Environmental light may regulate plant resistance, providing protection to the plant against the invading pathogen. The spectrum of light varies, underground and under the canopy of foliage. Light has properties of waves and particles and can induce deoxyribonucleic acid (DNA) damage and plant stress response. Excess and fluctuating light results in reactive oxygen species (ROS) accumulation (Wang et al., 2021). Photo-produced hydrogen per oxide and other ROS play a regulatory role in biotic and abiotic stress (Karpinski et al., 2003). The light signals are perceived and transduced into cellular responses by photoreceptor phototropins and cryptochromes, that absorbs ultraviolet-A (UV-A) or blue light and the phytochrome sense red/far-red light (Gyula et al., 2003). UV-B activates signal transduction pathway, salicylic acid (SA) leads to the expression of pathogenesis related (PR) proteins, exhibiting systemic acquired resistance in response to pathogen infection in tobacco leaves (Fujibe et al., 2000). The phytochrome (phy) (phyA and phyB) control the signaling pathway that interact with SA-mediated pathway leading to expression of PR-1 protein in response to pathogen attack (Genoud et al., 2002).
The pathogen living under the canopy, is confronted with an altered light spectrum of green and far-red light. Grey mold fungus Botrytis cinerea infects above ground parts of the plant. The (near)- UV, blue, green, red and far-red light affects its growth. The conidia of this necrotrophic phytopathogen are formed in light and sclerotia in constant darkness (Schumacher 2017). Green light suppresses conidial germination and mycelial growth rate of B. cinerea (Zhu et al., 2013). Blue light arrest spore formation in B. cinerea and then causes de-differentiation of conidiophore to sterile mycelia (Tan 1974). Far-red light re-promotes sporulation in B. cinerea as does near-UV and this effect of far-red is reversed by exposure to red or blue light (Tan 1975). Photoreceptors trigger different signal transduction cascades. Near-UV radiation and blue light (300 to 520 nm) induce negative phototropism of germ tube of B. cinerea but promoted infection-hypha formation on both onion scale and broad bean(Vicia faba) leaf epidermal strips, whereas positive phototropism-inducing red light (600 to 700 nm) suppressed infection hyphae (Islam et al., 1998). The inhibition of infection-hypha formation under red light suggests that red-light induced resistance of broad bean against B. cinerea (Islam et al., 1998).
The supplemental UV radiation prevents rose powdery mildew disease through activation of plant defense and direct suppression (Kobayashi et al., 2013). UV-B suppressed cucumber powdery mildew. The effect of UV-B was directly on pathogen causing powdery mildew rather than induced resistance of host (Suthaparan et al., 2014). In Alternaria alternata, blue light inhibits sporulation and red light reverses the effect. Indicating germination, sporulation and secondary metabolism are light regulated in A. alternata (Igbalajobi et al., 2019). Similarly, the near-UV radiation induced negative phototropism of Colletotrichum lagenarium, promote appressorium formation, while red light induced positive phototropism and suppressed it. The negative phototropism of germ tubes of C. lagenarium favors infection process by facilitating the contact tips of germ tubes with the host surface, while positive phototropism has the opposite effect (Islam and Honda1996).
The UV part of electromagnetic spectrum are UV-A (315 – 400 nm), UV-B (280-315) and UV-C (200-280nm). UV-C can trigger and regulate signaling pathways independent from its effect on the production of ROS (Urban et al., 2016). Epiphytic bacteria are affected by UV-C radiation as compared to endophytic bacteria because of poor penetration of UV-C in plant tissue (Vanhaelewyn et al., 2020). A high level of ROS generation is observed upon UV-B radiation (Rastogi et al., 2010). The spore exposed to solar radiation, it is the UV-B component that causes formation of cyclobutene pyrimidine dimers, whereas, the UV-A causes single and double strand breaks (Slieman and Nicholson 2000). UV-B and UV-C exposure may kill microorganisms (Vanhaelewyn et al., 2020).
Conidial production, survival, dispersal, germination, pathogenicity and virulence are affected by solar radiation. Conidia are killed by both UV-A and UV-B radiation. The exposure to sublethal doses of UV radiation may reduce conidial germination and virulence (Braga et al., 2015). The conidial germination and mycelial growth of Uncinula necator causing grape powdery mildew was reduced when exposed to UV-B radiation (Willocquet et al., 1996). UV-B radiation can suppress the urediospore germination of Puccinia striiformis f. sp. tritici (Pst) and the tolerance to UV-B radiation among the three Pst races were different (Cheng et al., 2014). UV-B radiation significantly reduced the radial growth of the fungus Alternaria solani. Suggesting that UV-B radiation reaching the earth surface may have adverse effect on the growth of this highly virulent fungus (Fourtouni et al., 2011). Light mediated plant resistance may control plant disease.
