The document discusses crop improvement in strawberries. It covers the botanical details of strawberries, their origin and distribution, related species, and genetic resources. It then discusses the inheritance patterns of strawberry traits, major breeding problems including disease resistance and yield, and objectives such as adapting to climate change. Principles and methods of breeding are also outlined, including introduction, selection, hybridization, polyploidy, mutation, and biotechnological approaches. Finally, salient achievements in each area are highlighted such as introducing disease resistance from wild relatives and developing varieties with improved yield, quality, and shelf life.
2. Botanical Name: Fragaria x ananassa
Ch. No.: The strawberry belongs to the Rosaceae family, which is in the
order Rosales. 2n = 8× = 56
Origin: The modern cultivated strawberry is a hybridization of two wild
strawberry species, Fragaria virginiana and Fragaria chiloensis, that
occurred in France in the 1700s. The Fragaria genus has a widespread
distribution, with various species growing throughout the Northern
Hemisphere.
INTRODUCTION
3. DISTRIBUTION
Strawberries are widely distributed and cultivated throughout the world,
including Europe, North America, South America, Asia, and Africa. In the
United States, California is the leading producer of strawberries, followed by
Florida and Oregon.
RELATED SPECIES
There are several related species of strawberries, including Fragaria vesca
(wild strawberry), Fragaria iinumae (Japanese Alpine strawberry), Fragaria
moschata (musk strawberry), and Fragaria daltoniana (Himalayan
strawberry).
5. The genetic resources of strawberry refer to the diverse genetic material that
exists within the species and related wild species, which can be used for
breeding and genetic improvement of the crop. The genetic diversity of
strawberry is important for developing new varieties with improved traits such
as disease resistance, yield, and fruit quality.
6. The genetic resources of strawberry are conserved in gene banks around the
world, such as the USDA National Plant Germplasm System, the Nordic
Genetic Resource Center, and the International Strawberry Genebank, located
in the Netherlands. These gene banks preserve a range of genetic material,
including wild and cultivated strawberry species, landraces, and modern
cultivars.
The wild relatives of the cultivated strawberry, such as Fragaria vesca,
Fragaria virginiana, and Fragaria chiloensis, are important genetic resources
for breeding programs. These species possess traits such as disease
resistance, tolerance to environmental stresses, and different fruit
characteristics that can be introgressed into cultivated varieties.
7. Modern breeding techniques such as marker-assisted selection (MAS) and
genomic selection (GS) are being used to improve the efficiency of breeding
and accelerate the development of new cultivars with desired traits. The
availability of genomic resources, such as the draft genome sequence of the
cultivated strawberry, is facilitating the identification of important genes and
traits and the development of molecular markers for use in MAS and GS.
In addition, new genetic resources such as genetically modified strawberries
and gene-edited strawberries have been developed using biotechnology. These
new genetic resources have the potential to improve traits such as disease
resistance, shelf life, and fruit quality, although their use and regulation remain
subject to controversy and debate.
9. The inheritance pattern of strawberry traits follows the basic principles of
Mendelian genetics. The cultivated strawberry is a diploid organism with 14
chromosomes, and most of its traits are controlled by multiple genes.
The inheritance of traits such as fruit size, shape, color, and flavor in
strawberry is complex, and often involves interactions between multiple
genes and environmental factors. For example, fruit color in strawberry is
controlled by several genes, including the FaMYB1 and FaMYB10 genes,
which regulate the production of anthocyanin pigments. Fruit flavor is also
influenced by multiple genes, including those involved in the biosynthesis of
volatile compounds such as esters and terpenoids.
10. Breeding programs for strawberry aim to improve the inheritance of desirable
traits such as disease resistance, yield, and fruit quality. This is achieved
through the selection and crossbreeding of cultivars with desirable traits, as well
as the use of advanced breeding techniques such as marker-assisted selection
(MAS) and genomic selection (GS). These techniques help to identify and select
plants with desirable genetic traits at an early stage, accelerating the breeding
process and improving the efficiency of trait selection.
