All of the new additions to the FNRIC website, fruitsandnuts.ucdavis.edu, would not be possible without the hard work of our expert reviewers. With over 115,000 visits per year our website is an important source of information and outreach to the public in California. To meet high quality standards established by UC Agriculture and Natural Resources and UC Davis the FNRIC requires a minimum of two expert reviewers per crop before new information is posted online.

We would like to acknowledge the contribution of our reviewers who span a wide range of backgrounds from growers, commodity groups, extension specialists, UC faculty, and farm advisors. We sincerely appreciate your willingness to take time out of your busy schedules to provide critical feedback and suggestions on all our new website content.

Expert reviewers:

Ted DeJong, Professor, Dept. of Plant Sciences at UCD

Vito Polito, Professor, Dept. of Plant Sciences at UCD

Chuck Leslie, Specialist in the UC Davis Walnut Breeding Program

Scott Johnson, UCCE Specialist Emeritus

Maxwell Norton, Merced and Mariposa County Farm Advisor

Louise Ferguson, UCCE Specialist

Janine Hasey, Sutter and Yuba County Farm Advisor

Joe Grant, San Joaquin County Farm Advisor

Steve Sibbett, Farm Advisor Emeritus

Bruce Lampinen, UCCE Specialist

Chuck Ingels, Sacramento County Farm Advisor

Craig Ledbetter, USDA ARS

Maria Badenes, Faculty at the Instituto Valenciano de Investigaciones Agrarias

Jeff Moersfelder, USDA ARS Germplasm Repository

Carolyn DeBuse, USDA ARS Germplasm Repository

John Preece, USDA ARS Germplasm Repository Director

Wes Hackett, Professor Emeritus and walnut consultant

Paul Mesple, fig grower with Mesple Farms and the California Fig Board

Brian Blain, pecan grower with Blain Farms and the California Pecan Growers Association

Bob McClain, California Pear Advisory Board

Kitren Glozer, Project Scientist, Dept. of Plant Sciences at UCD

Tom Gradziel, Professor, Dept. of Plant Sciences at UCD

We searched Web of Science for new almond (Prunus dulcis) orchard management research published in 2013. Below is a list of some new publications we found spanning a wide range of topics including global warming emissions, weed management, cold tolerance, irrigation, drought tolerance, and pollination. If you access this blog from a UC or ANR office you can click on the “url” listed to view the full paper.

University of California affiliated research on emissions from almond orchards

D. L. Schellenberg, M. M. Alsina, S. Muhammad, C. M. Stockert, M. W. Wolff, B. L. Sanden, P. H. Brown and D. R. Smart. 2012. Yield-scaled global warming potential from N2O emissions and CH4 oxidation for almond (Prunus dulcis) irrigated with nitrogen fertilizers on arid land. Agriculture Ecosystems & Environment. 155:7-15

Abstract: The optimum yield-scaled global warming potential (GWP) of perennial crops on arid land requires effective strategies for irrigation and fertilization. In 2009-2010, N2O emissions and CH4 oxidation were measured from an almond [Prunus dulcis (Mill.) D.A. Webb] production system irrigated with nitrogen (N) fertilizers. Individual plots were selected within a randomized complete block design with fertilizer treatments of urea ammonium nitrate (UAN) and calcium ammonium nitrate (CAN). Event-related N2O emissions from irrigation and fertilization were determined for seasonal periods of post-harvest, winter, spring and summer. Peak N2O emissions in summer occurred within 24h after fertilization, and were significantly greater from UAN compared to CAN (p<0.001). Cumulative N2O emissions from UAN were on average higher than CAN though not significantly different. Air temperature, water-filled pore space (WFPS), soil ammonium (NH4+) and soil nitrate (NO3-) showed significant positive correlation with N2O emissions and significant negative correlation was found for the number of days after fertilization (DAF). The percentage of N2O loss from N fertilizer inputs was 0.23% for CAN and 0.35% for UAN while CH4 oxidation offset 6.0-9.3% of N2O emissions. Total kernel yield was not significantly different between fertilizer treatments. Yield-scaled GWP for almond from CAN (60.9 kg CO(2)eq Mg-1) and UAN (91.9 kg CO(2)eq Mg-1) represent the first report of this metric for a perennial crop. These results outline effective irrigation and fertilization strategies to optimize yield-scaled GWP for almond on arid land. (C) 2012 Elsevier B.V. All rights reserved.

