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- Author or Editor: Jocelyne Kervella x
Peach powdery mildew (Podosphaera pannosa var. persicae) is a major disease of peach trees [Prunus persica (L.) Batsch]. Various studies on powdery mildew resistance have been conducted in peach. The present study was initiated to determine the inheritance of powdery mildew resistance found in the green leaf peach rootstock ‘Pamirskij 5’. Crosses were carried out between ‘Pamirskij 5’ and the susceptible red leaf peach rootstock ‘Rubira’®. Segregation analysis performed in F1 (1:0), F2 (3:1), and test cross (1:1) progenies indicated single dominant gene control of peach powdery mildew resistance in ‘Pamirskij 5’. Cosegregation analysis provided clear evidence that the loci for powdery mildew resistance and the leaf color trait are very closely linked in ‘Pamirskij 5’. The estimated distance between these loci was 0 ± 3.26 cM for the F2 and 0 ± 0.00 cM for the test cross populations.
Leaf emergence was studied on main and first-order shoots of peach and nectarine [Prunus persica (L.) Batsch.] trees belonging to nine standard cultivars, during their first growing season. The number of emerged leaves was recorded on main shoots (originating from the grafted buds) and on first-order shoots (inserted directly on main shoots). Similarly shaped leaf emergence curves were observed on main and first-order shoots for all the cultivars. Leaf emergence rate decreased gradually as the number of leaves increased. The number of emerged leaves could be modeled as a monomolecular function of accumulated thermal units. Significant differences were found between cultivars in a multiple analysis of variance of the model parameters, for main and first-order shoots. The ranking of the cultivars was similar for both types of shoots. Leaf emergence rate was lower on first-order shoots than on main shoots. Differentiating between shoot types is necessary for a reliable comparison of genotypes.
Genotypic variations in the length-diameter relationship of branches among peach and nectarine [Prunus persica (L.) Batsch.] cultivars were investigated. The length and basal diameter of all undamaged first-order shoots from 1-year-old trees of 14 cultivars and one accession were measured. Statistical analysis of the allometric relationship between length and basal diameter of shoots provided evidence of genotypic differences for that relationship, although the diameter of very short shoots did not differ between genotypes. A gradient existed from `Armking' with thin shoots (9 mm in diameter for 85.5-cm-long shoots) to `Flavorcrest' with thick shoots (16.4 mm in diameter for 85.5-cm-long shoots). Early selection for shoot thickness should be possible in breeding programs. The likely consequences of observed shoot thickness variations on the mechanical and hydraulic properties of shoots are discussed.
Prunus davidiana (Carr.), a wild species with poor fruit quality that is related to peach [Prunus persica (L.) Batsch], is used as a source of resistance to pests and diseases in peach breeding programs. Two genotypes of P. davidiana were studied for fruit biochemical composition and compared to three genotypes of P. persica (`Summergrand', `Bailey' and `Pamirskij'), and two P. persica × P. davidiana hybrids. Fruit of P. davidiana clones had higher malic acid, neochlorogenic and cryptochlorogenic acid and lower sucrose concentrations than fruit of all P. persica genotypes, even poor-quality Bailey. Differences in biochemical composition could be related to sensory evaluation. P. persica × P. davidiana hybrids had intermediate values between their parents for neochlorogenic acid concentration. They were similar to the P. persica parent for total soluble sugar, malic and citric acid, amino acid and catechin concentrations, indicating possible rapid progress for fruit quality in a breeding program.