Overall, the inheritance pattern of strawberry traits is complex, and
understanding the genetic basis of important traits is critical for the development
of new and improved strawberry varieties.
12. 1.Disease resistance: Strawberry is susceptible to a range of fungal, bacterial,
and viral diseases, including powdery mildew, botrytis fruit rot, and verticillium
wilt. Developing new varieties with improved disease resistance is a major
breeding priority, and many breeding programs focus on introgressing disease
resistance genes from wild relatives of the cultivated strawberry.
2.Yield: Strawberry yield can be affected by factors such as soil quality,
temperature, and water availability. Developing new varieties with higher yield
potential is a major breeding objective, and many breeding programs aim to
identify and select plants with desirable yield-related traits such as plant vigor,
fruit size, and fruit number.
13. 3.Fruit quality: Consumers value strawberries with desirable flavor, aroma, and
texture. Breeding programs aim to develop new varieties with improved fruit
quality traits, including sweetness, acidity, firmness, and aroma.
4.Adaptation to climate change: Climate change poses a significant challenge
to strawberry production, as rising temperatures and changing precipitation
patterns can affect yield and fruit quality. Developing new varieties with improved
tolerance to environmental stresses such as drought and heat is a priority for
breeding programs.
5.Labor costs: Strawberry cultivation requires significant labor inputs for tasks
such as hand harvesting and pest management. Developing new varieties with
traits such as mechanical harvesting ability and pest resistance can help to
reduce labor costs and increase efficiency in production.
15. 1.Disease resistance: A study conducted by researchers at the University of
California, Davis used genomic selection to identify markers associated with
resistance to powdery mildew and verticillium wilt in strawberry. The researchers
developed a model for predicting resistance to these diseases based on genomic
information, which could be used to improve disease resistance in breeding
programs (Folta et al., 2019).
2.Yield: Researchers at the University of Florida conducted a study to identify
genetic markers associated with yield and fruit quality traits in strawberry. The
study identified several genetic markers associated with fruit size, yield, and
firmness, which could be used in breeding programs to select for these traits
(Zhang et al., 2019).
16. 3.Fruit quality: A study conducted by researchers at the University of Hohenheim
in Germany used genome-wide association mapping to identify genetic markers
associated with fruit quality traits in strawberry. The study identified several genetic
markers associated with sugar content, acidity, and aroma, which could be used in
breeding programs to select for desirable fruit quality traits (Kleeberg et al., 2019).
4.Adaptation to climate change: Researchers at the University of California,
Davis conducted a study to identify genetic markers associated with tolerance to
high temperature in strawberry. The study identified several genetic markers
associated with heat tolerance, which could be used in breeding programs to
develop new varieties better adapted to rising temperatures (Hancock et al.,
2019).
6.Labor costs: A study conducted by researchers at the University of Florida
developed a model for predicting mechanical harvesting ability in strawberry. The
model used genetic markers associated with plant architecture and fruit
characteristics to predict which plants would be most suitable for mechanical
harvesting, potentially reducing labor costs in production (Zhang et al., 2020).
18. 1.Introduction: Introduction involves bringing in new genetic material from wild
relatives of the cultivated strawberry to increase genetic diversity in the breeding
population. This can be done through direct crosses with wild relatives or by
introgressing desirable traits from wild relatives into cultivated varieties. For
example, researchers at the University of Florida introgressed resistance to
anthracnose crown rot from a wild strawberry species into cultivated strawberry,
resulting in a new variety with improved disease resistance (Graham et al., 2014).
2.Selection: Selection involves choosing plants with desirable traits for use as
parents in breeding programs. Selection can be done based on phenotypic traits
such as fruit size, yield, and disease resistance or using molecular markers linked
to desired traits. For example, researchers at the University of California, Davis
developed a high-throughput phenotyping platform to screen strawberry plants for
fruit size and other yield-related traits, allowing for more efficient selection of
desirable parents in breeding programs (Wang et al., 2021).
