Peter Ojiambo was born and raised in Kenya. He earned a BS degree with first-class honors in 1994 and an MS degree in 1997 from the University of Nairobi. He received his PhD from the University of Georgia in 2004. In his doctoral thesis, he integrated ecological, mathematical, and statistical approaches to address the epidemiology of Septoria leaf spot of blueberry. In 2006, Ojiambo was hired as a post-doctoral fellow at the International Institute for Tropical Agriculture in Ibadan, Nigeria. His post-doctoral work resulted in 15 publications on the biology, epidemiology, and management of diseases of banana, maize, and soybean. In 2008, he was appointed assistant professor at North Carolina State University (NCSU), and he was promoted to associate professor in 2014. During this period, he held leadership roles in various capacities. He is currently the chair of graduate admissions for plant pathology at NCSU and also serves as the executive board member for the university's Center for Integrated Fungal Research. In addition, he serves on the advisory council for the USDA IPM Center (Southern Region) and is director of the Cucurbit Downy Mildew (CDM) IPM–PIPE project, a national effort of extension specialists in 24 states in the eastern United States.
Since 2008, Ojiambo's work has contributed significantly to our understanding of the epidemiology, population biology, and management of CDM, caused by Pseudoperonospora cubensis. Through his leadership of the CDM IPM–PIPE project, he coordinated the efforts of extension specialists to provide web-based advisories on the risk of disease outbreaks that would initiate fungicide applications. Growers can receive near real-time information on the risk of disease outbreak by email and text messages, and about 400 unique users have subscribed to this service. This decision-support system is widely recognized by growers and industry alike, and it is estimated to save about $11 million annually from reduced fungicide spraying. The success of the CDM IPM–PIPE project has been a model for similar initiatives, such as the USAblight project. Together with his graduate students and post-doctoral associates, Ojiambo has systematically improved the forecasting of CDM by incorporating aspects of pathogen survival during aerial dispersal with analytically tractable dispersion models. He was the first to show that disease severity at source fields should be considered in dispersion models to accurately predict the risk of outbreak. This finding was significant, because regional aerobiological models for plant pathogens are highly dependent on knowledge of spore escape from infected canopies. In addition, quantifying spore loads at the source is laborious, and Ojiambo's models provided an accurate assessment of spore availability based on disease severity. He also developed models to estimate the risk for CDM based on forecasted temperature and wetness duration and coupled them with spore dispersion models, making it possible to map at-risk areas and provide the information needed about when to apply the first fungicide spray.
Epidemiologists strive to understand spatial and temporal dynamics of epidemics using theoretical and empirical modeling frameworks with the objective of making theories operational by the simple specification of generated models. Ojiambo has been able to develop models within such a framework to advance our understanding of CDM dynamics in space and time in two ways. First, he applied the theory of spatial random effects within an uncertainty framework to estimate the risk of disease outbreak over a large geographical scale and for the first time, provided a measure of uncertainty in the risk of CDM outbreaks in the United States. This methodology ensures that risk estimates are unbiased due to inadequate control of factors that are spatially correlated with disease outbreaks. Second, his lab was the first of two labs to independently apply point pattern analysis in botanical epidemiology to analyze the spatial distribution of infected plants over a large geographical scale. He showed that infected plants in affected fields remained infectious for a long time and that a significant increase in disease control at the landscape level would be required to substantially reduce new outbreaks. Recently, Ojiambo provided empirical evidence that the spread parameter of the power law model for dispersal gradients may not be stable over multiple epidemics, as previously thought. Rather, the parameter value of 2 reported in the literature should be considered the lower limit of the rate of distance traveled by epidemic wave fronts that follow a power law dispersal function.
Ojiambo and his collaborators recently provided insights into the potential causes of the resurgence of CDM in the United States. Their findings showed that both mating types of P. cubensis are present in the United States, and they reported for the first time the occurrence of new pathotypes in the country. In addition, pathotype 3 isolates, which are of the A1 mating type, were found to be associated with one of the two lineages of P. cubensis that was specialized on Cucumis species. A novel component of Ojiambo's work is merging epidemiology and pathogen population genomics to better understand the genetic mechanisms and evolutionary processes that have driven the emergence and re-emergence of CDM. For example, his most recent work examines the evolution of P. cubensis pathotypes on evolutionary and epidemiological time scales. This is one of the first studies to show how population genomics can be used to elucidate the relative contributions of inter- and intra-specific processes, such as hybridization, genetic exchange, and selection in the evolution of host specificity.
Ojiambo's program is well grounded by an enviable record of publications not only on CDM but also on other pathosystems. During the past 10 years, Ojiambo has authored 55 refereed papers, three book chapters, and several abstracts and conference proceedings. In addition, he has presented 13 invited international talks and several national talks. Ojiambo has mentored 10 graduate students, three post-docs, and four visiting scientists, and he currently mentors four PhD students. He has served as section chair on the Annual Meetings Board of The American Phytopathological Society (APS), as a member of the APS Journal Strategy Task Force, and as vice-chair and chair of the APS Epidemiology Committee. He currently serves as an editor for Plant Pathology and as a senior editor for Phytopathology.
