Our second annual pomology extension course, Principles of Fruit and Nut Tree Growth, Cropping and Management, is underway at UC Davis. New and experienced growers working with all of the common fruit and nut crops grown in California are attending. In the first three days we have had a chance to learn about tree growth, pruning, pollination, root growth, irrigation and tree water use from a team of UC experts.

We spent Monday and Tuesday mornings in lecture learning about tree growth, bearing habits, chilling, dormancy, flower anatomy and pollination. On the first two afternoons our lead instructor, Professor DeJong (Plant Sciences Department, UC Davis) teamed up with Kevin Day (Farm Advisor in Tulare County and stone fruit expert) to teach pruning and root growth in the field.

On Wednesday Professor Shackel (Plant Sciences Department, UC Davis) gave us a thorough introduction to tree water use and irrigation with lectures and practical worksheets. In the afternoon everyone had the chance to learn how to measure plant water stress using a “pump-up” pressure bomb developed by Professor Shackel.

Hands on pruning demonstration and root excavation at the UC Davis teaching orchard:

 

Flower and fruit anatomy dissection:

 

 

Measuring plant water stress using a pressure bomb:

Imagine a pesticide sprayer smart enough to hit trees and turn off between them. What would that mean for your wallet? What would it mean for the rivers and streams near your orchard? View On Target, a video that shows how smart sprayer technology is helping farmers manage orchard pests with clever results:

• Substantially reduced pesticide use and cost
• Less pesticide movement to rivers and streams
• Full tree coverage
• Same efficacy as conventional sprayers
• Ease of use
• Valuable application data

Walt Bentley, retired UC IPM Advisor, narrates this video showing a smart sprayer in action.

Smart sprayer technology is based on the use of high frequency sound waves. An onboard computer directs sound waves toward trees. When sound waves are returned, a target is detected and the computer triggers nozzles to spray. When sound waves are not returned, a gap is identified, prompting the program to turn off nozzles.

Find the video on the UC IPM Mitigation Pesticide Hazards page at http://www.ipm.ucdavis.edu/mitigation/index.html. Scroll down to the second bullet under “Before application.” Remember this page the next time you plan a pesticide application. It will help you consider practices that minimize environmental and efficacy problems.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A search of Web of Science revealed a few new publications on drought stress and salt tolerance in Pistachio. I copied the citations, abstracts, and a link to the articles below. If you are working on a UC network with library access clicking on the "url" will enable you to download the full article. 

Drought stress

H. Abbaspour, S. Saeidi-Sar, H. Afshari and M. A. Abdel-Wahhab. 2012. Tolerance of Mycorrhiza infected Pistachio (Pistacia vera L.) seedling to drought stress under glasshouse conditions. Journal of Plant Physiology. 169. 7. 704-709.

url: http://www.sciencedirect.com/science/article/pii/S0176161712000879

The influence of Glomus etunicatum colonization on plant growth and drought tolerance of 3-month-old Pistacia vera seedlings in potted culture was studied in two different water treatments. The arbuscular mycorrhiza (AM) inoculation and plant growth (including plant shoot and root weight, leaf area, and total chlorophyll) were higher for well-watered than for water-stressed plants. The growth of AM-treated seedlings was higher than non-AM-treatment regardless of water status. P. K, Zn and Cu contents in AM-treated shoots were greater than those in non-AM shoots under well-watered conditions and drought stress. N and Ca content were higher under drought stress, while AM symbiosis did not affect the Mg content. The contents of soluble sugars, proteins, flavonoid and proline were higher in mycorrhizal than non-mycorrhizal-treated plants under the whole water regime. AM colonization increased the activities of peroxidase enzyme in treatments, but did not affect the catalase activity in shoots and roots under well-watered conditions and drought stress. We conclude that AM colonization improved the drought tolerance of P. vera seedlings by increasing the accumulation of osmotic adjustment compounds, nutritional and antioxidant enzyme activity. It appears that AM formation enhanced the drought tolerance of pistachio plants, which increased host biomass and plant growth. (C) 2012 Elsevier GmbH. All rights reserved.