Pollination

R. G. Danka, L. I. De Guzman, T. E. Rinderer, H. A. Sylvester, C. M. Wagener, A. L. Bourgeois, J. W. Harris and J. D. Villa. 2012. Functionality of Varroa-Resistant Honey Bees (Hymenoptera: Apidae) When Used in Migratory Beekeeping for Crop Pollination. Journal of Economic Entomology. 105. 2. 313-321.

url: http://www.bioone.org/doi/pdf/10.1603/EC11286

Abstract: Two types of honey bees, Apis mellifera L. (Hymenoptera: Apidae), bred for resistance to Varroa destructor Anderson & Trueman were evaluated for performance when used in migratory crop pollination. Colonies of Russian honey bees (RHB) and outcrossed bees with Varroa-sensitive hygiene (VSH) were managed without miticide treatments and compared with colonies of Italian honey bees that served as controls. Control colonies were managed as groups which either were treated twice each year against V. destructor (CT) or kept untreated (CU). Totals of 240 and 247 colonies were established initially for trials in 2008 and 2009, respectively. RHB and VSH colonies generally had adult and brood populations similar to those of the standard CT group regarding pollination requirements. For pollination of almonds [Prunus dulcis (Mill.) D. A. Webb] in February, percentages of colonies meeting the required six or more frames of adult bees were 57% (VSH), 56% (CT), 39% (RHB), and 34% (CU). RHB are known to have small colonies in early spring, but this can be overcome with appropriate feeding. For later pollination requirements in May to July, 94-100% of colonies in the four groups met pollination size requirements for apples (Malus domestica Borkh.), cranberries (Vaccinium macrocarpon Aiton), and lowbush blueberries (Vaccinium angustifolium Aiton). Infestations with V. destructor usually were lowest in CT colonies and tended to be lower in VSH colonies than in RHB and CU colonies. This study demonstrates that bees with the VSH trait and pure RHB offer alternatives for beekeepers to use for commercial crop pollination while reducing reliance on miticides. The high frequency of queen loss (only approximately one fourth of original queens survived each year) suggests that frequent requeening is necessary to maintain desired genetics.

S. Bayazit, B. Imrak and O. Caliskan. 2012. Determination of Pollen Production and Quality attributes of some Almond Cultivars (Prunus dulcis) and Selected Wild Almond (Amygdalus orientalis) Genotypes. International Journal of Agriculture and Biology. 14. 3. 425-429.

Abstract: This study was carried out to establish pollen production, viability and germination ratios for five almond genotypes of Amygdalus orientalis Mill. (Orientalis 5, Orientalis 6, Orientalis 7, Orientalis 9 & Orientalis 10) and four cultivars of Prunus dulcis Mill., (Nonpareil, Texas, Ferragnes & Ferraduel). For determination of pollen viability of selected almond genotypes, 2.3.5 Triphenyltetrazolium chloride and Fluorescent diacetat tests were made. Pollen germination ratios in vitro conditions were determined with petri dishes methods. For A. orientalis genotypes, pollen viability ratios according to the TTC test were found to be 61.80% and 72.88% in 2006 and 2007, respectively whereas the same ratios according to the FDA test carried out in 2006 and 2007 were 63.44% and 57.50%, respectively. The number of anthers in one flower, the number of pollen in one anther and the number of pollen in one flower were found higher in cultivars, whereas these traits turned out to be lower in A. orientalis genotypes. 'Orientalis 6' was notable pollen viability, the number of anthers in one flower, the number of pollen in one anther and the number of pollen in one flower, while the highest pollen germination percentage was recovered from 'Orientalis 9' had in 2006 and from 'Orientalis 5' in 2007. Morphological homogeneity (%) was found to be high in all orientalis types both experimental years. The results obtained with A. orientalis genotypes proved that they could well be employed as pollinizer for hybrid improving work to be made with almond cultivars. (C) 2012 Friends Science Publishers

Cold tolerance

P. M. Barros, N. Goncalves, N. J. M. Saibo and M. M. Oliveira. 2012. Functional characterization of two almond C-repeat-binding factors involved in cold response. Tree Physiology. 32. 9. 1113-1128.

