The ‘Colt’ rootstock (Prunus avium × Prunus pseudocerasus) is widely used in Chilean cherry orchards due to its high compatibility with sweet cherry cultivars and strong vegetative vigor. However, its low drought tolerance represents a significant limitation under reduced water availability, a condition that is becoming increasingly important for the sustainability of sweet cherry production.
In this context, a study published in Frontiers in Plant Science evaluated the effectiveness of biostimulants based on extracts of the brown seaweed Macrocystis pyrifera, applied either alone or in combination with the plant growth-promoting bacterium Pseudomonas koreensis AG 97, in improving the physiological and morphological responses of young ‘Colt’ plants.
Two types of seaweed extracts were compared: one obtained through alkaline hydrolysis (A1) and another through combined alkaline and enzymatic hydrolysis (A2). These treatments were evaluated alongside the bacterial treatment alone (B) and the combinations A1B and A2B. Plants were grown under both well-watered (WET) and deficit irrigation (DRY) conditions, allowing their responses to contrasting water regimes to be assessed.
Under WET conditions, which also included periods of substrate saturation and consequent temporary root-zone hypoxia, the A1B treatment produced particularly marked effects. The combination of seaweed extract and bacterial inoculation increased stomatal conductance by 90% and reduced leaf temperature by approximately 2 °C, suggesting an improved capacity to cope with stress associated with excessive moisture.
It also enhanced photochemical efficiency under low-light conditions and significantly stimulated shoot elongation, reaching approximately 23 cm compared with 10 cm in the control plants. The response was equally noteworthy under DRY conditions. When plant water potential declined below −1.1 MPa, A1B reduced stomatal conductance by approximately 70%, thereby limiting water loss and reducing defoliation to less than 15%, compared with 40% in plants receiving the bacterial treatment alone.
Moreover, plants treated with A1 and A1B maintained carbon assimilation rates above 41%, indicating greater photosynthetic performance during water deficit. Overall, the A1 extract obtained through mixed hydrolysis was the most effective treatment for improving drought tolerance in ‘Colt’ rootstocks.
Its effectiveness may be associated with the biochemical composition of the extract, particularly its high mannitol content, which may contribute to water-status regulation and stomatal closure. In contrast, inoculation with P. koreensis showed stronger effects under high-moisture conditions, increasing stomatal conductance and stem growth; however, these benefits declined as substrate temperatures decreased during autumn.
Finally, A1-treated plants developed larger leaves with lower dry matter content and lower leaf temperature, together with slightly higher photosynthetic efficiency. The approximately 7% increase in relative root biomass suggests a possible redistribution of resources toward the root system, potentially promoting root development and water uptake.
Overall, these findings indicate that M. pyrifera-based seaweed biostimulants, either applied alone or combined with plant growth-promoting bacteria (PGPB), represent a promising biologically based strategy for enhancing water-stress resilience, physiological performance, and growth of ‘Colt’ rootstocks under contrasting environmental and irrigation conditions.
Source: Cruzat-Hermosilla M, Alvear T, Gerding M, Brintrup M, Asmüssen MV, Garriga M and Calderón-Orellana A (2026), Macrocystis pyrifera seaweed extracts combined with Pseudomonas koreensis enhance growth and stomatal regulation in the sweet cherry rootstock ‘Colt’ under contrasting water conditions. Front. Plant Sci. 17:1813040. doi: 10.3389/fpls.2026.1813040
Image source: Stefano Lugli
Melissa Venturi
Ph.D. in Agricultural, Environmental, and Food Sciences and Technologies – Fruit Tree Physiology and Cultivation - Bologna, Italy
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