19. 3.Hybridization: Hybridization involves crossing two different parental lines to
produce new genetic combinations in the offspring. This can be done through
traditional breeding methods or using advanced techniques such as embryo
rescue or in vitro pollination. For example, researchers at the University of Florida
used embryo rescue to cross a diploid and a tetraploid strawberry parent to
produce a new hexaploid hybrid with improved fruit quality traits (Folta et al.,
2016).
4.Polyploidy: Polyploidy involves increasing the chromosome number in a plant,
resulting in larger cells and organs and potentially improved yield and quality
traits. This can be done through natural or induced polyploidization or by crossing
plants with different chromosome numbers. For example, researchers at the
University of Hohenheim in Germany induced polyploidy in strawberry using
colchicine treatment, resulting in new varieties with larger fruit and higher yield
potential (Krauss et al., 2014).
20. 5.Mutation: Mutation involves inducing genetic changes in a plant through
exposure to mutagenic agents such as radiation or chemicals. This can result in
new genetic variants with desirable traits such as disease resistance or improved
yield potential. For example, researchers at the University of California, Davis used
gamma radiation to induce mutations in strawberry plants and identified new
varieties with improved resistance to gray mold (Xu et al., 2021).
6.Biotechnological approaches: Biotechnological approaches involve using
genetic engineering techniques to introduce desirable traits into plants. This can
include introducing genes from other organisms or modifying existing genes in the
plant's genome. For example, researchers at the University of Florida used RNA
interference to silence a gene involved in fruit softening, resulting in new varieties
with improved postharvest shelf life (Zhang et al., 2015).
22. 1.Introduction: One of the major achievements of introduction in strawberry
breeding was the successful introgression of resistance to the fungal disease
Verticillium wilt from a wild strawberry species (Fragaria chiloensis) into
cultivated strawberry varieties. This was achieved by researchers at the
University of California, Davis, who identified resistance genes in the wild
species and transferred them into cultivated varieties through backcrossing
(Zorrilla-Fontanesi et al., 2011).
2.Selection: The use of selection in breeding has led to the development of
many new strawberry varieties with improved yield, quality, and disease
resistance traits. For example, the variety 'Florida Radiance' was developed
through selection for disease resistance and high yield potential, resulting in a
variety with improved resistance to anthracnose and other fungal diseases
(Whitaker et al., 2012).
23. 3.Hybridization: Hybridization has led to the development of many new
strawberry varieties with improved traits such as disease resistance, fruit quality,
and yield potential. For example, the variety 'Florida Beauty' was developed
through hybridization of two strawberry parents with complementary traits,
resulting in a variety with large fruit size, firm texture, and good flavor (Perkins-
Veazie et al., 2005).
4.Polyploidy: Induced polyploidization has led to the development of many new
strawberry varieties with improved yield and quality traits. For example, the
variety 'Florida Elyana' was developed through induced polyploidization of a
diploid strawberry parent, resulting in a variety with large, firm fruit and high yield
potential (Perkins-Veazie et al., 2009).
24. 5.Mutation: Mutation breeding has led to the development of many new
strawberry varieties with improved disease resistance, yield potential, and fruit
quality traits. For example, the variety 'Seascape' was developed through gamma
radiation-induced mutation, resulting in a variety with improved resistance to
powdery mildew and high yield potential (Weber et al., 2011).
6.Biotechnological approaches: Biotechnological approaches have led to the
development of many new strawberry varieties with improved traits such as
disease resistance, shelf life, and fruit quality. For example, researchers at the
University of California, Davis used RNA interference to silence a gene involved
in fruit softening, resulting in new varieties with improved postharvest shelf life
(Zhang et al., 2015).