url: http://treephys.oxfordjournals.org/content/32/9/1113.short

Abstract: Low temperature plays a crucial role in seasonal development of woody plants and may directly impact crop production, more particularly in temperate fruit trees. Given its high genetic variability and adaptability to different climatic conditions, almond (Prunus dulcis Mill.) is an interesting model to understand the mechanisms regulating low temperature sensing in fruit trees. In this paper, we report the cloning and characterization of two genes (PdCBF1 and PdCBF2) belonging to the C-repeat-binding factor (CBF) family of transcription factors. Southern blotting analysis showed that this family is composed of at least five members. In almond shoots propagated in vitro, transcription of these genes was rapidly induced by low temperature, suggesting an involvement in cold acclimation. Transactivation assays showed that PdCBF1 and PdCBF2 could bind to dehydration responsive element/C-repeat containing sequences, as activators of gene expression. In addition, induction of both PdCBFs by cold was higher towards the end of the day, which agreed with the expression pattern of PdDehydrin1, a predicted CBF target gene. Furthermore, PdCBF1 and PdCBF2 were also transiently induced by abscisic acid and drought treatments. Considering the bin mapping analysis that correlated PdCBFs and PdDHN1 (respectively in linkage groups 5 and 7) with two different quantitative trait locicontrolling blooming time, it is relevant to perform further association studies that may validate their effect on this trait.

Water stress and irrigation

G. Egea, M. M. Gonzalez-Real, A. Baille, P. A. Nortes, M. R. Conesa and I. Ruiz-Salleres. 2012. Effects of water stress on irradiance acclimation of leaf traits in almond trees. Tree Physiology. 32. 4. 450-463.

url: http://treephys.oxfordjournals.org/content/32/4/450.short

Abstract: Photosynthetic acclimation to highly variable local irradiance within the tree crown plays a primary role in determining tree carbon uptake. This study explores the plasticity of leaf structural and physiological traits in response to the interactive effects of ontogeny, water stress and irradiance in adult almond trees that have been subjected to three water regimes (full irrigation, deficit irrigation and rain-fed) for a 3-year period (2006-08) in a semiarid climate. Leaf structural (dry mass per unit area, N and chlorophyll content) and photosynthetic (maximum net CO2 assimilation, A(max), maximum stomatal conductance, g(s,max), and mesophyll conductance, g(m)) traits and stem-to-leaf hydraulic conductance (Ks-l) were determined throughout the 2008 growing season in leaves of outer south-facing (S-leaves) and inner northwest-facing (NW-leaves) shoots. Leaf plasticity was quantified by means of an exposure adjustment coefficient (epsilon = 1-X-NW/X-S) for each trait (X) of S- and NW-leaves. Photosynthetic traits and Ks-l exhibited higher irradiance-elicited plasticity (higher epsilon) than structural traits in all treatments, with the highest and lowest plasticity being observed in the fully irrigated and rain-fed trees, respectively. Our results suggest that water stress modulates the irradiance-elicited plasticity of almond leaves through changes in crown architecture. Such changes lead to a more even distribution of within-crown irradiance, and hence of the photosynthetic capacity, as water stress intensifies. Ontogeny drove seasonal changes only in the epsilon of area- and mass-based N content and mass-based chlorophyll content, while no leaf age-dependent effect was observed on epsilon as regards the physiological traits. Our results also indicate that the irradiance-elicited plasticity of A(max) is mainly driven by changes in leaf dry mass per unit area, in g(m) and, most likely, in the partitioning of the leaf N content.

P. Puerto, R. Domingo, R. Torres, A. Perez-Pastor and M. Garcia-Riquelme. 2013. Remote management of deficit irrigation in almond trees based on maximum daily trunk shrinkage. Water relations and yield. Agricultural Water Management. 126. 33-45.

