Dr. Rosemarie W. Hammond



Selected Publications

  • 2000. Zhao, Y., Hammond, J., Tousignant, M. E., and Hammond, R. W. Development and evaluation of a complementation-dependent gene delivery system based on cucumber mosaic virus. Arch. Virol. 145: 2285-2295.
  • 2000. Hammond, R. W., and Zhao, Y. Characterization of a tomato protein kinase gene induced by infection with Potato spindle tuber viroid. Mol. Plant Microbe Interact. 13: 903-910.
  • 2000. Hammond, R., and Howell, W. Control of cherry rugose mosaic disease enhanced by new assay technique. Good Fruit Grower. 51: 53-54.
  • 2000. Owens, R. A., Yang, G., Gundersen-Rindal, D., Hammond, R. W., Candresse, T., and Bar-Joseph, M. Both point mutation and RNA recombination contribute to the sequence diversity of citrus viroid III. Virus Genes. 20: 243-252.
  • 1999. Hammond, R. W., Crosslin, J. M., Pasini, R., Howell, W. E., and Mink, G. I. Differentiation of closely related but biologically distinct cherry isolates of Prunus necrotic ringspot virus by polymerase chain reaction. J. Virol. Meth. 80: 203-212.
  • 1999. Woo, Y-M., Itaya, A., Owens, R. A., Tang, L., Hammond, R. W., Chou, H-C., Lai, M. M. C., and Ding, B. Characterization of nuclear import of potato spindle tuber viroid RNA in permeabilized protoplasts. Plant J. 17; 627-635.
  • 1999. Badilla, R., Hammond, R., and Rivera, C. First report of potato spindle tuber viroid in Costa Rica. Plant Dis. 83: 1072.
  • 1999. Heuss, K., Liu, Q., Hammerschlag, F. A., and Hammond, R. W. A cRNA probe detects Prunus necrotic ringspot virus in three peach cultivars after micrografting and in peach shoots following long-term culture at 4°C. Hort Science 34: 346-347.
  • 1998. Bustamante, P. I., Hammond, R., and Ramirez, P. Evaluation of maize germplasm for resistance to maize rayado fino virus. Plant Disease 82:50-56.
  • 1998. Hammond, R. W. and Crosslin, J. U. Virulence and molecular polymorphism of Prunus necrotic ringspot virus isolates. Journal of General Virology 78:1815-1823.
  • 1997. Villalobos, W., Rivera, C., and Hammond, R. Occurrence of citrus viroids in Costa Rica. Journal of Tropical Biologia. 45:983-987
  • 1997. Hu, Y., Feldstein, P. A., Hammond, J., Hammond, R., and Owens, R. A. Destablization of potato spindle tuber viroid by mutations in the left terminal loop. J. Gen. Virology 78:1199-1206.
  • 1997. Hammond, R. W., Kogel, R., and Ramirez, P. Variability of geographically distinct isolates of maize rayado fino virus in Latin America. Journal of General Virology 78:3153-3159.
  • 1997. Ding, B., Kwon, M.-O., Hammond, R., and Owens, R. Cell-to-cell movement of potato spindle tuber viroid. Plant Journal 12:931-936.
  • 1996. Hammond, R. W. and Hammond, J. Plant Viruses and Viroids. In: Maintaining Cultures for Biotechnology and Industry. (Hunter-Cervera, J. C., and Belt, A., eds). Academic Press, New York. Pp. 229-249.
  • 1996. Kogel, R., Hammond, R. W., and Ramirez, P. Incidence and geographic distribution of maize rayado fino virus (MRFV) in Latin America. Plant Dis. 80:679-683.
  • 1996. Owens, R. A., Steger, G., Hu, Y., Fels, A., Hammond, R. W., and Riesner, D. RNA structural features responsible for potato spindle tuber viroid pathogenicity. Virology 222:144-158.


