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L.P. Baldridge and S.E. Newman

Most field production of woody ornamental plants involves clean cultivation of rows, performed by either mechanical or chemical means. Grass cover has been shown to reduce erosion, but may have a detrimental effect on the growth and vigor of young trees. Clover cover has been shown to not adversely affect plant growth. The objective of this study was to compare the relative merits of three row covers, clean cultivated, pine bark mulch and kobe lespedeza clover, in combination with two irrigation rates, low and high, on field-grown red bud and crape myrtle plants.

Crape myrtle and red bud plants were tallest and had a larger caliper when grown with a clean row or with pine bark mulch. Kobe lespedeza clover reduced plant growth of both species when supplemental irrigation was not provided. Clover reduced plant height and caliper of red bud even when irrigated. Generally, plants grown under pine bark mulch were more efficient in water use as shown by greater stomatal conductance in August.

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Khin San Wai and S.E. Newman

The response of Antirrhinum majus (snapdragon) cultivars (`Tampicoi' and `Rainier White') to night air temperatures (10C and 20C) and elevated root-zone temperature (26C and ambient) was studied. Height of plants grown with a heated root-zone were greater, compared to unheated at both night temperatures for both cultivars. Shoot dry weight of `Tampico' plants was reduced by heated root-zone temperature at 20C night air temperature. Raceme length was greater with heated root-zone temperature compared to unheated at 10C night air temperature. Days to flower were shorter with heated compared to unheated root-zone at both night air temperatures for both cultivars. Stomatal diffusive resistance was greater on plants with unheated compared to heated root-zone temperature at 10C night air temperature for `Rainier White'.

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L.G. Sanabria and S.E. Newman

Various uniconazole (Sumagic™) rates were either sprayed or drenched alone or in combination with 6-BA and GA4+7 (Promalin™) or dikegulac-sodium (Atrinal™) on Hibiscus rosa-sinensis `Brilliant'. The rates of uniconazole were 0, 5, 10, and 15 mg a.i./L; 6-BA and GA4+7, 25 mg a.i./L each; and dikegulac-sodium 1000 mg a.i./L.

Plant height was reduced by uniconazole when drenched at rates as low as 5 mg/L and 15 mg/L when sprayed. Dikegulac-sodium slightly counteracted the effects of uniconazole. Uniconazole activity was increased when either sprayed or drenched with application of 6-BA and GA4+7 resulting in greater height reduction.

Transpiration and stomatal diffusive resistance of plants drenched with uniconazole alone was erratic; however, when uniconazole was sprayed or drenched and mixed with 6–BA and GA4+7 or dikegulac-sodium transpiration increased.

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Steven E. Newman and Jeffrey S. Tant

An experiment was conducted to determine the influence of eight commercial root-zone media (four peat based and four pine bark based) on the effects of paclobutrazol applied to Euphorbia pulcherrima Willd. `Eckespoint Celebrate 2' as an impregnated spike or a drench. Paclobutrazol treatments had the least influence on stem elongation of poinsettias grown in the peat-based medium containing Bacctite, a compressed peat product designed to increase aeration and cation exchange capacity, or composted pine bark ground to a particle size that could pass through an opening 1 cm or smaller. Spikes were more effective at reducing shoot elongation than drenches. Spike treatments also resulted in lower bract dry-matter accumulation than drenches. Paclobutrazol applied as a spike to poinsettias at pinch could combine pinching and chemical growth regulator application into one simultaneous operation. Chemical name used: (±)-(R*,R*)-beta-[(4-chlorophenyl)methyl]-alpha-(1, 1,-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol).

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S. Reddy, J.A. Spencer and S.E. Newman

Leaflet surfaces of two blackspot (Diplocarpon rosae Wolf)-resistant roses (Rosa roxburghii Tratt and R. wichuraiana Crep.) and two susceptible roses (R. hybrida `Electron' and `Pascali') were compared using scanning electron microscopy to determine whether physical features of the leaflet surface were associated with resistance to the fungal invasion. The leaflet surface features of the resistant roses were dissimilar: R. roxburghii leaflet surface had protruding cells and was densely covered with amorphous wax platelets, whereas R. wichuraiana surface was smooth with less distinct epidermal cells and sparsely distributed wax granules. Leaflet surface patterns of both susceptible roses, however, were similar. The spores of D. rosae failed to germinate on R. roxburghii and R. wichuraiana. In contrast, the spores on `Electron' and `Pascal? germinated, with the germ tube penetrating the cuticle. There were no apparent morphological barriers on leaflet surfaces of R. roxburghii and R. wichuraiana to explain the observed resistance to fungal development.

