Krishna Subbarao grew up near Mysore, India, and received his B.S. and M.S. from the University of Mysore. He received his Ph.D. from Louisiana State University (LSU) in 1989. After two postdoctoral fellowships at LSU on soybean stem canker and UC Berkeley on fig diseases, he began his career at UC Davis where he is a professor in plant pathology.
Subbarao's seminal research contributions focus on soilborne fungal diseases affecting lettuce and other cool-season vegetable crops. Subbarao has pursued both field and lab-based inquiries to untangle complex disease problems. His research is highly inter-disciplinary and covers diverse areas including epidemiology, cultural and biological strategies for IPM, population genetics, ecology, evolution and systematics, molecular diagnosis, characterization of host resistance mechanisms, fungal genomics, and microbiome studies. He has developed environment-friendly and economical alternatives to soil fumigation in protecting cool-season vegetable crops. Subbarao is a previous recipient of the APS Syngenta Award in 2004 and Fellow in 2010. Since becoming APS Fellow, Subbarao has continued to make original contributions to plant pathology that have changed or continue to change the direction of research in plant pathology.
His recent research has provided crucial novel insights into the biology and management of Verticillium and Sclerotinia pathogens. He elucidated the likely origins, mode of movement, global diversity of Verticillium spp., pathogen genomics, and the nature and potential functions of microbiomes associated with Verticillium wilt. This research was compelled by the sudden emergence of Verticillium wilt of lettuce, not known to be a host until 1995. His work presented convincing evidence that V. dahliae strains pathogenic to lettuce were introduced into the production system via infested spinach seeds. Spinach was planted at increasing densities and acreage to satisfy the growing demand for baby spinach in ready-to-eat-salad mixes but the seed is produced in northern Europe and Washington State. This is a prime example of how insufficiently sanitized seeds can cause the stealthy but rapid emergence of new and destructive plant diseases. Analysis of the population structure of V. dahliae on a global scale indicated that V. dahliae is highly clonal, consisting of at least seven major lineages that are not linked to host or geography. Prevention of pathogen movement is thus essential for Verticillium wilt management. The data also showed that the potential origin of V. dahliae as a pathogen might lie in northern Europe. In addition, other Verticillium species are also carried by spinach seed and infect various crops. In a landmark study, Subbarao clarified the phylogenetic relationships and taxonomy of the genus Verticillium and described five new species. His study on the origin of V. longisporum, a diploid hybrid with a unique host range within Verticillium, is another seminal paper. The status of V. longisporum as a separate species was highly controversial. While confirming the separate species hypothesis, his group further showed that V. longisporum evolved at least three different times from four different lineages representing three distinct species. Such evolutionary scenarios involving multiple hybridizations are well documented for plants, but are rare for fungi.
Subbarao led the development of the online platform, VertShield, built to share data and diagnostic tools so that others around the world can reliably identify Verticillium pathogens and monitor their movement. Subbarao was also a co-leader in sequencing the first Verticillium genomes, which facilitated subsequent studies on genome evolution and pathogenicity mechanisms.
Subbarao is also an IPM pioneer. His previously developed broccoli residue amendment technique has now been widely adapted for Verticillium wilt management, in large part due to the phase out of methyl bromide. To elucidate the mechanism underpinning broccoli-mediated disease suppression, Subbarao analyzed soil microbiomes via sequencing. Results showed that soil bacteria related to known antagonists of fungal pathogens are more abundant in amended soils, suggesting that microbes play a key role in reducing Verticillium wilt severity in broccoli amended soils. This discovery also suggests that microbiome manipulation via other means may offer alternative control options and that many potential biocontrol agents await discovery.
Subbarao's contributions to the literature on Sclerotinia species are unique and numerous but the study of the mating type locus of S. sclerotiorum, a pathogen with a wide host range, stands out. His group demonstrated that parts of the mating type locus MAT in S. sclerotiorum was inverted in exactly half of all sexual progeny, independent of whether the inversion was present in the parent. This novel and original discovery indicates that mating type switching in filamentous ascomycetes may underlie this process.
Another profound contribution to advancing the quality of community research has been made through his excellent service as editor-in-chief (EIC) for Phytopathology from 2015 until 2017. He assumed this position when the publication landscape was undergoing enormous changes with competition to society-based journals coming from a multitude of open-access journals, and declining submissions in Phytopathology as a result. As EIC, he launched a series of new initiatives that have brought renewed vitality and visibility to the journal. The publication of monthly review articles has increased the impact of the journal. He also began the annual publication of themed Focus Issues on contemporary hot topics. Three of these published issues have become highly popular sources of significant, novel information. He encouraged submissions of articles in new areas such as the social, economic and political aspects to provide a comprehensive understanding of the impact of plant diseases. His customer-friendly initiatives have also significantly improved author experience, which have been replicated in other APS journals. These initiatives have not only raised the journal profile but have also resulted in manuscript submissions exceeding 400 annually for the first time in over 25 years. During his tenure, Phytopathology also for the first time obtained an impact factor >3 and is now solidly ranked in the top quartile of plant sciences journals. Subbarao’s scholarly accomplishments and his leadership as EIC will leave a lasting legacy on the field of plant pathology and the flagship journal of APS.
