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Thomas E. Marler and Aubrey Moore

declines in populations as a direct result of CAS invasions into Taiwan and Guam, respectively ( IUCN SSC, 2006b ). The most popular Cycas species in the international horticulture industry is Cycas revoluta ( Norstog and Nicholls, 1997 ). It is

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Bijan Dehgan, Joseph E. Durando, and Thomas H. Yeager

Cycas revoluta, an important ornamental palm-like plant of warmer regions of the world, often exhibits a foliar chlorotic/necrotic dieback in landscapes. Despite a weak correlation (r2 ≤ 0.28) of percent symptoms with soil nutrient levels or pH, symptom severity was correlated more notably (r2=0.49) with Mn and had even a higher correlation (r2 = 0.61) with the Fe : Mn ratio. Anatomical examination of chlorotic leaflets indicated an accumulation of tanniniferous cells but did not provide direct evidence of Mn deficiency. Although field surveys indicated a link between low Mn levels and Fe : Mn ratio in the plant and appearance of the disorder, the manifestation of symptoms could not be directly correlated with any edaphic factors. However, identical symptoms were induced in young plants by withholding Mn in a solution culture experiment. Application of chelated Mn on expanding leaves alleviated the disorder, but only for the current growth flush. Irrigation frequency in concert with other cultural practices probably are more responsible for development of symptoms than actual soil Mn inadequacy. In consideration of acute susceptibility of cycads to micronutrient deficiencies, plants should be supplied with a complete micronutrient fertilizer during growth in containers and before field planting.

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Laura M. R. Rinaldi

The micropropagation of Cycas revoluta Thunb. via somatic embryogenesis was tested on immature and mature embryos using 2,4-dichlorophenoxyacetic acid (2,4-D) in combination with benzyladenine (BA) or kinetin. In addition, the effect of media manipulation on the induction of adventitious buds was studied to optimize culture parameters for the regeneration of plantlets via organogenesis from mature embryos. Schenk and Hildebrandt basal medium containing six different NO3 -: NH4 + ratios (from 90:10 to 65:35) and BA at 9 μm was used. The development of induced buds occurred on the medium containing the identical NO3 -: NH4 + composition without growth regulators. The effects of two IBA concentrations on the rooting of elongated shoots were evaluated. The treatment of immature embryos with 2.26 μm 2,4-D and 0.44 μm BA and that of mature embryos with 0.9 μm 2,4-D and 4.40 μm BA promoted growth of embryogenic tissue followed by embryo formation that failed to develop further. Bud induction was obtained through the whole range of NO3 -: NH4 + ratios tested. Small decrease in these ratios affected subsequent differentiation and growth. Adventitious shoots obtained on 70% NO3 - showed two-fold increase in height and diameter compared with those regenerated on 75% NO3 -. Furthermore, 7% of the former produced at the shoot base adventitious shoots that have similar morphology to offset growing at the base of mature plant. The rooting percentage of shoots was low. Considering the difficulty in achieving somatic embryogenesis, these results suggested that among micropropagation techniques organogenesis can be applicable for production of Cycas, although rooting is still the limiting factor.

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M.Y.C. Goo and B.S. Sipes

Fourteen tropical ornamental plants were evaluated for their host status to a population of Radopholus citrophilus isolated from anthurium. No nematodes were recovered from the roots of Aglaonema commutatum, Caryota mitis, Cycas revoluta, Dracaena deremensis, Neodypsis decaryii, Ravenea spp., or Spathiphyllum wallisii 5 months after inoculation, making these plants nonhosts. Low numbers of R. citrophilus were recovered from the roots of Phoenix roebellinii, Rhapis excelsa, and Howea forsteriana, suggesting that they were poor hosts to this nematode population. Anthurium trifidum, Chamaedorea neathebella, Chamaedorea seifrizii, and Calathea variegata were hosts for the nematode, allowing population increases of 2.47 to 29.92 times the inoculation density. C. seifrizii and C. variegata represent new hosts of R. citrophilus.

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Thomas E. Marler, Anders J. Lindström, and L. Irene Terry

damage for 85 Cycas species sorted into the five Cycadaceae sections, mean ± sd. ( B ) Female butterfly ovipositioning eggs on Cycas revoluta leaf. ( C ) C. revoluta plant showing typical extensive butterfly damage to leaflets. Damage score ≈9

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Thomas E. Marler, Anders Lindström, and Jack B. Fisher

Several cycad species have entered the horticulture industry with Cycas revoluta Thunb. ( Fig. 1A ) represented more than any other taxa. All species of this group of dioecious gymnosperms are of value to collectors because of their ancient

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Robert H. Stamps and Daniel W. McColley

Five preemergence herbicides (prodiamine 0.5 G, prodiamine 65 WDG, dithiopyr 0.27 G, thiazopyr 2.5 G, and oxyfluorfen + pendimethalin 3 G) were evaluated for weed control and crop safety on 18 plants (Acer rubrum, Agapanthus africanus, Asparagus densiflorus, Camellia sasanqua, × Cupressocyparis leylandii, Cycas revoluta, Galphimia gracillis, Gelsemium sempervirens, Illicium parviflorum, Lantana camara, Loropetalum chinense, Myrtis communis, Ophiopogon jaburan, Plumbago, Quercus virginiana, Rhododendron, Viburnum suspensum, and Zamia floridana. Herbicides were applied at 1.7 kg a.i./ha, except for oxyfluorfern + pendimethalin, which was applied at 3.4 kg a.i./ha. Treatments were applied twice at 4-month intervals. Untreated and weed-free controls were used to determine herbicide effects on weeds and crops, respectively. All herbicide treatments reduced weed growth (dry-weight basis) and weeding times. Major weeds were dogfennel [Eupatorium capillifolium (Lam.) Small], southern crabgrass [Digitaria ciliaris (Retz.) Koeler], yellow woodsorrel (Oxalis stricta L.), tasselflower (Emilia spp.), and hairy crabweed [Fatoua villosa (Thumb.) Nakai]. Based on weed dry weights, overall weed control for the first 4 months was higher for diazopyr, thiazopyr, and prodiamine G than for the combination treatment. At 8 months, weed growth was similar for all herbicide treatments. The combination treatment was acutely phytotoxicity to more crops than the other treatments; however, phytotoxicity varied with crop, active ingredient, and formulation.

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Thomas E. Marler, Ross Miller, and Aubrey Moore

micronesica K.D. Hill and Cycas revoluta Thunberg trees. These two Cycas species were widely planted throughout the urban landscape before the pest invasions, and the regionally endemic C. micronesica was a dominant forest species. Coccobius fulvus

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Jack B. Fisher, Anders Lindström, and Thomas E. Marler

Nicholls, 1997 ) because many horticulturists do not distinguish the two very different groups of seed plants. The horticulture industry has contributed to the confusion by perpetuating the common name “sago palm” for Cycas revoluta Thunb. and “cardboard

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Thomas E. Marler

. yasumatsui damage to the donor plants ( Marler and Cruz, 2017 ). To more fully understand how Cycas plants respond to chronic A. yasumatsui infestations, Cycas revoluta Thunb. plants were experimentally infested and then tissues harvested to determine