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Toshio Hanada, Kyoko Fukuta, Hisayo Yamane, Tomoya Esumi, Ryutaro Tao, Thomas M. Gradziel, Abhaya M. Dandekar, Ángel Fernández i Martí, José M. Alonso, and Rafel Socias i Company

Most of the fruit tree species in the genus Prunus (Rosaceae), including almond [ Prunus dulcis (Mill.) D.A. Webb.], exhibit the S-RNase-based gametophytic self-incompatibility (GSI) system ( de Nettancourt, 2001 ; Yamane and Tao, 2009 ). The

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Sunitha H. Gurusinghe and Kenneth A. Shackel

Commercial harvesting of almonds [Prunus dulcis (Mill.) Webb.] with mechanical shakers is economical, but may also cause severe damage to the cambial zone, leading to the establishment of a deadly cankerous disease, ceratocystis. Irrigation is often cut off for some period of time before harvest, anticipating a reduction in the damage as a result of an increased strength of adhesion within the cambial zone between the bark and the wood. Mechanical failure can occur in the cambial zone proper and in the differentiating cells on either side of the cambial zone. In this study the shear force per shear area in the cambial zone (cambial strength) was measured to represent mechanical failure due to shaker damage. Cambial strength of branches with intact bark tissues could be reversibly influenced by the level of tissue hydration, with high cambial strength associated with increased tissue hydration, presumably a result of an increase in the turgor of cambial zone cells. Methods of measuring cambial strength were developed for branches and trunks to avoid the effects of reversible turgor changes. Irrigation regimes imposed before harvest had a substantial and progressive influence on tree stem water potential, stomatal conductance, and growth rate of almond trees. Statistically significant levels of within seasonal differences in rate of growth, stomatal conductance and tree water deficits found under different irrigation regimes did not show any correlation with the within seasonal fluctuations in cambial strength. Cambial strength always showed a similar pattern and a similar magnitude of seasonal increase from spring to summer (as previous authors have reported), superimposed over the within seasonal fluctuations, despite significant differences in tree water stress. Therefore, this study suggests that irrigation cut off may be an ineffective practice for the purpose of increasing cambial strength.

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Craig A. Ledbetter and Mark S. Sisterson

, IN Ledbetter, C.A. Palmquist, D.E. 2006a Comparing physical measures and mechanical cracking products of ‘Nonpareil’ almond [ Prunus dulcis (Mill.) D.A. Webb.] with two advanced breeding selections J. Food Eng. 76 232 237 Ledbetter, C.A. Palmquist, D

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Pedro Martinez-Gomez, Mary Ann Thorpe, and Thomas M Gradziel

Micrografts have proven a very useful technique when the early propagation of plant material is desired either to invigorate weak material, multiply selected genotypes, or obtained virus-free shoots. This is the situation with the recovery of haploid almond embryos, which occur at low frequency with sexual embryos in twin seeds (i.e., multiple embryos within the same seedcoat). Often these haploid plants show weak growth due to their haploid condition and their poorly developed state within twin seeds. Very little information is presently available, however, concerning the effectiveness of different micrografting techniques for almond. In this work, we examine the success of in vivo micrografting of `Nonpareil' almond seedlings under different conditions. Variables included type of micro-scion, the rootstock genotype, and the growth stage of the rootstock. Microscions tested included small (3 mm) micro-wedges from either unsprouted or recently sprouted buds. Rootstocks evaluated included the `Hanson' (peach × almond) hybrid, and Nemared and Nemaguard peach rootstocks. Rootstocks were grafted after either ≈3 weeks of growth, when the tissue was still herbaceous, or after ≈3 months of growth, when the tissue had become woody. Results show significant differences between the treatments. Findings will be discussed both in terms of effectiveness of different approaches and the advantages and disadvantages of their use in breeding programs.