url: http://www.sciencedirect.com/science/article/pii/S0378377413001108

Abstract: This study assesses the usefulness of the remote scheduling of regulated deficit irrigation (RDI) in almond based on the maximum daily trunk shrinkage signal intensity (SIMDS). The 2-year experiment was carried out in SE Spain on 12-year-old almond trees (Prunus dulcis (Mill.) D.A. Webb cv. Guara). Four irrigation treatments were established to evaluate soil-plant water status, yield and water productivity: (i) control treatment (CTL), irrigated to satisfy the maximum crop water requirements (ETc), (ii) RDI1 and (iii) RDI2, both established to maintain different target thresholds of SIMDS according to the phenological stage and (iv) farmer treatment (FRM), irrigated by the grower according to his own experience. In 2009 and 2010 strategies 1.3-2.2-1.6 (SIMDS target threshold for each tree development stages II-III, IV and V, respectively) and 1.6-2.8-1.6 were applied in RDI1, respectively, and strategies 1.0-2.8-1.3 and 1.0-3.2-1.0 in RDI2. A supervisory control and data acquisition platform (SCADA) was created to monitor and remotely manage the irrigation scheduling. The obtained results indicate that SIMDS is a suitable parameter for irrigation scheduling throughout the growing season. The greater or lesser accuracy of fit of the measured SIMDS values to the thresholds depended on the phenological stage and the target stress intensity. SIMDS threshold values higher than 2.8, which involve midday stem water potential (Psi(stem)) values lower than -1.9 MPa, were not suitable for almond irrigation management under our growing conditions. SIMDS-based RDI strategies were able to generate moderate to severe water stress in almond trees, which resulted in seasonal water savings around 50%. RDI strategies proved to be more cost-effective than full irrigation and farmer deficit irrigation treatment given the high price of irrigation water. (c) 2013 Elsevier B.V. All rights reserved.

Propagation

M. A. Mir, K. M. Bhat, Z. A. Rather, F. A. Peer, A. H. Pandit and G. Hussain. 2012. In vitro propagation of almond (Prunus dulcis) cv. Merced. Indian Journal of Agricultural Sciences. 82. 4. 312-317.

url: http://epubs.icar.org.in/ojs-2.3.1-2/index.php/IJAgS/article/view/16632

Abstract: Forced and unforced shoot tips were surface sterilized with different sterilant regimes and incubated under normal culture room conditions. Surface sterilization of explants with mercuric chloride 0.1% (w/v) for 10 min. was found effective in improving culture asepsis (51.66%) and explant survival (55.00%). Higher values for both these parameters were recorded with forced explants in comparison to unforced ones. Main effect of growth regulators and media was significant on explant establishment which was maximum (66.66%) on 1/2 MS media containing BAP + IBA (0.50+0.01 mg/l). Callusing at the base of initiating cultures was minimum (24.58%) with BAP+IBA (0.25+0.01 mg/l). Microshoots from the established cultures were subcultured on the MS media supplemented with BAP and NAA alone or in combination for axillary shoot proliferation. Maximum proliferated cultures (86.66%) with maximum shoot number/explant (15.61) and proliferation grade (4.00) was obtained with BAP+NAA (0.40+0.01 mg/l). BAP was found superior to NAA during axillary shoot proliferation. Microshoots (10-15 nun) from proliferated cultures were subcultured in root induction medium (MS medium supplemented with IBA) and incubated under darkness for 10 days at 24 +/- 1 degrees C and then transferred to root development medium (hormone-free MS medium) and incubated under normal culture room conditions. Highest rooting of microshoots (93.33%) with maximum root number/shoot (5.90) and root length (43.00 mm) was obtained with IBA (1.0 mg/l).

H. Yildirim, H. Akdemir, V. Suzerer, Y. Ozden and A. Onay. 2013. In vitro micrografting of the almond cultivars "Texas", "Ferrastar" and "Nonpareil". Biotechnology & Biotechnological Equipment. 27. 1. 3493-3501

url: http://www.diagnosisnet.com/bbeq/article/78f44933-e095-3484-e93c-1f8416224992

