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Ralph Scorza, Laurene Levy, Vern Damsteegt, Luz Marcel Yepes, John Cordts, Ahmed Hadidi, Jerry Slightom, and Dennis Gonsalves

Transgenic plum plants expressing the papaya ringspot virus (PRV) coat protein (CP) were produced by Agrobacterium-mediated transformation of hypocotyl slices. Hypocotyl slices were cocultivated with Agrobacterium tumefaciens strain C58/Z707 containing the plasmid pGA482GG/CPPRV-4. This plasmid carries the PRVCP gene construct and chimeric NPTII and GUS genes. Shoots were regenerated on Murashige and Skoog salts, vitamins, 2% sucrose, 2.5 μm indolebutyric acid, 7.5 μm thidiazuron, and appropriate antibiotics for selection. Integration of the foreign genes was verified through kanamycin resistance, GUS assays, polymerase chain reaction (PCR), and Southern blot analyses. Four transgenic clones were identified. Three were vegetatively propagated and graft-inoculated with plum pox virus (PPV)-infected budwood in a quarantine, containment greenhouse. PPV infection was evaluated over a 2- to 4-year period through visual symptoms, enzyme-linked immunosorbent assay, and reverse transcriptase PCR assays. While most plants showed signs of infection and systemic spread of PPV within l-6 months, one plant appeared to delay the spread of virus and the appearance of disease symptoms. Virus spread was limited to basal portions of this plant up to 19 months postinoculation, but, after 32 months symptoms were evident and virus was detected throughout the plant. Our results suggest that heterologous protection with PRVCP, while having the potential to delay PPV symptoms and spread throughout plum plants, may not provide an adequate level of long-term resistance.

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Kenneth C. Eastwell and Gabriel B. Kalmar

In certain cultivars of cowpea [Vigna unguiculata (L.) Walp.] that are operationally immune to cowpea mosaic virus strain SB (CPMV), coinoculation of CPMV with cowpea severe mosaic virus strain DG (CPSMV) reduces severity and delays expression of symptoms normally induced by CPSMV alone. In cultivars susceptible to both viruses, coinoculation delays development of symptoms in response to CPSMV. Using monoclonal antibodies for serological assays and virus-specific RNA probes for hybridization, it is demonstrated that the presence of CPMV in the inoculum yields a concomitant delay in the synthesis of CPSMV coat protein and replication of CPSMV RNA and restricts the transport of CPSMV out of infection centres. Only bottom component of CPMV containing RNA1 is required to offer protection against CPSMV. Destroying the integrity of CPMV RNA eliminates its protective capability. In cowpea cultivars that are operationally immune to CPMV, the presence of CPSMV in the inoculum is unable to compensate for events of CPMV replication that are inhibited. The lack of complementation suggests a high degree of specificity in the replication of these two comoviruses.

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D.M. Glenn, G. Puterka, T. van der Zwet, and R. Byers

Fruit production requires extensive use of pesticides to control pest damage and maintain high product quality. Hydrophobic particles alter the leaf surface due to the hydrophobic and reflective nature of the particles and impart characteristics that make the plant surface incompatible, and/or unrecognizable to the pest. Hydrophobic particles were applied to apple and pear in field and greenhouse studies. Specific diseases, insect pests, plant growth, and yield were monitored and evaluated on treated plants in comparison to untreated and chemically treated controls. Powdery mildew in apple and Fabrea leaf spot in pear were controlled by the hydrophobic particles. Aphids, mites, and psylla were controlled in apple and pear. Hydrophobic clays have the potential of cross-protection for several disease and insect pests while imparting beneficial horticultural effects that would increase long-term productivity and sustainability of fruit production systems.

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Min Wang, Mark W. Farnham, and Claude E. Thomas

Downy mildew, caused by Peronospora parasitica (Pers. Fr.) Fr., is one of the most economically important diseases of broccoli (Brassica oleracea L. Italica group). Previous studies have shown that resistance to downy mildew in broccoli is dependent on plant age with seedling resistance being independent of mature-plant resistance. The objectives of this study were to: 1) determine if valid evaluations for downy mildew resistance can be conducted at both the cotyledon and the three to four true-leaf stages on the same plants of a given broccoli entry; 2) determine if doubled-haploid (DH) lines derived from the resistant hybrid `Everest' also exhibit resistance to downy mildew and if so, characterize the resistance phenotype(s) in these lines; and 3) determine if identified resistant DH lines exhibit resistance to isolates of P. parasitica acquired from different geographic regions of the United States. Twenty-three DH broccoli inbreds and two commercial hybrids were evaluated for reaction at different developmental stages to infection by P. parasitica in a controlled environment. Results showed that broccoli plants can be evaluated for downy mildew resistance in a two-stage process. Inoculation at the cotyledon stage did not offer any cross-protection or otherwise influence the expression of reaction phenotype (RP) when the same plants were subsequently inoculated at the three to four true-leaf stage. Three different RPs to infection by P. parasitica were identified in DH inbreds. These were: 1) susceptibility at both the cotyledon stage and the true-leaf stage; 2) resistance at both the cotyledon and true-leaf stage; and 3) susceptibility at the cotyledon stage but resistance at the true-leaf stage. There was no effect of two pathogenic isolates from different geographic regions on RP of DH broccoli inbreds. Selection of plant resistance to downy mildew at the cotyledon stage will effectively identify plants with high levels of resistance at subsequent developmental stages.

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Grace Q. Chen

untransformed cells, the untransformed cells could be protected through efficient detoxification of the antibiotic by the transformed cells ( Christou, 1990 ; Dominguez et al., 2004 ; Schmulling and Schell, 1993 ). Such cross-protection is certainly possible

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Richard Manshardt

.T.-P. 1994 Papaya germplasm and breeding in Hawai’i Fruit Var. J. 48 146 152 Mau, R. Gonsalves, D. Bautista, R. 1989 Use of cross protection to control papaya ringspot virus at Waianae. Proc. 25 th Ann. Hawai’i Papaya Ind. Assoc. Conf. p. 77–84 Mekako, H

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Yu-Tsung Lin, Chia-Wei Lin, Chien-Hung Chung, Mei-Hsiu Su, Hsiu-Yin Ho, Shi-Dong Yeh, Fuh-Jyh Jan, and Hsin-Mei Ku

( Schulze et al., 1995 ). The occurrence of the escapes may be the result of inadequate selective pressure or cross-protection by secreted products of contaminating microbial cells ( Dong et al., 1991 ). Therefore, it is important to establish an efficient

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Nihat Guner, Luis A. Rivera-Burgos, and Todd C. Wehner

. Cultural controls such as treatment with mineral oil sprays and light-reflective surfaces, and cross-protection with weak ZYMV isolates showed limited effectiveness and required additional input costs. Therefore, genetic resistance remains the simplest

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Nihat Guner, Zvezdana Pesic-VanEsbroeck, Luis A. Rivera-Burgos, and Todd C. Wehner

). Chemical control of the vectors is not usually efficient to control the disease. Cultural controls such as treatment with mineral oil sprays, light-reflective surfaces, and cross-protection with weak PRSV-W isolates show limited effectiveness and require

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Karen R. Harris, Kai-Shu Ling, W. Patrick Wechter, and Amnon Levi

infestation of virus vectors ( Mutschler and Wintermantel, 2006 ), the use of a mild or attenuated virus strain to protect the plant from the virulent strain (cross-protection) ( McKinney, 1929 ), and genetic modification of plants ( Prins et al., 2008