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James A. Hardin, Michael W. Smith, Paul R. Weckler, and Becky S. Cheary

Knowledge of foliar nitrogen (N) concentration is important in pecan [Carya illinoinensis (Wang.) K. Koch] management protocols. Lower cost and/or rapid methods to determine foliar N are desirable and may result in improved management strategies as well as enable precision agricultural practices to be deployed in pecan production. This study investigates using a portable chlorophyll meter and Vis-NIR camera to rapidly determine pecan foliar N in situ. Relationships of SPAD values from a chlorophyll meter (Minolta SPAD 502Plus) and vegetative indices calculated from camera image data to foliar N determined by chemical analysis were investigated. SPAD readings were taken monthly from May through October on ‘Pawnee’, ‘Kanza’, and ‘Maramec’ pecan cultivars in Oklahoma in 2010. Images of the same ‘Pawnee’ and ‘Kanza’ trees were collected in September and October of 2010 with a truck-mounted multispectral camera using ambient light. Correlation of foliar N to SPAD values was poor in May for all cultivars but distinct significant linear relationships were found for ‘Maramec’ and ‘Pawnee’ for each of the other months tested with R 2 ranging from 0.40 to 0.87. Data from ‘Kanza’ had significant relationships in June and October with R 2 of 0.39 and 0.72, respectively. Normalized difference vegetative index (NDVI) and reflectance data extracted from Vis-NIR camera images were significantly correlated to foliar N in both months of the study on ‘Pawnee’ but only in September for ‘Kanza’. The various relationships had R 2 between 0.21 and 0.51.

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Michael W. Smith, Margaret E. Wolf, Becky S. Cheary, and Becky L. Carroll

Two studies were conducted to determine if selected grass and dicot species had an allelopathic interaction with pecan (Carya illinoinensis Wangenh. C. Koch). Leachate from pots with established grasses or dicots was used to irrigate container-grown pecan trees. Leachates from bermudagrass [Cynodon dactylon (L.) Pers.], tall fescue (Festuca arundinacea Shreb. cv. Kentucky 31), redroot pigweed (Amaranthus retroflexus L.), and cutleaf evening primrose (Oenothera laciniata Hill) reduced leaf area and leaf dry weight about 20% compared to the controls. Bermudagrass, tall fescue, and primrose leachate decreased pecan root weight 17%, trunk weight 22%, and total tree dry weight 19% compared to the control. In a second study, trees were 10% shorter than the control when irrigated with bermudagrass or pigweed leachate.

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Charles T. Rohla*, Michael W. Smith, Niels O. Maness, and William R. Reid

Trees with about the same crop load were hand thinned to 1, <2, or <3 fruit per cluster or not thinned while the ovule was about one-half expanded. Treatments were replicated three times. Vegetative, and bearing terminal, lateral and shoots with secondary growth were tagged in October, and flowering was determined the following year. Shoots and roots were sampled during dormancy and analyzed for organically bound N, and K. Results indicated that branches with secondary growth produced substantially more shoots and flowers than other branch types. The unthinned trees produced fewer total flowers per branch, had a lower percentage of branches with flowering shoots, and smaller flower clusters than thinned trees. Organically bound N in the roots and shoots was not affected by crop load. Crop load appeared to be negatively related to K concentration in roots <1 cm in diameter, but not in roots >1 cm in diameter. The data suggest that neither N nor K were limiting in trees with large crops.

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Niels O. Maness, Michael W. Smith, C. Zhang, and Gerald H. Brusewitz

Techniques to reduce the oil content of shelled pecans using supercritical CO2 have been developed, and the effect of partial oil extraction on kernel quality is being investigated. Extraction conditions induce little kernel damage and allow for up to 30% oil reduction. Extraction temperature, at 40 or 80C, influenced kernel color. Regardless of temperature, extracted nut meat was lighter in color. Testa color increased in redness for kernels extracted at 80C compared to kernels extracted at 40C. Extracted oil was amber. Fatty acid composition of oil obtained with supercritical CO2 was essentially the same as oil obtained by organic solvent extraction and by cold press. Investigations to determine the effect of oil reduction on pecan shelf life are described. This research was supported by U.S. Department of Agriculture grant 92-34150-7190, Oklahoma Center for Advancement of Science and Technology grant AR4-044, and the Oklahoma Agricultural Experiment Station.

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Darrell Sparks, William Reid, I.E. Yates, Michael W. Smith, and Thomas G. Stevenson

The influence of fruiting stress on shuck decline, nut quality, and premature germinaiton was evaluated on trees of pecan [Carya illinoensis (Wangenh.) C. Koch]. Fruit at the liquid endosperm state were removed from trees with a mechanical shaker to reduce crop load by 0%, 25%, 41%, 56%, or 77%. Shuck decline and premature germination decreased and kernel quality increased with a reduction in crop load. An excessive fruit load or fruit stress elevated the incidence of shuck decline, previously referred to as shuck disease, tulip disease, shuck die-back, or late season shuck disorder; decreased kernel development; and increased premature germinaiton. Shucks were dissected from fruit ranging from healthy to those with premature shuck opening and examined by scanning electron, transmission electron, and light microscopy. Fungal growth was detectable, but only after tissue degeneration had occurred. Thus, results indicate the onset of shuck decline is caused by stress associated with an excessive crop load and not a pathological disorder. Fungal growth is a secondary, not a primary, factor in deterioration of shucks with decline.

