scholarly journals Insensitivity to Ridomil Gold (Mefenoxam) Found Among Field Isolates of Phytophthora capsici Causing Phytophthora Blight on Bell Pepper in North Carolina and New Jersey

Plant Disease ◽  
1998 ◽  
Vol 82 (6) ◽  
pp. 711-711 ◽  
Author(s):  
Greg Parra ◽  
Jean Ristaino
Keyword(s):  
North Carolina ◽  
New Jersey ◽  
Cultural Practices ◽  
Phytophthora Capsici ◽  
Significant Proportion ◽  
Bell Pepper ◽  
Economic Losses ◽  
Mating Types ◽  
Phytophthora Blight ◽  
Field Isolates

Phytophthora blight caused by the pathogen Phytophthora capsici has caused economic losses in bell pepper and cucurbit fields in the U.S., and the prevalence of the disease has increased in recent years. The pathogen can be dispersed in soil, with surface water, and via splash dispersal from the soil to foliage. Management of the disease relies on modifications in cultural practices, crop rotation, and judicious use of fungicides. Disease occurred in fields that were sprayed with multiple applications of Ridomil Gold (mefenoxam) according to labeled recommendations in 1997. Mefenoxam is the active enantiomer contained in the racemic fungicide metalaxyl. Mefenoxam was widely used on bell pepper for the first time in 1997, but disease was widespread. Insensitivity to mefenoxam and metalaxyl has not been reported previously in field isolates of P. capsici. However, selection for metalaxyl insensitive isolates in the laboratory after mutagenesis has been reported. Insensitivity to metalaxyl has been reported among other Oomycete pathogens including Phytophthora infestans, Pseudoperonospora cubensis, Peronospora tabacina, Bremia lactucae, and Pythium spp. Infected plants were collected from 12 fields in North Carolina by the authors and one additional field in New Jersey (courtesy of Steve Johnston). Infected plants (10 to 30 per field) were surface disinfested in 10% bleach and plated on selective media to isolate P. capsici. Colonies of the pathogen were transferred to V8 juice agar or maintained on cornmeal agar slants. Mefenoxam-amended V8 juice agar was prepared at levels of 0, 5, and 100 ppm. Screening for sensitivity was conducted by placing agar plugs containing the pathogen onto two replicate plates of mefenoxam-amended media at each concentration. Isolates were categorized as sensitive if growth was less than 40% of the unamended control at 5 ppm. Intermediate isolates exhibited growth greater than 40% of the unamended control at 5 ppm but less than 40% of the unamended control at 100 ppm mefenoxam. Insensitive isolates exhibited growth greater than 40% of the unamended control at 100 ppm mefenoxam. Concentrations of the fungicide used to screen for insensitivity were within the range applied in the field. Thus far, 161 isolates have been screened for sensitivity. Of these, 54 isolates were classified as sensitive, 15 as intermediate, and 92 or 57% of the isolates were insensitive. Three quarters of the fields sampled contained insensitive isolates and insensitivity ranged from 11 to 80% within fields. Both A1 and A2 mating types were recovered from some fields and insensitive isolates occurred among both mating types. Isolates that were insensitive to mefenoxam were also insensitive to metalaxyl. A significant proportion of the isolates obtained from infected plants in fields where Ridomil Gold has been used recently were insensitive. The ability of insensitive isolates to cause disease on fungicide-treated plants will be studied in further experiments. Isolates collected between 1988 and 1994 were screened and all isolates were sensitive to metalaxyl (Ridomil 2E). A dramatic shift in populations of P. capsici to insensitivity to the new metalaxyl substitute mefenoxam has occurred in bell pepper fields in a 3-year period.

scholarly journals Resistance to Mefenoxam and Metalaxyl Among Field Isolates of Phytophthora capsici Causing Phytophthora Blight of Bell Pepper

Plant Disease ◽  
2001 ◽  
Vol 85 (10) ◽  
pp. 1069-1075 ◽  
Author(s):  
Gregory Parra ◽  
Jean Beagle Ristaino
Keyword(s):  
North Carolina ◽  
Phytophthora Capsici ◽  
Effective Concentration ◽  
Bell Pepper ◽  
Mating Types ◽  
Phytophthora Blight ◽  
Field Isolates ◽  
The Mean ◽  
First Time ◽  
Important Disease

