2018 ASHS Annual Conference

Bacterial Leaf Spot (BLS) caused by the bacterium Xanthomonas campestris pv. vitians (Xcv) affects yield and quality of lettuce production in North America. Due to unpredictable nature of outbreak, preventive and post-infection control of the disease are impractically expensive. Therefore, breeding lettuce with high resistance to BLS is a priority for public and private breeding sectors. In Florida, environmental conditions are conducive for disease development, due to the high humidity and temperatures. In conditions favorable for disease development, the entire crop may be lost. During the season of 2017 – 2018 we recovered five new isolates of Xcv which caused disease outbreak in susceptible lettuce cultivars. Our previous tests indicate that plant introduction (PI) 358001-1 has complete resistance to Florida strains of BLS. PI is a leaf-type lettuce that bolts faster than commercial cultivars used at the EAA (Everglades Agricultural Area). Breeding efforts are in place by the University of Florida to transfer the resistance from this PI into romaine and crisphead lettuce. The lettuce breeding program of the University of Florida continues to screen lettuce PIs and cultivars from the National Plant Germplasm System (NPGS) of the GRIN – USDA to identify additional sources of resistance. Fifty-eight PIs and seven cultivars were tested with two isolates of BLS collected in Florida; with the resistant PI 358001-1 and susceptible ‘Okeechobee’ as controls. Significant differences were found in disease severity of tested material when inoculated with isolates Sc8b (P<0.0001) and L7 (P=0.0136). PIs 278080, 342898, 667690 and cv. Batavia Reine des Glaces showed none to minimal disease when inoculated with isolate Sc8b; PIs 342516, 419088, 601115 612665, 667709, 667690 and cv. La Brillante were as resistant as PI 358001-1 when inoculated with isolate L7. Furthermore, 44 PIs plus 6 cultivars were tested in California for their reaction to isolate BS0347. Cultivar ‘La Brillante’ and PI 251246 were used a resistant and susceptible controls, respectively. Significant differences (P<0.0001) in disease severity were found among accessions tested in California. PIs 278080, 342441, 342473, 591052,657639, 665198, 665203, 667690, 667709did not show any disease symptoms or were as resistant as the check cv. ‘La Brillante’. Further tests are needed to confirm these findings and to assess if resistance in PIs 278080 and 6667690 is strain specific. Accessions with resistance to multiple strains of the pathogens could be used in Florida and California lettuce breeding programs.