Abstract: A successful micrografting technique for the almond cultivars (cvs) "Texas", "Ferrastar" and "Nonpareil" was developed using in vitro germinated seedlings as rootstocks and axenic shoot cultures established from mature tree sources as microscions. In vitro germinated seedlings, which developed 14 days after culturing in the modified Murashige and Skoog (MS) medium, were decapitated and used as rootstock. Shoot culture initiation from three almond cvs ("Texas", "Ferrastar" and "Nonpareil') was successfully achieved by culturing mature shoot tips from forced nodal buds, about 4-6 mm, on a modified MS medium containing I mg.L-1 benzyl adenin (BA). Slit micrografting on epicotyl and on hypocotyls were equally successful (83.3 % to 100 %). Grafting success was dependent on the rootstock type and lenght of the scion. Grafting success varied between 83.33 % and 100 % depending on the cultivar, when the scion contained I, 2, and 3 nodes. When almond scions, about 1.5 cm long, were micrografted on germinated seedling and cultured on proliferation medium (PM), the mean shoot length was 19.84 mm, 16.50 mm, 26.93 mm for the cvs "Texas", "Ferrastar" and "Nonpareil" respectively Micro grafts could be easily cultured on a hormone-free semi-solid MS medium and were potted out after 4 to 6 weeks of culture growth. Rooted micrografted plantlets were successfully acclimatized and transferred to potting mix with 100 % survival. Although low percentages of variation were obtained in tested cvs (3.70 %, 6.25 % and 10.2 % in "Texas", "Ferrastar" and "Nonpareil'), molecular analysis showed that the developed micrografting technique produces genetically stable plantlets, at least up to 6 months of sub-culturing in cvs "Ferrastar" and "Nonpareil". The described micrografting technique could be used for rejuvenation of shoot explants of mature elite almond cultivars and it also has potential use in the commercial production of other almond cultivars. Biotechnol. & Biotechnol. Eq. 2013, 27(1), 3493-3501

Weed management

A. Shrestha, M. Moretti and N. Mourad. 2012. Evaluation of Thermal Implements and Organic Herbicides for Weed Control in a Nonbearing Almond (Prunus dulcis) Orchard. Weed Technology. 26. 1. 110-116

url: http://www.wssajournals.org/doi/abs/10.1614/WT-D-11-00083.1

Abstract: Sustainable weed management strategies are needed for organic orchard systems. A study was conducted in an almond orchard in Fresno, CA from 2009 to 2011. Treatment comparisons included steam, flame, and broad applications of either lemongrass oil or D-limonene. An untreated control was also included. The experimental design was a randomized complete block with four replications. Weekly evaluations on percent weed control were taken and weed biomass was sampled 4 to 8 wk after treatment (WAT). Weed control and biomass differed between seasons but, in general, steam and flame provided as much as 95% control 1 WAT. However, the effects lasted only 3 to 4 wk as new weeds emerged or the treated weeds overcame the suppressive effects of the thermal treatments. Weed biomass was 95% lower in the steam-and flame-treated plots compared with the untreated plots in summer. Both steam and flame were more effective on certain erect-growing broad-leaved weed species than on prostrate-growing weeds and grasses. Lemongrass oil provided very little weed control. However, D-limonene provided up to 95% weed control 1 WAT and in one experiment 53% control was observed up to 5 WAT. This herbicide also resulted in lower weed biomass than the untreated and the thermal-treated plots. Monthly applications of steam or flame or applications of D-limonene every 5 to 6 wk may have to be made to adequately suppress weeds in organic almond orchards. Cost estimates of propane use were $41 to 56 ha(-1) and $26 ha(-1) for the steam and flame treatments, respectively. The cost of D-limonene was estimated as $275 ha(-1). To optimize weed control and costs, these tools may need to be used in combination rather than by themselves.

Kernel quality

R. Sanchez-Perez, G. Arrazola, M. L. Martin, N. Grane and F. Dicenta. 2012. Influence of the pollinizer in the amygdalin content of almonds. Scientia Horticulturae. 139. 62-65.

url: http://www.sciencedirect.com/science/article/pii/S0304423812001033

Abstract: Bitter kernel taste in almonds is a monogenic trait, being bitter recessive. Bitterness depends on the content of the cyanogenic glucoside amygdalin, whose concentration can be more than 1000 times higher in bitter kernels than in sweet ones. Although previous studies showed that the bitter taste of almonds was not influenced by the pollinizer, nothing is known about the influence of the pollinizer on the amygdalin content of the kernel. In order to study the possible effect of the pollinizer on the content of amygdalin, we analyzed seeds from four cultivars: Del Cid (SkSk: sweet), Marcona (Sksk: sweet), Garrigues (Sksk: slightly bitter) and S3067 (sksk: bitter), which were crossed with four different pollinizers: Ramillete (SkSk: sweet), Atocha (Sksk: sweet), S3065 (Sksk: slightly bitter) and S3067. Results showed that when a sweet pollinizer was involved, the content of amygdalin could be reduced by up to 21%, compared to the bitter x bitter crosses. (C) 2012 Elsevier B.V. All rights reserved.

