Arundo species are perennial rhizomatous grass belonging to the tribe Arundinae (subfamily Arundinoideae: Poaceae) (Barker et al., 1999). Arundo donax, in particular, is one of the largest of the herbaceous grasses (Perdue, 1958), growing in dense clumps and attaining heights of up to 8–9 m (Lewandowski et al., 2003). With such impressive growth rates, A. donax is a leading candidate for cultivated biomass in Mediterranean climates (Angelini et al., 2009; Cosentino et al., 2006) and is also being considered as an energy crop in North America (Gilbert at al., 2008; Lewandowski et al., 2003). Many of the advantages of A. donax as an energy crop include a high yield potential (up to 63.1 Mg·ha−1 of dry matter), high lignin and cellulose content, rapid growth rate (up to 0.7 m·week−1 under favorable conditions), high carbon sequestration, widely adaptable to marginal sites, low irrigation and nutrient requirements, and minimal soil tillage, (Lewandowski et al., 2003).
Arundo donax is generally found in alluvial, riparian habitats, such as along the borders of lakes or ditches, but can tolerate a wide range of diverse ecological conditions (Perdue, 1958; Vollmer et al., 2008). The native origin of A. donax has been variously reported as southern Asia (Bell, 1997; Dudley, 2000), eastern Asia (Polunin and Huxley, 1987), and countries surrounding the Mediterranean Sea (Perdue, 1958), though a recent study has provided evidence that A. donax likely originated in Asia and subsequently spread into the Mediterranean region (Mariani et al., 2010). A. donax also has been widely dispersed by humans throughout subtropical and warm-temperate regions for diverse applications including musical instruments, paper and pulp, and woven baskets (Perdue, 1958). In North America, A. donax was introduced into southern California in the early 1800s for erosion control with latter introductions being made in Texas and Florida as late as the 1940s (Bell, 1997; Perdue, 1958). Since its introduction, giant reed has been widely cultivated in North America and has escaped cultivation in some areas (Perdue, 1958).
Genetic diversity is important for the selection, cultivation, and potential breeding of A. donax with desirable traits including high biomass yields, resistance to pest and diseases, and regional adaptability. Unfortunately, a low level of genetic diversity has been reported for A. donax in southern North America and southern Europe (Ahmad et al., 2008; Hardion et al., 2012; Khudamrongsawat et al., 2004; Lewandowski et al., 2003; Mariani et al., 2010; Pilu et al., 2014). For example, the G:N ratio of unique genotypes (G = unique genotypes and N = samples) was 0.050 in France and 0.011 in the United States (Ahmad et al., 2008), and ranged from 0.083 to 0.093 in two studies in Italy (Mariani et al., 2010; Pilu et al., 2014). However, Khudamrongsawat et al. (2004) reported a G:N ratio of 0.41 indicating a more moderate level of genetic diversity in 97 accessions collected from eight populations along the Santa Ana River in southern California. The low level of genetic diversity for A. donax in Europe and the United States has been attributed to its lack of sexual reproduction and limited diversity in founding introductions. Reproduction of A. donax is almost exclusively asexual by clonal spread by rhizome extension and by aquatic dispersal of rhizomes and stem fragments (Johnson et al., 2006; Mariani et al., 2010; Perdue, 1958). A. donax has shown a very limited capacity to produce viable seed attributed to early gamtetophytic failure (Hardion et al., 2015).
Despite the relative lack of genetic diversity within A. donax, Cosentino et al. (2006) reported significant levels of variation in biomass yield among accessions in field trials in southern Italy. For example, the aboveground 2nd year biomass yield of clones from 39 different populations ranged from 14.9 to 34.2 Mg·ha−1 per year of dry matter, with an average of 22.1 Mg·ha−1 per year. Expanding germplasm collections with accessions from other areas, particularly Asia, may capture greater genetic diversity.
The base chromosome number for Arundo has been reported as x = 6 or 12 (Hardion et al., 2011, 2013; Lewandowski et al., 2003). This confusion arises due to the high chromosome numbers resulting from multiple whole genome duplication events (Connor and Dawson, 1993, and discussed in Christopher and Abraham, 1971). However, Hardion et al. (2011, 2013, 2014) concluded x = 6 seemed to be the most suitable theoretical base number based on cytology of Arundinoideae and related taxa. Several cytotypes have been reported ranging from 2n = 12x (≈72) to 2n = 18x (≈108) (Bucci et al., 2013; Christopher and Abraham, 1971; Haddadchi et al., 2013).
Although there is limited genetic diversity within North American and southern European A. donax, there is evidence for substantial differences in yield between genotypes. Further, there has been no characterization of wild collected Arundo from South Asia. Thus, the objective of this study was to evaluate genetic diversity, cytogenetics (ploidy, chromosome numbers, and relative genome sizes) and biomass yields of Arundo taxa collected from North America and South Asia, to identify candidate genotypes for future development of North American bioenergy feedstocks.
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