2012 Annual Report
We grew, harvested, cleaned and cataloged seeds from leafminer-resistant plants selected from our field trials last fall. An experiment was designed and repeated to identify two S2 red romaine populations from the cross of ‘Batavia Reine des Glaces x Eruption with BLS resistance equivalent to ‘Batavia Reine des Glaces'. Resistance to Xcv in ‘Little Gem’ is due to a hypersensitive response (HR), a rapid leaf necrosis at the site of infection. We determined that a single gene is responsible for the HR (hypereactive response) derived from the cross Clemente x Little Gem. We also identified HR to Xcv in the ‘La Brilliante’. A set of 91 RILs from the cross Salinas 88 x La Brillante to a greenhouse inoculation test to quantify the resistance levels among the RILs. This population has an existing genetic map, which was used in quantitative trait loci analysis to identify a single region on chromosome 2 responsible for BLS resistance in ‘La Brillante’.
We evaluated over 1,800 accessions for their resistance to downy mildew in at least one trial. In addition, more than 300 accessions were tested for their deterioration after minimal processing for salad and storing in the modified atmosphere environment Evaluations of resistance and post-harvest quality were performed on all breeding lines that are targeted for release in 2013: two leaf-type lines GRxIce-1052 and GRxIce-1053, and the romaine type line RH08-0464. So far, all evaluations confirmed good resistance to downy mildew and acceptable levels of post-harvest deterioration in all three breeding lines.