scholarly journals Incorporation of Temperature and Solar Radiation Thresholds to Modify a Lettuce Downy Mildew Warning System

2002 ◽  
Vol 92 (6) ◽  
pp. 631-636 ◽  
Author(s):  
B. M. Wu ◽  
A. H. C. van Bruggen ◽  
K. V. Subbarao ◽  
H. Scherm
Keyword(s):  
Solar Radiation ◽  
Downy Mildew ◽  
Disease Incidence ◽  
Characteristic Curve ◽  
Warning System ◽  
Effect Of Temperature ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Leaf Wetness ◽  
High Solar Radiation

The effect of temperature on infection of lettuce by Bremia lactucae was investigated in controlled environment studies and in the field. In controlled conditions, lettuce seedlings inoculated with B. lactucae were incubated at 15, 20, 25, or 30°C during a 4-h wet period immediately after inoculation or at the same temperatures during an 8-h dry period after the 4-h postinoculation wet period at 15°C. High temperatures during wet and dry periods reduced subsequent disease incidence. Historical data from field studies in 1991 and 1992, in which days with or without infection had been identified, were analyzed by comparing average air temperatures during 0600 to 1000 and 1000 to 1400 Pacific standard time (PST) between the two groups of days. Days without infection had significantly higher temperatures (mean 21.4°C) than days with infection (20.3°C) during 1000 to 1400 PST (P < 0.01) but not during 0600 to 1000 PST. Therefore, temperature thresholds of 20 and 22°C for the 3-h wet period after sunrise and the subsequent 4-h postpenetration period, respectively, were added to a previously developed disease warning system that predicts infection when morning leaf wetness lasts ≥4 h from 0600 PST. No infection was assumed to occur if average temperature during these periods exceeded the thresholds. Based on nonlinear regression and receiver operating characteristic curve analysis, the leaf wetness threshold of the previous warning system was also modified to ≥3-h leaf wetness (≥0900 PST). Furthermore, by comparing solar radiation on days with infection and without infection, we determined that high solar radiation during 0500 to 0600 PST in conjunction with leaf wetness ending between 0900 and 1000 PST was associated with downy mildew infection. Therefore, instead of starting at 0600 PST, the calculation of the 3-h morning leaf wetness period was modified to start after sunrise, defined as the hour when measured solar radiation exceeded 8 W m-2 (or 41 μmol m-2 s-1 for photon flux density). The modified warning system was compared with the previously developed system using historical weather and downy mildew data collected in coastal California. The modified system was more conservative when disease potential was high and recommended fewer fungicide applications when conditions were not conducive to downy mildew development.

scholarly journals Evaluation of a Disease Warning System for Downy Mildew of Grapes

Plant Disease ◽  
2000 ◽  
Vol 84 (5) ◽  
pp. 549-554 ◽  
Author(s):  
L. V. Madden ◽  
M. A. Ellis ◽  
N. Lalancette ◽  
G. Hughes ◽  
L. L. Wilson
Keyword(s):  
Linear Model ◽  
Downy Mildew ◽  
Environmental Conditions ◽  
Generalized Linear Model ◽  
Disease Incidence ◽  
Warning System ◽  
Plasmopara Viticola ◽  
Effective Control ◽  
Subsequent Infection ◽  
Grape Downy Mildew

An electronic warning system for grape downy mildew— based on models for the infection of leaves of Vitis lambrusca, production of sporangia by Plasmopara viticola in lesions, and sporangial survival—was tested over 7 years in Ohio. Grapevines were sprayed with metalaxyl plus mancozeb (Ridomil MZ58) when the warning system indicated that environmental conditions were favorable for sporulation and subsequent infection. Over the 7 years, plots were sprayed from one to four times according to the warning system, and from four to 10 times according to the standard calendar-based schedule (depending on the date of the initiation of the experiment). The warning system resulted in yearly reductions of one to six sprays (with median of three sprays). Disease incidence (i.e., proportion of leaves with symptoms) in unsprayed plots at the end of the season ranged from 0 to 86%, with a median of 68%. Incidence generally was very similar for the warning-system and standard-schedule treatments (median of 7% of the leaves with symptoms), and both of these incidence values were significantly lower (P < 0.05) than that found for the unsprayed control, based on a generalized-linear-model analysis. Simplifications of the disease warning system, where sprays were applied based only on the infection or sporulation components of the system, were also effective in controlling the disease, although more fungicide applications sometimes were applied. Effective control of downy mildew, therefore, can be achieved with the use of the warning system with fewer sprays than a with a standard schedule.

