Further studies are needed to validate the identified markers in different citrus species and environments

The gap

Evidence profile

Sourced from the future work and future-work section of the source papers, classified as general, drawn from work published between 2024 and 2026, spanning 2 journals. Those papers have been cited 43 times in total.

Supporting evidence — 3 representative gaps

• Review on blueberry drought tolerance from the perspective of cultivar improvement (2024) · Frontiers in Plant Science · cited 24× · doi

  Analysis of previous studies revealed several limitations with blueberry drought tolerance research. First, most studies only focused on shoot traits related to drought without investigating how root anatomy and physiology influences blueberry drought tolerance. Drought studies without a comprehensive evaluation of both shoot and root mechanisms cannot reveal the whole picture of drought tolerance. Second, most studies only evaluated cultivars based on physiological or molecular traits without evaluating fruit yield or quality. As a high-value fruit crop, desirable fruit quality and adequate yield are must-have traits for any cultivar to be commercially adopted and considered drought tolerant. It is therefore essential to correlate physiological traits with fruit traits to identify tolerant genotypes. Third, existing studies only evaluated a small collection of cultivars for drought tolerance, whereas large- scale cultivar screening accompanied by genomic information is needed to reveal diverse drought tolerance mechanisms and underlying quantitative trait loci (QTL) or genes. As a result of limited cultivar evaluation, progress in QTL/gene discovery has been slow for drought tolerance and no molecular-assisted drought tolerance breeding has been reported in cultivated blueberries. Fourth, drought tolerance evaluation requires labor-intensive phenotyping, and a lack of high-throughput phenotyping tools for drought tolerance screening in blueberries is a major bottleneck especially for large-scale cultivar evaluation. 6.1 Limited understanding of blueberry root architecture and physiology in relation to drought tolerance Having a prolific root system is considered a major mechanism for avoiding drought by the uptake of more water from the soil (Erb, 1993; Farooq et al., 2012). Yet, the role of root architecture and physiology in drought tolerance is not well understood in blueberry as most studies focused on the shoot instead of root response to drought. Most, if not all, of the previous studies used container- grown plants in greenhouses or rain-out shelters for the ease of managing drought stress levels. However, a plant’s ability to absorb water in deeper layers of the soil through a large or deep root system cannot be well evaluated when roots are confined in a limited space. For example, rabbiteye blueberries are known for their deeper and tougher root systems and better drought tolerance in field conditions compared to other cultivated ecotypes (Davies and Johnson, 1982; Erb, 1993). However, previous studies focusing mainly on shoot physiological responses were not able to reveal true differences in drought tolerance between RE and SHB blueberries (Estrada et al., 2015; Zhang et al., 2022). Compared to RE cultivars, SHB stems showed stronger mechanical support and safer water transport structures, despite a lower hydraulic conductivity (Zhang et al., 2022). On the other hand, a plant’s ability to uptake water from the soil to alleviate drought stress was omitted in previous studies and therefore the full picture of blueberry drought tolerance is yet to be understood. Among the few studies investigating the response of blueberry root systems to drought, only root to shoot ratio was studied and contrasting observations were reported. Davies and Johnson (1982) studied drought response in the RE cultivar Bluegem and did not find significant changes in root to shoot ratio under water stress (Davies and Johnson, 1982). Alternatively, Cameron et al. (1989) found that two NHB cultivars Jersey and Bluecrop had a higher root to shoot ratio under severe water stress than well-watered conditions and that Bluecrop partitioned a higher percentage of dry weight to shoots compared to Jersey. The lack of studies evaluating root mechanistic responses to drought is likely due to difficulties in phenotyping roots and the challenges associated with evaluating drought tolerance in field-grown plants as compared to container-grown plants. In the future, it would be beneficial to investigate the physiological responses of roots to drought and the distribution of roots related to drought tolerance. This could be done, for example, by screening container- or field-grown plants treated with water stress and by studying root distribution and other traits using nondestructive (e.g., X-Ray tomography, mini- rhizotron systems) or destructive approaches (digging roots out using soil core or standard excavation method) (Kuijken et al., 2015; Wasaya et al., 2018). High-throughput phenotyping tools for root image analysis will be needed to improve the efficiency of manual root phenotyping, which can be very labor intensive especially for large datasets (Kuijken et al., 2015; Wasaya et al., 2018; Atkinson et al., 2019). Additionally, integrating soil moisture sensing technologies, such as time domain reflectometry or neutron

  generalfuture work
  Keywords: drought tolerance root shoot water blueberry traits cultivar phenotyping soil stress roots previous evaluation cultivars
• Molecular Mechanisms and Experimental Strategies for Understanding Plant Drought Response (2026) · Plants · cited 19× · doi

