Factors Affecting Mechanical Transmission of Tomato spotted wilt virus to Peanut (Arachis hypogaea)

Tomato spotted wilt virus (TSWV) is the type member of the genus Tospovirus in the family Bunyaviridae (13). TSWV is a serious plant pathogen affecting several important crop plants throughout the world (15). In the southern United States, peanut or groundnut (Arachis hypogaea L.) is severely affected by TSWV (1,4,10,11,18). Losses due to TSWV in peanut were estimated at several millions of dollars in Georgia alone (22). In peanut, TSWV induces a wide range of symptoms. Foliar symptoms include chlorotic spots, chlorotic streaks, mosaic, ring spots, concentric rings, necrotic spots, and yellowing. Plants infected at an early stage are often severely stunted, resulting in serious yield losses (4,11). TSWV is transmitted by thrips in a persistent manner (8). Western flower thrips (Frankliniella occidentalis) and tobacco thrips (F. fusca) are the major vectors associated with TSWV epidemics in peanut in Georgia (19,20). Insecticidal applications to control thrips are largely ineffective in reducing TSWV in peanut (19,20). Growing resistant cultivars has been an important tactic for managing this disease. Several new cultivars with field resistance to TSWV are available, and more are in various stages of development (4–6). Recently, the impact of TSWV in Georgia’s peanut crop has been reduced by integration of a multiple factor management program. The central thrust of the program has been the use of resistant cultivars such as Georgia Green, Virugard, and MDR98 (2). Breeding for resistance to TSWV is based on the performance of breeding lines under natural occurrence of the disease in the field. Under field conditions, all plants may not be exposed to thrips-borne TSWV inoculum. Therefore, the level of true resistance cannot be assessed based on only field observations. Successful inoculation of TSWV to individual plants by mechanical methods or vectors are necessary to evaluate the level of resistance in a genotype to be used in breeding programs. Availability of a highly efficient method for mechanical transmission would enable such screening and would facilitate quick identification of sources of TSWV resistance. Previous reports (3,12,16) utilized standard inoculation procedures to transmit TSWV to peanut. Most of these methods involved maintaining TSWV in Nicotiana benthamiana. We report a protocol that ensures efficient and reliable mechanical transmission of TSWV to peanut.