Light is a modulator of plant immune response. Different light qualities evoke photoreceptor-mediated signaling cascade that can modify nuclear gene expression (Delprato et al., 2015). Light influence the establishment of systemic acquired resistance (SAR). Several defense mechanisms such as activation of phenylalanine ammonia-lyase, accumulation of salicylic acid (SA), expression of the pathogenesis-related protein 1 (PR-1) and hypersensitive response (HR) are light dependent (Zeier et al., 2004). In dark or in dim light, SA-induced PR gene expression in response to pathogens and HR are highly reduced (Genoud et al., 2002). Light sensing and light acclimatory processes govern pathogen defense pathways (Karpinski et al., 2003). The rose plant exposed to continuous light significantly reduced conidial production and germinability as well as severity of disease caused by Podosphaera pannosa the causal agent of powdery mildew (Suthaparan et al., 2010a). Accumulation of jasmonic acid, production of phytoalexin camalexin and transcriptional induction of pathogen-inducible myrosinase were noticeable in dark (Zeier et al., 2004).
Perception of light signal by different photoreceptor is an important event of light sensory mechanism. The regulation of plant growth by light signal involves three main families of photoreceptors, the phytochromes, cryptochromes and phototropins, that are known as the red (R) and far red (FR) light absorbing phytochromes and the ultraviolet-A (UV-A)/blue light-absorbing cryptochromes and phototropins (Schafer and Nagy 2006). Inactivation of photoreceptor phytochrome B (phyB) by a low red/far-red ratio (R:FR) increased Arabidopsis plant susceptibility to necrotrophic fungus Botrytis cinerea (Cerrudo et al., 2012). Plant may integrate light and jasmonate signals to modify their growth and development while defending themselves from pathogen and pest attack (Kazan and Manners 2011). The induction of PR-1 by SA is controlled by both phyA and phyB photoreceptor (Genoud et al., 2002). Arabidopsis plant defense response against bacterial pathogen Pseudomonas syringae depends on time of the day and availability of prolonged light period. Phytochrome regulates SAR than local defense (Griebel and Zeier 2008). Light is essential for rice defense response resulting in HR and accumulation of peroxidase and lignin-like compound (Guo et al., 1993). Exposure to red light during dark interval may be as effective as continuous illumination in suppressing powdery mildew in rose plant (Suthaparan et al., 2010b).
Buck et al.(2010) suggests urediniospore when exposed to strong light could inactivate rust fungi on plant surface or in atmosphere. The release and dissemination of pathogens spores is an important aspect of disease spread. Pathogens spores are dispersed as airborne spores. The fungal airborne spores were more abundant at night than during the day, associated with conducive environmental condition for germination and plant infection (Gilbert and Reynolds 2005). The movement of fungal plant pathogens in the atmosphere is characterized by liberation, drift and deposition. Deposition of spores of Giberella zea at night is a strategy for Fusarium head blight of wheat (Schmale III et al., 2006). Both infrared and shorter red wavelength stimulated spore release (Leach 1975).
Light may suppress Pseudomonas syringae pv. tabaci a hemibiotrophic bacterial pathogen in tobacco leaves through accumulation of hydrogen peroxide (H2O2) during infection (Cheng et al., 2016). All fungi that are photoresponsive seem to be sensitive to light at the blue/ near UV-A range (Fuller et al., 2015). The red, blue and green wavelength of light can induce disease resistance in plants against many phytopathogens (Assefa and Gobena 2019). Green light suppresses mycelial growth and conidial germination of Botrytis cinerea (Zhu et al., 2013).
The ultraviolet-B (UV-B) component of solar radiation plays a role in natural regulation of blister blight disease in the field (Gunasekera et al., 2003). Sporulation of pathogen Bremia lactucae causing lettuce downy mildew was significantly reduced when conidial suspension was exposed to UV-B prior to inoculation (Wargent et al., 2006). UV radiation can induce expression of plant genes required for pathogen resistance. UV-induced DNA damage promotes resistance to Hyaloperonospora parasitica a biotrophic pathogen in Arabidopsis plants normally susceptible to the pathogen (Kunz et al., 2008). The UV activate transcription gene for defense including pathogenesis-related protein chitinase, b-1,3-glucanase, phenylalanine ammonia-lyase and stilbene synthase (El Ghaouth et al., 2003; Bonomelli et al., 2004). Plants have acquired diverse capability to sense and defend themselves from pathogens.
