Widening the genetic basis of virus resistance in tomato

New and old accessions of Lycopersicon chilense (LA 1932, LA 1938 and LA 1963), L. peruvianum (PI-143679 and PI-126944), and L. hirsutum (UPV-16910) recently reported as resistant to TSWV, TYLCV and PepMV, viral agents responsible for the most severe economic losses in tomato crop in Spain, were selected as male parents for crosses with L. esculentum in order to widen the genetic basis of virus resistance in tomato. After the analysis of the nature and severity of the barriers found in each case, crossability barriers between wild and cultivated species were circumvented by using several techniques. Crosses with pollen mixture (1:1, wild:cultivated) were successful in obtaining interspecific hybrids with the two L. chilense accessions (LA 1932 and LA 1963) that exhibited more relaxed post-cigotic barriers. Embryo rescue was also successful in crosses with these accessions and also in crosses with L. peruvianum accessions in which embryos beyond the globular stage were found (PI-143679). However, a combination of two or more strategies was necessary in crosses with those accessions exhibiting more severe crossability barriers. Mixture pollen crosses (10:1, wild: cultivated), combined with embryo rescue, allowed for the recovery of hybrids with LA 1938. Stigma and pistil complementation with H3BO3 and GA(3), followed by immature seed culture was found to be an effective method for the production of novel interspecific hybrids with PI-126944, the accession with the highest level of resistance to TSWV and TYLCV. By using the best combination of techniques we also backcrossed these interspecific hybrids to tomato to generate the BC1 progeny. The new genes introgressed will be useful to obtain new tomato varieties resistant to TSWV, TYLCV and PepMV (C) 2002 Elsevier Science B.V. All rights reserved.