Incidence of Phytophthora blight in bell pepper fields that were sprayed for the first time with Ridomil Gold (mefenoxam) according to labeled recommendations was higher in North Carolina in 1997 than in previous years. Mefenoxam is the more active enantiomer contained in the racemic fungicide metalaxyl. A total of 150 isolates were obtained from 17 fields at eight grower locations. Among isolates from all locations, 30% were classified as sensitive, 10% as intermediate, and 59% were resistant to mefenoxam. Mefenoxam-resistant isolates were found in 82% of the fields sampled (14 of 17 fields). The proportion of resistant isolates in individual (fields ranged from 28 to 100%. The mean effective concentration (EC50) values for mefenoxam-sensitive isolates was 0.568 μg ml-1 (ranging from 0.12 to 1.1 μg ml-1), whereas the mean EC50 value for mefenoxam-resistant isolates was 366.5 μg ml-1 (ranging from 3 to 863 μg ml-1). The mean EC50 value for metalaxyl-sensitive isolates was 0.27 μg ml-1 (ranging from 0.00002 to 1.3 μg ml-1) and for metalaxyl-resistant isolates was 470.34 μg ml-1 (ranging from 10 to 966 μg ml-1). The greatest proportion of resistant isolates came from fields where mefenoxam was used alone rather than in combination with other fungicides. Both mating types were found among resistant isolates, suggesting that these isolates may persist in soil in subsequent years. Field isolates of Phytophthora capsici resistant to mefenoxam on pepper have not been reported previously and now pose new challenges for management of this important disease.

Fitness and competitive ability of field isolates of Phytophthora capsici resistant or sensitive to fluopicolide

Plant Disease ◽  
2020 ◽  
Author(s):  
Li Wang ◽  
Pingsheng Ji
Keyword(s):  
Mycelial Growth ◽  
Competitive Ability ◽  
Phytophthora Capsici ◽  
Bell Pepper ◽  
Vegetable Production ◽  
Vegetable Crops ◽  
Phytophthora Blight ◽  
Field Isolates ◽  
Significant Difference ◽  
The World

Phytophthora blight, caused by Phytophthora capsici, is one of the most destructive diseases in the production of solanaceous and cucurbitaceous vegetable crops. Fluopicolide has been used to control the disease; however, reduced efficacy of the fungicide was observed in Georgia. P. capsici isolates were collected from commercial vegetable fields in Georgia in 2018 and 2019 to determine sensitivity to fluopicolide, which were phenotyped to have 43.1% of the isolates as resistant. The fitness of resistant (R) and sensitive (S) isolates was assessed through mycelial growth and sporulation assays exposed to the fungicide (0 or 50 µg/ml). Fluopicolide did not reduce mycelial growth, sporangial production and zoospore germination of the resistant isolates. In the absence of fluopicolide, there was no significant difference between the R and S isolates in sporangial production, but mycelial growth and zoospore germination of the R isolates was greater than the S isolates (P = 0.01 and 0.001, respectively). The R isolates had similar ability as S isolates to induce disease on ‘Aristotle’ bell pepper, and most of the R and S isolates caused the same level of disease on ‘Paladin’. Inoculating squash fruit using different R:S ratios and recovering R and S isolates after 5 cycles of inoculation resulted in similar trends in changes of R vs. S isolates ratios. Overall it appeared that fitness and competitive ability of the R isolates were not reduced compared to the S isolates. This is the first report of the occurrence of field isolates of P. capsici resistant to fluopicolide in the world. The results have significant implications in providing guidance for growers to avoid or limit use of this fungicide in vegetable production.

scholarly journals Fitness of Isolates of Phytophthora capsici Resistant to Mefenoxam from Squash and Pepper Fields in North Carolina

Plant Disease ◽  
2008 ◽  
Vol 92 (10) ◽  
pp. 1439-1443 ◽  
Author(s):  
Adalberto C. Café-Filho ◽  
Jean Beagle Ristaino
Keyword(s):  
North Carolina ◽  
Phytophthora Capsici ◽  
Colony Growth ◽  
Relative Fitness ◽  
In Planta ◽  
Phytophthora Blight ◽  
In Vivo Experiments ◽  
First Time

