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G.C. Percival

Aims of this investigation were to determine whether chlorophyll fluorescence values obtained from excised leaves of woody perennials subjected to salinity stress under laboratory conditions provided a measurable indicator of whole plant salinity tolerance. Laboratory tests consisted of measurements of the ratio of variable to maximal chlorophyll fluorescence (Fv/Fm) performed on excised leaves taken from thirty woody perennials following immersion in salt solutions ranging from concentrations of 2% to 7%. Based on reductions in Fv/Fm of excised leaves following salinity treatments plants were ranked in order of tolerance. Whole plants of six of the thirty species tested were then subjected to a foliar applied salt at a concentration of 7% and placed under glass for 14 weeks. Damage to, and recovery of whole plants from salt damage as measured by chlorophyll fluorescence, leaf necrosis and chlorophyll content mirrored tolerance ranking of excised leaves under laboratory conditions. In addition, based on reductions in plant growth at the cessation of the experiment, salt tolerance followed a similar order as that obtained from Fv/Fm values of excised leaves. Results indicate that testing of excised leaf material of woody perennials under laboratory conditions using chlorophyll fluorescence offers a potentially quick, reliable and inexpensive procedure that can provide a useful means of estimating whole plant salt tolerance.

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Jean-Michel Hily, Ralph Scorza*, and Michel Ravelonandro

We have shown that high-level resistance to plum pox virus (PPV) in transgenic plum clone C5 is based on post-transcriptional gene silencing (PTGS), otherwise termed RNA silencing (Scorza et al. Transgenic Res. 10:201-209, 2001). In order to more fully characterize RNA silencing in woody perennial crops, we investigated the production of short interfering RNA (siRNA) in transgenic plum clones C3 and C5, both of which harbor the capsid protein (CP) gene of PPV. We used as a control, plum PT-23, a clone only transformed with the two marker genes, NPTII and GUS. We show in the current report that C5 constitutively produces two classes of siRNA, the short (21-22 nucleotides) and long (≈27 nucleotides) species in the absence of PPV inoculation. Transgenic susceptible clone C3 and the control clone PT-23, when healthy, produce no siRNA. Upon infection, these clones produce only the short siRNA (21-22 nt). This siRNA production suggests that plum trees naturally respond to virus infection by initiating PTGS or PTGS-like mechanisms. This study also suggests that high-level virus resistance in woody perennials may require the production of both the short and long size classes of siRNA, as are produced by the resistant C5 plum clone.

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Sanliang Gu, Leslie H. Fuchigami, and Victor Sahakian

Applicability of processed fiber (methane digested cow manure) as a substitute for peatmoss for production of various containerized perennial woody plant species with various fertilization and fumigation practices was investigated in this study. Liner plants of five species and rooted cuttings of 41 species were potted in various media containing processed fiber as the replacement of peatmoss with or without fertilization and fumigation, with commercial mix as control. Plants varied in their responses to the media, fertilization, and/or fumigation. Most plant species performed well in the media containing processed fiber. The physical and chemical properties of processed fiber, either alone or mixed with other media components, were satisfactory for producing woody perennial species even with less fertilization and no fumigation.

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Wei Hao, Rajeev Arora, Anand K. Yadav, and Nirmal Joshee

freezing tolerant than ‘Lucknow-49’, it appears that CA response of guava genotypes may be somewhat different from those for temperate zone woody perennials in terms of the relationship between freezing tolerance and water status of tissues. On the other

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Rajeev Arora, Lisa J. Rowland, and Karen Tanino

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Lisa J. Rowland, Elizabeth L. Ogden, Rajeev Arora, Chon-Chong Lim, Jeffrey S. Lehman, Amnon Levi, and Ganesh R. Panta

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Mary Ann Rose

Timing nutrient application to periods of high nutrient demand could increase nutrient use efficiency and reduce the potential for fertilizer leaching or runoff. However, current recommendations for field nursery and landscape ornamentals (extension publications) suggest fertilizing in late fall and early spring despite research with perennial fruit crops that demonstrates low uptake potential during those times. Research is needed to resolve this apparent conflict. Application rates for woody ornamentals, established in the 1960s and 1970s, also need reexamination in the light of environmental concerns.

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Melinda Knuth, Bridget K. Behe, Charles R. Hall, Patricia Huddleston, and R. Thomas Fernandez

for woody perennials and one for herbaceous perennials. We used a combination of product attributes and levels that represented three plant types (genera), three price levels, three water sources during production (grown in the nursery with fresh water

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Jean-Michel Hily, Michel Ravelonandro, Vern Damsteegt, Carole Bassett, Cesar Petri, Zongrang Liu, and Ralph Scorza

-Hc-Pro gene sequences under the 35S -cauliflower mosaic virus promoter. To apply ihpRNA technology efficiently and effectively for the production of functional PTGS in woody perennials, in this study we tested the effects of different lengths of PPV

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Lisa J. Rowland, Anik L. Dhanaraj, Dhananjay Naik, Nadim Alkharouf, Ben Matthews, and Rajeev Arora

factors limiting growth of woody perennials in North America ( Quamme, 1985 ). Periodic winter freezes result in serious losses in fruit, nut, and ornamental crops. Consequently, a major emphasis of many breeding programs on woody plants is the development