Russeting in Apple: Molecular Basis, Mechanism and Consequences

• Applicants: Professor Dr. Thomas Debener; Professor Dr. Moritz Knoche
• Subject Area: Plant Cultivation, Plant Nutrition, Agricultural Technology
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 386934299

Russeting is an important disorder of fruit surfaces of many fruit crops including apple. Russeting is the formation of a periderm. Microscopic cracks (microcracks) in the primary fruit skin are considered the first visible sign of russeting. However, not all microcracks result in russeting. Microcracks somehow trigger formation of a periderm, but the nature of this trigger is unknown. The objectives of our proposal are to (1)provide a detailed account of the anatomical and biophysical changes occurring during russet formation and to identify their consequences for the barrier properties of the fruit surface and (2) identify the initial trigger and sequence of events on a molecular level that result in russeting. We will use a combination of anatomical, biophysical and molecular approaches. We focus on skin anatomy, microcracking of the cuticle, its relationships with peg formation and factors potentially causing stress concentration. The anatomical data serve as a developmental time scale to which physical and molecular changes during russeting will be related. The biophysical properties of the russeting skin composite include its permeability to water and gas and its rheological properties. Finally, molecular studies will identify the initial and primary trigger(s) that precede(s) and induce(s) periderm formation. We focus on moisture induction of russeting using split fruit treatment because (1) under orchard conditions this is the most frequent cause of russeting and (2) the split fruit system allows to directly compare russeting and non-russeting surfaces on the same fruit. In addition, other modes of induction (PGRs, mechanical wounding), or naturally occurring russeting (russeting vs. non-russeting sports and cultivars) will be considered. They serve as a control to distinguish primary signals/ events (strain, turgor etc.) from secondary signals/events (downregulation of cutin synthesis, upregulation of suberin synthesis, etc.). The data generated will help to identify the mechanistic basis of russeting. A better understanding of its causes is a prerequisite to develop avoidance strategies to minimize the risk for such defects.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Bishnu Prasad Khanal