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Tissue concentrations of Ca, Mg, and K were determined across immature leaves of lettuce (Lactuca sativa L. `Buttercrunch') at different stages of enlargement using electron microprobe x-ray analysis. The analysis was with a wavelength dispersive spectrometer to permit detection of low concentrations of Ca. Patterns of mineral accumulation in immature leaves that were exposed were compared to patterns of accumulation in leaves that were enclosed within a developing head. The leaves developing without enclosure were free to transpire and developed normally whereas leaves developing with enclosure were restricted in transpiration and developed an injury that was characteristic of Ca deficiency. In the exposed leaves, Ca concentrations increased from an average of 1.0 to 2.1 mg·g-1 dry weight (DW) as the leaves enlarged from 5 to 30 mm in length. In the enclosed leaves, Ca concentrations decreased from 1.0 to 0.7 mg·g-1 DW as the leaves enlarged from 5 to 30 mm in length. At the tips of these enclosed leaves a larger decrease was found, from 0.9 to 0.3 mg·g-1 DW during enlargement. Necrotic injury first became apparent in this tip area when the concentration was ≈0.4 mg·g-1 DW. Magnesium concentrations across the exposed leaves were similar to concentrations across the enclosed leaves, and did not change with enlargement. Magnesium concentrations averaged 3.5. mg·g-1 DW in both enclosed and exposed leaves during enlargement from 5 to 30 mm. In both exposed and enclosed leaves, K concentrations increased during enlargement from 40 to ≈60 mg·g-1 DW. Potassium concentrations were highest toward the leaf apex and upper margin where injury symptoms occurred, and this may have enhanced injury development. This research documents the critical low levels of Ca (0.2 to 0.4 mg·g-1 DW) that can occur in enclosed leaves of plants and which apparently leads to the marginal apex necrosis of developing leaves seen frequently on lettuce and other crops.
An electron microprobe was used to determine tissue concentrations of Ca across 20-mm-long leaves of `Green Lakes' crisphead lettuce (Luctuca sativa L.) with and without tipburn injury. Concentrations within the fifth and 14th leaves, counted from the cotyledons, from plants grown under controlled-environment conditions were compared to concentrations within similar leaves obtained from plants grown under field conditions. Only the 14th leaf from plants grown under controlled-environment conditions developed tipburn. Injured areas on these leaves had Ca concentrations as low as 0.2 to 0.3 mg·g-1 dry weight. Uninjured areas of tipburned leaves contained from 0.4 to 0.5 mg·g-1 dry weight. Concentrations across the uninjured 14th leaf from field-grown plants averaged 1.0 mg·g-1 dry weight. Amounts across the uninjured fifth leaves from both environments averaged 1.6 mg·g-1 dry weight. In contrast, Mg concentrations were higher in injured leaves than in uninjured leaves and thus were negatively correlated with Ca concentrations. Magnesium concentrations averaged 4.7 mg·g-1 dry weight in injured leaves compared with 3.4 mg·g-1 dry weight in uninjured leaves from both environments. Magnesium concentrations were uniform across the leaf. Potassium concentrations were highest at the leaf apex and decreased toward the base and also decreased from the midrib to the margin. Potassium averaged 51 mg·g-1 dry weight in injured and uninjured leaves from both environments. No significant differences in K concentration were present between injured and uninjured leaves. This study documented that deficient concentrations of Ca were present in areas of leaf tissue developing tipburn symptoms and that concentrations were significantly higher in similar areas of other leaves that had no symptoms. This study also documented that Ca concentrations were significantly lower in enclosed leaves that exhibited tipburn symptoms than in exposed leaves that did not exhibit tipburn. Also, the amounts of Ca in plants that developed tipburn in controlled environments were lower than in plants of the same cultivar that did not develop tipburn in field plantings. The reduced levels of Ca in plants grown in controlled environments were associated with faster development rates compared with field-grown plants.
Abstract
The young developing leaves of 20-day-old lettuce plants (Lactuca sativa L. ‘Buttercrunch’) were enclosed by aluminized polyethylene sheaths to decrease transpiration and reduce Ca transport. The plants were grown in recirculating solution culture systems using a modified half-strength Hoagland’s solution under cool-white fluorescent lamps with a photosynthetic photon flux of 350 μmol·s−1·m−2 in a 16:8-hr (light:dark) period. Air temperature and humidity were 20°C and 65%, respectively. After 4 days of enclosure, 53% of the inner leaves (leaves one to 3 cm in length) were tipburned. After the same period, less than 1% of the inner leaves on control plants were tipburned. The concentration of Ca in enclosed inner leaves was 0.63 mg·g−1 dry weight, compared to 1.48 mg·g−1 dry weight in inner leaves that were not enclosed. The Ca concentration in transpiring outer leaves of all plants was 9.9 mg·g−1 dry weight. The Mg concentration in enclosed inner leaves was 2.25 mg·g−1 dry weight, compared to 2.34 mg·g−1 dry weight in inner leaves that were not enclosed. This research documents that enclosure of leaves at the growing point, as would occur with normal head development, is sufficient to create a limiting concentration of Ca in the enclosed tissue and encourage tipburn development.
