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Marcos R. Sachet, Idemir Citadin, Silvia Scariotto, Idalmir dos Santos, Pedro H. Zydek and Maria do Carmo B. Raseira

leaf area with a shot hole in the center of the lesion, indicating a probable hypersensitive reaction. This reaction is mainly determined by the metabolic capacity of the plant and could lead to a high degree of disease resistance. Although BLS is

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Thomas J. Molnar, Megan Muehlbauer, Phillip A. Wadl and John M. Capik

PowerMarker: Integrated analysis environment for genetic marker data Bioinformatics 21 2128 2129 Mmbaga, M.T. Sauvé, R.J. 2004 Multiple disease resistance in dogwoods ( Cornus spp.) to foliar pathogens J. Arboriculture 30 2 101 107 Molnar, T.J. Capik, J

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Kim S. Lewers, Patricia R. Castro, John M. Enns, Stan C. Hokanson, Gene J. Galletta, David T. Handley, Andrew R. Jamieson, Michael J. Newell, Jayesh B. Samtani, Roy D. Flanagan, Barbara J. Smith, John C. Snyder, John G. Strang, Shawn R. Wright and Courtney A. Weber

15 cultivars and performed well for yield, fruit size, flavor, attractiveness, firmness, and foliar disease resistance ( Strang et al., 2016 ). In replicated tests in plasticulture near Geneva, NY, Zone 6a, ‘Flavorfest’ yield and fruit weight were

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Atsushi Kono, Akihiko Sato, Yusuke Ban and Nobuhito Mitani

their disease resistance and tolerance to berry cracking. Tetraploid hybrid cultivars have been developed, and their production is now increasing with the aid of the innovative application of plant growth regulators such as gibberellic acid to young

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Ryan J. Hayes, Karunakaran Maruthachalam, Gary E. Vallad, Steven J. Klosterman and Krishna V. Subbarao

important and unique resource for the identification of useful new genes. Screening diverse Lactuca for disease resistance is often complicated by correlations with morphology, maturity, or rate of bolting. In the V. dahliae –lettuce pathosystem, disease

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Jareerat Chunthawodtiporn, Theresa Hill, Kevin Stoffel and Allen Van Deynze

’ ( Guerrero-Moreno and Laborde, 1980 ). Several theories for the genetic basis of this disease resistance have been proposed. For example, early studies suggested simple genetic resistance involving one or a few genes ( Ortega et al., 1991 ; Reifschneider et

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Zenaida Viloria and Jude W. Grosser

Interploid hybridization was conducted using `Key' lime [Citrus aurantifolia (Cristm.) Swing.], `Lakeland' limequat hybrid [C. aurantifolia × Fortunella japonica (Thumb.) Swing.], Palestine sweet lime (C. limettioides Tan.), `Etrog' citron (C. medica L.), and seven lemon [C. limon (L.) Burm. F.] varieties as female progenitors and five allotetraploid somatic hybrids {`Hamlin' sweet orange [C. sinensis (L.) Osbeck] × `Femminello' lemon (C. limon)]; `Key' lime × `Valencia' sweet orange (C. sinensis); `Valencia' sweet orange × rough lemon (C. jambhiri Lush); Milam lemon (purported C. jambhiri hybrid) × `Femminello' lemon (C. limon); and `Valencia' sweet orange × `Femminello' lemon} and two autotetraploids [`Giant Key' lime (C. aurantifolia) and `Femminello' lemon] as pollen progenitors. A few tetraploid × diploid crosses were also performed. Thirty-five parental cross combinations were accomplished in 2000, 2001, and 2002. The breeding targets were seedlessness, cold-tolerance, and disease resistance. Triploid hybrids were recovered through embryo culture. Generation of triploid citrus hybrids was affected by several factors including sexual compatibility, cross direction, embryo developmental stage, pollen viability, as well as horticultural practices and climatic conditions. Efficiency of triploid hybrid production was higher in diploid × tetraploid crosses than the reciprocal. Many more triploid hybrids were generated from lemon seed progenitors compared to the other acid citrus fruit progenitors. `Todo el Año', `Lisbon', and `Limonero Fino 49' showed the highest sexual compatibility. Embryo germination rate and normal plant recovery were also higher in lemons as compared to the other seed progenitors. Low winter temperatures might have affected the hybrid production efficiency from tropical acid fruit progenitors. A total of 650 hybrids (mostly triploid) were transferred to soil. The novel genetic combinations of these progenies should be valuable for the genetic improvement of acid citrus fruit (lemons and limes).

