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Mikal Saltveit, Youngjun Choi, and Francisco Tomás-Barberán

A wound signal originates at the site of injury in lettuce [Lactucasativa (L.)] leaf tissue and propagates into adjacent tissue where it induces a number of physiological responses that include increased phenolic metabolism with the de novo synthesis of phenylalanine ammonia lyase (PAL, EC 4.3.1.5), the synthesis and accumulation of soluble phenolic compounds (e.g., chlorogenic acid), and subsequent tissue browning. Exposing excised mid-rib leaf tissue to vapors (20 μmol·g-1 FW) or aqueous solutions (100 mm) of n-alcohols inhibited this wound-induced tissue browning by 40% and 60%, respectively. Effectiveness of the alcohol increased linearly from ethanol to the seven-carbon heptanol, and then was lost for the longer n-alcohols 1-octanol and 1-nonanol. The 2- and 3-isomers of the effective alcohols did not significantly reduce wound-induced phenolic accumulation at optimal 1-alcohol concentrations, but significant reductions did occur at much higher concentrations (100 μmol·g-1 FW) of the 2-, and 3-isomers. The active n-alcohols were maximally effective when applied during the first 2 h after excision, and were ineffective if applied 12 h after excision. Phospholipase D (PLD) and its product phosphatidic acid (PA) are thought to initiate the oxylipin pathway that culminates in the production of jasmonic acid, and PLD is specifically inhibited by 1-butanol, but not by 2- or 3-butanol. These results suggest that PLD, PA, and the oxylipin pathway may be involved in producing the wound signal responsible for increased wound-induced PAL activity, phenolic accumulation, and browning in fresh-cut lettuce leaf tissue.

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D.C. Ramsdell, V.A. Adler, and C.R. Kesner

Twenty-one declining `Stanley' prune (Prunus domestica L.) commercial orchards in the southwestern, west-central, and northwestern regions of Michigan's lower peninsula were surveyed for prune brown line disease, associated with tomato ringspot virus (TmRSV). Fifty trees from each orchard were examined for a brown line and pitting-grooving symptoms beneath the bark at the graft union. Inner bark and cambium were taken at the graft union for ELISA testing for TmRSV. Dagger nematodes (Xiphinema americanum Cobb 1913) (the vector) were extracted from soil samples and enumerated. Dandelions (a TmRSV weed host) also were tested for TmRSV. Information on orchard cultural practices and orchard histories was compiled. The percentage of trees ELISA-positive for TmRSV ranged from 4% to 82%, with a mean of 27.9%. The percentage of orchards in the northwestern, west-central, and southwestern regions in which TmRSV was detected by ELISA was l8.0%, 32.3%, and 35.1%, respectively. There was a strong positive correlation between the percentage of trees with a brown line at the graft union and the percentage of trees in which TmRSV was detected at each location. The brown line symptom is a good indicator for the presence of TmRSV, but graft-union pitting and grooving did not correlate strongly with the presence of the virus. TmRSV was detected in dandelion plants in 63% of the orchards tested. Dandelion densities, which ranged from <0.5 to 10/m2, did not correlate positively with percentage of ELISA-positive trees. Numbers of dagger nematodes ranged from 0 to 132 per cm3 of soil. Vector nematode populations correlated positively with ELISA-positive trees from southwestern Michigan, but not in the other two regions. Orchard age, which ranged from 6 to 22 years, did not seem to relate to the percentage of trees in which TmRSV was detected, nor did the source of the plant material used to establish the orchards. Both `Myrobalan' and peach rootstocks were heavily infected. Preplant and at-planting applications of fenamiphos as a strip treatment were ineffective in preventing infection. We believe that TmRSV is endemic in Michigan orchard soils and that the virus is not being introduced to new orchards through the use of infected planting material.

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Christopher J. Clark and Douglas M. Burmeister

Development of browning induced in `Braeburn' apple (Malus ×domestica Borkh.) fruit by a damaging CO2 concentration was monitored weekly using magnetic resonance imaging (MRI) during a 4-week storage trial (0.5 °C, 2 kPa O2/7 kPa CO2). Discrete patches of high-intensity signal, distributed randomly throughout the fruit, were observed in multislice images of samples after 2 weeks of storage; these patches were eventually confirmed as being sites of browning reactions after dissection at the end of the trial. Subsequently (weeks 3 and 4), signal intensity at sites of incipient damage increased and patches enlarged and coalesced. After 2 weeks of storage, the extent of affected tissue, averaged across all image slices, was 1.5%, increasing to 15.9% and 21.3% after 3 and 4 weeks. The average rate at which tissue damage spread in individual slices was 0.81 (range: 0–3.70) cm2·d–1 between weeks 2 and 3, declining to 0.32 (range: 0–1.55) cm2·d–1 in the final week. Tissue damage induced under these conditions did not spread at the same rate at all locations within individual fruit, nor was it preferentially located toward the stem or calyx ends of the fruit.

