Naidu Rayapati, native of India, earned a B.S. degree in biology (1975), an M.S. degree in botany (1977), and a Ph.D. degree in plant virology (1985) from Sri Venkateswara University, Tirupati, India. After completing postdoctoral research at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) (1987–1989) and in the Department of Plant Pathology, University of Kentucky (1989–1992), he worked at ICRISAT (1992–1998) on virus disease problems in developing countries, especially in sub-Saharan Africa. Subsequently, Rayapati served as a consultant virologist with the Crop Protection Programme (CPP) of the Department for International Development (DFID), United Kingdom, until 1999, working on groundnut (= peanut) rosette disease virus complex (GRD) in Malawi and Uganda. He then worked (1999–2004) on Tomato spotted wilt virus (TSWV) in the Department of Plant Pathology, University of Georgia (UGA), Athens. In November 2004, Rayapati joined the faculty of the Department of Plant Pathology, Washington State University–Irrigated Agriculture Research and Extension Center, Prosser, to develop a program on virus diseases of grapevine and other crops of economic significance to Washington State’s agriculture.
Rayapati elucidated the epidemiology of GRD and deployed sustainable disease management strategies by developing partnerships among a multidisciplinary team of scientists from ICRISAT, the United Kingdom, the United States, and national programs in sub-Saharan Africa with funding from DFID-CPP and the Peanut Collaborative Research Support Program (Peanut CRSP) of the U.S. Agency for International Development (USAID). GRD, with an estimated annual loss of $156 million, severely impacts the food security of smallholder farmers in sub-Saharan Africa. This disease has two main symptom forms and involves three causal agents, Groundnut rosette assistor virus (GRAV), Groundnut rosette virus (GRV), and its satellite RNA (sat-RNA), that are transmitted by the aphid Aphis craccivora. After developing molecular diagnostic tools for the three agents with Frances Kimmins at the Natural Resources Institute and with David Robinson at the Scottish Crop Research Institute (SCRI), United Kingdom, Rayapati showed that GRV and sat-RNA are always found together but can separate from GRAV in nature. Consequently, plants showing GRD symptoms do not necessarily contain GRAV. Diseased plants lacking GRAV do contribute to yield loss but are “dead ends” for disease spread, since the coat protein of GRAV that encapsidates GRV and sat-RNA is necessary for aphid transmission. He showed that a single vector aphid may acquire GRAV, GRV, and sat-RNA but does not always transmit all three agents, resulting in the separation of GRAV from GRV and sat-RNA in time and space. Rayapati showed that viruliferous aphids can transmit GRV and sat-RNA when probing mesophyll cells and cause GRD, but salivation into phloem sieve elements is essential for the transmission of all three agents. Elucidating the unique mode of transmission explained the lack of correlation between disease incidence and spread in the field. The presence of biotypes of A. craccivora differing in host-plant preference and transmission efficiency was also demonstrated.
In collaboration with Mike Deom (UGA), Rayapati determined the genetic diversity among GRD agents from different regions of sub-Saharan Africa. With Kimmins, he identified new sources of resistance in peanuts to the vector aphid, which broadened the genetic base of resistance against the disease. With funding from DFID-CPP, they deployed two new GRD-resistant varieties, suited to farmer and consumer preferences, for increased yields to alleviate poverty in Malawi and Uganda. Peanut CRSP has recently estimated that adoption of these varieties could contribute $47 million annually to Uganda’s economy.
Rayapati has characterized several economically important viruses of peanut in Asia and Africa. In collaboration with Mike Mayo (SCRI) and Deom, he found genetic differences in the RNA-2 of geographically distinct isolates of Peanut clump virus (from West Africa) and Indian peanut clump virus, resulting in them being named as distinct species. With Said Ghabrial (University of Kentucky), he showed that strains of Peanut stunt virus (PSV) are reassortants between sat-RNA replication supporting and nonsupporting strains of PSV, resulting in the classification of the PSV strains into two distinct subgroups. Rayapati’s collaboration with scientists at ICRISAT, UGA (Jim Demski), and University of Florida (Bill Dawson) provided the basis for classification of Cowpea mild mottle virus as a distinct species in the genus Carlavirus and of Peanut bud necrosis virus as a new species in the genus Tospovirus. He also found two distinct luteoviruses that cause stunt disease in chickpea. Rayapati, with John Sherwood and Deom (UGA), determined the nature of N-linked oligosaccharides of the envelope membrane glycoproteins of TSWV to better understand tospovirus–thrips interactions.
Rayapati trained several scientists in plant virology and developed collaborative partnerships in Asia and Africa. With colleagues at ICRISAT, the International Center for Agricultural Research in the Dry Areas, Syria (Khalid Makkouk), the International Institute of Tropical Agriculture (IITA), Nigeria (Jackie Hughes), and scientists in developed countries, regional training courses were developed for scientists in Africa and Asia. His collaborative efforts with Hughes led to the first-ever conference on “Plant Virology in Sub-Saharan Africa” in 2001, which enabled virologists from sub-Saharan Africa to develop region-wide strategies to manage virus diseases that limit food production and farm income. Recently, Rayapati obtained a USAID-linkage grant with IITA to conduct research on virus diseases of cassava in Nigeria and funds through the Integrated Pest Management Collaborative Research Support Program (USAID) to address thrips-borne tospoviruses in vegetables in South and Southeast Asia. He also obtained funding to strengthen the capacity of the Indian agricultural research community in managing virus diseases under the U.S.-India Agriculture Knowledge Initiative.
Rayapati is an author/coauthor of more than 40 journal articles, review articles, technical reports, training course manuals, and a textbook. He has served as an ad hoc reviewer and on the APS Tropical Plant Pathology and Virology Committees. He has been an invited participant in several international conferences and technical meetings. Rayapati’s contributions and achievements range from characterizing viruses, understanding the molecular aspects of viruses, and addressing practical aspects of virus disease problems of great significance to international agriculture. Rayapati promotes the international exchanges of knowledge and technologies and develops strategic research partnerships between scientists from developed and developing countries to increase food security in subsistence agriculture in developing countries.
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