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W. Kaminski and R. Rom


Catalase activity in peach flower buds was found to be comparatively high before winter dormancy. Chilling at 5°C resulted in a decrease in catalase activity. The lowest level was reached near the end of dormancy. Flower buds of cultivars requiring a longer chilling requirement had the greatest depression in catalase activity. The onset of 25°C temperature following a few days at 5°C delayed change in catalase activity during the next 5°C chilling period and resulted in a condition comparable to prolonged dormancy. Flower buds near the end of rest or in a post dormant rest when placed at 25°C showed a rapid increase in catalase activity. A flower bud’s ability to rejuvenate its catalase level is correlated with it’s flowering ability. Free internal O2 due to the catalase system may trigger peach flower bud development.

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M. Wisniewski, T. Artlip, R. Webb, C. Bassett, and A. Callahan

During the past several years we have been involved in identifying seasonally regulated proteins and genes from peach bark. In the present study, we describe the cloning of a protease inhibitor from a cDNA library made from winter bark tissues. A partial clone obtained from the library was extended to full length by 5' RACE. The full-length cDNA clone (final3b) is 613 bp in length, not including the poly A+ tail. The open reading frame of 237 bp codes for a 79 amino acid protease inhibitor related to the defensin family of proteins. This family of small, cysteine-rich, extracellular proteins play a role in the plantís defense response through their antifungal properties. Sequence comparison of the encoded protein using BLAST analysis revealed significant homology to protease inhibitors from Glycine max, Arabidopsis thaliana, and a defensin protein from bell pepper (Capsicum annuum). Similar to these other cysteine-rich proteins, the peach defensin contains a consensus cys arrangement and is predicted to have an amino terminal signal peptide, presumably targeting it for extracellular transport. RNA-blot analysis indicated that the gene is seasonally expressed in bark tissues of 1-year-old shoots. Transcript abundance of final3b increased in the fall, reached a peak in midwinter and then decreased. The gene was also expressed during early stages of fruit development. RNA-blot analysis of the gene in other tissues, and in response to environmental stress and wounding, is in progress.

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Marilyn L. Warburton and Fredrick A. Bliss

Previous studies of peach germplasm using pedigree information and isozyme polymorphism data have shown limited diversity in the U.S. gene pool. To further investigate the genetic diversity among peach cultivars grown in different regions of the United States, 94 RAPD markers were used to estimate the genetic distances among 136 cultivars. Of the 12 clusters formed in a dendrogram, the 90 U.S. cultivars and breeding lines and most of those from Europe and Latin America grouped to only three clusters, while the 23 peach entries from India, Pakistan, Russia, Okinawa, and China, as well as the almond cultivar used as an outgroup, were distributed among the other nine clusters. Therefore, the genetic diversity within temperate U.S. peach germplasm is quite limited, and to expand the variability, additional germplasm should be obtained, especially from Asia. Comparison of genetic similarity based on inbreeding coefficients with similarity coefficients based on the RAPD data produced a correlation of 0.395, which is comparable to values in similar investigations in other crops. Thus, similar conclusions can be drawn from these two sources of information. RAPD data are useful particularly when pedigree information is incomplete, there has been substantial selection within breeding populations, and a high proportion of alleles are identical in state but not by descent.

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Anne M. Gillen and Fredrick A. Bliss

Peach rootstock breeding may be accelerated by utilization of molecular markers linked to the root-knot nematode resistance locus (Mi) to screen segregating populations. A genetic linkage map was constructed using RFLP markers in an F2 population (PMP2) that is segregating for this locus. PMP2 is derived from a controlled cross of the relatively diverse peach rootstocks Harrow Blood (susceptible) and Okinawa (homozygous resistant). Bulked Segregant Analysis was applied using RAPD markers. A single small (227 base pairs) RAPD marker was found to be linked to the dominant resistant allele of Mi at a distance of 10 cM. This new marker joined the Mi locus to the RFLP linkage map and showed that two dominant RFLP markers are located between the RAPD marker and Mi. RFLPS are expensive, time-consuming and RAPD markers are unreliable, and therefore both are unsuitable for screening breeding populations. We attempted to convert the RAPD marker to a more breeder-friendly CAPS marker. The converted CAP marker was dominant. Attempts to convert the CAP marker to a co-dominant marker were not successful. The utility of the CAP marker was tested in an open pollinated F2 population derived from the F1 parent of PMP2 and in several rootstocks. The genetic linkage map was compared to other Prunus maps. The PMP2 linkage group containing the Mi locus can be related to the peach × almond linkage group which contains the phosphoglucomutase Pgm-1 locus.

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Zuguo Cai, Wenfang Zeng, Liang Niu, Zhenhua Lu, Guochao Cui, Yunqin Zhu, Lei Pan, Yifeng Ding, and Zhiqiang Wang

accessions in Prunus . M = DNA marker, CK = blank control with double-distilled H 2 O replacing DNA template, codes 1–20 = 20 representative accessions belonging to five species ( P. davidiana , P. kansuensis , P. ferganensis , P. mira , and P. persica

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Dario J. Chavez, Thomas G. Beckman, and José X. Chaparro

on Rehder’s (1940) taxonomic treatment: P. persica-Prunus dulcis , Prunus domestica-Prunus salicina , and Prunus cerasus-Prunus fruticosa monophyletic clades. Two major groups, the Amygdalus - Prunus group and the Cerasus - Laurocerasus

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Elizabeth E. Rogers and Craig A. Ledbetter

horticultural traits. To this end, numerous large segregating populations were created to provide a means of linking molecular markers to specific phenotypic categories. Prunus persica (L.) Batsch cv. Harrow Blood, a cold-hardy but root knot nematode

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

mapping program JoinMap 2.0 ( Stam and Van Ooijen, 1995 ) from Prunus kansuensis ‘Honggengansutao’ × P. persica ‘Bailey’ BC 1 population. Numbers identifying the linkage groups are shown on the top of each group. The names of the loci are shown on the

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Xiaojuan Zong, Brandon J. Denler, Gharbia H. Danial, Yongjian Chang, and Guo-qing Song

organogenic callus of sweet cherry ( Prunus avium L.) Plant Cell Tissue Organ Cult. 90 201 214 Gentile, A. Monticelli, S. Damiano, C. 2002 Adventitious shoot regeneration in peach [Prunus persica (L.) Batsch] Plant Cell Rep. 20 1011 1016 Hammatt, N. 1993

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Chunxian Chen and William R. Okie

Peach ( Prunus persica ) was domesticated several thousand years ago in China and subsequently introduced to Persia, the Mediterranean, the Americas, and elsewhere ( Faust and Timon, 1995 ). Cultivars selected for cool dry climates generally do not