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Richard J. McAvoy, Bernard B. Bible and Michael R. Evans

The early onset of bract necrosis in poinsettia (Euphorbia pulcherrima Willd. ex. Klotzch) is characterized by small dark-stained spots that precede the development of enlarged necrotic lesions. Electron micrographs of adaxial epidermal and subepidermal tissues with early symptoms of necrosis revealed large, electron-dense deposits in cell vacuoles. These spherical bodies resembled condensed tannins observed in the epidermal tissues of peach and apple fruit. Chemical analysis of bract tissues confirmed the presence of condensed tannins. Furthermore, there were higher concentrations of condensed tannin in bract samples with 2-mm-diameter lesions than in samples with lesions <0.5 mm (equivalent to catechin concentrations of 59 and 13 mg·g-1 fresh mass, respectively). No tannin bodies were observed in parallel samples of healthy-appearing bracts in which only trace concentrations of condensed tannins were measured (0.2 mg·g-1 fresh mass). The evidence suggests an association between condensed tannin accumulation in localized areas of the bract and the early appearance of bract necrosis symptoms.

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S Uknes, T. Delaney, B. Vernooij, L. Friedrich, S. Williams, D. Chandler, K. Weymann, H. Kessmann, D. Alexander, E. Ward and Ryals J. Ciba

Systemic acquired resistance is a broad spectrum inducible defense response that is associated with the expression of a set of genes (SAR genes). Expression of one of these genes (PR-1a from tobacco) in transgenic tobacco confers increased tolerance to two oomycete pathogens.

A direct role for salicylic acid (SA) in signaling SAR has been established in tobacco by analysis of transgenic tobacco expressing salicylate hydroxylase (SAH, an enzyme that inactivates SA by conversion to catechol). Tobacco plants that express SAH are blocked in the accumulation of SA and the development of SAR when responding lo TMV. Furthermore, both Arabidopsis and tobacco expressing SAH have altered pathogen induced lesion morphology, exemplified by larger spreading lesions.

Putative mutants in SAR gene expression were isolated by screening M2 Arabidopsis plants for altered expression of PR-1 and PR-2 or for sensitivity to pathogen infection following INA treatment. The putative mutants all into two major classes,constitutive (cim, constitutive immunity) and non-inducible (nim, non-inducible immunity). Several cim mutants exhibits a disease lesion phenotype in the absence of pathogen.

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Kathleen B. Evensen, Joseph M. Russo and Harriet Braun

Grading criteria are proposed for judging potatoes (Solanum tuberosum) for chip quality and yield. The criteria were derived from a decision-making scheme developed from expert opinions, U.S. Dept. of Agriculture grades, and a statistical evaluation of stored potatoes. The criteria are presented as ranges of acceptable values for a limited set of variables found to be important for chip quality and yield. These variables include bruising, cracks, cuts, fusarium dry rot, lesions, and scab. The proposed criteria, besides being a practical decision-making tool for processors, could serve as a knowledge base for potato expert systems and the development of mechanized sorting equipment.

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William J. Bramlage

`Cortland' and `Delicious' apples were stored at 0C for up to 25 weeks, and at 20C in either open boxes or non-sealed poly bags for up to 8 weeks. At 20C, lesions occurred mostly around lenticels, but with some calyx bronzing and scald-like symptoms on shaded areas. At 0C, typical scald symptoms occurred. At both temperatures, high concentrations of alpha-farnesene and conjugated trienes occurred in conjunction with symptom appearance, and both these concentrations and discolorations decreased with later harvest of fruit. Scald development appeared to be chilling-enhanced, but not chilling-dependent.

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Atsushi Kono, Akihiko Sato, Yusuke Ban and Nobuhito Mitani

’, and ‘Jakaranda’ (descendants of ‘Koenigin der Weingaerten’ × ‘Pearl of Csaba’) had previously been reported as resistant ( Evans, 1971 ). Yun et al. (2006) evaluated 61 cultivars by scoring the numbers of lesions on leaves in a greenhouse after

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Sandra E. Branham, Mark W. Farnham, Shane M. Robinson and W. Patrick Wechter

, suitable for market production, have only been identified in B. juncea ( Wechter et al., 2007 , 2013 ), which led to the successful development of a resistant mustard green cultivar Carolina Broadleaf ( Wechter et al., 2016 ). Herein, we report the first

