Identification and Manipulation of Resistance to Tomato Spotted Wilt Virus Derived From Solanum peruvianum

IDENTIFICATION AND MANIPULATION OF TSWV RESISTANCE IN Solanum peruvianum Luis Felipe Gordillo Morales Department of Plant and Wildlife Sciences Doctor of Philosophy Chapter 1 Abstract The domesticated tomato Solanum lycopersicum (L.), formerly known as Lycopersicon esculentum is a genetically well-studied crop species with high-density linkage and molecular maps based on crosses done between cultivated tomato and its distant related wild species. Wild tomato species harbor a wealth of resistance to many pathogens that have been introgressed into domesticated tomato for genetic control of diseases and pests and for improvement of many agronomic traits. The wild tomato S. peruvianum (L.) is the source of the Sw-5 gene, characterized and mapped to chromosome 9 of the tomato genome and introgressed into elite tomato germplasm, providing resistance to the tospovirus Tomato spotted wilt virus (TSWV). TSWV has been reported to be a major problem for tomato growers in many parts of the world, which in some cases, has resulted in tomato fields having been abandoned for some time. Additionally, there are reports that new races of TSWV have evolved that overcome Sw-5. TSWV replicates in both, plant cells and in the alimentary canal cells of thrips and then transmitted to plants by this insect acting as a vector. Both, TSWV and thrips have co-evolved to infest and infect more than 1090 plants species in over 100 families, thrips becoming resistant to pesticides and easily escaping by hiding deep in plant parts. World trade has disseminated thrips all over the world and environmental pressures have forced TSWV to recombine its RNA to overcome new resistance. Chapter 2 Abstract The United States Department of Agriculture Research Service (USDA) and the Tomato Genetics Resource Center (TGRC) Lycopersicon peruvianum germplasm collections (16,335 plants from 285 accessions) were screened with the TSWV isolates TSWV6 from Hawaii, and Anwa-1 from anemone in Western Australia. Using TSWV6 to screen for resistance, 10,634 L. peruvianum plants from 280 accessions were screened; resulting in, 168 (60%) accessions with 1437 (14%) plants indicating resistance, with all 1,404 89S (Sw-5/Sw-5) and 1,456 89R (Sw-5/Sw-5) controls infected. When using Anwa-1 for screening 864 (15%) of 5,701 L. peruvianum’s uninfected from 106 of the 181 accessions tested, and 472 (95%) of the 495 89S and 421 (73%) of the 574 89R controls infected. Fifty-four of the 172 accessions tested with both isolates were resistant to one isolate but not the other. Additionally, more accessions from the USDA than from the TGRC collection indicating resistance. TSWV resistant accessions were somewhat equally distributed throughout the L. peruvianum geographic range with an observation that northern Chile/southern Peru seemed to have an unusually high portion of accession indicating resistance. The value of Sw-5 is discussed in relationship to potential additional sources of TSWV resistance. Chapter 3 Abstract Sw-5 derived from Solanum peruvianum (L.) confers resistance to Tomato spotted wilt virus (TSWV). A unique TSWV isolate from Hawaii (TSWV6) overcomes Sw-5 in our trials when tested on near isogenic lines (NILs) controls 89R (Sw-5/Sw-5), and 89S (Sw5/Sw-5). Both lines were 100% infected. Our TWSV6 resistance screening trials of S. peruvianum accessions indicate resistance in line PI 128660, although repeated testing of cuttings of putatively resistant plants suggests less than 100% penetrance. We have developed interspecific hybrids and some backcrosses between S. lycopersicum (L.) and TSWV6 resistant PI 128660 lines. To circumvent the postzygotic genetic barrier, we used embryo rescue to obtain the F1 and the BC1P1 generations. We screened the F1, BC1P1, BC2P1, and BC3P1 generations by mechanically inoculating them with TSWV6. Apparently uninfected plants were selected and tested for the presence/absence of TSWV6 by enzymelinked immunosorbent assay (ELISA). Fewer plants indicating TSWV6 resistance in the BC2P1 and BC3P1 to the point where there were no significant differences between the TSWV susceptible controls and BC3P1 when tested in either the greenhouse or in the field with common isolates of TSWV or the TSWV6 isolate.