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  • Author or Editor: John R. Potter x
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Dormant stock plants of apple (Malus domestica Borkh.) rootstocks M.26 and Ottawa 3; Rhododendron `Britannia', `Purple Splendour', and `Unknown Warrior'; and mountain laurel (Kalmia latifolia L.) `Ostbo Red' and seedlings were forced to grow at 18 or 28 °C in continuous darkness or 14-h photoperiods. Etiolated shoots were then acclimated to light with or without aluminum foil wrapped around their bases to keep the bases etiolated. Shoots forced in diurnal light were neither etiolated nor wrapped and served as controls for the etiolation treatments. Compared to controls, wrapping etiolated stems improved rooting of M.26 (60% vs. 82%) and `Ottawa 3' (81% vs. 97%) apple and of `Britannia' (76% vs. 90%) and `Unknown Warrior' (80% vs. 91%) rhododendron. Etiolation improved rooting percentage of `Unknown Warrior' regardless of wrapping. Regardless of etiolation, forcing `Ottawa 3' at 18 °C improved rooting percentage (92% vs. 74%) and roots per cutting (12 vs. 7) compared to forcing at 28 °C. Etiolated mountain laurel cuttings generally rooted best at 18 °C; control cuttings rooted best at 28 °C.

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Abstract

Leafy cuttings of Rhododendron catawbiense Michx. ‘Roseum Elegans’ were rooted under 0%, 55%, or 95% shade in a greenhouse. Compared to the low-light treatment, higher light induced high photosynthetic rates, high sucrose and starch levels, and low leaf water potential, but these differences only persisted for the initial part of the 23-week rooting period and did not influence subsequent rooting percentage. However, in cuttings receiving 95% shade, dry weights of leaves and stems and rootball size were relatively small after 23 weeks, suggesting that growth was reduced by lack of photosynthate. The reduced size of cuttings rooted under 95% shade apparently did not affect vigor because the size of the above-ground portion of all plants was equal after 2 months of growth in a greenhouse.

Open Access

Abstract

Root formation on leafy cuttings of Pisum sativum L. ‘Alaska’ was reduced by about 50% when net photosynthesis was adjusted to the compensation point by reducing the light intensity, reducing the CO2 concentration, or by blocking CO2 exchange with an antitranspirant. Rooting was also reduced by 50% when cuttings were given only enough photoperiod at saturating light to maintain a carbon balance similar to that of the treatments which reduced net photosynthesis to the compensation point. In addition to decreasing rooting, these treatments lowered sucrose and glucose levels in the basal portion of the cuttings compared to controls. Our photosynthesis and carbohydrate data indicate that the supply of current photosynthate to the base of pea cuttings is important to rooting.

Open Access

Abstract

Storage of Rhododendron catawbiense Michx. ‘Roseum Elegans’ cuttings in moist burlap bags at 21° or 2°C for 21 days did not consistently reduce the percentage of rooting or rootball size. During storage, leaf water potential (ψw) of the cuttings increased from −0.47 MPa initially to −0.27 MPa after 14 days, regardless of storage temperature. Carbohydrate concentrations in the bases of the cuttings changed with time and storage temperature, but apparently neither these changes nor changes in ψw were large enough to influence subsequent rooting.

Open Access

Abstract

CO2 enrichment (1200 μl CO2/liter of air) during rooting increased the number of roots per cutting from 7.4 to 12.0 in Peperomia glabella A. Dietr. ‘Variegata’. CO2 enrichment increased length and dry weight of root systems and fresh and dry weights of whole cuttings in P. glabella, Fuchsia magellanica Lam., Peperomia nivalis Miq., Hemigraphis alternata T. Anderson, and Begonia × argenteo-guttata V. Lemoine but not in Osmanthus heterophyllus P.S. Green ‘Rotundifolius’, Ficus pumila L., and Pelargonium × hortorum L.H. Bailey ‘Sprinter Scarlet’. After 4 weeks of growth at 330 μl CO2/liter, only P. nivalis retained the size differential due to CO2 enrichment.

Open Access

In hazelnut (Corylus avellana L.), vigorous vegetative growth and traditional orchard practices that include little or no pruning combine to produce a dense, shady canopy. A study designed to quantify the effect of shade on reproduction and photosynthetic rate in this shade-tolerant species was undertaken to assess whether some degree of pruning might improve productivity. Shade cloth was used to exclude 30%, 47%, 63%, 73%, or 92% of ambient sunlight from whole `Ennis' and `Barcelona' trees from mid-May until harvest. Photosynthetic light response curves were obtained for leaves that had developed in full sunlight, deep inside the canopy of unshaded trees, or in 92% shade. Light-saturated net photosynthetic rates were 12.0, 6.1, and 9.3 μmol·m-2·s-1 of CO2 and dark respiration rates were 2.0, 1.1, and 0.7 μmol·m-2·s-1 of CO2, respectively, for the three light regimes. Light-saturated photosynthetic rates of leaves from 30% or 63% shade differed little from the control (0% shade). Area per leaf increased by 49% and chlorophyll concentration (dry weight basis) by 157% as shading increased from 0% to 92%. Shading to 92% reduced specific leaf weight (68%), stomatal density (30%), light compensation point (69%), and dark respiration rate (63%) compared to controls. Female inflorescence density declined by about one-third and male inflorescence density by 64% to 74% in the most heavily shaded trees of both cultivars compared to controls. Shade was more detrimental to yield than flowering: yield per tree dropped by >80%, from 2.9 to 3.4 kg in full sun to 0.6 to 0.9 kg in 92% shade. Shade reduced yield primarily by decreasing nut number and secondarily by decreasing nut size. The incidence of several kernel defects increased as shade increased. Therefore, hazelnut leaves showed considerable capacity to adapt structurally and functionally to shade, but improving light penetration into the canopy would probably increase orchard productivity.

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A long-term experiment in the same site was planted to evaluate potential yield, nematode, and disease problems with tomatoes (Lycopersicon esculentum Mill.) in a strip-till system. Treatments consisted of conventional tillage (CT) and strip tillage (ST), rye (Secale cereale L.), wheat (Triticum aestivum L.), and perennial ryegrass (Lolium perenne L.) cover crops and a 2-year rye–tomato rotation. Results of the first 5 years indicate a decrease in tomato yield over time for both tillage treatments and cover crops. Tomato yields were lower following wheat and perennial ryegrass than rye. Strip-tillage reduced yield compared to conventional tillage in only 1 year out of 6. Yield increased overall for treatments in 1992, with highest yield in the rye–tomato rotation. Bacterial speck/spot symptoms on foliage, although minor, were significantly greater in ST than in CT plots during the last 3 years. No major consistent trends in incidence and severity of bacterial and fungal diseases and of disorders of fruit were evident during the 5-year period, and neither fruit yield nor quality were significantly affected by these factors. Root-knot nematodes (Meloidogyne hapla Chitwood) were numerically less numerous in the rye–tomato rotation than in other treatments; both root-knot and root lesion nematodes [Pratylenchus penetrans (Cobb)] tended to be less numerous under CT than under ST. Tomatoes grown under reduced tillage appear more sensitive to plant parasitic nematodes and preceding cover crops than in conventional tillage.

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