As part of my ongoing research on walnut improvement, particularly in stress-prone regions, I’ve explored micropropagation, somatic embryogenesis, grafting techniques, and molecular breeding to enhance abiotic stress tolerance in Persian walnut. I'm interested in exchanging insights on how tissue culture, gene editing (e.g., CRISPR/Cas9), or molecular marker-assisted selection can be more efficiently applied to develop drought-tolerant cultivars.
Have you implemented or studied any novel techniques for stress tolerance in nut trees or woody perennials? I welcome your feedback, case studies, or references to recent advances in this area.
Relevant works:
Lotfi N, Soleimani A, Vahdati K, Çakmakçı R. (2019) Comprehensive biochemical insights into the seed germination of walnut under drought stress. Scientia Horticulturae 250:329-43.
Sadat-Hosseini M, Vahdati, K, Boroomand N, Arab MM, Asadi-Yekta S. (2019). How walnut roots respond to drought stress: a morphological and anatomical study. South-Western Journal of Horticulture, Biology and Environment 10 (2): 51-64.
Rezaei Qusheh Bolagh F, Solouki A, Tohidfar M, Zare Mehrjerdi M, Izadi-Darbandi A, Vahdati K (2020) Agrobacterium-mediated transformation of Persian walnut using BADH gene for salt and drought tolerance, The Journal of Horticultural Science and Biotechnology, 95(4): 1-10.
Arab MM, Brown PJ, Abdollahi-Arpanahi R, Sohrabi SS, Askari H, Aliniaeifard S, Mokhtassi-Bidgoli A, Mesgaran MB, Leslie CA, Marrano A, Neale DB, Vahdati K (2022) Genome-wide association analysis and pathway enrichment provide insights into the genetic basis of photosynthetic responses to drought stress in Persian walnut. Horticulture Research: 1-38.
Lotfi N, Soleimani A, Çakmakçı R, Vahdati K, Mohammadi P (2022) Characterization of plant growth-promoting rhizobacteria (PGPR) in Persian walnut associated with drought stress tolerance. Scientific Report 12, 12725.
Arab MM, Askari H, Aliniaeifard S, Mokhtassi-Bidgoli A, Estaji A, Sadat-Hosseini M, Sohrabi SS, Mesgaran MB, Leslie CA, Brown PJ, Vahdati K (2023) Natural variation in photosynthesis and water use efficiency of locally adapted Persian walnut populations under drought stress and recovery. Plant Physiology and Biochemistry. 201, 107859.Habibi A, Sarikhani S, Arab MM, Soltani M, Aliniaeifard S, Roozban Mahmoud Reza, Vahdati K (2024) Drought and heat stress interactions: Unveiling the molecular and physiological responses of Persian walnut. Plant Physiology and Biochemistry. 217: 109237.
Lotfi N, Soleimani A, Vahdati K, Wei Wang, Mohammadi P (2025) Bio-priming walnut seeds with novel PGPR strains enhances germination and drought resilience under osmotic stress. Scientia Horticulturae. 344: 114073.
Lotfi N, Vahdati K, Kholdebarin B and Amiri R (2010) Drought-induced accumulation of sugars and proline in radicle and plumule of tolerant walnut varieties during germination phase. Acta Horticulturae. 861:289-296.
Lotfi N, Vahdati K, Kholdebarin B, Hassani D and Amiri R (2010) Peroxidase, guaiacol peroxidase and ascorbate peroxidase activity accumulation in leaves and roots of walnut trees in response to drought stress. Acta Horticulturae. 861:309-316.
Arab MM, Marrano A, Abdollahi-Arpanahi R, Leslie CA, Cheng H, Neale DB, Vahdati K. (2020). Combining phenotype, genotype, and environment to uncover genetic components underlying water use efficiency in Persian walnut. Journal of Experimental Botany 71(3):1107-1127.
I think you already have a lot of knowledge about this topic and have done extensive literature search, but I have summarized some points in a document form. Maybe you could gain further insights from it.
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Yes, I agree you have a lot of knowledge about the topic however, here are some Key Recommendations for Walnut Breeders
Leverage tissue culture and micropropagation systems as platforms for both mass propagation and gene editing.
Utilize CRISPR/Cas9 technology to precisely engineer or activate stress-related genes, focusing on known drought-related pathways (e.g., ABA signaling, osmoprotection).
Identify, validate, and apply molecular markers linked to drought tolerance, especially those relating to root traits, antioxidative mechanisms, or osmotic adjustment.
Integrate physiological screening (e.g., proline levels, enzyme assays) with genotypic selection for more robust MAS pipelines.
Explore ancient and diverse germplasm for novel sources of resilience. I hope this helps.
Kourosh Vahdati
You have listed main methods applied for improving drought tolerance in walnuts, including biotechnological approaches. I agree to Sunday Kaura that your experience in this field is probably among the best.
However, the main issue remains unclear. Is the problem a total lack of available water in the soil for walnut roots, short or long periods without sufficient rain or irrigation, or is it due to a water shortage caused by global warming leading to increased transpiration and evaporation? Is this a major concern for old walnut orchards (limited number of climate factors changed), or are we looking for a solution for new areas (many new stress factors) where walnut production could be established? Targets are important for strategy choice. Simple initial root growth stimulation may be more effective than sophisticated metabolic changes. 15 years ago, there was a lot of excitement about the root-stimulating Vigor Effect (Syngenta), caused by a neonicotinoid product. Plants seemed to perform much better under drought stress, but not so well in areas with high soil humidity. Me and some Brazilian colleagues believe that neonicotinoids act as antagonists of stress -caused flavonoid-mediated suppression of auxin transport in roots, but this has not been properly proven.
Effective improvement of drought tolerance in walnut (Juglans regia L.) relies on combining genetically modified rootstocks (e.g., targeting JrGA20ox1) with molecular marker-assisted breeding, gene transformation, and advanced tissue culture techniques. Emerging gene editing tools like CRISPR/Cas9 offer promising precision for developing stress-resilient cultivars.
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