Abstract
‘Carolina Nugget’ (Fig. 1) is a moist sweet potato developed at N.C. State Univ. in 1954. In 1957 and 1958, it was tested throughout North Carolina in regional tests as the experimental clone NC 172. Although it never has been released officially as a cultivar, it has been grown for commercial use in several southern states under many different names (e.g., Red Nugget, Carolina Nugget, Golden Nugget). The formal release and naming of this sweet potato cultivar should alleviate the confusion that has occurred when growers market or buy plant material.
Abstract
‘Cortland’/Mailing (M) 7 apple trees (Malus domestica Bork.) which were treated at planting time with commercial root promoters, containing either naphthaleneacetamide (NAAm) + naphthaleneacetic acid (NAA), indolebutyric acid (IBA) + fertilizer, or the ectomycorrhizal fungus Pisolithus tinctorius, increased terminal growth. P. tinctorius was superior to either rooting compound for increasing total growth, and only P. tinctorius increased root weight. Colonization of the root system by P. tinctorius was not observed, although the roots of P. tinctorius-treated trees appeared to have more endomycorrhizae. The growth increase was not due to increased nutrient uptake.
The gas exchange of tomato (Lycopersicon esculentum Mill cv. Spring Giant VF) plants exposed to an ethephon root drench of 5 μl·liter-1 or 50 μl·liter-1 was examined for 9 days. Photosynthesis showed a biphasic response to ethephon, wherein elevations of 13.2% and 16.7% were observed over control plants for two of the measurement days for the 50 and 5 μl ethephon/liter concentrations, respectively. Stomatal conductance showed a large increase at 50 μl ethephon/liter on day 2, while 5 μl·liter -1 did not show this difference. A biphasic response of photosynthesis may explain some of the intraspecific variation found in the literature describing ethylene-induced gas-exchange alterations.
Commercial sweetpotato fields are established with asexually derived propagules as either cut or pulled plants. Micropropagation and somatic embryogenesis were/are being investigated to improve seed production. Micropropagation of sweetpotato is utilized in California as part of its seed production program. Several studies have been conducted or are ongoing in North Carolina to evaluate the utility of micropropagation as part of its certification program. In 1992, yield was increased in `Beauregard' with micropropagated plants compared with plants that were derived from the North Carolina Certified Seed Program. However, there were no yield increases in four years of comparisons when `Jewel' and `White Delight' were micropropagated. A trend towards early bulking has consistently been observed in micropropagated `Jewel', `White Delight' and Beauregard. Early plant growth and yields of plants (`White Star') obtained from somatic embryos, micropropagation or vine cuttings were compared. Plants derived from somatic embryos grew slower and yielded less root weight than cut plants; however, more storage roots were obtained from plants obtained from somatic embryos indicating high yield potential if root bulking is achieved.
Abstract
2-Chloro-9-hydroxyfluorene-9-carboxylic acid (chlorflurenol) 3 at 50 or 100 ppm increased fruit production of a gynoecious cucumber (Cucumis sativus L. cv. MSU 713-5) under field conditions of both normal and reduced pollination. A monoecious cultivar, ‘Wisconsin SMR 18’, treated with (2-chloroethyl) phosphonic acid (ethephon) and then chlorflurenol produced over twice as many fruit as the control when pollen was plentiful, and more than 4 ⨯ as many when pollen supply was limited. Ethephon sprays alone increased pistillate flower formation on the monoecious cultivar but did not increase fruit set. Chlorflurenol treatments increased the proportion of fruit in the smaller, more valuable size grades and appear advantageous for mechanically harvested pickling cucumbers.
No reduction in yield and quality of pecan nuts or leaf mineral nutrient concentration occurred when 100 lb/acre of N was applied through a drip-irrigation system compared with 200 lb/acre applied either all broadcast or half broadcast and half fertigated. Yield of `Stuart', percentage kernel of `Schley', and nut size of both cultivars were increased by irrigation or irrigation and fertigation. The 100 lb/acre N-all-fertigated treatment resulted in less soil pH reduction and less loss of K, Ca, and Mg from soil underneath the tree canopy than broadcast treatments. No evidence of excessive soil pH reduction in the wetted zone of fertigated trees was noticed. Calcium and Mg were higher within than outside the wetted zone.
Nitrogen at rates of 112 or 224 kg·ha-1 was applied to nonirrigated and drip irrigated mature pecan trees for 9 years. Some irrigated trees received 224 kg·ha-1 N either all broadcast or ½ through the drip irrigation. Other drip irrigated trees received only 112 kg·ha-1 all through the drip irrigation system. Fertigation was in 4 equal monthly doses beginning April 1. Irrigation increased yield for 2 years for Schley and 3 years for Stuart. Nut size was increased by irrigation in 6 years for Schley and 8 years for Stuart. Applying ½ N through the irrigation system caused no detrimental effect on yield or nut quality. The lower rate of N all applied through the drip irrigation system gave yield and nut quality as good as the higher rate either all broadcast or ½ broadcast and ½ fertigated.