Abstract
Fusarium wilt caused by Fusarium oxysporum f. sp. pisi (Fop) is one of the most destructive diseases of pea worldwide. Control of this disease is difficult and it is mainly based on the use of resistant cultivars. While monogenic resistance has been successfully used in the field, it is at risk of breakdown by the constant evolution of the pathogen. New sources of quantitative resistance have been recently identified from a wild relative Pisum spp. collection. Here, we characterize histologically the resistance mechanisms occurring in these sources of quantitative resistance. Detailed comparison, of the reaction at cellular level, of eight pea accessions with differential responses to Fop race 2, showed that resistant accessions established several barriers at the epidermis, exodermis, cortex, endodermis and vascular stele efficiently impeding fungal progression. The main components of these different barriers were carbohydrates and phenolic compounds including lignin. We found that these barriers were mainly based on three defense mechanisms including cell wall strengthening, formation of papilla-like structures at penetration sites and accumulation of different substances within and between cells. These defense reactions varied in intensity and localization between resistant accessions. Our results also clarify some steps of the infection process of F. oxysporum in plant and support the important role of cell wall-degrading enzymes in F. oxysporum pathogenicity.
Highlights
Fusarium oxysporum Schl. f. sp. pisi Snyd. and Hans. (Fop) is an important pathogen causing vascular wilt of field pea (Pisum sativum L.) worldwide (Rubiales et al, 2015)
FAA-fixed sections were stained with a mixture of alcian green:safranin (AGS) (Joel, 1983)
Semi-thin (2 μm) histo-resin sections of Karnovsky-fixed samples were stained with 0.1% toluidine blue O (TBO) in citrate buffer for 5 min
Summary
Fusarium oxysporum Schl. f. sp. pisi Snyd. and Hans. (Fop) is an important pathogen causing vascular wilt of field pea (Pisum sativum L.) worldwide (Rubiales et al, 2015). Four different races of Fop, named 1, 2, 5, and 6, have been described so far (Infantino et al, 2006). Races 1 and 2 are widely distributed, while races 5 and 6 are, to date, only important in western Washington State (Infantino et al, 2006). Control of soil-borne fungal diseases is mainly achieved by the integration of different disease management procedures. Among these methods, the use of resistant cultivars is widely recognized as the safest, most economical and most effective crop protection method (Ciancio and Mukerji, 2008; Rubiales et al, 2015). Resistance to Fop races 1, 5, and 6 is conferred
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