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J.L. Maas, C. Gouin-Behe, J.S Hartung and S.C. Hokanson

Bacterial angular leafspot disease (BALD) of strawberry, caused by Xanthomonas fragariae Kennedy & King, has dramatically affected commercial fruit and plant production throughout the world. Leaf lesions may kill leaves, while lesions on sepals make fruit unmarketable. The bacterium can kill stolon-tip plantlets that are being rooted for transplanting. Since plants become systemically infected, there is no adequate chemical control for BALD under conditions that favor development and spread of the disease. Strawberry is the only host and no cultivars or advanced selections have proven resistant to this disease. We screened 23 Fragaria ×ananassa, 13 F. chiloensis, 56 F. virginiana, and 2 F. vesca genotypes for resistance to two pathogenic isolates of X. fragariae (ATCC-33239, the original strain from Minnesota and Xf-3 from North Carolina). Leaves were inoculated by forcing bacterial suspensions into leaves under pressure with a syringe barrel and plunger. Plants were incubated in a moisture chamber for 3 days, followed by 1 week under mist and then placed on a greenhouse bench. Experiments were done twice for obviously susceptible reactions and three and four times for questionable and resistant reactions, respectively. Only two genotypes were found to show a resistant reaction: 80-4-38 (`Earliglow' (F. virginiana clone SG-26 from Georgia) and F. virginiana clone SG-89 (=Luby MS 7-7 from Minnesota). Each of these genotypes exhibited typical hypersensitive responses by walling-off inoculation areas. All other genotypes exhibited typical BALD symptoms 5 weeks after inoculation with both isolates.

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C. Stevens, V. A. Khan, J. L. Lu, C. L. Wilson, E. Chalutz, M. K. Kabwe and Z. Haung

Jewel sweetpotato storage roots previously treated with ultraviolet (UV–C) light and then stored for 30 days before artificial inoculation with Fusarium solani showed increased resistance to Fusarium root rot; as indicated by reduced lesion size, the rate of decay development of rotted tissues. There was a hormetic relationship between the incidence of Fusarium root rot and UV–C doses. The optimum dose of UV which reduced Fusarium root rot was 3.6× 104 ergs/mm2. Exposure of sweetpotato to UV–C doses promoted phenylalanine ammonia–lyase (PAL)4 production with the maximum PAL activity occurring at 3.6×104 ergs/mm2. Crude extracts from UV–C treated sweetpotatoes reduced germination, germ tube elongation and growth of F. solani when compared to untreated extracts.

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Yan Shi, C.R. Rom and J.C. Correll

Apple bitter rot, caused by Glomerella cingulata is an economically important disease in the Southeastern U.S. Development of resistant cultivars may be an important way to control this disease. To evaluate the apple germplasm resistance, it is necessary to understand variation in virulence of isolates so that appropriated isolates can be selected for screening procedures. Examination of virulence was performed on four Arkansas isolates (G667, G668, G959 and G960) on `Golden Delicious' fruit. The fruit were wound-inoculated with a 100 μl spore suspension (107 spores/ml), then incubated in dew chamber at 28C and 100% RI-I. Differences in virulence were detected among the isolates in terms of lesion diameter and depth. Isolate G959 was statistically (p=.05) more virulent than two isolates (G667 and G668) examined. Additional isolates from difference geographical locations will be examined for virulence in future studies.

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P.G. Braun, P.D. Hildebrand and A.R. Jamieson

Twenty-five cultivars of red raspberry (Rubus idaeus L.) and one purple raspberry (R. occidentalis L. × R. idaeus L.) were evaluated for their resistance to fire blight caused by Erwinia amylovora (Burr.) Winslow et al. Actively growing raspberry cane tips were wound inoculated with three isolates of the pathogen and disease development was assessed over 17 days. Three methods of evaluating resistance were used: area under the disease progress curve (AUDPC), a weighted AUDPC called the area under the disease severity curve (AUDSC), and lesion length. A wide range of resistance levels was observed, but no cultivars were symptomless. Primocane-fruiting cultivars tended to be more resistant than floricane-fruiting ones. Of the three E. amylovora isolates used in this study, one was significantly more virulent than the other two, but no cultivar × isolate interaction was detected.