Highly Efficient Agroinoculation Method for Tomato Plants with Tomato Yellow Leaf Curl Kanchanaburi Virus

Tomato yellow leaf curl disease caused by begomoviruses is a serious threat to tomato (Solanum lycopersicum L.) production. If begomoviruses, transmitted by whitefly (Bemisia tabaci), infect tomato plants during early growth, production can be almost entirely lost. Tomato yellow leaf curl Kanchanaburi virus (TYLCKaV), a bipartite Begomovirus, is emerging as an important threat to solanaceous crop production in Southeast Asia. The lack of mechanical transmission of some begomoviruses is a major experimental constraint. In this study, an agroinoculation method using TYLCKaV in tomato plants was established. Partial tandem repeats of TYLCKaV DNA A and DNA B were constructed and cloned to a binary pGreenII vector, and their infectivity was tested. Co-inoculation of TYLCKaV DNA A and DNA B to Nicotiana benthamiana L. produced typical begomoviral symptoms, and both of the viral DNA components accumulated in the upper uninoculated leaves, suggesting systemic infection of TYLCKaV. Two agroinoculation methods were conducted on tomatoes. First, excised sections of tomato shoots were agroinoculated with a soaking procedure. Although two Agrobacterium tumefaciens strains were tested, approximately 40% of inoculated plants only showed viral symptoms for EHA105. Second, agrobacterium from a cultured petri dish was directly inoculated with a colony inoculation procedure. When EHA105 was used, approximately 92% of inoculated plants showed viral symptoms. Sequencing the recovered viral DNA from the upper uninoculated leaf clarified that TYLCKaV had successfully infected the tomato plants. The colony inoculation procedure is labor-saving, and viral symptoms develop in susceptible tomato plants within approximately a month from sowing the seeds. This method could contribute to simple and speedy evaluation of TYLCKaV resistance of tomato plants.