Bleeding sap of plants – a new bio-resource for antagonistic endophytes discovered

Abstract: Climate change increases abiotic and biotic stress levels for plants and affects the economic and environmental aspects of agricultural management systems. Especially perennials, woody plants are faced to recurring stresses particularly reliant on reserves to support seasonal growth phases. In Vitis vinifera L. spring growth flush is mainly sustained by the remobilization process. Here, we applied a direct selection strategy to obtain cultivable microorganisms from first bleeding sap for potential application as biological control and stress protecting agents (BCAs, SPAs).Seven different bleeding saps (BS1-BS7) showed specific bacterial communities; whereas the Pseudomonadaceae-specific communities clustered in two groups using cultivation-independent fingerprints. Microorganisms isolated from R2A, Sabouraud and methanol containing agar were found in almost all samples ranging from log10 3.4 ± 0.6 to 7.6 ± 0.8. Selected microorganisms were genotypically characterized with amplified rDNA restriction analysis (ARDRA) and BOX-fingerprints. Additionally, we performed in vitro assays to identify antagonism against phytopathogens, and the ability to recover after dry-off and growth at high salt concentrations. A higher antagonistic potential was found against the fruit pathogen Botrytis cinerea compared to the root rotting pathogen Rhizoctonia solani. The isolated microorganisms showed the highest, significantly different percentage of antagonists against B. cinerea in BS3 (R2A 66.7%), BS6 (methanol 100.0%), and BS5 (Sabauroud 66.7%). Altogether, the proportion of antagonists was impressively high; herewith a new bioressource was discovered. Knowledge about structure and function of bleeding sap supports vineyard management in regard to the application of BCAs and SPAs against environmental stresses.