Host cell wall composition and localized microenvironment implicated in resistance to basal stem degradation by lettuce drop (Sclerotinia minor)

Authors: Simko, Ivan; MAMO, BULLO ERENA - University Of California; FOSTER, CLIFTON - Michigan State University; ADHIKARI, NEIL - University Of California; SUBBARAO, KRISHNA - University Of California

Submitted to: BMC Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2024
Publication Date: 7/28/2024
Citation: Simko, I., Mamo, B.E., Foster, C.E., Adhikari, N.D., Subbarao, K.V. 2024. Host cell wall composition and localized microenvironment implicated in resistance to basal stem degradation by lettuce drop (Sclerotinia minor). BMC Plant Biology. 24. Article 717. https://doi.org/10.1186/s12870-024-05399-5.
DOI: https://doi.org/10.1186/s12870-024-05399-5

Interpretive Summary: Lettuce is the leading, commercially produced, leafy vegetable in the world but is susceptible to diseases such as downy mildew, Fusarium and Verticillium wilts, and lettuce drop among others. Lettuce drop is a highly destructive disease that affects lettuce at any stage of its growth cycle. We have recently identified soft basal stem as a plausible susceptibility factor under controlled environmental conditions in a greenhouse. Analysis of stem and root cell wall composition in six accessions with varied growth habits and resistance levels provided evidence that hemicellulose constituents and lignin polymers are strongly correlated with disease phenotypes and basal stem mechanical strength. These findings suggest that the stem lignin content (particularly guaiacyl and syringyl) and xylose (carbohydrate) could thus serve as biomarkers for identifying accessions and breeding lines more resistant to lettuce drop. Basal stem degradation by lettuce drop was moderated by localized microenvironment conditions around the stem base of the plants.

Technical Abstract: Sclerotinia spp. are generalist fungal pathogens, infecting over 700 plant hosts worldwide, including staple field crops. The use of host resistance in disease management is the most environmentally friendly and economical approach to produce heathy plants; however, complete resistance to Sclerotinia diseases is rare, and partial resistance often correlates with undesirable developmental traits. We have recently identified soft basal stem as a plausible susceptibility factor to Sclerotinia minor infection in lettuce (Lactuca sativa) under controlled environmental conditions in a greenhouse. Analysis of stem and root cell wall composition in five L. sativa and one L. serriola accessions with varied growth habits and resistance levels provided evidence that hemicellulose constituents and lignin polymers are strongly correlated with disease phenotypes and basal stem mechanical strength. Simple carbohydrates, except xylose, were elevated, although not consistently significantly, in the cell walls of both the basal stem and root tissues of lettuce accessions susceptible to Sclerotinia spp. Accessions most resistant to basal stem degradation by lettuce drop consistently contained significantly higher levels of syringyl, guaiacyl, and xylose, but lower levels of fucose in stems. These findings suggest that stem cell wall polymers recalcitrant to breakdown by lignocellulolytic enzymes could underlie stem strength-mediated resistance to degradation by Sclerotinia spp. The lignin content (particularly guaiacyl and syringyl) and xylose could thus serve as biomarkers for identifying accessions and breeding lines more resistant to lettuce drop. Basal stem degradation by S. minor was moderated by localized microenvironment conditions around the stem base of the plants.