Length of the juvenile phase seems to be the main obstacle of the fruit tree breeding program because of the land area required for breeding plots, the fact that it is time-consuming, and costly nursery management, all restricting breeding advancement. A large variation in tree architecture and other morphological characters was found in different fruit species, for example, apple (Lespinasse, 1977), pear (Sansavini and Musacchi, 1994), and peach (Scorza, 1984). Implementation of these traits for progeny selection in the breeding program demands genetic studies to distinguish the environmental and the genetic variances from the phenotypic variances, to calculate the expected genetic contribution in the form of heritability, and to estimate their combining ability (Gallais, 1989; Hill et al., 1998). Efficient early selection techniques were applied on seedlings younger than 2 years old (Alston and Battle, 1992; Kazlovskaya, 2005; Koc et al., 2009; Larsen et al., 2006; Segura et al., 2006). Traits of blooming and ripening dates (Hansche et al., 1966; Kester, 1965; Tancred et al., 1995) and fruit quality (Brown, 1960; Dicenta et al., 1993; Kester et al., 1977) have been widely used for study of their inheritance in fruit tree species. In most cases, data collected from the successive years were as replications to estimate the genetic and non-genetic variance. Morphological characteristics regarding tree growth habit (Sampson and Cameron, 1965), the compact habit (Lapins, 1974), dwarfism (Alston, 1976; Decourtye, 1967), and spur types (Alston and Watkins, 1974; Decourtye and Lantin, 1969) were used for genetic analysis. As a result of annual shoot development, tree size is an always increasing variable. Several studies showed that shoot length decreases during consecutive annual biological cycles in several species and in different cultural and climatic conditions. In apricot and apple trees, the mean number of nodes per annual shoot decreased over successive years (Costes et al., 2003) as a result of a decrease in the number of newly formed shoots. In addition, the decrease in the mean number of nodes was similar for all shoots of similar ages within the trees, whichever their branching orders (Costes et al., 2003). However, the final size cannot be predicted from a single-year measurement but from successive years. The phenotypic variance of annual shoot length also decreases on time (Costes et al., 2004). Large variation in time of ripening has been noted in apple cultivars, which facilitates classifying them into nine classes of earliness from extremely early to very late ripening (Watkins and Smith, 1982). Earliness has been found to have relatedness with several morphological traits such as leaf length, seedling height, trunk diameter, leaf chlorophyll concentration, and number of branches (Kazlovskaya, 2005). Tancred et al. (1995) investigated the inheritance of ripening date in apples and obtained high heritability and additive genetic components of variance. Heritability of phenotypic variance in a selection would present in the next generation (Falconer, 1981; Hanson, 1963). However, accurate heritability estimates may be obtainable if phenotypes will present in many trees of successive years (Hardner et al., 2002; Liebhard et al., 2003; Yao and Mehlenbacher, 2000). Heritability has been estimated using several full-sib progenies (Durel et al., 1998; Oraguzie et al., 2001; Tancred et al., 1995). Recently, Liebhard et al. (2003) estimated genetic and environmental variance and identified some emphasized qualitative trait loci for tree height, collar diameter, and phenological traits in apple offspring. Most genetic studies on the inheritance of the columnar tree habit suggested that a single dominant gene, Co, was implicated (Lapins, 1974, 1976). Brown (1960) found the progeny mean for fruit shape to be approximately equal to the midparent value, but the progeny mean for fruit size was less than the midparent value. Isozymic genes showed promise as markers for a limited number of specific characters but there was insufficient polymorphism among cultivated apples limiting their use in a breeding program (Alston and Battle, 1992). Correspondence between phenotypic and genotypic indices of Danish populations of European crab apple (M. sylvestris) confirmed that relying exclusively on either morphological or molecular characters as diagnostic markers in studies of hybridization between M. ×domestica and M. sylvestris might lead to fallible results (Larsen et al., 2006). The main aims of the current study were: 1) to evaluate the effect of maternal and paternal parent on morphological characteristics of offspring; 2) to compare the performance of 3- and 4-year-old seedlings obtained from different cross combinations between early and late ripening cultivars; 3) to estimate the heritability of morphological traits using progenies from both open and controlled pollinations of apple cultivars; and 4) to analyze correlations between traits and develop an efficient method for selecting desirable progenies in early growth stages of the juvenile phase. The parents were selected based on the previous evaluations made on 108 cultivars and genotypes existing in the national commercial apple cultivar collection using ab apple descriptor (Watkins and Smith, 1982), revealing high genetic variations in phenological, pomological, morphological traits regardless of ripening time (Hajnajari, 2008).
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