Validation of weather and leaf wetness forecasts for a lettuce downy mildew warning system

2001 ◽  
Vol 23 (4) ◽  
pp. 371-383 ◽  
Author(s):  
B.M. Wu ◽  
K.V. Subbarao ◽  
A.H.C.van Bruggen ◽  
G.G.H. Pennings
Keyword(s):  
Downy Mildew ◽  
Warning System ◽  
Leaf Wetness ◽  
Lettuce Downy Mildew

scholarly journals Application and validation of a warning system for grapevine downy mildew controlusing fungicides

2013 ◽  
Vol 39 (1) ◽  
pp. 10-15 ◽  
Author(s):  
Erlei Melo Reis ◽  
Olavo Roberto Sônego ◽  
Cristiano de Sales Mendes
Keyword(s):  
Downy Mildew ◽  
Warning System ◽  
Leaf Wetness ◽  
Warning Systems ◽  
Conventional System ◽  
Grapevine Downy Mildew ◽  
Growing Seasons ◽  
Plant Disease Control ◽  
Target Disease ◽  
Electronic Sensors

Most warning systems for plant disease control are based on Vinho, in Bento Gonçalves - RS, during the growing seasons 2000/ weather models dependent on the relationships between leaf wetness 01, 2002/03 and 2003/2004, using the grape cultivar Isabel. The duration and mean air temperature in this period considering the conventional system used by local growers was compared with the target disease intensity. For the development of a warning system to new warning system by using different cumulative daily disease severity control grapevine downy mildew, the equation generated by Lalancette values (CDDSV) as the criterion to schedule fungicide application and et al. (7) was used. This equation was employed to elaborate a critical reapplication. In experiments conducted in 2003/04, CDDSV of 12 - period table and program a computerized device, which records, though 14 showed promising to schedule the first spraying and the interval electronic sensors, leaf wetness duration, mean temperature in this between fungicide applications, reducing by 37.5% the number of period and automatically calculates the daily value of probability of applications and maintaining the same control efficiency in leaves infection occurrence. The system was validated at Embrapa Uva e and bunches, similarly to the conventional system.

Loss of chlorophyll with limited reduction of photosynthesis as an adaptive response of Syrian barley landraces to high-light and heat stress

1999 ◽  
Vol 26 (6) ◽  
pp. 569 ◽  
Author(s):  
Michel Havaux ◽  
Florence Tardy
Keyword(s):  
High Temperature ◽  
Chlorophyll Content ◽  
Flux Density ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Arid Environments ◽  
Strong Light ◽  
Carotenoid Concentration ◽  
High Solar Radiation ◽  
Barley Landraces

The Syrian barley landrace Tadmor is adapted to semi-arid environments and characterized by a reduced chlorophyll content (ca −25% on a leaf area basis) compared to improved barley genotypes, such as the European variety Plaisant. Tadmor leaves had reduced stomatal conductance (gS ) compared to Plaisant leaves both under well-watered conditions and during water stress. Both Tadmor and Plaisant barley seedlings were progressively acclimated to high temperature (39°C) and high photon flux density (1600 µmol photons m −2 s −1 ). During acclimation, the chlorophyll content of Tadmor leaves further decreased whereas the carotenoid concentration remained virtually unchanged, leading to a marked increase in the carotenoid:chlorophyll ratio. The chlorophyll content of acclimated Tadmor leaves was reduced to approximately half of the chlorophyll content of Plaisant leaves grown under the same conditions. Loss of chlorophyll in Tadmor leaves was not observed when only one environmental factor was increased (temperature or photon flux density). In the improved variety, both chlorophylls and carotenoids accumulated during acclimation to heat and strong light, leading to an almost constant carotenoid:chlorophyll ratio. The loss of chlorophyll in the Syrian landrace was associated with limited changes in the photosynthetic characteristics of the leaves (oxygen evolution, electron transport quantum yield, chlorophyll antenna size of photosystem II). Plaisant leaves, but not Tadmor leaves, exhibited symptoms of oxidative damage during growth in strong light at high temperature. When the stomata were closed, sudden exposure to bright light caused a smaller increase in leaf temperature in Tadmor than in Plaisant. Taken together, our results suggest that the ‘low chlorophyll’ feature of Syrian barley landraces is related to their drought adaptation which is manifested by a low g S : the very low chlorophyll content decreases leaf absorbance which, in turn, reduces the potentially damaging heating effect of high solar radiation in droughted plants whose stomata are closed.

