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P. Martínez-Gómez, M. Rubio, F. Dicenta, and T.M. Gradziel

Sharka [(plum pox virus (PPV)] mainly affects Prunus species, including apricot (Prunus armeniaca L.), peach (Prunus persica L.), plum (Prunus salicina Lindl., Prunus domestica L.), and, to a lesser degree, sweet (Prunus avium L.) and sour cherry (Prunus cerasus L.). Level of resistance to a Dideron isolate of PPV in seven California almond [P. dulcis (Miller) D.A. Webb], five processing peach cultivars, and two peach rootstocks was evaluated. In addition, almond and peach selections resulting from interspecific almond × peach hybridization and subsequent gene introgression were tested. Evaluations were conducted in controlled facilities after grafting the test genotypes onto inoculated GF305 peach rootstocks. Leaves were evaluated for PPV symptoms during three consecutive cycles of growth. ELISA-DASI and RT-PCR analysis were also employed to verify the presence or absence of PPV. Peach cultivars and rootstocks showed sharka symptoms and were ELISA-DASI or RT-PCR positive for some growth cycles, indicating their susceptibility to PPV. Almond cultivars and almond × peach hybrids did not show symptoms and were ELISA-DASI and RT-PCR negative, demonstrating resistance to PPV. Two (almond × peach) F2 selections as well as two of three backcrossed peach selections also showed a resistant behavior against the PPV-D isolate. Results demonstrate a high level of resistance in almond and indicate potential for PPV resistance transfer to commercial peach cultivars.

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Kristi K. Barckley, Sandra L. Uratsu, Thomas M. Gradziel, and Abhaya M. Dandekar

The California almond industry is the largest supplier of almonds [Prunus dulcis (Miller) D.A. Webb] in the United States and throughout the world. Self-incompatibility is a major issue in almond production as it greatly affects nut set. In this study, we determined full-length sequences for alleles Sa - Si, determined the genotypes of 44 California cultivars, and assigned the cultivars to cross-incompatibility groups (CIGs). Newly identified S-alleles led to an increase in the number of CIGs. A pairwise distance tree was constructed using the aligned amino acid sequences showing their similarity. Four pairs of alleles (Sc and Se, Sg and Sh, Sd and Sj, and Sb and Sf) showed high sequence similarity. Because of its simplicity, reproducibility, and ease of analysis, PCR is the preferred method for genotyping S-alleles.

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Ali Lansari, Dale E. Kester, and Amy F. Iezzoni

The mean inbreeding and coancestry coefficients were calculated for almond, Prunus dulcis (Miller) D.A. Webb, cultivars from the United States, France, Spain, Israel, and Russia. To improve cultivars to meet market demand, the recurrent use of four selections as parents in U.S. breeding programs has resulted in a mean inbreeding coefficient (F) of 0.022 in this collection. In France, a single cultivar, Ferralise, has an inbreeding value of F = 0.250, while cultivars of other almond-producing countries are noninbred (F = 0). Due to the use of common parents, U.S., Russian, and Israeli cultivars share coancestry, while coancestries also exist between French and Spanish almond germplasm. Cultivars of known parentage in the United States, Russia, Israel, France, and Spain trace back, respectively, to nine, eight, three, four, and three founding clones. Future almond-breeding programs may narrow the genetic base and thereby limit genetic gain.

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Pere Arús, Carmen Olarte, Miguel Romero, and Francisco Vargas

This research was supported in part by funds of project PA86-0125 from Comisión Interdepartamental de Ciencia y Tecnología. We are indebted to S. Arulsekar, D.E. Kester, E. Ritter, and K. Tobutt for their comments on the manuscript. The cost of

