|MICHELMORE, RICHARD - University Of California
Submitted to: Eucarpia Conference on Lettuce and Leafy Vegetables
Publication Type: Abstract Only
Publication Acceptance Date: 2/13/2015
Publication Date: 4/14/2015
Citation: Hayes, R.J., Michelmore, R., Bull, C.T. 2015. Genetics and breeding of bacterial leaf spot resistance. EUCARPIA Leafy Vegetables Congress, April 14-17, 2015, San Pedro del Pinatar, Spain.
Technical Abstract: Bacterial leaf spot (BLS) caused by the pathogen Xanthomonas campestris pv. vitians (Xcv) is a globally important disease of whole head and baby leaf lettuce that reduces crop yield and quality. Host resistance is the most feasible method to reduce disease losses. Screening Lactuca accessions has identified resistance, though most cultivars used for commercial production are susceptible. Batavia Reine des Glaces, Iceberg, Salad Crisp and other cultivars express incomplete resistance to Xcv. High-level race-specific resistance is known in a few lettuce cultivars and wild species. The Batavian cultivar La Brillante along with the Latin cultivars Pavane and Little Gem express a hypersensitive response (HR) to California strains of Xcv resulting in high-level resistance. The HR in La Brillante is due to a single dominant gene, named Xanthomonas resistance 1 (Xar1), located on linkage group 2. The genes conferring the HR in Pavane and Little Gem are either allelic or closely linked with Xar1. Breeding resistant iceberg cultivars has resulted in eight publically released inbred lines using either the Xar1 gene or resistance derived from Iceberg and Salad Crisp. Breeding resistant cultivars for use in baby leaf production is challenged by the need to breed resistance into the diverse types grown as baby leaf. We developed a breeding scheme that uses early generation testing to select populations that are uniform for BLS resistance but variable for leaf morphology and color. To demonstrate the breeding scheme, we conducted selection for BLS resistance and red-colored leaves among progeny from Batavia Reine des Glaces × Eruption (red colored leaves and Xcv susceptible). Two populations were developed with uniform levels of resistance equivalent to Batavia Reine des Glaces and variable leaf morphology and color. These populations can be used to select for diverse types of lettuce suitable for baby leaf production and with BLS resistance.