Despite the wide adoption of mefenoxam (Ridomil Gold EC) for vegetables in North Carolina, the incidence of Phytophthora blight on pepper (Capsicum annuum) and squash (Cucurbita pepo) is high. Seventy-five isolates of Phytophthora capsici were collected in five pepper and one squash field in order to assess mefenoxam sensitivity. The relative fitness of resistant and sensitive isolates was contrasted in vitro by their respective rates of colony growth and their ability to produce sporangia in unamended V8 juice agar medium. In in vivo experiments, the aggressiveness of isolates on pepper was evaluated. The frequency of resistant isolates in North Carolina populations was 63%, considerably higher than resistance levels in areas where mefenoxam is not widely adopted. Resistant isolates grew on amended media at rates >80 to 90% and >100% of the nonamended control at 100 μg ml-1 and 5 μg ml-1, respectively. Sensitive isolates did not growth at 5 or 100 μg ml-1. All isolates from three fields, including two pepper and a squash field, were resistant to mefenoxam. Populations from other fields were composed of either mixes of sensitive and resistant isolates or only sensitive isolates. Response to mefenoxam remained stable during the course of in vitro and in planta experiments. Occurrence of a mefenoxam-resistant population of P. capsici on squash is reported here for the first time in North Carolina. When measured by rate of colony growth, sporulation in vitro, or aggressiveness in planta, fitness of resistant isolates was not reduced. Mefenoxam-resistant isolates from squash were as aggressive on pepper as sensitive or resistant pepper isolates. These results suggest that mefenoxam-resistant populations of P. capsici are as virulent and fit as sensitive populations.

scholarly journals Novel Peptide-Based Inhibitors for Microtubule Polymerization in Phytophthora capsici

2019 ◽  
Vol 20 (11) ◽  
pp. 2641
Author(s):  
Sang-Choon Lee ◽  
Sang-Heon Kim ◽  
Rachel A. Hoffmeister ◽  
Moon-Young Yoon ◽  
Sung-Kun Kim
Keyword(s):  
Antifungal Agents ◽  
Homo Sapiens ◽  
Phytophthora Capsici ◽  
Inhibitory Effect ◽  
Economic Losses ◽  
Phytophthora Blight ◽  
Beta Tubulin ◽  
Ic50 Values ◽  
And Migration ◽  
Nanomolar Range

The plant disease Phytophthora blight, caused by the oomycete pathogen Phytophthora capsici, is responsible for major economic losses in pepper production. Microtubules have been an attractive target for many antifungal agents as they are involved in key cellular events such as cell proliferation, signaling, and migration in eukaryotic cells. In order to design a novel biocompatible inhibitor, we screened and identified inhibitory peptides against alpha- and beta-tubulin of P. capsici using a phage display method. The identified peptides displayed a higher binding affinity (nanomolar range) and improved specificity toward P. capsici alpha- and beta-tubulin in comparison to Homo sapiens tubulin as evaluated by fluorometric analysis. One peptide demonstrated the high inhibitory effect on microtubule formation with a nanomolar range of IC50 values, which were much lower than a well-known chemical inhibitor—benomyl (IC50 = 500 µM). Based on these results, this peptide can be employed to further develop promising candidates for novel antifungal agents against Phytophthora blight.

scholarly journals Suppression of Phytophthora Blight in Bell Pepper by a No-Till Wheat Cover Crop

1997 ◽  
Vol 87 (3) ◽  
pp. 242-249 ◽  
Author(s):  
Jean B. Ristaino ◽  
Gregory Parra ◽  
C. Lee Campbell
Keyword(s):  
Cover Crop ◽  
Cultural Practices ◽  
Irrigation System ◽  
Disease Incidence ◽  
Cropping System ◽  
Bell Pepper ◽  
Phytophthora Blight ◽  
Plastic Mulch ◽  
Initial Inoculum ◽  
No Till

Four mechanisms of dispersal of propagules of Phytophthora capsici were investigated through modifications in cultural practices and fungicide applications in field plots of bell pepper (Capsicum annuum). Dispersal of soil inoculum was suppressed, and final incidence of disease was 2.5 to 43% when stubble from a fall-sown, no-till, wheat cover crop was present. Final disease incidence was 71 to 72% and pathogen spread occurred within and across rows when all dispersal mechanisms were operative in plots of pepper planted into bare soil. Final disease incidence was 42 to 78% with black plastic mulch when a sporulating pepper fruit placed on the surface served as the source of initial inoculum. The fungicide metalaxyl applied in the irrigation system did not suppress within-row spread of surface inoculum from a sporulating fruit on plastic, but did limit across-row spread; final disease incidence in metalaxyl-treated plots was 11.5 to 14%. Pathogen dispersal mechanisms were modified most dramatically by the no-till cropping system. Thus, simple changes in cultural practices can have dramatic effects on the development of Phytophthora epidemics. Ecologically based disease management strategies have the potential to reduce our reliance on agrichemicals in this and similar pathosystems.