V. Bagheri, M. H. Shamshiri, H. Shirani and H. R. Roosta. 2012. Nutrient Uptake and Distribution in Mycorrhizal Pistachio Seedlings under Drought Stress. Journal of Agricultural Science and Technology. 14. 1591-1604.

url: http://www.sid.ir/En/VEWSSID/J_pdf/8482012S14.pdf

This study was conducted to determine the effects of arbuscular mycorrhizal fungi (Glomus mosseae and Glomus intraradices) symbiosis on mineral uptake of two pistachio cultivars (Pistacia vera cv. Qazvini and Pistacia vera cv. Badami-Riz-Zarand) grown in the greenhouse under different drought stress levels. Drought stress (DS) reduced the mycorrhizal colonization in both cultivars as well as nutrient uptake. The mycorrhizal plants had higher P, K, Zn and Mn concentrations than non-mycorrhizal plants regardless of soil moisture conditions while Cu and Fe concentrations were unchanged. Distribution of elements was affected by AMF treatments where all except P were accumulated more in leaves than in roots. Contrastingly, under drought conditions, the absorbed elements tended to remain in root tissue. In the case of P and Mn uptake, Qazvini was superior in comparison with Badami. In conclusion, it is suggested that AMF inoculation improves drought tolerance of pistachio cultivars at least in part through the enhanced uptake of slowly diffusing mineral ions such as PO42- and Zn2+. Moreover, arbuscular mycorrhizal (AM) colonization provides better osmotic adjustment which can be correlated with K+ accumulation in top portions of inoculated plants. Results of this study also emphasized that 'Qazvini' cultivar may be more tolerant to drought than 'Badami'.

Salt tolerance

N. Bastam, B. Baninasab and C. Ghobadi. 2013. Improving salt tolerance by exogenous application of salicylic acid in seedlings of pistachio. Plant Growth Regulation. 69. 3. 275-284.

url: http://link.springer.com/article/10.1007/s10725-012-9770-7

Salicylic acid (SA) is a common, plant-produced signal molecule that is responsible for inducing tolerance to a number of biotic and abiotic stresses. An experiment was therefore conducted to test whether the application of SA at various concentrations (0, 0.10, 0.50, or 1.00 mM) as a foliar spray would protect pistachio (Pistacia vera L.) seedlings subjected to salt stress (0, 30, 60, or 90 mM NaCl). SA improved growth rate of pistachio seedlings under salt stress and increased relative leaf chlorophyll content, relative water content, chlorophyll fluorescence ratio, and photosynthetic capacity as compared with the control at the end of salt stress. SA ameliorated the salt stress injuries by inhibiting increases in proline content and leaf electrolyte leakage. It appeared the best ameliorative remedies of SA obtained when pistachio seedlings were sprayed at 0.50 and 1.00 mM.

H. Benhassaini, A. Fetati, A. K. Hocine and M. Belkhodja. 2012. Effect of salt stress on growth and accumulation of proline and soluble sugars on plantlets of Pistacia atlantica Desf. subsp atlantica used as rootstocks. Biotechnologie Agronomie Societe Et Environnement. 16. 2. 159-165.

The effect of salt stress on several physiological and biochemical parameters of Pistacia atlantica Desf. subsp. atlantica plantlets was studied under controlled conditions in a climatic room. The plants were grown in pots and irrigated with a Hoagland nutrient solution during 120 days. Then, the plantlets were treated for 10 days with 100, 200, and 400 meq.l(-1) NaCl + CaCl2, added to the Hoagland nutrient solution. The applied salts caused stress on the young Pistacia plantlets by reducing the growth of roots and shoots. The amount of free proline in leaves increased significantly with salinity under all treatments, to reach a maximum rate at the highest salinity concentration (400 meq.l(-1)) for all the plantlets. On the other hand, a significant difference in relative water content (RWC) was noted under the effect of 400 meq.l(-1) of NaCl + CaCl2. The plantlets stressed at 100 meq.l(-1) did not exhibit any influence of the salt on RWC, but their accumulation of sugars was much higher than at 200 meq.l(-1). At 400 meq.l(-1) the plantlets also accumulated a high content of soluble sugars, and after seven days of stress, their accumulation rose with the increasing salt concentration. The content of proline and soluble sugars in P. atlantica subsp. atlantica rootstock was very high, indicating that P. atlantica subsp. atlantica can be used as rootstock for Pistacia vera as it is more tolerant to salinity.

