How are blue berries turned into super‑plants?

The highbush blueberries, those blue berries you see in muffins, hide a genetic secret. To make varieties more resistant and productive, scientists cross different Vaccinium species, but differences in chromosome numbers (ploidy) make the crossing tricky. One solution is lab‑induced polyploidy: plants are grown in tissue culture and pushed to duplicate their chromosomes. Often, “chimeras” appear—branches with cells of different ploidy—that are unstable and usually discarded. The new study compared two techniques to separate these chimeras and obtain uniformly polyploid plants. The first, axillary shoot induction, takes existing side shoots. The second, adventitious shoot induction, grows new shoots from undifferentiated cells. The results are striking: 89 % of adventitious shoots from line 145.11 and 82 % from line 169.40 became solid polyploids, versus only 25 % and 53 % with axillary shoots. This method recovers genetically stable plants, ready for selecting new blueberry varieties that are healthier and more productive. In practice, the adventitious technique acts like a “reset,” removing unstable parts and leaving only the strongest genetic material for the next generation of blue fruits.

Polyploid induction in Vaccinium exploits chemicals such as oryzalin or colchicine, which disrupt mitotic spindle formation, preventing chromatid separation and producing cells with doubled chromosome numbers. In tissue culture, vegetative meristems are briefly exposed to these agents, then transferred to regeneration media. The outcome is a heterogeneous population of mixoploid cells, where some lines retain the original ploidy (diploid, tetraploid, or hexaploid) while others acquire a new ploidy. Chimeras arise when cells of different ploidy coexist within the same meristem, creating tissue sectors with periclinal mutations (mutations affecting all tissues derived from a single mother cell). Identifying periclinal mutants is crucial because they transmit the mutation to the progeny. Chimera dissociation occurs by stimulating adventitious shoot formation: superficial cells of the tissue, more prone to polyploidy, generate independent new organs. This process favors the selection of solid lines, as adventitious shoots derive from a more homogeneous cell population compared to axillary shoots, which preserve the original meristem structure. Cytogenetic analysis (fluorescence in situ hybridization, FISH) confirms ploidy stability in adventitious shoots, whereas axillary shoots show greater variability. Applying this technique overcomes ploidy barriers among Vaccinium species, expanding the genetic pool available for selecting traits such as disease resistance, cold tolerance, and higher anthocyanin content. Moreover, generating solid polyploid plants reduces the risk of genomic instability in subsequent generations, accelerating breeding cycles and facilitating the introgression of wild genes into commercial cultivars. In summary, chimera dissociation via adventitious shoots represents a methodological advance that combines tissue‑culture biotechnology and cytogenetics to boost genetic diversity and resilience in blueberry crops.