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D.K. Harris, A.D. Owings and S.E. Newman

Poinsettias and other floral crops when treated with the growth retardant uniconazole, Sumagic™, are more compact in growth habit. They have also been shown to have reduced stem strength. Calcium applied as a drench has been demonstrated to increase plant height and plant dry weight of poinsettias. Unicomazole reduced plant height without affecting dry weight. Bract color was more intense when calcium was applied as a weekly spray. Poinsettia plants had greater levels of foliar calcium when applied as a drench. Poinsettia plants sprayed and drenched with calcium and treated with uniconazole had greater levels of foliar calcium, however, this was not significantly greater than the control plants treated with uniconazole alone. The lowest level of foliar calcium was observed in uniconazole treated plants where calcium was applied as a spray. Uniconazole applications weakened the stein structure of poinsettias as with other floral crop species.

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D.K. Harris, A.D. Owings and S.E. Newman

Uniconazole has been demonstrated to not only reduce plant height, but suppress the development of xylem and phloem in stem tissue. Supplemental calcium nutrition in poinsettias has been demonstrated to reduce marginal bract necrosis, reduce leaf puckering and increase stem strength. Studies were conducted to determine the influence of uniconazole on Gutbier V-14 Glory poinsettias grown with supplemental calcium applied either as a foliar spray or a media drench.

Supplemental calcium applications improved the growth habit of uniconazole treated poinsettia plants. Bract coloration was intensified by foliar applications of calcium and uniconazole.

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J.M. Sherman, K.S. Reddy, S.E. Newman and J.A. Spencer

Most modern roses are highly susceptible to the disease blackspot caused by the fungus Diplocarpon rosae. This contrasts to species roses that are resistant to the disease. To gain information on the biochemical factors in this resistance mechanism, we are studying the involvement of proteins. Soluble proteins of modern roses and species roses were extracted and analyzed by SDS-PAGE. When healthy leaves were examined, there were no distinct differences in the protein patterns, indicating that there are no constitutive proteins involved in the disease resistance mechanism. There were no differences between healthy and infected leaves of resistant genotypes. When detached leaves of some susceptible types were infected with the fungus new proteins seemed to appear in the healthy region surrounding the blackspot lesion. These proteins may be involved in resisting the spread of the pathogen.

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J. M. Sherman, K. S. Reddy, S. E. Newman and J. A. Spencer

The objective of this study was to determine if blackspot (Diplocarpon rosae, Wolf) resistance and susceptibility is expressed in callus derived from known resistant and susceptible genotypes of roses. Established callus lines of blackspot susceptible hybrid tea roses `Pascali' and `Tropicana' and blackspot resistant species roses Rosa roxburghii and R. setigera were inoculated directly with a blackspot conidia suspension. Uninoculated callus served as controls. Cultures were incubated at 25°C for 28 days in the dark. An evaluation of the appearance and precent change in fresh weight indicated that for all genotypes tested, inoculation resulted in a decline in tissue appearance and rate of weight increase. These results indicated that in vitro. resistance to blackspot differs from the resistance found in whole plants.

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K.S. Reddy, S.E. Newman, J.A. Spencer and R.N. Paul

Blackspot disease, caused by Diplocarpon rosae, is a devastating disease of garden roses. Most hybrid teas and floribundas are susceptible to this disease in contrast to many species roses, which are resistant. The basis of this resistance is not known. The first barrier to invasion by the pathogen is the outer surface of the leaf. The physical nature of this surface may influence the attempted infection, landing, germination and penetration by the fungal spore and may cause a failure of infection. The leaf surfaces of susceptible and resistant genotypes were observed using SEM that allowed examination of the fine structure of the leaf surface. The characteristics of the leaf surface topography including wax structures were pictorially compared and visual concepts developed in relation to the dynamic nature of the leaf surface in space and time as leaf is infected by the pathogen.