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Eddo Rugini

In the olive Olea europaea (L.), the polyamides (PAs), putrescine, spermidine, and spermine, when added exogenously at a concentration of 1 mm in the in vitro rooting medium, combined with 5 μm auxin concentration, promoted early rooting and increased the final rooting percentage and the number of roots per explant. The effect was less evident in olive explants rooted with the basal blanching method; thin-layer chromatography of total endogenous PAs in `these explants revealed lower levels on day 2 compared with controls, while by day 5 PA concentrations in both had fallen to similar levels. Furthermore, putrescine decreased the pH of the medium by 0.5 units around the explants. PAs had little effect on apple Malus pumila (Mill.) and no effect on almond Prunus dulcis (Miller) D.A. Webb and pistachio Pistacia vera (L.). There were also some positive effects observed, but only in olive, when rooting was induced by Agrobacterium rhizogenes in auxin-free medium. Few plantlets showed agropine-positive roots.

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Chockpisit Channuntapipat, Margaret Sedgley, and Graham Collins

Leaf explants were taken from mature leaves of two almond [Prunus dulcis (Miller) D.A. Webb] cultivars, Ne Plus Ultra and Nonpareil selection 15-1, and maintained in vitro to grow shoot tips. Shoot tips were grown also from a pre-existing in vitro culture of an almond-peach rootstock, P. dulcis `Titan' × P. persica `Nemaguard'. The shoot tips were harvested, cryopreserved, and tested for survival after 3 days and then at intervals of 3 months up to two years. The mean survival was 80% for `Ne Plus Ultra', 54% for `Nonpareil', and 78% for the hybrid rootstock, and there were no significant differences in survival between 3 days and 24 months. The effects of in vitro culture and cryopreservation on DNA integrity were examined by both RAPD-PCR, and restriction enzyme digestion followed by RAPD-PCR, using DNA from the original trees from which the explants were derived, from leaves regrown from cultures that had undergone several passages of in vitro culture, and from leaves regrown from cryopreserved shoot tips. No detectable differences were found between the DNA fingerprints of each DNA sample using RAPD-PCR with seven different 10-mer primers. However, differences were detected when the DNA was first digested with the isoschizomeric pairs, Hpa II/Msp I and Bsp 143 I/Mbo I and then subjected to RAPD-PCR with six different 10-mer primers. Changes in the structure and methylation of DNA were found that were probably related to the process of in vitro culture, and in addition, methylation changes were detected that were probably associated with the cryopreservation process. These changes did not appear to be caused by the vitrification solution used before immersion of shoot tips in liquid nitrogen. While cryopreservation appears to be an ideal method for the long-term storage of almond germplasm, the significance of the alterations to both methylation and structure of DNA needs to monitored in regenerated plants, especially as they relate to agronomic performance when the regenerants become reproductively mature.

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Thomas Gradziel, Bruce Lampinen, Franz Niederholzer, and Mario Viveros

‘Sweetheart’ is a new almond [ Prunus dulcis Miller (D.A. Webb)] cultivar from the breeding program of the University of California at Davis, CA. ‘Sweetheart’ kernels have a cordate shape and very high oleic acid content and so are similar to the

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Marie Pairon, Anne-Laure Jacquemart, and Daniel Potter

subgenera of Prunus (e.g., Rehder, 1940 ). They were shown to be conserved in species of subgenera Amygdalus (L.) Focke [e.g., P. persica , Prunus dulcis (Miller) D.A. Webb], Prunus (e.g., Prunus armeniaca L.), and Cerasus (Miller) Focke (e

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María Engracia Guerra, Ana Wünsch, Margarita López-Corrales, and Javier Rodrigo

’ almond [ Prunus dulcis (Mill.) D. A. Webb] Amer. J. Bot. 69 913 920 Ramming, D.W. 1994 Plum. Register of new fruit and nut varieties. Brooks and Olmo. List 36 HortScience 29 955 956 Rodrigo, J. Herrero, M. 1996 Evaluation of pollination as the cause of

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Thomas Gradziel and Bruce Lampinen

Origin ‘Kester’ is a new almond [ Prunus dulcis Miller (D.A. Webb)] cultivar from the breeding program of the University of California at Davis, CA. ‘Kester’ is cross-compatible and shows good overlap with the later bloom of the dominant California