scholarly journals Sensitivity of Phytophthora capsici on Vegetable Crops in Georgia to Mandipropamid, Dimethomorph, and Cyazofamid

Plant Disease ◽  
2012 ◽  
Vol 96 (9) ◽  
pp. 1337-1342 ◽  
Author(s):  
K. L. Jackson ◽  
J. Yin ◽  
P. Ji
Keyword(s):  
Disease Management ◽  
Mycelial Growth ◽  
Phytophthora Capsici ◽  
Chemical Compounds ◽  
Bell Pepper ◽  
Vegetable Production ◽  
Vegetable Crops ◽  
Phytophthora Blight ◽  
Significant Component ◽  
Serious Disease

Phytophthora blight, caused by Phytophthora capsici, is a serious disease in vegetable production, and selective use of fungicides continues to be a significant component of disease management programs. The effect of three chemical compounds—mandipropamid, dimethomorph, and cyazofamid—on asexual stages of P. capsici collected from bell pepper and cucurbits in Georgia was assessed in this study. Forty isolates of P. capsici were determined to be sensitive to mandipropamid and dimethomorph based on mycelial growth, zoospore germination, and sporangial production. Concentrations that were 50% effective (EC50 values) of mandipropamid that inhibited mycelial growth, zoospore germination, and sporangial production of the isolates averaged 0.03, 5.70, and 0.02 μg/ml, respectively. EC50 values of dimethomorph in inhibiting mycelial growth, zoospore germination, and sporangial production averaged 0.24, 0.10, and 0.46 μg/ml, respectively. The majority of isolates were either resistant or intermediately sensitive to cyazofamid at 500 μg/ml or lower concentrations based on mycelial growth or sporangial production, although all the isolates were sensitive to this compound based on zoospore germination, with an average EC50 of 0.04 μg/ml. The results indicated that P. capsici populations in Georgia have not developed resistance to mandipropamid and dimethomorph whereas, for the majority of the isolates, certain asexual stages were resistant to cyazofamid.

scholarly journals Performance and Tolerance to Phytophthora Blight of Bell Pepper Varieties

2013 ◽  
Vol 23 (3) ◽  
pp. 382-390 ◽  
Author(s):  
Amara R. Dunn ◽  
Lindsay E. Wyatt ◽  
Michael Mazourek ◽  
Stephen Reiners ◽  
Christine D. Smart
Keyword(s):  
New York ◽  
Phytophthora Capsici ◽  
Fruit Size ◽  
Bell Pepper ◽  
Plant Structure ◽  
Phytophthora Blight ◽  
Marketable Yield ◽  
Breeding Lines ◽  
History Of ◽  
Low Incidence

In 2011, total marketable yield, fruit size, and number of lobes; fruit discoloration due to silvering; and plant structure were compared among eight commercial green bell pepper (Capsicum annuum) varieties and four breeding lines at three field sites in central New York. Tolerance to phytophthora blight (Phytophthora capsici) was also assessed at one of these sites. No wilting or plant death due to phytophthora blight was observed on the four breeding lines. ‘Paladin’, ‘Intruder’, and ‘Aristotle’ had the highest levels of tolerance to phytophthora blight, among the commercial varieties and maintained their yields in the presence of disease. In the absence of phytophthora blight, yields from these three varieties were comparable to susceptible varieties, but fruit tended to be smaller, and incidence of silvering was high in ‘Paladin’ and ‘Intruder’. Less silvering was observed on ‘Aristotle’ fruit. Total marketable yields from the breeding lines and percent of fruit with four lobes was comparable to the commercial varieties, and some breeding lines also had a low incidence of silvering, but fruit were smaller and set later in the season. Overall, this study suggests that ‘Paladin’, ‘Intruder’, and ‘Aristotle’ will yield well in fields with a history of severe phytophthora blight, but new large-fruited varieties with low incidence of silvering and good tolerance to phytophthora blight are needed.