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Derek P. Whitelock, Gerald H. Brusewitz, Michael W. Smith, and Xihai Zhang

This study examined the effects of high humidity (>95%) and airflow on fresh peach [Prunus persica (L.) Batsch.] quality. Peaches were stored in high airflow at 98%, 88%, and 67% relative humidity (RH) (6, 5.6, and 4.3C, respectively) and negligible airflow at 100%, 95%, and 81% RH (6, 5.6, and 4.3C, respectively). Fruit weight loss, penetrometer force, impact variables, and bruise occurrence from a single 15-cm drop impact were measured over 20 days of storage. Fruit stored at a low vapor pressure deficit had a lower rate of weight loss, with drop impact values characteristic of firmer fruit than fruit stored at higher vapor pressure deficits. High airflow increased weight loss and decreased fruit firmness, but had only a secondary effect on localized humidity. Penetrometer force and bruise occurrence were less sensitive than drop impact variables in detecting differences in fruit firmness due to treatments.

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Niels O. Maness, Jamal Bizri, Michael W. Smith, C. Zhang, and Gerald H. Brusewitz

Partial oil extraction is being investigated as a means to increase oxidative stability and provide reduced fat pecan halves. Supercritical extraction with carbon dioxide provided a means to extract twenty to thirty percent of resident oil, with little to no kernel damage and leaving no harmful residues in the kernel or the extracted oil. Variances in extraction time, temperature, pressure and total carbon dioxide volume used for extraction with a continuous flow extractor will be discussed. Fatty acid composition of oils extracted using supercritical carbon dioxide was essentially the same as oils obtained by solvent extraction and by cold press. Fatty acid yield in the oils was greater for supercritical extraction compared to the other two methods. Oxidative stability for extracted and unextracted pecans, determined using an accelerated aging technique, will be compared. Supported by USDA grant 92-34150-7190 and the Oklahoma Agricultural Experiment Station.

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Ravindranath V. Kanamangala, Neils O. Maness, Michael W. Smith, Gerald H. Brusewitz, and Sue Knight

Shelf life is a major problem in the marketing of pecans, particularly at the retail level. A procedure to extend the shelf life of pecans was described. The full-oil and supercritical carbon dioxide extracted (22% and 27% reduced-oil) native pecan kernels packaged in standard air mixture (21% O2, 79% N2), stored for up to 37 weeks at 25 °C and 55% RH, were subjected to hexanal analysis, sensory analysis, and determination of lipid class changes, that occur as the pecans age. Hexanal concentration of reduced-oil pecans was negligible throughout the storage, while full-oil pecans reached excessive levels by 22 weeks. Hexanal analysis was in agreement with the sensory scores. Free fatty acid lipid class was selectively extracted during the partial oil extraction process. Reduction in free fatty acids, and an overall reduction in lipid content on a per kernel basis, decreased the sites for oxidative deterioration and contributed to enhanced shelf-life of pecans. Work was supported by OCAST grant AR4-044 and the Oklahoma Agricultural Experiment Station.

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Charles T. Rohla, Michael W. Smith, Niels O. Maness, and William Reid

The most significant horticultural problem facing pecan producers is alternate bearing. Four pecan [Carya illinoinensis (Wangenh.) C. Koch] cultivars were chosen, two with low to moderate and two with severe alternate-bearing tendencies, to compare selected characteristics related to irregular bearing. The cultivars were Colby and Peruque (low to medium alternate-bearing tendency) and Osage and Giles (high alternate-bearing tendency). Vegetative shoots and fruit-bearing shoots in the terminal and lateral position on 1-year-old branches were tagged in October, and flowering was determined the next spring. Shoot and root samples were collected while dormant and then analyzed for organically bound nitrogen (N), potassium (K), and nonstructural carbohydrate concentrations. As expected, ‘Colby’ and ‘Peruque’ had a lower alternate-bearing tendency than ‘Giles’ and ‘Osage’. Cultivars with a low alternate-bearing tendency had a larger return bloom on the bearing shoots in the terminal position than the other shoot types. Cultivars with a high alternate-bearing tendency had a lower return bloom on bearing terminal shoots than vegetative shoots. Bearing shoots in the lateral position usually had a lower return bloom than the other shoot types regardless of cultivar. Neither root nor shoot N, K, or nonstructural carbohydrate concentrations appeared to be closely related to the alternate-bearing characteristics of the four cultivars. The unique characteristic identified for low alternate-bearing cultivars was their ability to produce as many or more flowers and flowering shoots the next year on previously bearing terminal shoots compared with previously vegetative shoots. In high alternate-bearing cultivars, return bloom of bearing terminal shoots was suppressed relative to their vegetative shoots.

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Gregory L. Reighard, Michael L. Parker, Gerard W. Krewer, Thomas G. Beckman, Bruce W. Wood, John Ed Smith, and Johnny Whiddon