Periodic Reporting for period 1 - FROOTS (Fast-tracking ROOTStock breeding in olive)
Période du rapport: 2021-05-01 au 2023-04-30
Environmental adaptation plays a pivotal role in the successful cultivation of crops within specific geographic regions. Olive cultivars that exhibit resilience to a variety of abiotic constraints such as cold temperatures, heat stress, water scarcity, and nutrient-deficient soils have naturally evolved over millennia due to inadvertent selection. Nevertheless, these resilient cultivars often lack other desirable agronomic traits. While the potential for combining both sets of characteristics exists, the development of new cultivars with heightened abiotic stress tolerance is not a primary focus in current global olive breeding programs. Rootstock breeding emerges as a promising avenue to address some of the challenges posed by abiotic stressors.
The selection of rootstock tailored to specific environmental conditions holds significant potential to address societal challenges within the European Union. The practice of employing rootstocks is prevalent across a wide spectrum of economically significant tree species, but in olives it could help to mitigate some challenges, especially food security and sustainable agriculture, empowerment of rural areas and adaptation to the effects of climate change. This can be achieved by identifying and obtaining new olive rootstock that due to their tolerance to abiotic factors and other characteristics, can: 1) decrease machinery, labour and chemical inputs to plants and soil; 2) increase the efficiency of water and soil use; 3) improve the quality of the product; and 4) improving olive growing in marginal areas. Moreover, the project offers substantial promise due to its capacity to expand the genetic diversity available for desirable rootstock attributes while concurrently facilitating the growth of the preferred scion cultivar, as well as by the techniques developed for the implementation of rootstock breeding.
The objectives proposed in FROOTS have been accomplished as described below:
- Objective 1: Methods have been developed to identify drought resistance in young olive plants
- Objective 2: An early grafting methodology has been developed for young olive plants.
- Objective 3: The methodology from the other objectives is being used to screen for drought resistance sexually-produced breeding populations.
The selection of rootstock tailored to specific environmental conditions holds significant potential to address societal challenges within the European Union. The practice of employing rootstocks is prevalent across a wide spectrum of economically significant tree species, but in olives it could help to mitigate some challenges, especially food security and sustainable agriculture, empowerment of rural areas and adaptation to the effects of climate change. This can be achieved by identifying and obtaining new olive rootstock that due to their tolerance to abiotic factors and other characteristics, can: 1) decrease machinery, labour and chemical inputs to plants and soil; 2) increase the efficiency of water and soil use; 3) improve the quality of the product; and 4) improving olive growing in marginal areas. Moreover, the project offers substantial promise due to its capacity to expand the genetic diversity available for desirable rootstock attributes while concurrently facilitating the growth of the preferred scion cultivar, as well as by the techniques developed for the implementation of rootstock breeding.
The objectives proposed in FROOTS have been accomplished as described below:
- Objective 1: Methods have been developed to identify drought resistance in young olive plants
- Objective 2: An early grafting methodology has been developed for young olive plants.
- Objective 3: The methodology from the other objectives is being used to screen for drought resistance sexually-produced breeding populations.
FROOTS was structured into three scientific Working Packages (WP) aimed at the research objectives, with the inclusion of WP4, dedicated to the dissemination, communication, and exploitation of results, and WP5, designed for training in teaching and supervision. Throughout the course of the fellowship, Milestones have served as essential control points. At Milestone 1 enabled us to make informed decisions regarding the most reliable drought resistance indicators. This milestone carries great importance since it served as the pivotal point for deciding the allocation of effort within WP3. Milestone 2, which aims the development of the "micrografting" technique allowed the start of WP3.
Work Package 1: Drought resistance indicators in grafted plants
Several methods have been tested to identify drought tolerance in olive plants. This WP presented some difficulties at the start due to the variability in plant material from different nurseries, plant propagation methods, etc. After some initial experiments, the experiments that provided the best methodology to discriminate tolerance to drought in olive plants were the minimum leaf conductance and the biomass partitioning experiments. These procedures have allowed to determine, together with the literature, the most suitable olive cultivars to use an controls in water deficit experiments.
Work Package 2: Rapid “micrografting” technique
The initial results of the project have enabled the establishment of grafting techniques in olive seedlings. Grafting in olive seedlings has been successful under specific conditions of plant health, humidity, temperature, and light. Grafting techniques in olive seedlings have been similar to those used in herbaceous plants. The age of the plant also influences the success rate, although some success has been achieved in very young plants shortly after germination. In addition, various types of plant material have been successfully grafted, including seedling, micropropagated plants. The determination has been conducted using a diverse range of plant materials from WP1 and WP3, which vary in terms of age, juvenility stage, and the method used for their reproduction. The reconnection of vascular tissues after grafting, necessary for the survival of the grafted plant, has been demonstrated using a fluorescent marker applied to the root and visualized in the grafted part of the plant using a microscope to identify whether reconnection of xylem tissue has occurred (Figure 1). Currently, experiments are underway to determine the precise timing of these vascular reconnection processes, which would provide valuable information for both seedling grafting and the determination of incompatibility mechanisms at early stages, as well as for understanding the grafting process in olive and other woody species. The development of these procedures represent Milestone 2.