Chill requirements

O. Elloumi, M. Ghrab, H. Kessentini and M. Ben Mimoun. 2013. Chilling accumulation effects on performance of pistachio trees cv. Mateur in dry and warm area climate. Scientia Horticulturae. 159. 80-87.

url: http://www.sciencedirect.com/science/article/pii/S0304423813002215

Pistachios (Pistacia vera L.) are widely grown in the arid rainfed areas of Tunisia. However, pistachio production is still low with important variation between years. This study investigated the responses of pistachio trees to variable winter chilling and annual precipitation. It was carried out in an experimental orchard of Mateur, the most important Tunisian cultivar in central Tunisia (34 degrees 94'11 '', 10 degrees 60'82 '') for a period of twelve years from 1997 to 2008. Yield correlated poorly with precipitation (varying on the range of 80-300 mm/year during the 12 years) and showed a moderate alternate bearing index of 0.63. However, flowering and nut yield of pistachio trees was a function of chill accumulation computed as chilling hours (CH), chill units (CU) or chilling portions (CP) depending on using Crossa-Raynaud, Utah or Dynamic models, respectively. For Mateur cultivar, the threshold chilling accumulation appeared to be 206 CH, 539 CU or 36 CP depending on the model used. Under this level, pistachio production was clearly affected. Warm winters with low chilling caused erratic floral bud break, delayed flowering, sparse foliage and decreased yield. With inadequate winter chilling, chemical treatments with hydrogen cyanamide (Dormex) at 2 and 4% increased floral bud break, advanced flowering period and improved vegetative growth of pistachio trees in comparison to the untreated control. As a conclusion, better prediction of chill accumulation must be achieved in the warm production region of Tunisia. To that effect, the Dynamic model showed the lowest coefficient of variation compared to the chilling hours and Utah models and seemed to better reflect what is happening on the field under our warm winter regions. (C) 2013 Elsevier B.V. All rights reserved.

FNRIC BANNER

To maximize pomegranate quality fruit should be picked when fully ripe because they do not ripen off the tree. Pomegranate should be carefully maintained in cold storage after harvest because fruit are susceptible to chilling injury (CI). CI following exposure to temperatures below 5°C (41°F) during storage and transport for longer than 4 weeks is a major cause of deterioration during marketing. The incidence and severity of CI depends upon storage temperature, duration and cultivar (Photo 1). The minimum safe storage temperature is 5°C (41°F) for up to 8 weeks, if decay is not a problem. For longer storage, the temperature should be at 7^oC (45⁰F) to avoid chilling injury, but decay (Botrytis cinerea) and weight loss may become a limitation. A postharvest application of the fungicide Fludioxonil (Scholar) is approved for use on pomegranates with a 5ppm maximum residue limit to control decay development and prolong storage (Photo 2). However, pomegranates must be dipped in the fungicide solution because the botrytis spores are usually in the calyx area of the fruit, which are not adequately covered by postharvest spraying during packaging. After dipping surface moisture must be removed with a fan to eliminate free moisture on the fruit when stored in a box or bin. Under these storage conditions, pomegranates should be cooled to 7⁰C (45⁰F) as soon as possible after harvest and fungicide application. Fruit should be kept at 7⁰C (45⁰F) with relative humidity between 90-95% during storage and transportation to attain a postharvest-life longer than 8 weeks, depending on the cultivar.

Photo 1. Pomegranate chilling injury (CI) external symptoms include brown discoloration (scald) of the skin, pitting, and increased susceptibility to decay. Internal CI symptoms include brown discoloration of the white segments separating the arils and pale color (loss of red color) of the arils.

Photo 2. Gray mold (botrytis) on pomegranates

Author Information

Carlos H. Crisosto

Pomologist and Specialist, Plant Sciences Department, University of California Davis

Director of the Fruit & Nut Research & Information Center

chcrisosto@ucdavis.edu

References

•  Elyatem, S. M. and A. A. Kader. 1984. Post-harvest physiology and storage behavior of pomegranate fruits. Scientia Horticulturae 24:287-298.

• Kader, A. A., A. Chordas, and S. Elyatem. 1984. Responses of pomegranates to ethylene treatment and storage temperature. California Agriculture 38(7 & 8):14-15.

•  Palou, L., C.H. Crisosto, and D. Garner.  2007.  Combination of postharvest antifungal chemical treatments and controlled atmosphere storage to control gray mold and improve storability of ‘Wonderful’ pomegranates. Postharvest Biology and Technology 43: 133-142.

•  Hummer K.E., Pomper, K.W., Postman, J.D., Graham, C.J., Stover, E., Mercure, E.W., Aradhya, M., Crisosto, C.H., Ferguson, L., Thompson, M.M., Byers, P.,  and F. Zee.2012. Emerging Fruit Crops. Chapter 4, pp.97-147. In: (M. L. Badenes and D.H. Byrne, eds.) Fruit Breeding. Springer, NY, NY. 875 pp.