Self-incompatibility in the Rosaceae family 

J. Wu, C. Gu, M. A. Khan, J. Y. Wu, Y. B. Gao, C. L. Wang, S. S. Korban and S. L. Zhang. 2013. Molecular Determinants and Mechanisms of Gametophytic Self-Incompatibility in Fruit Trees of Rosaceae. Critical Reviews in Plant Sciences. 32. 1. 53-68.

url: http://www.tandfonline.com/doi/abs/10.1080/07352689.2012.715986#.UqixvfRDt8E

Abstract: Self-incompatibility is an important genetic mechanism that prevents inbreeding and promotes genetic polymorphism and heterosis in flowering plants. Many fruit species in the Rosaceae, including apple, pear, plum, apricot, sweet cherry, Japanese apricot, and almond, exhibit typical gametophytic self-incompatibility (GSI) controlled by an apparently single multi-allelic locus. This locus encodes at least two components from both the pollen and the pistil, and controls recognition of self- and non-self pollen. Recently, the GSI system has been investigated at the molecular and cellular levels in Rosaceae, and findings have provided some important insights as to how these two genes interact within pollen tubes that lead to specific inhibition of germination and/or growth of self-pollen tubes. In this review, molecular features of S-determinants of both pistil and pollen, identification of S-alleles, mechanisms of self- incompatibility break-down, and evolution of S-alleles are presented. Moreover, hypothetical signal transduction models in a self-incompatible system in Rosaceae are proposed based on recent findings that indicate that several signal factors are involved in GSI responses.

During this season, I have been asked several times about the proper storage conditions for ‘Fuyu’ persimmons. ‘Fuyu’ persimmons completely lose their astringency before harvest and can be consumed, contrary to ‘Hachiya’, while they are still firm.  In general, harvest time is determined according to the fruit color and size. The best method of harvesting is to clip the fruit with small clippers (orange clippers) from the tree, leaving the calyx attached to the fruit.  It is also possible to snap the fruit from the tree but this practice is not recommended as it may injure the fruit and adjoining shoot.  During harvesting and packaging fruit must be handled carefully to avoid bruising, which is likely to result in marking which becomes visible as the fruit ripens.  Penicillium, Botrytis and Cladosporium fungi may infect ‘Fuyu’ persimmons during storage, especially, if the skin has been damaged during postharvest handling. 

Fuyu’ persimmons are very sensitive to chilling injury which is expressed by fast fruit softening, flesh browning, translucency (jelly-like consistency) during and after storage.  These symptoms appear more severe after 2-4 days at 68^oF (20^oC) following storage.  Chilling injury is more rapid and severe at 41^oF (5^oC), especially, combined with ethylene exposure.  Studies led by Dr. Kader in our department demonstrated that exposure to 1 and 10 ppm ethylene at 68^oF (20^oC) resulted in accelerated softening to less than 4 pounds (limit for marketability) after 6 and 2 days, respectively.  Exposure to 1 and 10 ppm ethylene at 41^oF (5^oC) will induce fruit firmness below 4 pounds (soft) after 15 and 8 days, respectively.  Therefore, the use of 1-MCP, ethylene removal and/or exclusion during packaging and storage at 32^oF (0^oC) operations is strongly recommended for maintaining quality and extending ‘Fuyu’ persimmons storage life potential.

The annual Statewide Pistachio Day will be held on Wednesday January 29^th, 2014 at the Visalia Convention Center. Each year Pistachio Day is organized by University of California Cooperative Extension Specialists, Farm Advisors, and the California Pistachio Research Board to bring pistachio growers the latest research-based production practices. Pistachio Day is attended by prospective and current pistachio growers, production managers, and pest control consultants.

Presenters will provide up to date information on a wide range of topics including:

   - Pest, disease, and nutrient management

   - Pistachio varieties and rootstocks grown in California

   - The pistachio collection at the USDA Germplasm Repository

Register today or submit a sponsorship application to reserve your spot.

Check the main Pistachio Day website soon for information about PCA and continuing education credits.