Work Package 3: Drought resistance in rootstock breeding populations
This work package has worked on implementing the most effective method identified in WP1 for high-throughput phenotyping of a significant number of sexually reproduced plants resulting from controlled crosses. Germplasm resources chosen for evaluation in this WP were selected based on documented drought tolerance as well as from the results obtained in WP1 (see previous section). This way, cultivars ‘Cornicabra’ and ‘Hojiblanca’ were selected as tolerant and cultivars ‘Cornezuelo de Jaén’ and ‘Manzanilla de Sevilla’ were selected as susceptible. Three test breeding populations were targeted for their development with the mentioned parents: Tolerant (T) x T, T x Sensitive (S), and S x S. To ensure accurate comparisons, the selected parents were asexually propagated for proper assessment alongside seedling plants. Seeds from those combinations were germinated and will be evaluated soon.
Work Package 1: Drought resistance indicators in grafted plants
Several methods have been tested to identify drought tolerance in olive plants. This WP presented some difficulties at the start due to the variability in plant material from different nurseries, plant propagation methods, etc. After some initial experiments, the experiments that provided the best methodology to discriminate tolerance to drought in olive plants were the minimum leaf conductance and the biomass partitioning experiments. These procedures have allowed to determine, together with the literature, the most suitable olive cultivars to use an controls in water deficit experiments.
Work Package 2: Rapid “micrografting” technique
The initial results of the project have enabled the establishment of grafting techniques in olive seedlings. Grafting in olive seedlings has been successful under specific conditions of plant health, humidity, temperature, and light. Grafting techniques in olive seedlings have been similar to those used in herbaceous plants. The age of the plant also influences the success rate, although some success has been achieved in very young plants shortly after germination. In addition, various types of plant material have been successfully grafted, including seedling, micropropagated plants. The determination has been conducted using a diverse range of plant materials from WP1 and WP3, which vary in terms of age, juvenility stage, and the method used for their reproduction. The reconnection of vascular tissues after grafting, necessary for the survival of the grafted plant, has been demonstrated using a fluorescent marker applied to the root and visualized in the grafted part of the plant using a microscope to identify whether reconnection of xylem tissue has occurred (Figure 1). Currently, experiments are underway to determine the precise timing of these vascular reconnection processes, which would provide valuable information for both seedling grafting and the determination of incompatibility mechanisms at early stages, as well as for understanding the grafting process in olive and other woody species. The development of these procedures represent Milestone 2.
Work Package 3: Drought resistance in rootstock breeding populations
This work package has worked on implementing the most effective method identified in WP1 for high-throughput phenotyping of a significant number of sexually reproduced plants resulting from controlled crosses. Germplasm resources chosen for evaluation in this WP were selected based on documented drought tolerance as well as from the results obtained in WP1 (see previous section). This way, cultivars ‘Cornicabra’ and ‘Hojiblanca’ were selected as tolerant and cultivars ‘Cornezuelo de Jaén’ and ‘Manzanilla de Sevilla’ were selected as susceptible. Three test breeding populations were targeted for their development with the mentioned parents: Tolerant (T) x T, T x Sensitive (S), and S x S. To ensure accurate comparisons, the selected parents were asexually propagated for proper assessment alongside seedling plants. Seeds from those combinations were germinated and will be evaluated soon.
In this project, attempts have been made to evaluate the existence of differences among cultivars in minimum leaf conductance and in vegetative growth and assimilate allocation under water stress conditions. The experimental protocol for leaf minimum conductance determination used in this study has demonstrated significant advantages, such as its simplicity and efficiency, allowing for the evaluation of a large number of varieties in relatively short periods without requiring expensive instrumentation. The project has also enabled the establishment of a seedling grafting technique in young olive seedlings.
Furthermore, FROOTS has demonstrated the presence of genetic diversity in terms of drought tolerance in olive and mechanisms to identify this trait in an olive population. In conclusion, the project underscores the potential of selecting rootstocks tailored to specific environmental conditions to address significant societal challenges within the European Union. This approach, which is common across economically important tree species, holds the promise of alleviating various challenges, including food security, sustainable agriculture, rural empowerment, and climate change adaptation, especially in the context of olive cultivation.
Furthermore, FROOTS has demonstrated the presence of genetic diversity in terms of drought tolerance in olive and mechanisms to identify this trait in an olive population. In conclusion, the project underscores the potential of selecting rootstocks tailored to specific environmental conditions to address significant societal challenges within the European Union. This approach, which is common across economically important tree species, holds the promise of alleviating various challenges, including food security, sustainable agriculture, rural empowerment, and climate change adaptation, especially in the context of olive cultivation.