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Ray F. Dawson and F.W. Owen Smith

Production of rubber from Hevea brasiliensis (Willd. ex A. Juss) Muell.-Arg. (Euphorbiaceae) is greatest in southeastern Asia where the South American leaf blight disease is absent. Except for the Pacific Piedmont of Guatemala, plantation production in the Americas is limited severely by the now widespread presence of the pathogen Microcyclus ulei (P. Henn.) Arx. Mean latex yields from trees growing on the Piedmont approximate those of Indonesia and Malaysia, with little evidence of damage from leaf blight. The scope and scale of the Guatemalan anomaly suggest that environmentally modulated escape rather than previously assumed disease resistance may be the key to successful production of natural rubber in this hemisphere. The Guatemalan industry is presently well-organized to service regional markets in Mexico and the Caribbean Basin. Given due attention to environmental analysis, it may serve also as a model for the development of regional production facilities in other parts of tropical America.

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Kimberly H. Krahl and William M. Randle

Although Petunia hybrida Vilm., a major bedding plant, is susceptible to many diseases, no formal disease resistance studies have been conducted. Botrytis cinerea Pers. ex Fr. is a ubiquitous pathogen, causing great damage to greenhouse-grown ornamental crops, including petunia. In this study, a screening procedure for B. cinerea resistance in petunia was developed and 48 diverse petunia phenotypes were screened for resistance to B. cinerea in two seasons, spring and fall. The range of variability for resistance to B. cinerea in petunia was wide and continuous. Spearman's rank correlation coefficients between seasons were significant and moderate. While the majority of phenotypes displayed less than a 10% difference in mean percent infection in spring vs. fall seasons, several phenotypes displayed large differences that require further testing. One cultivar, `Pink Sensation Improved', exhibited low and consistent mean percent infection in both spring and fall and, therefore, may be a useful source of resistance to B. cinerea in petunia.

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Jack E. Staub, Fenny Dane, Kathleen Reitsma, Gennaro Fazio and Anabel López-Sesé

Genetic relationships among 970 cucumber (Cucumis sativus L.) plant introductions (PIs) in the U.S. National Plant Germplasm System (NPGS) were assessed by observing variation at 15 isozyme loci. Allozyme frequency data for these PIs were compared to allozyme variation in heirloom and modern (H&M) cultivars released from 1846-1985 (H&M cultivars; 178 accessions), and experimental commercial (EC) germplasm (EC germplasm; 82 accessions) in use after 1985. Multivariate analysis defined four distinct groups of accessions (Groups A-D), where Group A consisted of PIs received by the NPGS before 1992, Group B contained PIs from India and China obtained by NPGS after 1992, Group C consisted of EC germplasm, and Group D contained H&M cultivars. Morphological, abiotic stress (water and heat stress tolerance) and disease resistance evaluation data from the Germplasm Resources Information Network (GRIN) for the PIs examined were used in conjunction with estimates of population variation and genetic distance estimates to construct test arrays and a core collection for cucumber. Disease resistance data included the evaluation of angular leafspot [Pseudomonas lachrymans (E.F. Smith) Holland], anthracnose [Colletotrichum lagenarium (Ross.) Ellis & Halst], downy mildew [Pseudoperonospora cubensis (Berk. & Curt) Rostow], rhizoctonia fruit rot (Rhizoctonia solani Kuhn), and target leafspot [Corynespora cassiicola (Berk. & Curt) Wei] pathogenicity. The test arrays for resistance-tolerance to angular leafspot, anthracnose, downy mildew, rhizoctonia fruit rot, target leafspot, and water and heat stress consisted of 17, 16, 17, 16, 17, 16, and 16 accessions, respectively. The core collection consisted of accessions in these test arrays (115) and additional 32 accessions that helped circumscribe the genetic diversity of the NPGS collection. The core collection of 147 accessions (115 + 32) represents ≈11% of the total collection's size (1352). Given estimates of genetic diversity and theoretical retention of diversity after sampling, this core collection could increase curatorial effectiveness and the efficiency of end-users as they attempt to identify potentially useful germplasm.