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K.V. Kommineni, J.M. Gillett, and D.C. Ramsdell

In a greenhouse study, fifty 1-year-old `Stanley'/`Myrobalan 29C' plum (Prunus sp.) trees were inoculated with tomato ringspot nepovirus (ToRSV) by either nematode inoculation or slash inoculation to compare how inoculation effects the onset of the prune brown line (PBL) disease. In six tests (over 2 years), slash-inoculated trees had a higher percentage of ToRSV infection than nematode-inoculated trees when root and bark samples were tested by enzyme-linked immunosorbent assay (ELISA). ELISA differences between the two treatments were significant by chi-square analysis. None of the ToRSV positives by ELISA developed a brown line at the graft union. In a second experiment, five rootstock (`Myrobalan 29C', `Marianna 4001', `Marianna 2624', `Marianna GF8-1', and `St. Julian 655-2') and five scion (`Carolyn Harris', `New York 58.900.12', `Stanley', `Valor', and `70031') combinations (total combination = 25) were established in a field plot in Traverse City, Mich., and infected with ToRSV by slash and nematode inoculation. All five rootstocks were infected, with incidences of 40% to 60% ToRSV infections after 3 years. `Marianna 2624' had the lowest incidence of PBL (5%) compared to `Myrobalan 29C', which had the highest incidence (30%). The scion 70031 in combination with either `Myrobalan 29C' or `Marianna 4001' rootstocks, produced PBL in 100% of the trees. ToRSV was detected by ELISA and northern hybridization assays. ELISA consistently detected more positives when root or bark tissues were tested, and northern hybridization assay consistently detected more positives when rootstock sucker leaves were used.

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Wol-Soo Kim* and Young Kim

Sweet persimmon, `Fuyu', is the major cultivar for MA storage, but browning of blossom end part (BBEP) and darkening are occurring during storage and decrease fruit qualities in fresh fruit markets in Korea. The symptom of BBEP of fruit started to occur on the blossom end part and spread to the middle and stem end part. These fruits lose their marketable values. Calcium has very important role in cell membrane in physical and physiological. This study was conducted to investigate the effect of soluble Ca treatments of fertigation (FG) and foliar application (FA) on soil properties, tree growth and fruit quality and on the occurrence of BBEP. Ca content was high in Ca FA and Ca + IBA FG compared to other treatments. This increase might affect the soil pH, and so pH followed the same pattern of Ca content in soil. In leaves and fruits, Ca content was much higher in Ca Ca FA and Ca + IBA, Ca FG, respectively. Ca content in fruit parts showed stem end part “middle part” blossom end part. In fruit quality, fruit firmness, soluble solid content and fruit weight did not show any tendency in treatments. The occurrence rate of BBEP was very low 14% in Ca FA and 20% in Ca FG than 50% in control. These results showed that Ca content in soil, leaves and fruits was increased by soil FG and FA and the increased Ca content in blossom end part have a negative relationship with BBEP in sweet persimmon.

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Mark J. Bassett

Common bean (Phaseolus vulgaris L.) plant introduction 527829 (formerly Lamprecht M0048) has dark seal-brown (DSB) seedcoats and pink flowers. An investigation was conducted to determine the genotype of DSB seedcoat color. M0048 was crossed with Florida breeding line 5-593, which has genotype P [C r] D J G B V Rk. A series of crosses involving M0048, 5-593, and three genetic tester stocks (v BC2 5-593, c u BC2 5-593, and b v BC2 5-593) led to determination of the genotype. Data analysis indicated that M0048 has the genotype P [? R] J G B v lae, where DSB color is produced by the interaction of R with B. Crosses between [? R] and testers with [C r] always produced seedcoat mottling in F1, except where V masks the effect. The cross [? R] B v (DSB) × c u BC2 5-593 (cartridge buff seedcoat) produced marbled seedcoats (black/cartridge buff) with genotype [? R]/[c u ?] B V. No way was found to determine whether the mottled or marbled seedcoat patterns were controlled at C or R; hence, the allelic ambiguity is indicated with a question mark. Illustrations are provided showing the difference between seedcoat mottling (a highly variable low-contrast patterning) and seedcoat marbling (a less variable high-contrast patterning, usually with cartridge buff as the background color). The development of a new genetic tester stock, [? R] b v BC3 5-593, was described, where [? R] b v gives unpatterned dominant red seedcoat color.