References:
Assefa, A. and Gobena, A. 2019 Review on Effect of Light on Disease Development and Management of Horticultural Crops under Protected Cultivations. Int. J. Forestry and Horti. (IJFH) 5(3): 5 – 18
doi.org/10.20431/2454-9487.0503002
Bonomelli, A., Mercier, L., Franchel, J., Baillieul, F. F., Benizri, E. and Mauro, M-C. 2004 Response of Grapevine Defenses to UV-C Exposure. Am. J. Enol. and Vitic. 55(1): 51 – 59
doi: 10.5344/ajev.2004.55.1.51
Buck, J. W., Dong, W. and Mueller, D. 2010 Effect of Light Exposure on In Vitro Germination and Germ Tube Growth of Eight Species of Rust Fungi. Mycologia.102(5): 1134 – 1140
doi: 10.3852/09-283
Cerrudo, I., Keller, M. M., Cargnel, M. D., Demkura, P. V., de Wit, M., Patitucci, M. S., Pierik, R., Pieterse, C. M. J. and Ballare, C. L. 2012 low Red/Far-red Ratio Reduce Arabidopsis Resistance to Botrytis cinerea and Jasmonate Responses Viaa COI1-JAZ10-dependent Salicylic Acid-Independent Mechanism. Plant Physiol. 158(4): 2042 – 2052
doi: 10.1104/pp.112.193359
Cheng, D-D., Liu, M-J., Sun, X-B., Zhao, M., Chow, W. S., Sun, G-Y., Zhang, Z-S. and Hu, Y-B. 2016 Light Suppressed Bacterial Population through the Accumulation of Hydrogen Peroxide in Tobacco Leaves Infected with Pseudomonas syringae pv. tabaci. Front. Plant Sci. 7: 512
doi: 10.3389/fpls.2016.00512
Delprato, M. L., Krapp, A. R. and Carrillo, N. 2015 Green Light to Plant Responses to Pathogens: The Role of Chloroplast Light-Dependent Signaling in Biotic Stress. Photochem. Photobiol. 91(5): 1004 – 1011
doi.org/10.1111/php.12466
El Ghaouth, A., Wilson, C. L. and Callahan, A. M. 2003 Induction of Chitinase Beta-1,3-Glucanase and Phenylalanine Ammonia Lyase in Peach Fruit by UV-C Treatment. Phytopathol. 93(3): 349 – 355
doi: 10.1094/PHYTO.2003.93.3.349
Fuller, K. K., Loros, J. J. and Dunlap, J. C. 2015 Fungal Photobiology: Visible Light as a Signal for Stress and Time. Curr. Genet. 61(3): 275 – 288
doi: 10.1007/s00294-014-0451-0
Genoud, T., Buchala, A. J., Chua, N-H. and Metraux, J-P. 2002 Phytochrome Signaling Modulates the SA-Perceptive Pathway in Arabidopsis. Plant J. 31(1): 87 – 95
doi: 10.1046/j.1365-313x.2002.01338.x
Gilbert, G. S. and Reynolds, D. R. 2005 Nocturnal Fungi: Airborne Spores in the Canopy and Understorey of a Tropical Rain Forest. Bio Tropica 37(3): 462 – 464
doi.org/10.1111/j.1744-7429.2005.00061.x
Griebel, T. and Zeier, J. 2008 Light Regulation and Daytime Dependency of Inducible Plant Defenses in Arabidopsis: Phytochrome Signaling Controls Systemic Acquired Resistance Rather than Local Defense. Plant Physiol. 147(2): 790 – 801
doi: 10.1104/pp.108.119503
Gunasekera, T. S., Paul, N. D. and Ayres, P. G. 2003 The Effects of Ultraviolet-B (UV-B: 290 – 320 nm) Radiation on Blister Blight Disease of Tea (Camellia sinensis). Plant Pathol. 46(2): 179 – 185
