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Fengge Hao, Lirong Wang, Ke Cao, Xinwei Wang, Weichao Fang, Gengrui Zhu and Changwen Chen

–Agrobacterium interaction, the transcript of PR1 gene could not be detected, indicating that SAR was not induced in the host organism ( Lee et al., 2009 ). Crown gall disease is a serious problem in horticultural crops worldwide, including peach, and using plant

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Ke Cao, Lirong Wang, Gengrui Zhu, Weichao Fang, Chenwen Chen and Pei Zhao

) of the Prunus reference map ( Claverie et al., 2004 ; Dirlewanger et al., 2004 ; Van Ghelder et al., 2010 ). The RMia gene also is a dominant gene carried by the peach cultivars Nemaguard and Nemared ( Ramming and Tanner, 1983 ) and the almond

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H.J. Jia, K. Mizuguchi, K. Hirano and G. Okamoto

Effects of fertilizer application levels on fruit texture and flesh pectin compositions of a melting peach were investigated. Hakuho trees (Prunus persica Batsch) were supplied with normal (M), high (H; M × 2), and superhigh (SH; M × 4) levels of complete liquid fertilizer twice a week. Flesh firmness of the H and SH treatment fruit was lower than that of M treatment fruit at the hard-mature and firm-mature stages, although no difference was detected at the full ripe stage. Sensory scores for flesh texture at the full ripe stage were highest in the N treatment fruit and lowest in the SH treatment fruit. The content of water-soluble polyuronides (WSP) in flesh was highest in SH fruit and lowest in M fruit at the hard-mature stage, although the difference became smaller at the full ripe stage. Molecular mass analysis using a gel filtration column revealed that water-soluble polysaccharides in alcohol-insoluble solids (AIS) of the H and SH fruits had a peak of high molecular mass, ≈200 kDa, at the hard-mature stage, and the molecular mass decreased gradually to ≈23 kDa at the full ripe stage. In the M fruit, however, the molecular mass was rather constant during the ripening period, 112 kDa even at the full ripe stage. The analysis of acidic fractions (pectin) in the polysaccharides using an ion exchange column, as well as juice gellation test by adding Ca and Tris buffer, also indicated that high levels of fertilizer application impairs an early degradation of flesh polyuronides resulting in the accumulation of low-molecular-weight WSP. This may ultimately cause the inferior flesh texture of overfertilized peach fruit.

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E.W. Pavel and T.M. DeJong

Peach [Prunus persica (L.) Batsch] fruit thinning was used to reduce the competition for assimilates among peach fruits and to identify periods of source- and sink-limited growth during development. Individual fruit size, based on diameter or calculated dry matter accumulation, increased in trees with lower crop loads compared to fruits of unthinned trees in three peach cultivars. Relative growth rate analysis indicated that peach fruit growth was apparently limited by the assimilate supply (source-limited) or by its genetic growth potential (sink-limited) during specific growth periods. In stage I and at the beginning of stage III of the double-sigmoid growth curve, periods of source-limited growth occurred in the later-maturing cultivars Flamecrest and Cal Red. Peach fruit growth was apparently sink-limited during stage II of the growth curve when fruit relative growth rates were similar for the thinning treatments. Fruit growth in `Spring Lady', an early maturing cultivar, appeared to be primarily source-limited during the season. Although total fruit dry matter production was reduced by thinning, individual fruit dry weight on thinned trees was higher than that on trees with a heavy crop load. This typical thinning response was apparently caused by the differences in the amount of time that fruits grew under sink-vs. source-limited conditions with different crop loads. Final crop yield depended on fruit count per tree and on the available assimilate supply, and was affected by the individual fruit growth potential.

