Lettuce (Lactuca sativa L.) germplasm resistant to bacterial leaf spot caused by race 1 of Xanthomonas hortorum pv. vitians (Brown 1918) Morinière et al. 2020

Bacterial Leaf Spot (BLS) is a disease that threatens lettuce (Lactuca sativa L.) production in warmer temperatures and high relative humidity, conditions that are conducive to unpredictable disease outbreaks and thus potentially resulting in total crop loss. BLS also causes problems in other major lettuce producing areas in the US and worldwide. To date, three races of the pathogen, Xanthomonas hortorum pv. vitians (Brown in J Agric Res 13:367–388, 1918; Morinière et al. in Syst App Microbiol 43:1260–1287, 2020 formerly known as X. campestris pv. vitians, were described in the US and Canada; though only race 1 has been confirmed thus far in Florida. Lettuce germplasm with a diverse set of resistance alleles is needed to improve resistance to BLS utilized in current commercial cultivars. In this study, plant introductions (PIs) from the National Plant Germplasm System (NPGS) and heirloom lettuce cultivars were tested against three isolates of the pathogen in Florida and two isolates in California. PI 667690 and PI 667709 were identified to be resistant to isolates of race 1 from both Florida and California. Allelism tests indicate that resistance found in these PIs is allelic to Xcvr (Xanthomonas campestris vitians resistance), a previously identified resistance gene detected in PI 358001–1. The two new sources of resistance offer a different set of morphological characteristics that can be useful in breeding programs than those found in PI 358001–1.