References:
Braga, G. U. L., Rangel., D. E. N., Fernandes, E. K. K. and Flint, S. D. 2015 Molecular and Physiological Effects of Environmental UV Radiation on Fungal Conidia. Curr. Genet. 61(3): 405 – 425
doi: 10.1007/s00294-015-0483-0
Cheng, P., Ma, Z., Wang, X., Wang, C., Li, Y., Wang, S. and Wang, H. 2014 Impact of UV-B Radiation on Aspects of Germination and Epidemiological Components of Three Major Physiological Races of Puccinia striiformis f. sp. tritici. Crop Protection 65: 6 – 14
doi.org/10.1016/j.cropro.2014.07.002
Fourtouni, A., Manetas, Y. and Christias, C. 2011 Effects of UV-B Radiation on Growth, Pigmentation and Spore Production in the Phytopathogenic Fungus Alternaria solani. Can. J. Bot. 76(12): 2093 – 2099
doi: 10.1139/b98-170
Fujibe, T., Watanabe, K., Nakajima, N., Ohashi, Y., Mitsuhara, I., Yamamoto, K. T. and Takeuchi, Y. 2000 Accumulation of Pathogenesis-Related Proteins in Tobacco Leaves Irradiated with UV-B. J. Plant Res. 113: 387 – 394
doi.org/10.1007/PL00013946
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
Gyula, P., Schafer, E. and Nagy, F. 2003 Light Perception and Signaling in Higher Plants. Curr. Opin. Plant Biol. 6(5): 446 – 452
doi: 10.1016/s1369-5266(03)00082-7
Igbalajobi, O., Yu, Z. and Fischer, R. 2019 Red- and Blue Light Sensing in the Plant Pathogen Alternaria alternata Depends on Phytochrome and the White-Collar Protein LreA. mBio. 10(2): e00371 – 19
doi: 10.1128/mBio.00371-19
Islam, S. Z. and Honda, Y. 1996 Influence of Phototropic Response of Spore Germ Tubes on Infection Process in Colletotrichum lagenarium and Bipolaris oryzae. Mycoscience 37: 331 – 337
doi.org/10.1007/BF02461305
Islam, S. Z., Honda, Y. and Sonhaji, M. 1998 Phototropism of Conidial Germ Tubes of Botrytis cinerea and its Implication in Plant Infection Processes. Plant Disease 82(8): 850 – 856
doi.org/10.1094/PDIS.1998.82.8.850
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: 10.1016/s1369-5266(03)00061-x
Kobayashi, M., Kanto, T., Fujikawa, T., Yamada, M., Ishiwata, M., Satou, M. and Hisamatsu, T. 2013 Supplemental UV Radiation Controls Rose Powdery Mildew Disease Under Greenhouse Conditions. Environ. Control. Biol. 51(4): 157 – 163
doi: 10.2525/ecb.51.157
Rastogi, R. P., Singh, S. P., Hader, D-P. and Sinha, R. P. 2010 Detection of Reactive Oxygen Species (ROS) by the Oxidant-Sensing Probe 2’,7’-dichlorodihydroflurescein Diacetate in the Cyanobacterium Anabaena variabilis PCC 7937. Biochem. Biophys. Res. Commun. 397(3): 603 – 607
doi: 10.1016/j.bbrc.2010.06.006
Schumacher, J. 2017 How Light Affects the Life of Botrytis. Fungal Gen. Biol. 106: 26 – 41
doi.org/10.1016/j.fgb.2017.06.002
Slieman, T. A. and Nicholson, W. L. 2000 Artificial and Solar UV Radiation Induces Strand Breaks and Cyclobutane Pyrimidine Dimers in Bacillus subtilis Spore DNA. Appl. Environ. Microbiol. 66(1): 199 – 205
doi: 10.1128/aem.66.1.199-205.2000
Suthaparan, A., Stensvand, A., Solhaug, K. A., Torre, S., Telfer, K. H., Ruud, A. K., Mortensen, L. M., Gadoury, D. M., Seem, R. C. and Gislerod, H. R. 2014 Suppression of Cucumber Powdery Mildew by Supplemental UV-B Radiation in Greenhouses can be Augmented or Reduced by Background Radiation Quality. Plant Dis. 98(10): 1349 – 1357
doi: 10.1094/PDIS-03-13-0222-RE
Tan, K. K. 1974 Blue-Light Inhibition of Sporulation in Botrytis cinerea. J. Gen. Microbiol. 82(1): 191 – 200
doi.org/10.1099/00221287-82-1-191
Tan, K. K. 1975 Interaction of Near-Ultraviolet, Blue, Red and Far-Red Light in Sporulation of Botrytis cinerea. Transaction of British Mycological Society 64(2): 215 – 222
doi.org/10.1016/S0007-1536(75)80105-7
Urban, L., Charles, F., de Miranda, M. R. A. and Aarrouf, J. 2016 Understanding the Physiological Effects of UV-C Light and Exploiting its Agronomic Potential before and After Harvest. Plant Physiol. Biochem. 105: 1 – 11
doi: 10.1016/j.plaphy.2016.04.004
Vanhaelewyn, L., Van der Straeten, D., de Coninck, B. and Vandenbussche, F. 2020 Ultraviolet Radiation from a Plant Perspective: The Plant-Microorganism Context. Front Plant Sci. 11: 597642
doi: 10.3389/fpls.2020.597642
Wang, D., Dawadi, B., Qu, J. and Ye, J. 2021 Light-Engineering Technology for Enhancing Plant Disease Resistance. Front Plant Sci. 12: 805614
doi: 10.3389/fpls.2021.805614
Willocquet, L., Colombet, D., Rougier, M., Fargues, J. and Clerjeau, M. 1996 Effect of Radiation Especially Ultraviolet B on Conidial Germination and Mycelial Growth of Grape Powdery Mildew. Eur. J. Plant Pathol. 102: 441 – 449
doi.org/10.1007/BF01877138
Zhu, P., Zhang, C., Xiao, H., Wang, Y., Toyoda, H. and Xu, L. 2013 Exploitable Regulatory Effects of Light on Growth and Development of Botrytis cinerea. J Plant Pathology 95(3): 509 – 517
doi: 10.4454/JPP.V9513.038
BIOLOGICAL PROCESSES- A NATURE'S GIFT 