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D.E. Kester, T.M. Gradziel, K.A. Shackel, and W.C. Micke

Noninfectious bud-failure (BF) is a genetic disorder in almond, associated with nursery source selection. Previously (Kester, PASHS, 1968), the latent potential for BF (BFpot) was shown to be heritable but its phenotypic expression (BFexp) varied among individual seedlings of a populations as a function of age. Vegetative propagation perpetuates BFpot of individual propagules (Kester and Asay, JASHS, 1978b) but the subsequent age of BFexp within individual plants is a function of accumulated exposure to high summer temperature and growth (Kester and Asay, JASHS 1978a). A recent 7-year “somatic heritability” study of 12 commercial nursery sources (Kester et al., HortScience 1998abst) portrays the total range of variability of BFpot and BFexp within the entire `Carmel' almond clonal population and includes a pattern of BF increase in consecutive vegetative propagation cycles that mimics patterns produced by phase change (i.e., juvenile > mature) phenomena (Hartmann et al., 1997). Although phase change potential is heritable in seedling populations, phase change expression is not (Kester, HortScience 1983). Furthermore phase changes can be reversed under particular conditions during consecutive vegetative propagations (Hartmann et al., 1997). In contrast, evidence shows that BF produces permanent changes in genotype that are heritable and irreversable. High correlations exist between BFpot of individual source blocks, individual trees and individual budsticks and the age and severity of BFexp in progeny trees. The apparent continuous change in BFpot and BFexp within clones appears to be the pattern of expression of different populations of increasingly defective (?) somatic cells that result from consecutive sequences of change during annual cycles of growth and generations of vegetative propagation.

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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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J.L. Espada and A.J. Felipe

Group-author : R. Socias i Company

Low levels of fruit set were measured in a commercial almond [Prunus amygdalus Batsch, syn. Prunus dulcis (Mill.) D.A. Webb] orchard during 3 years. Low sets may be attributed mostly to orchard design, as cultivars are distributed in contiguous rows where pollen interchange among different cultivars is not facilitated. An appropriate orchard design and proper bee management are essential for commercial yields in self-incompatible almond cultivars.

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

Almond [Prunus dulcis (Mill.) D.A. Webb] breeding programs require successful techniques for pollen storage. We studied the pollen viability of two almond cultivars, `Ramillete' and `Desmayo Largueta', during 8 weeks of storage, in conditions that simulated standard situations including storage at 4, 22, and 4 °C alternating with 22 °C (4 °C/22 °C). Viability remained at 60% or more for 2 weeks under all three conditions. After the second week, germination capacity decreased rapidly at 22 °C, but remained above 50% for as long as 8 weeks at 4 °C or 4 °C/22 °C.

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Farbod Youssefi, Patrick H. Brown, and Steve A. Weinbaum

It has been proposed that a pool of amino N, whose size is determined by aboveground N demand, cycles in the plant and regulates soil N uptake by exerting an inhibitory effect at the root level. Several experiments were carried out to study this hypothesis in almond trees [Prunus dulcis (Mill.) D.A. Webb]. Based on the evidence found, there is an association, at the whole tree level, between sap N content and soil N uptake. The data are consistent with the possibility that increased phloem sap amino acids result in decreased uptake of soil N.

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Dale E. Kester, Warren C. Micke, and Mario Viveros

`Jeffries', a mutant of `Nonpareil' almond [Prunus dulcis (Mill.) D.A. Webb], showed “unilateral incompatibility” in that its pollen failed to fertilize cultivars in the `Carmel' (CIG-V), `Monterey' (CIG-VI), and `Sonora' (CIG-VII) pollen cross-incompatibility groups (CIGs), as well as specific cultivars (`Butte', `Grace', and `Valenta') whose CIG group is unknown. `Jeffries' is not self-compatible, but produced good set when pollinated by 12 almond cultivars representing the entire range of CIGs involving `Nonpareil' parentage, as well as the parent `Nonpareil'. It was concluded that the `Jeffries' mutant—both gametophyte and sporophyte—expressed a loss of a single S allele of the `Nonpareil' genotype.