COMPARATIVE RESPONSES OF PHOTOSYNTHESIS TO GROWTH TEMPERATURE IN SOYBEAN (Glycine max [L.] Merrill) CULTIVARS

1988 ◽  
Vol 68 (2) ◽  
pp. 419-425 ◽  
Author(s):  
F. CAULFIELD ◽  
J. A. BUNCE
Keyword(s):  
Glycine Max ◽  
Photosynthetic Photon Flux Density ◽  
Temperature Acclimation ◽  
Effect Of Temperature ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Maturity Group ◽  
Photosynthetic Rates ◽  
Glycine Max L ◽  
Maturity Groups

The effect of temperature during growth on the photosynthetic characteristics of soybean (Glycine max [L.] Merrill) was studied using cultivars from Maturity Group 00 (Altona, Fiskeby V, Flambeau, Maple Presto, McCall) and MG VIII (Hampton 266–A, Hardee, Johnston, Kirby). In one experiment plants were grown with 950 μmol m−2s−1 photosynthetic photon flux density (PPFD) at 18, 20, 25 and 30 °C. When grown at 20 °C, MG 00 cultivars averaged significantly higher rates of photosynthesis measured at 25 °C and saturating PPFD than did MG VIII cultivars. Cultivars were also grown with a PPFD of 540 μmol m−1 at 17.5, 20.0, 22.5 and 25.0 °C. Maturity Group 00 cultivars averaged higher photosynthetic rates than MG VIII cultivars at the 20.0 and 22.5 °C growth temperatures. The other growth environments produced no significant differences between maturity groups. Photosynthetic rates differed between cultivars, but not maturity groups, after exposure to a single night with a gradual temperature decline to 8 °C. Photosynthetic rates recovered in 28 h. Two cultivars, Altona and Johnston, were grown outdoors at three times during one growing season at Beltsville, and their maximum photosynthetic rates changed depending on the temperatures during leaf development, in agreement with the data from the controlled environment studies.Key words: Soybean, Glycine max [L.] Merrill, photosynthesis, temperature, acclimation

The effect of shade on flowering of Piceaglauca

1984 ◽  
Vol 14 (6) ◽  
pp. 830-832 ◽  
Author(s):  
Robert D. Marquard ◽  
James W. Hanover
Keyword(s):  
Environmental Factors ◽  
Solar Radiation ◽  
Flux Density ◽  
Tree Height ◽  
White Spruce ◽  
Tree Size ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Spectral Quality ◽  
Active Radiation

Differences in fecundity and tree size of white spruce (Piceaglauca (Moench) Voss) were observed within a mixed Picea plantation differentially shaded by a hardwood stand. To relate environmental factors to tree height and fecundity, the plantation was divided into four regions based on the time of the day each region first received direct solar radiation. Thirty percent of the white spruce in the most shaded and 76% in the sunniest region flowered. Photon flux density, spectral quality, and ambient temperature were measured throughout the plantation. Trees in the most shaded region were significantly shorter and received 18% less photosynthetically active radiation than trees in the sunniest region. Photon flux density within the plantation best explained differences in fecundity and tree size.

scholarly journals A Consideration for the Light Environmental Modeling under Tropical Rainforest Canopies