doi.org/10.1046/j.1365-3059.1997.d01-216.x
Guo, A., Reimers, P. J. and Leach, J. E. 1993 Effect of Light on Incompatible Interactions between Xanthomonas oryzae pv oryzae and Rice. Physiol. Mol. Plant Pathol. 42(6): 413 – 425
doi.org/10.1006/pmpp.1993.1031
Karpinski, S., Gabrys, H., Mateo, A., Karpinska, B. and Mullineaux, P. M. 2003 Light Perception in Plant Disease Defense Signaling. Curr. Opin. Plant Biol. 6(4): 390 – 396
doi.org/S1369-5266(03)00061-X
Kazan, K. and Manners, J. M. 2011 The Interplay between Light and Jasmonate Signaling during Defense and Development. J. Exp. Bot. 62(12): 4087 – 4100
doi: 10.1093/jxb/err142
Kunz, B. A., Dando, P. K., Grice, D. M., Mohr, P. G., Schenk, P. M. and Cahill, D. M. 2008 UV-Induced DNA Damage Promotes Resistance to the Biotrophic Pathogen Hyaloperonospora parasitica in Arabidopsis. Plant Physiol. 148(2): 1021 – 1031
doi: 10.1104/pp.108.125435
Leach, C. M. 1975 Influence of Relative Humidity and Red-Infrared Radiation on Violent Spore Release by Drechslera turcica and Other Fungi. Phytopathol. 65(11): 1303 – 1312
doi: 10.1094/Phyto-65-1303
Schafer, E. and Nagy, F. 2006 Photomorphogenesis in Plants and Bacteria. Function and Signal Transduction Mechanisms. 3rd Edition. Springer, Dordrecht. The Netherlands. 662
Schmale III, D. G., Bergstrom, G. C. and Shields, E. J. 2006 Night-time Spore Deposition of the Fusarium Head Blight Pathogens Giberella zeae in Rotational Wheat Fields. Can. J. Plant Pathol. 28(1): 100 – 108
doi.org/10.1080/07060660609507276
Suthaparan, A., Stensvand, A., Torre, S., Herrero, M. L., Pettersen, R. I., Gadoury, D. M. and Gislerod, H. R. 2010a Continuous Lighting Reduces Conidial Production and Germinability in the Rose Powdery Mildew Pathosystem. Plant Dis. 94(3): 339 – 344
doi: 10.1094/PDIS-94-3-0339
Suthaparan, A., Torre, S., Stensvand, A., Herrero, M. L., Pettersen, R. I., Gadoury, D. M. and Gislerod, H. R. 2010b Specific Light Emitting Diodes can Suppress Sporulation of Podosphaera pannosa on Greenhouse Roses. Plant Dis. 94(9): 1105 – 1110
doi: 10.1094/PDIS-94-9-1105
Wargent, J. J., Taylor, A. and Paul, N. D. 2006 UV Supplementation for Growth Regulation and Disease Control. Acta Hortic. 711: 333 – 338
doi: 10.17660/ActaHortic.2006.711.45
Zeier, J., Pink, B., Mueller, M. J. and Berger, S. 2004 Light Conditions Influence Specific Defense Responses in Incompatible Plant-Pathogen Interactions: Uncoupling Systemic Resistance from Salicylic Acid and PR-1 Accumulation. Planta 219(4): 673 – 683
doi: 10.1007/s00425-004-1272-z
Zhu, P., Zhang, C., Xiao, H., Wang, Y., Toy, H. and Xu, L. 2013 Exploitable Regulatory Effects of Light on Growth and Development of Botrytis cinerea. J. Plant Pathol. 95(3): 509 – 517
doi: 10.4454/JPP.V9513.038
BIOLOGICAL PROCESSES- A NATURE'S GIFT 