NC 1 CELBR and NC 2 CELBR: Early Blight and Late Blight-resistant Fresh Market Tomato Breeding Lines

Abstract

NC 1 CELBR and NC 2CELBR are sister lines developed in a long-term breeding program in North Carolina to combine early blight and late blight resistances into adapted fresh-market tomato backgrounds. The pedigree of the two breeding lines traces back to NC 215E-1(93), a large-fruited determinate line with moderate resistance to the foliage blight phase of early blight and high resistance to the stem lesion phase of early blight (Fig. 1). NC 215 E-1(93) has a complex pedigree extending back to NC EBR-1, which has moderate foliage resistance to early blight derived from the Lycopersicon hirsutum L. (currently Solanum habrochaites S. Knapp & D.M. Spooner) source PI 126445 and NC EBR-2, which has moderate foliage resistance and a high level of stem lesion resistance to early blight derived from Campbell 1943 (Gardner, 1988). The Ph-2 gene for late blight resistance was derived from Richter’s wild tomato, and the Ph-3 gene was derived from L. 3707, a selection of the Lycopersicon pimpinellifolium L. (currently Solanum pimpinellifolium L.) line PI 365957 obtained from the Asian Vegetable Research and Development Center (AVRDC). The Ph-2 and Ph-3 genes from these small-fruited sources were backcrossed into NC 215E-1(93) to develop large-fruited lines, which were then crossed to combine the Ph-2 and Ph-3 genes into the early blight resistant background derived from NC 215E-1(93). The resultant F1 hybrid, NC 03220, was selfed, and 96 F2 generation plants were tested in growth chambers using detached leaf inoculations (Brusca, 2003) for combined resistance to isolates (Ph2-OC and Ph3-OC) that specifically overcame Ph-2 and Ph-3. Plants exhibiting a high level of resistance to inoculation with the two isolates (Ph2-OC and Ph3-OC) separately and in combination were selfed in the greenhouse, and F3 generation plants were evaluated in the field for combined resistance to early blight and late blight. Selections were made in the field for the best horticultural traits, including fruit size and smoothness combined with resistances to early blight and late blight. The field selections, 33EB-1(2004) and 45EB2(2004), leading to NC 1 CELBR and NC 2 CELBR, respectively, were derived from a single F2 plant that was homozygous for the Ph-2 and Ph-3 genes combined based on field trials in 2004 and subsequent years and verified by detached leaf inoculations in the growth chamber (Brusca, 2003).