2014 ◽  
Vol XL-7 ◽  
pp. 217-220 ◽  
Author(s):  
M. Yoshimura ◽  
M. Yamashita
Keyword(s):  
Solar Radiation ◽  
Tropical Rainforest ◽  
Light Condition ◽  
Photosynthetic Photon Flux Density ◽  
Environmental Modeling ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Forest Region ◽  
Direct Light ◽  
Sky Conditions

Photosynthetic Active Radiation (PAR) is the most important light source for plant photosynthesis. It is known that most of PAR from solar radiation is well absorbed by the surface. The canopy is the surface in forest region, consists an aboveground portion of plant community and formed by plant crowns. On the other hand, incident solar radiation is fluctuating at all times because of fluctuating sky conditions. Therefore, qualitative light environmental measurements in forest are recommended to execute under stable cloudy condition. In fact, it is quite a few opportunities to do under this sky condition. It means that the diffuse light condition without the direct light is only suitable for this measurement. <br><br> In this study, we challenged the characterization the forest light environment as its representativeness under no consideration of sky conditions through analysis huge quantities of instantaneous data which obtained under the different sky conditions. All examined data were obtained under the different sky conditions at the tropical rainforest canopy as one of the typical fluctuating sky conditions regions. An incident PAR is transmitted and scattered by different forest layers at different heights. Various PAR data were measured with quantum units as Photosynthetic Photon Flux Density (PPFD) at different forest heights by the quantum sensors. By comparing PPFDs at different heights with an incident PPFD, relative PPFDs were calculated, which indicate the degree of PPFD decrease from the canopy top to lower levels. As the results of these considerations, daily averaging is confirmed to be cancelled sky fluctuating influences.

scholarly journals Regeneration of Dracaena surculosa Through Indirect Shoot Organogenesis

HortScience ◽  
2010 ◽  
Vol 45 (8) ◽  
pp. 1250-1254 ◽  
Author(s):  
Juanxu Liu ◽  
Min Deng ◽  
Richard J. Henny ◽  
Jianjun Chen ◽  
Jiahua Xie
Keyword(s):  
Shoot Organogenesis ◽  
Disease Incidence ◽  
Adventitious Shoots ◽  
Leaf Explants ◽  
Basal Medium ◽  
Shoot Formation ◽  
The United States ◽  
Photon Flux ◽  
Photon Flux Density ◽  
Stem Explants

This study established a method of regenerating Dracaena surculosa Lindl. ‘Florida Beauty’ through indirect shoot organogenesis. Bud, leaf, and stem explants were cultured on a Murashige and Skoog basal medium supplemented with N6-(2-isopentyl) adenine (2iP) at 12.3 and 24.6 μM with 3-indoleacetic acid (IAA) at 0, 1.1, and 2.3 μM, respectively, and 2iP at 36.9, 49.2, 61.5, and 73.8 μM with IAA at 1.1 and 2.3 μM, respectively. Calluses were induced from leaf explants but failed to produce adventitious shoots. Calluses were also induced from stem and bud explants cultured on the basal medium containing 12.3 μM 2iP and 2.3 μM IAA, 24.6 μM 2iP or higher with either 1.1 or 2.3 μM IAA. The highest callus induction frequency was 63.2% from stem explants and 69.6% from bud explants when they were cultured on the basal medium supplemented with 49.2 μM 2iP and 2.3 μM IAA. The highest shoot formation frequency was 65.7% from stem-derived callus cultured on the basal medium containing 61.5 μM 2iP and 1.1 μM IAA and 88% from bud-derived callus cultured with 49.2 μM 2iP and 1.1 μM IAA. The highest number of shoots per piece of stem- and bud-derived calluses was 3.8 and 6.7, respectively. Adventitious shoots developed better root systems in the basal medium supplemented with 2.0 μM IAA. Plantlets after transplantation into a soilless substrate grew vigorously in a shaded greenhouse under a maximum photosynthetic photon flux density of 300 μmol·m−2·s−1. Neither disease incidence nor somaclonal variants were observed in the regenerated population. This established method could be used for efficient micropropagation of D. surculosa, and the availability of tissue-cultured liners could reduce the dependency on imported cuttings, which often bring new or invasive pests into the United States.

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