Baldcypress, Taxodium distichum (L.) Rich., is a species of ecological significance in the southeastern United States (Arnold, 2008; Pezeshki and DeLaune, 1994). It is highly valued for its ornamental characteristics and site adaptability (Arnold, 2008; Dirr, 2009). The genus Taxodium Rich. includes three different varieties: baldcypress [Taxodium distichum (L.) Rich. var. distichum], pondcypress [Taxodium distichum var. imbricarium (Nutt.) Croom], and Montezuma cypress [Taxodium distichum var. mexicanum (Carrière) Gordon] (Denny and Arnold, 2007). With the inclusion of these varieties, the native range of Taxodium extends from the east coast of the United States to central Texas and south into Mexico (Denny and Arnold, 2007). Although the species is highly adaptable, certain environmental factors do affect its growth. Taxodium displays stress-induced responses when grown in high pH soils, exposed to prolonged drought, or when salt-laden spray from irrigation contacts the foliage (Arnold, 2008; Denny, 2007; Dirr, 2009). Denny (2007) conducted provenance screenings for tolerance to these stresses and recommended that studies be conducted on asexual propagation by cuttings of subsequent clonal selections.
Taxodium is typically commercially propagated in one of three ways. It is grown from seed, grafted, or produced by cuttings. Baldcypress seeds are easily germinated with proper stratification; however, seedling material lacks uniformity (Dirr, 2009; Pezeshki and DeLaune, 1994). Grafting is a reliable but more expensive method of propagating baldcypress (Dirr, 2009; Thomsen, 1978). Alternatively, vegetative propagation by cuttings yields uniform plants and through selection can be used to expedite narrow sense heritable genetic improvement in this species (Pezeshki and DeLaune, 1994). Previous studies have shown relatively high percentages of rooting for Taxodium cuttings (Copes and Randall, 1993; King, 2010; Pezeshki and DeLaune, 1994; St. Hilaire, 2003; Zhou, 2005), supporting further commercialization of the practice.
Copes and Randall (1993) reported 58% rooting of baldcypress when using 3-year-old ramets that were initially taken from 20-year-old ortets. The authors attributed this higher percentage to the 50% moisture content of the rooting substrate, which was the wettest tested. Pezeshki and DeLaune (1994) found that the rooting percentage of hardwood baldcypress cuttings decreased significantly (P ≤ 0.05) when cuttings were taken from branch tips of 25- to 50-year-old trees vs. 1-year-old trees. When the cuttings taken from the 1-year-old trees were treated with a 1000 mg·kg−1 powder form of indole-3-butyric acid (IBA) (ROOTONE®; Ferti-lome Co., Bonham, TX), they rooted at a similar percentage as those that received no IBA. Cuttings treated with IBA had significantly greater (P ≤ 0.05) shoot dry weights (Pezeshki and DeLaune, 1994). This is in contrast to the results of St. Hilaire (2003) who found that softwood cuttings of T. distichum var. mexicanum showed an increase in rooting percentage with increasing concentrations of IBA. In 1 year of the study, rooting percentages were 48% and 82% for 3000 and 8000 mg·L−1 IBA, respectively. Cuttings over all treatment combinations rooted at an average of 65% the first year and 10% the next year. This indicates that the age of the ortet may be a limiting factor in successful propagation. This result agrees with the previously discussed study by Pezeshki and DeLaune (1994). Zhou (2005) reported that rooting percentages increased for a baldcypress clone T302 (T. distichum var. distichum × T. distichum var. mexicanum) with the application of increasing levels of K-IBA. Cuttings treated with 5,000 and 10,000 mg·L−1 K-IBA rooted at 57.6% and 68.1%, respectively. Cuttings treated with 0 and 2500 mg·L−1 K-IBA rooted at the significantly lower (P ≤ 0.05) rates of 16.6% and 22.2%, respectively (Zhou, 2005).
The objective of the current study was to determine the clonal responses to K-IBA across seasonal developmental stages of cuttings and to determine whether rooting and callus percentages and rooted cutting quality (root number, length, and mass) would be sufficient for commercial production should these clones be released to industry.
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