scholarly journals Characterizing Sources of Resistance to Phytophthora Blight of Pepper Caused by Phytophthora capsici in North Carolina

2019 ◽  
Vol 20 (2) ◽  
pp. 112-119
Author(s):  
Camilo H. Parada-Rojas ◽  
Lina M. Quesada-Ocampo
Keyword(s):  
North Carolina ◽  
Phytophthora Capsici ◽  
The United States ◽  
Field Trials ◽  
Fruit Rot ◽  
Phytophthora Blight ◽  
Sources Of Resistance ◽  
Crown Root ◽  
Different Levels ◽  
Important Disease

Phytophthora blight, caused by Phytophthora capsici, is an important disease of peppers in the United States and worldwide. P. capsici causes crown, root, and fruit rot as well as foliar lesions in peppers. Field trials were conducted in 2015 and 2016 to evaluate 32 commercial and experimental pepper cultivars against a mixed-isolate inoculum in North Carolina. Cultivars Martha-R and Meeting were classified as highly resistant to P. capsici, and Paladin was classified as resistant. Intermediate resistance to P. capsici in the field was observed with Fabuloso, Revolution, Vanguard, Archimedes, Aristotle, Ebano-R, and Declaration. Greenhouse experiments were conducted to determine the response of 48 pepper cultivars when inoculated individually with two isolates from North Carolina and an isolate from Michigan. Isolates exhibited different levels of virulence in pepper cultivars screened for resistance. Landraces CM334 and Fidel as well as the cultivars Martha-R, Meeting, and Intruder were categorized as highly resistant or resistant to the three isolates tested. Overall, highly resistant cultivars tended to respond similarly to field mix inoculations and greenhouse single isolate inoculations.

scholarly journals First Report of Blight of Field Peppers Caused by Phytophthora capsici in Ontario

Plant Disease ◽  
2000 ◽  
Vol 84 (6) ◽  
pp. 705-705 ◽  
Author(s):  
T. R. Anderson ◽  
R. Garton
Keyword(s):  
Phytophthora Capsici ◽  
Sweet Pepper ◽  
Fluorescent Light ◽  
Mating Types ◽  
Phytophthora Blight ◽  
Essex County ◽  
First Report ◽  
Diameter Range ◽  
Run Off ◽  
Internal Surfaces

In August 1994, a disease of sweet peppers (Capsicum annuum L.) and butternut squash (Cucurbita pepo L.) was observed in a 2-ha field near Harrow, Essex County, ON, Canada. In 1995, a similar disease was noted on peppers at two locations 30 km apart in Essex County. In 1997, the disease occurred on peppers in a 20-ha field in the vicinity of the 1994 outbreak. Yield loss was estimated at 40 to 60% in pepper fields and 20% in the affected squash field. Brown, necrotic lesions were more prevalent on pepper fruits and upper stems and lateral branches than basal stems. Affected plants occurred in lower areas of fields that had been flooded by rain or irrigation. Gray, floccose masses of sporangia were evident on fruits and stems under humid conditions and on the internal surfaces of infected fruits. Symptoms were similar to those described for Phytophthora blight of pepper (1). Squash infections occurred where fruits contacted soil. Isolations were made from sections of fruit, stems, and leaves of pepper and squash plants with symptoms of disease on lima beans (Difco Laboratories, Detroit) or 20% V8 agar medium and incubated at 22°C. Phytophthora capsici was readily isolated from all plants with disease symptoms. Observations of colony morphology and growth were made on cultures on 20% V8 agar at 25°C under continuous fluorescent light. Sporangia were papillate and averaged 45 ± 5.9 × 27 ± 3.5 μm in size (range 28 to 58 × 21 × 39 μm). Oospores were spherical and 23 ± 2.9 μm in diameter (range 16 to 28 μm) and, when the external wall was included, were 28 ±2.7 μm in diameter (range 23 to 37 μm). Pedicels varied in length, averaging 63 ± 30.9 μm (range 9 to 129 μm). These observations are similar to those described for P. capsici (2). Mating type was determined by coculture with isolates obtained from A. F. Schmitthenner (OARDC, Wooster, OH) designated A1 and A2. Oospore development was determined after 10 days growth at 25°C on 20% V8 agar. Mating types A1 and A2 occurred among Ontario isolates from pepper and squash. In 1995, 13 of 15 isolates tested were A1, and in 1997, 1 of 5 was A1. Both mating types were found in the same field. Pathogenicity of pepper and squash isolates was tested by inoculating greenhouse-grown pepper cvs. Merlin and North Star at the 5-leaf stage by adding 5 ml of a spore suspension (1,000 sporangia per ml) to the crown and adjacent soil or sprayed on the foliage until run off. Plants were covered in plastic bags for 24 h. Wilting and plant death occurred at 4 and 10 days, respectively, with both cultivars. Crown-inoculated plants wilted prior to development of brown lesions on lower stems at the soil line. Symptoms on foliar-inoculated plants were first observed on young tissue at growing points and stem nodes. P. capsici was reisolated from affected tissue. This is the first report of Phytophthora blight of sweet pepper in Ontario. References: (1) L. H. Leonian. Phytopathology 12:401, 1922. (2) P. H. Tsao and A. Alizadeh. 1988. Proceedings of the 10th International Cocoa Research Conference. Santo Domingo, Dominican Republic, pp. 441–445.

