Aruppillai Suthaparan was born in Sri Lanka, and received his PhD in plant pathology in 2010 from the Norwegian University of Life Sciences (NMBU) where he is currently a research scientist. He is nominated for the William Boright Hewitt and Maybelle Ellen Ball Hewitt Award specifically for his pioneering research on the use of UV and visible light to suppress powdery mildews. Members of the Erysiphaceae are among the most widespread and destructive fungal pathogens of plants. Their capacity to cause loss and adapt to various fungicide classes makes them especially difficult to control when crops are produced in controlled environments such as greenhouses and high tunnel systems. Powdery mildews have evolved to sense, interpret, and use light to direct their development. Dr. Suthaparan’s work has revealed how we can use the evolved relationships between these pathogens and light to their detriment and to the advantage of crop producers.
Powdery mildew mycelia are hyaline, and devoid of common phenolic pigments thought to provide protection from UV light. With the exception of absorptive haustoria in host epidermal cells, powdery mildews are wholly external to the host, and occupy a niche that makes them among the most exposed of plant pathogens, in particular to UV light. Despite a lack of physical defenses against UV, such as pigmentation, powdery mildews thrive in this niche. They do so because DNA damaged by UV undergoes immediate photoreactivation and repair by light-driven photolyases (Beggs, 2002. Photochem. Photobiol. Sci.; Essen and Klar, 2006. Cell. Mol. Life Sci.). Work by Suthaparan provided a novel means to suppress diverse powdery mildews of rose, cucumber, tomato, strawberry, grape, rosemary and aster with supplemental UV light (Plant Dis. 96:1653-1660) through a practical demonstration of its enhanced efficacy when applied during night hours (116-P, 2012 APS Annual Meeting; Plant Dis. 98:1349-1357), thereby circumventing photoreactivation. This discovery not only enhanced the efficacy of UV treatments in suppression of diverse powdery mildews, it allowed the use of a lower UV dose that reduced the risk of UV-induced phytotoxicity to the host. Parallel work by Wojciech et al. not only confirmed the enhanced efficacy of nighttime UV treatments against Podosphaera aphanis (2016. Can. J. Plant Pathol. 38:430-439), but expanded the demonstrated efficacy to include Botrytis cinerea, and additive benefits when coupled with post-UV-applied biocontrol agents (2016. Phytopathology 106:386-394).
Dr. Suthaparan’s subsequent work elucidated the photobiochemical and genetic underpinnings of how powdery mildews survive in a daytime environment bathed in UV light. Both blue light and UVA decreased the efficacy of a given dose of UV, presumably because they upregulate the systems that repair UV damage to pathogen DNA. Red light, which itself had been shown to suppress conidiation, was synergistically effective in enhancing the suppression of powdery mildew by UV when applied after UV treatments during nighttime hours (Plant Dis. 98:1349-1357). Thus, the background radiation associated with UV exposure had the potential to either augment or reduce the efficacy of the UV treatment upon disease suppression. He compared the action spectra across the range of the UVC and UVB to UVA (250 to 400 nm) to identify wavelengths within this range that are uniquely suited to the purpose of suppressing growth of powdery mildews while minimizing damage to the host due to phytotoxicity. While wavelengths from 250 nm to 280 nm exhibited similar efficacy against tomato powdery mildew (Oidium neolycopersici), use of a near-monochromatic source producing a peak at 280 nm exhibited the greatest dose differential between fungitoxicity and phytotoxicity (J. Photochem. Phytobiol. B. 156:41-49). This finding provided valuable target parameters for light emitting diode manufacturers seeking to produce LED products that optimize this technology for crop production. Dr. Suthaparan’s 2017 publication relating optimal UV dose to the prior daily light integral (J. Photochem. Photobiol B. 175:141-148) provided the theoretical as well as practical basis to match UV dose in both field and controlled environments based upon preconditioning of light-mediated DNA repair. The 2018 publication explained the potential lighting strategy, with the possibility of extending the day length by selection and combination of right wavelengths within the optical radiation range for the best disease suppressive effect (J. Photochem. Photobiol. B. 178:631-640. His work has further expanded into the areas of photoreceptor genes involved in light-mediated DNA repair (116-P, 2012 APS Annual Meeting and 143-P, 2017 APS Annual Meeting), as well as ovicidal effects of nighttime applications of UV against eggs of phytophageous mites (299-P, 2017 APS Annual Meeting; Gartneryket 114:44-45).
Dr. Suthaparan’s work is the nucleus around which has formed an international collaborative effort involving NMBU, the Norwegian Institute of Bioeconomy Research (NIBIO), Cornell University, University of Florida, USDA-ARS, and the Lighting Research Center at Rensselaer Polytechnic Institute (http://www.lightandplanthealth.org). Dr. Suthaparan is a leading member of a transdisciplinary team that is now applying the work across a broad range of crops and growing environments, with support of grants from the National Research Council of Norway, two USDA-SCRI grants (2014-51181-22381and 2014-511181-22377), and a grant from the USDA Organic Research and Extension Initiative (2015-51300-24135). This level of support from funding agencies on two continents (see Suthaparan’s CV), spanning the range from highly applied to fundamental, is a good indication of the high regard in which this work is held, and the perceived potential of his findings to lead to entirely new approaches to the suppression of plant diseases through the manipulation of their natural relationships and responses to light. Aspects of his work are foundational to the thesis projects of four current PhD students in the US and Norway. His work was featured in seven oral and poster presentations (see Suthaparan CV; 13-0,142-P, 143-P, 147-P, 152-P, 297-P, 297-P, 299-P), as well as an Idea Café (Why Light Matters – Anticipated and unanticipated effects of light of plant pathogens) at the 2017 APS Annual Meeting in San Antonio, and was the inspiration for the 2018 ICPP concurrent session “Why Light Matters: New Concepts, Tools, and Practices and Enhanced Plant Health”.
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