A necrotic disorder occurs on upper leaves of many oriental hybrid lily (Lilium L.) cultivars, including the most-widely-grown `Star Gazer'. We term this disorder “upper leaf necrosis” (ULN) and hypothesize that it is a calcium (Ca) deficiency. We demonstrated that Ca concentration in necrosed tissues was nearly six-fold below that of normal leaves (0.10% vs. 0.57% dry weight), and that Ca concentration was negatively associated with percentage necrosed leaf area. It was concluded that ULN is a Ca deficiency disorder. When the symptoms were slight, early ULN symptoms appeared as tiny depressed spots on the lower surface of the leaf, or as water-soaked areas when the disorder was severe. Most commonly, ULN began on the leaf margin. The injured areas turned brown, leading to leaf curling, distortion, or tip death. ULN occurred on leaves associated with flower buds and leaves immediately below the flower buds. For the plants grown from 16-18 cm circumference bulbs, the five leaves directly below the flower buds and larger leaves associated with the 1st and the 2nd flower buds were most susceptible. In general, flower buds were not affected by ULN, and continued to develop and flower normally, even though they were associated with subtending, highly distorted leaves. Eighty-five percent of plants began to exhibit ULN symptoms 30-40 days after planting (i.e., 24-34 days after shoot emergence). This was the stage when the 6th or 7th leaf under the bottom flower bud was just unfolded. Light was not the main factor that initiated ULN, however, ULN severity was greatly increased by light reduction, as leaf transpiration was reduced.
Yao-Chien Chang and William B. Miller
Yao-Chien Chang and William B. Miller
Upper leaf necrosis (ULN) on Lilium `Star Gazer' has been shown to be a calcium (Ca) deficiency disorder. Initial symptoms of ULN tend to appear on leaf margins. Before flower buds are visible, young expanding leaves are congested and overlap each other on the margin. In the current study, we examined the relationship between leaf enclosure, transpiration, and upper leaf necrosis. We demonstrated that low transpiration rate and enclosure of young leaves played an important role in the occurrence of ULN. Young expanding leaves are low transpiration organs. The younger the leaf, the lower the transpiration rate and Ca concentration. Leaf enclosure further reduced transpiration of these young leaves and promoted ULN. Upper leaf necrosis was suppressed by manually unfolding the leaves using a technique we refer to as artificial leaf unfolding (ALU). ALU minimized leaf congestion, exposing leaves that were previously enclosed. We demonstrated that the effect of ALU was not the consequence of thigmomorphogenesis, as ULN was not reduced by mechanical perturbation in lieu of ALU. With ALU, transpiration of upper leaves was significantly increased and Ca concentration of the first leaf immediately below the flower buds was increased from 0.05% to 0.20%. We concluded that leaf enclosure promoted ULN occurrence, and ALU suppressed ULN primarily by increasing transpiration. The use of overhead fans to increase airflow over the tops of the plants significantly reduced both ULN incidence and severity.
Yao-Chien Chang, Karen Grace-Martin, and William B. Miller
Upper leaf necrosis (ULN) on Lilium `Star Gazer' is a calcium deficiency disorder. In this study, we evaluated the efficacy of foliar Ca sprays and bulb Ca dipping on reducing ULN. Necrosis severity of a single leaf was determined by an index from 0 (healthy) to 5, based on symptom progression and necrosed leaf area. Single leaf severity was then summed for all leaves to yield a whole-plant severity rating. Single daily applications of 25 mm calcium chloride or calcium nitrate sprays for 14 days significantly suppressed the degree of symptom expression; whole-plant severity was reduced from 18 (severely necrosed) to below 3 (essentially unnoticeable). Five single applications at 3.5-day intervals were not effective, even at concentrations up to 150 mm. At concentrations of 100 and 150 mm, 14 daily sprays of calcium chloride or calcium nitrate were toxic and caused leaf tip yellowing; calcium chloride caused more severe phytotoxicity than did calcium nitrate. For effectiveness of foliar Ca sprays, it was necessary to have the Ca solution reach the enclosed, young, expanding leaves. Preplant bulb immersion in calcium chloride was not effective even at concentrations as high as 400 mm for up to 16 hours.
