Helicoverpa armigera management: A review of AVRDC's research on host plant resistance in tomato

Tomato fruitworm (TFW), Helicoverpa armigera (Hübner), is the most destructive pest of tomato (Lycopersicon esculentum Mill) in South and Southeast Asia. Research was initiated at AVRDC in 1980 to identify sources of resistance to this pest and to breed TFW-resistant tomato lines suitable for the region. Germplasm screening revealed high levels of TFW resistance only in the wild Lycopersicon species, particularly L. hirsutum and L. pennellii. Consequently TFW resistance breeding research focused on introgressing resistance from the wild species into the cultivated tomato. In the first resistance breeding efforts from 1981 to 1988, L. hirsutum accessions 76W-PI134417-A and 77W-PI134417-1 were selected as donor parents in a backcrossing program with L. esculentum. Backcross lines with significantly lower pest damage were derived from this program but all were invariably small-fruited and not commercially acceptable. From 1988 to 1995, a second attempt was undertaken using L. pennellii accession LA 716 as the resistance donor parent. Selection of resistant progenies was based initially on TFW damage and subsequently on acylsugar content, the compound that confers insect resistance, in leaves. We failed to find backcross progenies with acylsugar levels near that of the donor parent. Furthermore, progenies with higher acylsugar levels also showed low pollen production and other undesirable horticultural traits. From 1994 to 1996, in collaboration with Cornell University, an attempt was made to introgress the fruitworm resistance genes from LA 1777 (L. hirsutum f. typicum) using QTL mapping. However, none of the near isogenic lines carrying individual L. hirsutum introgressions associated with fruitworm resistance showed resistance. Our research demonstrated the presence of high levels of TFW-resistance in several wild tomato accessions but our efforts to introgress this resistance into the cultivated tomato in order to combine it with acceptable fruit qualities did not succeed. Future of such classical breeding approach is discussed.