  Given the intricacies of plants’ drought responses, a comprehensive analysis of plant  physiology, integrating diverse methodological approaches, is inevitable to fully decipher  survival  mechanisms.  While  traditional  breeding  of  plants  showing  drought-resilient  traits remains fundamental, it is often too slow to keep pace with rapid environmental  changes. Therefore, the most effective immediate strategy seems to be molecular screening  https://doi.org/10.3390/plants15010149    Plants 2026, 15, 149  35  of  60  to identify currently existing resilient plants’ varieties and incorporate them into agricul- ture. However, looking further ahead, the accelerating rate of global temperature rise sug- gests that this may not be sufficient; consequently, genetic engineering of new plant vari- eties  will  possibly  become  an  inevitable  approach  to  ensure  long-term  crop  resilience.  Nevertheless, more research is still required to successfully generate such drought-resili- ent genetically modified crops [483]. For this reason, to achieve food safety and preserve  biodiversity for the future, the studies of plants’ drought response should take into con- sideration following aspects:   Accurately quantifying and standardizing drought severity on plants (e.g., by meas- uring soil water content or Ψw) to reflect realistic deficits, thereby ensuring transla- tional validity of laboratory results. An alternative could be to use a liquid medium  containing PolyEthylene Glycol (PEG); however, this method may not fully reflect  the water stress that plants experience in nature.  To  enable  valid  comparisons  across  independent  studies,  the  research  framework  should include a minimum set of crucial physiological parameters, such as leaf water  potential, photosynthetic efficiency, oxidative stress parameters, and pigment analy- sis. This standardized baseline is essential for distinguishing the actual physiological  status of a stressed plant.     Categorizing the studied species or cultivars within established drought resistance  strategies would enable the translation of research data into practical, useful infor- mation for other scientists and breeders.  Functional  redundancy  within  transcription  factor  families  (e.g.,  WRKY,  NAC,  DREB)  often  masks  the  impact  of  single-gene  modifications.  Future  research  must  incorporate  multi-omics  approach  to  map  regulatory  hubs,  enabling  simultaneous  editing of multi-genes or trait stacking. Manipulating entire gene clusters is necessary  to bypass redundancy and engineer robust drought resilience.  In nature, drought stress rarely occurs in isolation. Therefore, experimental designs  should consider realistic combinations of various factors, such as water scarcity, high  irradiance, heat waves, and elevated atmospheric CO2 levels, projected over the com- ing decades, providing a comprehensive picture of the climatic relationships relevant  to plant survival in future agroecosystems.   Author Contributions: Conceptualization, A.M. (Adrianna Michalak) and K.M.; writing—original  draft preparation, A.M. (Adrianna Michalak), K.M., K.D., K.P., L.B., A.M. (Anna Misiewicz), A.M.  (Angelika Maj), M.S. and I.W., writing—review and editing, A.M. (Adrianna Michalak), K.M. and  K.K.; Visualization, A.M. (Adrianna Michalak). All authors have read and agreed to the published  version of the manuscript.  Funding: This research received no external funding.  Data Availability Statement: No new data were created or analyzed in this study.  Conflicts of Interest: The authors declare no conflicts of interest.

  generalfuture work
  Keywords: plants drought plant water adrianna michalak future stress comprehensive inevitable fully survival resilient often incorporate
• DArTseq molecular markers associated with water stress tolerance and size reduction in citrandarins rootstocks (2026) · Frontiers in Plant Science · doi

  Further studies are needed to validate the identified markers in different citrus species and environments. Research on the genetic mechanisms underlying drought tolerance and reduced vigor is necessary. Investigation of other traits related to drought tolerance, such as root architecture and hormonal regulation, is required. Studies on the application of DArTseq molecular markers in citrus breeding programs are needed.

  generalfuture-work sectionevidence 4/5
  Keywords: further studies needed validate identified markers different citrus

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