Sweet Immunity: The Effect of Exogenous Fructans on the Susceptibility of Apple (<i>Malus × domestica</i> Borkh.) to <i>Venturia</i> <i>inaequalis</i>

• Main Authors: Anze Svara, Łukasz Paweł Tarkowski, Henry Christopher Janse van Rensburg, Evelien Deleye, Jarl Vaerten, Nico De Storme, Wannes Keulemans, Wim Van den Ende
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: International Journal of Molecular Sciences
• Subjects: apple; scab; fructans; <i>Malus</i>; <i>Venturia</i>; leaves
• Online Access: https://www.mdpi.com/1422-0067/21/16/5885
• ISSN: 1661-6596; 1422-0067

There is an urgent need for novel, efficient and environmentally friendly strategies to control apple scab (<i>Venturia inaequalis</i>), for the purpose of reducing overall pesticide use. Fructans are recently emerging as promising “priming” compounds, standing out for their safety and low production costs. The objective of this work was to test a fructan-triggered defense in the leaves of apple seedlings. It was demonstrated that exogenous leaf spraying can reduce the development of apple scab disease symptoms. When evaluated macroscopically and by <i>V. inaequalis</i>-specific qPCR, levan-treated leaves showed a significant reduction of sporulation and <i>V. inaequalis</i> DNA in comparison to mock- and inulin-treated leaves, comparable to the levels in fosetyl-aluminum-treated leaves. Furthermore, we observed a significant reduction of <i>in vitro</i> mycelial growth of <i>V. inaequalis</i> on plates supplemented with levans when compared to controls, indicating a direct inhibition of fungal growth. Variations in endogenous sugar contents in the leaves were followed during priming and subsequent infection, revealing complex dynamics as a function of time and leaf ontogeny. Our data are discussed in view of the present theories on sugar signaling and fructan-based immunity, identifying areas for future research and highlighting the potential use of fructans in apple scab management in orchards.