Michael V. Mickelbart and Mary Lu Arpaia
Effect of salinity (1.5, 3.0, 4.5, or 6.0 dS·m-1) on growth and physiology of 1-year-old `Hass' avocado (Persea americana Mill.) trees on one of three rootstocks, `Thomas', `Toro Canyon', or `Duke 7', was investigated to determine the relative salinity tolerance of these rootstocks and to determine possible reasons for any observed differences in tolerance. Leaves of trees on `Thomas' rootstock had the highest leaf Na+, Cl-, and necrosis compared to trees on the other two rootstocks. Exposure to salinity resulted in decreased growth of shoots on all rootstocks, but was greatest on `Thomas' and least on `Duke 7'. The oldest leaves on all rootstocks had the highest proportion of leaf necrosis, whereas younger leaves exhibited almost no necrosis. Salinity reduced net CO2 assimilation (A) and chlorophyll concentrations of scion leaves on all rootstocks, but more in older leaves than in younger leaves. Although the effects of salinity on A were greater for trees on `Thomas' on one measurement date, overall, rootstock differences in A were not significant for any leaf age. Differences in response to salinity among rootstocks were noted primarily in morphological traits such as growth and leaf necrosis, rather than physiological traits such as gas-exchange and water relations. Based on overall growth and physiological response to salinity, trees on `Thomas' performed poorest, whereas trees on `Duke 7' exhibited the greatest salt tolerance. The relative tolerance of the various rootstocks appeared to be due primarily to their ability to exclude Na+ and Cl- from the scion.
Nagehan D. Köycü, John E. Stenger, and Harlene M. Hatterman-Valenti
Elemental sulfur is commonly applied for powdery mildew (Erysiphe necator) protection on winegrape (Vitis sp.). The product may be used in a diversified, integrated disease management system to help prevent fungicide resistance to products with other modes of action. Additionally, sulfur may be used as a control option in organic systems. Applications of sulfur have been known to cause phytotoxic injury to susceptible winegrape cultivars, particularly those stemming from fox grape (Vitis labrusca) parentage. To improve recommendations to producers in the northern Great Plains region of the United States, a comparison of injury incidence and severity, as well as effects on yield characteristics was undertaken for 13 regional cultivars exposed to three sulfur rates (0, 2.4, and 4.8 lb/acre a.i.) at a North Dakota State University Research Station near Absaraka, ND. Overall, four cultivars (Bluebell, Baltica, Sabrevois, and King of the North) of the 13 cultivars tested showed phytotoxic symptoms. Injury severity and incidence of these cultivars differed between years and across rates. ‘Bluebell’ showed consistent and severe sulfur injury symptoms. Injury to the other three susceptible cultivars tended to vary by the given environment, with King of the North generally showing the lowest injury response. Injury symptoms were not found to be associated with the overall yield or cluster weight. Results suggest that alternative spray programs that exclude sulfur-based fungicides should be recommended for ‘Bluebell’, ‘Baltica’, ‘Sabrevois’, and ‘King of the North’, whereas sulfur-based fungicides may be applied to ‘Alpenglow’, ‘ES 12-6-18’, ‘Frontenac’, ‘Frontenac Gris’, ‘La Crescent’, ‘Marquette’, ‘Somerset Seedless’, ‘St. Croix’, and ‘Valiant’. Observations on fruit ripening in 2014 suggest that future research is needed to determine if a reduction of fruit quality may occur in some seasons with repeated sulfur applications or with successive annual sulfur applications for susceptible cultivars if used in an organic production system.
Steven P.C. Groot, Sierd Zijlstra, and Johannes Jansen
Powdery mildew-resistant (PMR) cultivars of cucumber (Cucumis sativus L.) grown in greenhouses in the Netherlands during winter show chlorosis on the full-grown leaves of the main stem. The symptoms are yellowing and occasional necrosis between the main veins of the leaves, resembling symptoms of P toxicity. Severity of the chlorosis may vary from one winter to another. Variation is also observed in the severity of the symptoms between cultivars and individual plants of a cultivar. High P nutrition results in an increase of the severity of chlorosis and provides a better discriminating environment for the selection of PMR genotypes that are less susceptible for leaf chlorosis.
Suejin Park, Youyoun Moon, and Nicole L. Waterland
life compared with the control ( Table 1 ). Some treatments caused leaf necrosis, especially at the higher concentration of NaCl, NaNO 3 , BaCl 2 , Ba(NO 3 ) 2 , and mannitol ( Table 1 , Fig. 2 ). Under water deficit, all treatments at the higher
Ockert Greyvenstein, Terri Starman, Brent Pemberton, Genhua Niu, and David Byrne
. The total number of shoots with at least one abscised flower and the number of shoots with no visible sign of flower abscission were recorded on each plant ( Fig. 6A ). The presence or absence of leaf necrosis was scored on the 10th day for each of the
Janelle E. Glady, N. Suzanne Lang, and Erik S. Runkle
Veronica foliage and thus should be used with caution. Ethephon applied to Dianthus did not abort flower buds at the rates and frequencies used, severely stunted internode extension growth, and caused deformed growth and marginal leaf necrosis
Matthew G. Blanchard and Erik S. Runkle
’ and Lovely Penguin ‘Emperor’, respectively. Data are for Year 2 only. Discussion In this study, Odontioda grown at a day temperature of 26 °C or higher developed leaf necrosis, and inflorescences aborted; thus, plants were