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C.E. Johnson, J.T. Payne, W.A. Young and E.W. Bush

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C.E. Johnson, J.T. Payne, M.L. Robbins and W.A. Young

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Elina D. Coneva and John A. Cline

The purpose of this research was to determine the effectiveness of three blossom-thinning compounds on crop density and fruit quality of two peach cultivars. Treatments consisted of 15 ml·L–1 and 30 ml·L–1 ammonium thiosulphate, 30 ml·L–1 and 40 ml·L–1 decyl alcohol, and 40 ml·L–1 lime sulfur. Treatments were applied to `Redhaven' and `Harrow Diamond' peach trees at two phenological stages: 80%, and 100% full bloom in 2002 and 2003. In both years, treatments reduced the crop density in both cultivars, and in 2003 the amount of hand thinning required to adjust the crop load was significantly reduced. Fruit size from several blossom-thinned treatments was comparable with that observed from hand-thinned trees. However, treatments caused significant leaf phytotoxicity to `Harrow Diamond' trees in 2003, likely a result of hand spray gun applications. These data indicate that chemical sprays at bloom can be used successfully to reduce fruit set, but are very environmentally, dose, and cultivar dependent.

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Maria José Aranzana, Joaquim Carbó and Pere Arús

A sample of 210 cultivars of Prunus persica (L.) Batsch, with a wide range of fruit and plant characteristics, was studied for variability using nine polymorphic amplified fragment length polymorphism (AFLP) primer combinations. Forty-seven AFLPs allowed identification of 196 (93%) different genotypes, 187 of which could be distinguished with three primer combinations. Eleven cultivars with the same AFLP phenotype corresponded to known somatic mutations (sports), but from the four sports of the `Springcrest' group, two (`Maycrest' and `Queencrest') differed at three AFLPs from the others (`Starcrest' and `Early Maycrest'). Cluster analysis allowed differentiation of most cultivars with nonmelting fruit flesh, generally used for canning, from the melting-flesh peach and nectarine cultivars used for fresh consumption.

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Elina Coneva and John A. Cline

Adjusting the crop load of peaches [Prunus persica (L.) Batsch] by hand thinning is currently required to ensure marketable size of most cultivars grown in Ontario. A novel approach to adjust cropping by inhibiting flowering using gibberellic acid (GA3) was tested in an orchard experiment in which GA3 was applied at 7, 10, and 13 weeks after full bloom to mature `Redhaven' peach trees. Late GA3 treatments increased soluble solids concentration (SSC) in the season of application. A significant interaction between GA3 rate and time of application was observed on increased fruit firmness in the current season. Increasing rates of GA3 decreased flowering the following season in a quadratic fashion, resulting in a 41% to 90% diminished requirement for hand thinning. This translated into lower crop loads and yields for GA3-treated trees at harvest compared with untreated control trees. However, GA3-treated trees had larger mean fruit size and improved fruit size distribution the year after GA3 application. Advanced fruit ripening was also evident by increased fruit SSC and decreased fruit firmness, likely an indirect effect of GA3 on crop load. GA3 application timing significantly increased overall tree growth measured by the changes in trunk cross-sectional area.

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Rajeev Arora, Michael Wisniewski and Lisa J. Rowland

Seasonal changes in cold tolerance and proteins were studied in the leaves of sibling deciduous and evergreen peach [Prunus persica (L.) Batsch]. Freezing tolerance [defined as the subzero temperature at which 50% injury occurred (LT50)] was assessed using electrolyte leakage. Proteins were separated by sodium dodecyl sulfate polyacrylamide-gel electrophoresis. Electroblots were probed with anti-dehydrin and anti-19-kD peach bark storage protein (BSP) antibodies. Leaf LT50 decreased successively from -5.8 °C on 18 Aug. to -10.3 °C in the evergreen genotype and from -7.0 °C to -15.0 °C in the deciduous genotype by 14 Oct. Protein profiles and immunoblots indicated the accumulation of a 60- and 30-kD protein during cold acclimation in the leaves of deciduous trees; however, levels of these proteins did not change significantly in the evergreen trees. Immunoblots indicate that the 60-kD protein is a dehydrin-like protein. Gel-electrophoresis and immunoblots also indicated that the 19-kD BSP progressively disappeared from summer through fall in leaves of deciduous peach but accumulated to a high level in bark tissues. A similar inverse relationship was not evident in evergreen peach.