Search

Verticillium wilt is one of the most devastating soilborne diseases in lettuce, and the use of host resistance is the most optimal choice for its management. This study focused on identifying and mapping the genetic loci for resistance against Verticillium dahliae race 3 in a mapping population of 200 F2:3 families developed from a cross between moderately resistant red-leaf lettuce ‘Sentry’ and susceptible green-leaf lettuce ‘La Brillante’. The population was genotyped using the tunable genotyping-by-sequencing (tGBS) approach. An ultra-high-density genetic linkage map containing 34,838 single nucleotide polymorphism markers grouped into 1,734 bins was constructed using F2 progeny and a sliding window approach. Three quantitative trait loci (QTLs) for resistance to V. dahliae race 3 were located on linkage groups (LGs) LG 2 ( qVR3-2.1) and LG 4 ( qVR3-4.1 and qVR3-4.2). Each of these QTLs explained up to ∼10% of the total phenotypic variation for the trait. At each locus, the resistance alleles were derived from cultivar Sentry that is partially resistant to the pathogen. Additional loci resistant to the disease are expected in this population, and transgressive segregation indicates that some of those loci could originate from the susceptible cultivar La Brillante. In addition, two QTLs for plant development were identified on LG 2 ( qIPD-2.1) and LG 7 ( qIPD-7.1), although no relationship was detected between resistance in these genotypes and the rate of plant growth. A major effect of QTL for red leaf color was detected on LG 9 ( qRLC-9.1). Candidate genes linked to some of the QTLs for V. dahliae race 3 resistance, plant development, and leaf color were identified. The QTLs for resistance identified in Sentry could diversify the resistance gene pool and provide an alternative tool to manage a newly emerged V. dahliae race 3. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

SENESCENCE-ASSOCIATED GENE 13 (SAG13) of Arabidopsis is a widely conserved gene of unknown function that has been extensively used as a marker of plant senescence. SAG13 induction occurs during plant cell death processes, including senescence and hypersensitive response, a type of programmed cell death that occurs in response to pathogens. This implies that SAG13 expression is regulated through at least two different signaling pathways affecting these two different processes. Our work highlights a contrasting role for SAG13 in regulating resistance against disease-causing biotrophic bacterial and necrotrophic fungal pathogens with contrasting infection strategies. We provide further evidence that SAG13 is not only induced during oxidative stress but also plays a role in protecting the plant against other stresses. SAG13 is also required for normal seed germination, seedling growth, and anthocyanin accumulation. The work presented here provides evidence for the role of SAG13 in regulating multiple plant processes including senescence, defense, seed germination, and abiotic stress responses. SAG13 is a valuable molecular marker for these processes and is conserved in multiple plant species, and this knowledge has important implications for crop improvement.

The lettuce downy mildew pathogen, Bremia lactucae, is an obligate oomycete that causes extensive produce losses. Initial chlorotic symptoms that severely reduce the market value of the produce are followed by the appearance of white, downy sporulation on the abaxial side of the leaves. These spores become airborne and disseminate the pathogen. Controlling lettuce downy mildew has relied on repeated fungicide applications to prevent outbreaks. However, in addition to direct economic costs, heterogeneity and rapid adaptation of this pathogen to repeatedly applied fungicides has led to the development of fungicide-insensitivity in the pathogen. We deployed a quantitative PCR assay-based detection method using a species-specific DNA target for B. lactucae coupled with a spore trap system to measure airborne B. lactucae spore loads within three commercial fields that each contained experimental plots, designated EXP1 to EXP3. Based upon these measurements, when the spore load in the air reached a critical level (8.548 sporangia per m3 air), we advised whether or not to apply fungicides on a weekly basis within EXP1 to EXP3. This approach saved three sprays in EXP1, and one spray each in EXP2 and EXP3 without a significant increase in disease incidence. The reduction in fungicide applications to manage downy mildew can decrease lettuce production costs while slowing the development of fungicide resistance in B. lactucae by eliminating unnecessary fungicide applications.