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Matthew D. Kleinhenz, Christopher C. Gunter, and Jiwan P. Palta

A direct comparison was made of several commercially available calcium sources applied on two different schedules for their effectiveness in increasing tuber medullary and periderm tissue calcium concentrations in 170–284-g tubers of the cultivar Atlantic grown on a Plainfield sandy loam. Plots (6 x 3 m) were arranged in a CR design in 1993 and a RCBD in 1994 (eight replications). Paired measurements of tuber Ca concentration and internal quality (±hollow heart, ±internal brown spot) were made on individual tubers produced in plots with no additional or additional Ca (168 kg Ca/ha) supplied from either gypsum, liquid calcium nitrate, or NHIB. Two Ca and N application schedules were compared: 1) application at emergence and hilling (non-split), 2) application at emergence, hilling, and 4 and 8 weeks after hilling (split). All plots received 224 kg H/ha balanced with ammonium nitrate. In general, tuber yield and grade were unaffected by treatments in 1993 and 1994, but overall percent A-grade was lowest and percent B-grade highest in 1993 compared with 1994 data. In 1993, all treatments receiving Ca had greater mean tuber medullary and periderm tissue Ca concentration values and a greater percentage of tubers with an elevated Ca concentration compared with non-Ca-supplemented controls. The overall incidence of tuber internal defects was 5% in 1993. All split schedule treatments receiving Ca showed 0% internal defects. In contrast, nearly 8% of the tubers from control plots showed some defect. The medullary tissue Ca concentration of 65% of the tubers having either defect was below the median value of Ca concentration for the entire experiment in 1993. Similar evaluations are underway for the 1994 crop. These data suggest that tuber calcium concentration may be related to the incidence of these internal defects.

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Charles A. Powell, Michael S. Burton, Robert R. Pelosi, Phyllis A. Rundell, Mark A. Ritenour, and Robert C. Bullock

The population densities of the brown citrus aphid (BrCA) (Toxoptera citricidus Kirkaldy) and the spirea aphid (SA) Aphis spiraecola Patch were monitored by scouting weekly for 6 years in a replicated citrus plot treated with 7 insect control regimes: Admire (imidacloprid) applied at 12, 6, 3, or 2 month intervals; Temik applied annually; Meta-Systox-R applied annually; or no insect control. The numbers of both aphid species varied greatly from month to month and year to year. The brown citrus aphid was normally only detected in the fall (August through December) with populations peaking in September, October, or December depending on the year. The spirea aphid could be detected throughout the year during years when overall populations were high. Spirea aphid populations often peaked both in the spring and fall. Annual applications of Temik or Metasystox were ineffective in reducing aphid populations. Generally, all four Admire treatment regimes controlled aphids, although at least 2 annual Admire treatments per year were required to control the spirea aphid during some years.

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Ahmed A. Tawfik and Jiwan P. Palta

We have shown that tuber calcium can be enhanced by supplying soluble forms of calcium near the tuber stolon region during bulking. In the present study we applied calcium nitrate or N-HIB during bulking (hilling, 3 and 6 wks after hilling) by injecting these Ca sources into sprinkler irrigation line. Field plots were established with cv `Russet Burbank' in sandy loam soil containing about 1200 Kg Ca ha-1. All plots received equal amounts of nitrogen. Plots receiving only nitrogen (as NH4NO3) at the same time served as split N controls and the plots receiving complete nitrogen by the time of hilling (non-split N) served as the grower control.

In 1990 compared to non-split-N control a consistently higher tuber yield was obtained with split-N, N-HIB (113 Kg.Ca ha-1) calcium nitrate (113 Kg Ca ha-1). However, these differences were not significant. Tuber calcium contents were increased with N-HIB and calcium nitrate. After 5 months of storage the incidence of soft rot and of internal brown spot was significantly reduced. In 1991 N-HIB (113 Kg ha-1) gave significantly higher tuber yield than other treatments. Tuber calcium contents were increased with both calcium nitrate and N-HIB treatments. After four months of storage incidence of internal brown spot was reduced by calcium nitrate and N-HIB although calcium nitrate was most effective. These results demonstrate that it is possible to improve tuber calcium contents by application of 113-226 Kg Ca ha-1 during bulking even in a soil containing sufficient calcium for plant growth.

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Zhipeng Huang, Phyllis A. Rundell, Xiong Guan, and Charles A. Powell

Four field sources of citrus tristeza virus (CTV) (Y3, Y6, Y7 and Y23) collected from grapefruit trees at groves in Fort Pierce, Florida, and isolate T36 were used to evaluate the transmission and separation of different virus genotypes by single brown citrus aphids (BrCA). Analysis of the field sources of CTV by inoculation to indicator plants, ELISA and RT-PCR showed that Y6 was a decline-inducing isolate and Y23 a nondecline-inducing isolate. Assays of genotype by RT-PCR indicated that Y6 contained the T36 genotype while Y23 contained the T30 genotype. Both Y3 and Y7 were a mixture of decline-inducing and nondecline-inducing CTV isolates and were a mixture of T36 and T30 genotypes. When Y6 and Y23 were the acquisition host for single BrCA, only the T36 or T30 genotypes, respectively, were detected by RT-PCR in `Mexican' Lime receptor plants. Only the T36 genotype was transmitted to receptor plants from infected Y3 and Y7 plants although these acquisition plants contained more than one genotype. No T3 or VT genotypes were detected in any acquisition or receptor plants. CTV genotype mixtures in the various field sources were separated by single BrCA transmission and that the T36 genotype in T36/T30 mixtures was more easily transmitted than the T30 genotype when the acquisition plant was `Duncan' grapefruit and the receptor plant was `Mexican' lime.