Bearded iris (Iris ×hybrida Hort.), characterized by a thick and bushy “beard” on three falls (lower petals), refers to the large artificial hybrid population in the Iris genus. They have extraordinary prevalence and great commercial value as a result of their attractive appearance, ease of cultivation, and propagation (Harkess et al., 2010; Li et al., 2016; Zhao et al., 2016). To satisfy increasing commercial needs, newly emerging bearded iris cultivars are generated primarily by hybridization (Azimi et al., 2018). However, in the history of iris breeding, the hybridization programs were conducted mainly according to breeders’ experience. Most of the new cultivars were produced after a large amount of hybridization was practiced without explicit purpose, leading to a waste of time and labor (The American Iris Society, 1978). Because of this, the phenotypic traits of the offspring were usually unclear as a result of the complexity of the bearded iris’ genetic background (Guo, 2000). Therefore, systematic scientific research is important to investigate trait inheritance in bearded iris.
Heritability evaluation is one of the most fundamental steps in a breeding program to gain access to new genetic changes and to create new cultivars with specific traits (Azimi et al., 2018). Characteristics with high heritability can be useful for hybrid selection in iris breeding (Azimi et al., 2018). Over the past decades, researchers have carried out several studies about the trait inheritance in Iris related particularly to heritability. In candy lily (hybrids of I. dichotoma and I. domestica), the genetic variation of six traits was investigated and a high heritability of leaf width (55.95%) was observed (Ruan et al., 2017). For I. pumila, the broad-sense heritability of 26 traits were evaluated and the floral traits were found to be less variable than vegetative traits (Tucic et al., 1990). Moreover, Azimi et al. (2018) evaluated the genetic differences among 43 hybrids produced by I. spuria and seven I. germanica cultivars, and a relatively high broad-sense heritability was observed for PH, standard width, standard height, flower size, and leaf width (LW). In our previous research on bearded iris, WF and the number of flowers per scape (NFS) had the greatest broad-sense heritability (91.47%) and strict-sense heritability (53.96%), respectively (Fan et al., 2017).
The previously mentioned studies have revealed the inheritance of phenotypic traits in Iris to some extent. However, previous research about phenotypic variation only included the F1 generation, rather than investigating more offspring populations such as the F2, BC1P1, and BC1P2 generations. As a result, the conclusions drawn from the studies did not completely reflect the inheritance in bearded iris, thus hampering the breeding process (Anderson, 1996; Araujo et al., 2002; Tucic and Avramov, 1996). Therefore, comprehensive investigations of phenotypic traits in the F1, F2, BC1P1, and BC1P2 generations are clearly needed in iris breeding.
The bearded iris ‘Indian Chief’ [tall bearded (TB)] is one of the most popular and widely applied cultivars in China because of its velvety petals, ideal height, and strong resistance to root rot disease. ‘Indian Chief’ is usually chosen as the maternal parent in bearded iris breeding because of its poor pollen vigor and sparse pollen content in stamens (Austin, 2005). Another cultivar, Sugar Blues (TB), appears to be an ideal pollen donator (Fan et al., 2017).
In this research, four bearded iris offspring populations, including F1, F2, BC1P1, and BC1P2, were generated through hybridization between ‘Indian Chief’ and ‘Sugar Blues’. The objectives of this study were 1) to evaluate the variation of phenotypic traits, thus estimating the improvement of these traits over their parents; 2) to calculate the broad-sense heritability of the 15 tested traits to evaluate more completely the efficiency of direct selection; 3) to estimate the correlations between the tested phenotypic traits, making it possible to forecast the performance of certain traits by observing correlations and simplify the process of breeding; and 4) to analyze the proportion of flower colors in the offspring generations to generate more offspring with target flower colors.
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