, and its high biomass production.