Agrobacterium-mediated inoculation of PSTVd cDNAs onto tomato reveals the biological effect of apparently lethal mutations

      Potato spindle tuber viroid (PSTVd) mutants which contain alterations in the terminal loops of the rod- like native structure have previously been reported from our laboratory. PSTVd-P contains mutations at positions 2, 4, and 6 in the left terminal loop; PSTVd-R+, a sequence permutation of PSTVd-R, contains the same mutations at positions 177 and 178 in the right terminal loop as PSTVd-R and contains in addition a 1-nucleotide G insertion at position 176. PSTVd-P, PSTVd-R and PSTVd-R+ were noninfectious when either cDNA or SP6-generated RNA transcripts were used as inoculum onto tomato cotyledons. In the current study, mutant and wild-type PSTVd constructs were mobolized into Agrobacterium tumefaciens and used for stem inoculation of tomato plants. Agrobacterium-mediated inoculation of the mutant and wild-type constructs has confirmed the inability of the PSTVd-P mutant to establish an infection. The PSTVd-R+ mutant and/or sequence variants derived in vivo can establish an infection, although PSTVd-R+ progeny and replicative intermediates appear to be primarily restricted to the gall and root tissues of the plant and only occasionally are progeny detectable in the newly developing leaves. The reduced level of viroid accumulation from the PSTVd-R+ mutant appears to be consistent with the mutant viroid replicating/accumulating only in a limited number of cells or cell types. The mutations in the right terminal loop may alter interactions with specific host components and thereby disrupt the normal pattern of intercellular transport of the viroid or limit its replication to a cell type but not abolish replication per se.

Variability of geographically distinct isolates of maize rayado fino virus in Latin America

      We have examined the molecular epidemiology of the leafhopper-borne maize rayado fino virus (MRFV) in Latin America. The coat protein gene and 3' non-translated region of 14 isolates of MRFV collected from Latin America and the United States were sequenced and phylogenetic relationships examined. The nucleotide sequence revealed remarkable conservation, with a sequence similiarity of 88-99%. Phylogenetic analysis of sequence data obtained from a 633 bp fragment showed that MRFV has diverged into three main clusters, i.e. the geographically distinct northern and southern isolates and the Colombian isolates. Significant differences between the isolates collected from Colombia, previously named maize rayado colombiana virus, based upon differences in symptomatology and serological relationships to MRFV, and the other MRFV isolates, provides additional evidence supporting its designation as a unique strain of MRFV. back to top of the page



Evaluation of maize germplasm for resistance to maize rayado fino virus

      Maize rayado fino virus (MRFV) causes severe yield losses in maize (Zea mays L.) in Latin America with reductions of 40 - 50% on indigenous genotypes and 100% in some new cultivars. A collection of 20 different maize genotypes was obtained from the Center for the Improvement of Maize and Wheat (CIMMYT, Mexico), Estacion Experimental Fabio Baudrit (EEFB-Alajuela), and the Consejo Nacional de la Producion (CNP-Costa Rica). Enzyme-linked immunosorbent assay (ELISA) and symptom severity were used to evaluate the responses of the maize genotypes to MRFV under screenhouse conditions. Two genotypes from the CIMMYT germ plasm collection (accession nos. 2980-93 and 3974) showed mild and delayed symptoms and low MRFV concentrations as determined by ELISA. back to top of the page



Virulence and molecular polymorphism of Prunus necrotic ringspot virus isolates

      Prunus necrotic ringspot virus (PNRSV) occurs as numerous strains or isolates that vary widely in their pathogenic, biophysical, and serological properties. Prior attempts to distinguish pathotypes based upon physical properties have not been successful; our approach was to examine the molecular properties that may distinguish these isolates. The nucleic acid sequence was determined from 1.65 kbp RT-PCR products derived from RNA 3 of 7 distinct isolates of PNRSV that differ serologically and in pathology on sweet cherry. Sequence comparisons of ORF 3a (putative movement protein) and ORF 3b (coat protein) revealed single nucleotide and amino acid differences with strong correlations to serology and symptom types (pathotypes). Sequence differences between serotypes and pathotypes were also reflected in the overall phylogenetic relationships between the isolates. back to top of the page
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