Collection of Azolla microphylla in Paraguay and Its Characterization by Allozymes and DNA-RAPDs

Abstract

Azolla Lam. is a genus of freshwater aquatic ferns which lives symbiotically with a nitrogen-fixing cyanobacterium. There are seven designated species (Lumpkin & Plucknett, 1982), three of which grow natively in the neotropics and subtropics. A. microphylla Kaulf. (MI in this paper) is the only one whose range reportedly lies entirely within the tropics. From an arbitrary focal point at the Galapagos Islands, its distributlion extends north into the West Indies and Central America, and also across northern and central South America (Schofield & Colinvaux, 1969; Morton & Wiggins, 1971). Within South America, MI is purportedly centered in the lowlands of Brazil (Svenson, 1944). The MI species, or the MI X A. filiculoides (FI) hybrid (Van Cat et al., 1989), is also a superior Azolla for application as a biofertilizer with irrigated rice. Its rapid growth in hot, humid regions of South and Southeast Asia, combined with greater fungal resistance, makes MI more desirable than the indigenous A. pinnata (Maybbayad, 1987; Ventura et al., 1987; Choonluchanon et al., 1988; Liu & Zheng, 1989). The MI which have become field accessions are stored in the Azolla germplasm collection at the International Rice Research Institute (IRRI) in the Philippines. All of the MI accessions from which hybrids and F1 progeny have been made were collected in northwest Paraguay in 1979. MI 4017 and 4018, among the most heat-tolerant of the tested germplasm, are commonly grown in IRRI fields at Los Bafios and South Cobato (Ventura et al., 1987). A second survey was sponsored by IRRI in 1988 to gather additional agroecotypes of Azolla. This paper discusses the genetic results found from that survey. METHODS