scholarly journals Bell Pepper (Capsicum annum L.) Crop as Affected by Shade Level: Fruit Yield, Quality, and Postharvest Attributes, and Incidence of Phytophthora Blight (caused by Phytophthora capsici Leon.)

HortScience ◽  
2014 ◽  
Vol 49 (7) ◽  
pp. 891-900 ◽  
Author(s):  
Juan Carlos Díaz-Pérez
Keyword(s):  
Phytophthora Capsici ◽  
Net Photosynthesis ◽  
Fruit Yield ◽  
Bell Pepper ◽  
Soluble Solids ◽  
Growth And Yield ◽  
Phytophthora Blight ◽  
Ir Radiation ◽  
Capsicum Annum ◽  
Yield Quality

High temperatures can be detrimental to bell pepper, resulting in reduced fruit yield and increased incidences of fruit disorders such as sunscald and blossom-end rot. Shade nets are used to modify the crop microenvironment to improve plant growth and yield. The objectives were to evaluate effects of shade level on fruit yield, quality, and postharvest attributes and the incidence of Phytophthora blight (caused by Phytophthora capsici Leon.) in bell pepper (Capsicum annum L.). Experiments were conducted in Tifton, GA, in 2008 (with cv. Heritage) and 2009 and 2010 (with cvs. Camelot, Lafayette, Sirius, and Stiletto). Bell pepper plants were grown under shade levels of 0% (unshaded, as a control), 30%, 47%, 63%, and 80%. Shade level affected fruit yield, quality, postharvest attributes, and incidence of Phytophthora blight in plants. Total marketable (Fancy and US1) fruit yield increased with increasing shade level to a maximum at 35% shade and then decreased with further increments in shade level. Relative to unshaded plants, marketable yields were improved by 119% (2008) and 43% (2009 and 2010) at 35% shade level. US2 and cull (sunscald) fruit number declined with increasing shade level. ‘Camelot’ produced among the greatest number and yield of marketable fruit; ‘Sirius’ had the heaviest fruit and greatest number of culls. Fruit nitrogen (N), phosphorus (P), and potassium (K) concentrations increased and aluminum (Al), molybdenum (Mo), and nickel (Ni) decreased with increasing shade level. ‘Lafayette’ had the highest fruit concentration of N, calcium (Ca), sulfur (S), manganese (Mn), and zinc (Zn). Fruit soluble solids and percent of fruit dry weight decreased with increasing shade level; fruit water loss rate and bacterial soft rot incidence were unaffected. Fruit skin a* and b* values decreased in yellow fruit cultivars (‘Lafayette’ and ‘Sirius’) with increased shade level. Incidences of Phytophthora blight in plants and fruit sunscald decreased with shade level. Beneficial effects of shading on bell pepper were associated with a reduction in irradiation, air temperature, and soil temperature under shaded conditions resulting in amelioration of heat stress in the plants. Optimal shade level for maximal fruit yield was that which maximized the cooling effect resulting from reduction of infrared (IR) radiation and minimized the decrease in net photosynthesis resulting from reduction in photosynthetically active radiation (PAR).

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