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

Authors: SANDOYA, GERMAN - University Of Florida; ROSENTHAL, EMMA - Pennsylvania State University; Simko, Ivan; RODRIGUES-PORTO, LIS - University Of Florida; WADLINGTON, WILLIAM - University Of Florida; BULL, CAROLEE - Pennsylvania State University; CARROLL, AMANDA - University Of Florida

Submitted to: Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2022
Publication Date: 8/20/2022
Citation: Sandoya, G.V., Rosenthal, E., Simko, I., Rodrigues-Porto, L.N., Wadlington, W.H., Bull, C.T., Carroll, A. 2022. Lettuce (Lactuca sativa L.) germplasm resistant to bacterial leaf spot caused by race 1 of Xanthomonas hortorum pv. vitians (Brown 1918) Moriniére et al. 2020. Journal of Plant Pathology. 104:993–1008. https://doi.org/10.1007/s42161-022-01123-0.
DOI: https://doi.org/10.1007/s42161-022-01123-0

Interpretive Summary: Bacterial Leaf Spot (BLS) is a disease that threatens the lettuce (Lactuca sativa L.) production in mild temperatures and high relative humidity conditions that are conducive to unpredictable disease outbreaks thus potentially resulting in total crop loss. BLS causes problems also in other major lettuce producing areas in the US and worldwide. To date, three races of the bacterial pathogen, Xanthomonas hortorum 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 genetics conferring resistance is necessary 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 BLS 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. 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 provide a different set of morphological characteristics than those found in PI 358001-1, which can also be advantageous in breeding programs.

Technical Abstract: Bacterial Leaf Spot (BLS) is a disease that threatens lettuce (Lactuca sativa L.) production in major lettuce producing areas in the US and worldwide. Mild temperatures and high relative humidity in these regions are conducive to unpredictable disease outbreaks potentially resulting in total crop loss. To date, three races of the BLS pathogen, Xanthomonas hortorum pv. vitians (Brown, 1918) Moriniére et al. 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 BLS resistance gene detected in PI 358001-1. The two new sources of BLS resistance also possess different morphological characteristics from those found in PI 358001-1 and that can be useful in breeding programs.