Crape Myrtle Science: Genetics, Breeding, and Pest Biology

The Science of Crape Myrtles

This expert guide examines crape myrtles through the lens of genetics, breeding science, and pest biology. Understanding the molecular basis of key traits and the biology of emerging pests enables informed breeding and management decisions.

Genetics and Genomics

Genome Characteristics

Parameter	Value
Chromosome number	2n = 48 (most species)
Ploidy	Hexaploid (likely)
Plastome size	~152,200 bp
Plastome genes	112 (78 protein-coding)

Plastome Structure

Recent studies assembled L. indica plastomes revealing:

Typical angiosperm quadripartite structure
Large single-copy region (LSC)
Small single-copy region (SSC)
Two inverted repeats (IR)
GC content: 37.6%

Genetic Diversity

Molecular marker studies have shown:

High diversity within L. indica cultivars
L. indica as maternal donor for most cultivars
Distinct gene pools by geographic origin
Multiple independent domestication events

Hybridization Genetics

L. indica × L. fauriei crosses:

Parent	Contribution
L. indica	Flower color, bloom size, cultivar traits
L. fauriei	Disease resistance, bark character, tree form

Inheritance patterns:

Disease resistance appears quantitative
Flower color shows complex inheritance
Bark exfoliation intermediate to fauriei-like

Breeding History and Programs

Historical Development

Period	Location	Focus
400+ CE	China	Selection from wild
1700s	Japan	L. fauriei cultivation
1960s-present	USA	Interspecific hybridization
2000s-present	Multiple	Continued improvement

U.S. National Arboretum Program

Key contributions:

Interspecific hybridization (Egolf, Pooler)
"Indian Tribe" cultivar series
Disease resistance breeding
Cold hardiness improvement

Breeding timeline:

Year	Cultivar	Notes
1978	'Natchez'	First major release
1980s	'Muskogee', 'Tuscarora', etc.	Expanded series
2000s	Continued releases	Newer cultivars

Current Breeding Objectives

Trait	Priority	Progress
Powdery mildew resistance	High	Good in hybrids
CMBS resistance/tolerance	Emerging	Research stage
Cold hardiness	Moderate	Zone 6 achieved
Compact growth	Growing	Many dwarf cultivars
Novel colors	Moderate	Ongoing
Extended bloom	Moderate	Some progress

Flower Color Biochemistry

Pigment Classes

Pigment Type	Colors Produced
Delphinidin	Purple, blue-violet
Cyanidin	Pink, red
Pelargonidin	Orange-red (rare in Lagerstroemia)
White	Absence of anthocyanins

Genetic Control

Flower color in Lagerstroemia involves:

Structural genes (CHS, CHI, F3H, DFR, ANS)
Regulatory genes (MYB, bHLH, WD40)
Modification genes (glycosylation, methylation)

Color Inheritance

Cross	Expected Offspring
White × White	White
Red × White	Pink or variable
Purple × Red	Variable (purple, red, intermediate)
Purple × White	Lavender or variable

Complex inheritance patterns suggest:

Multiple loci involved
Incomplete dominance at some loci
Possible epistatic interactions

Bark Exfoliation Biology

Mechanism

Bark exfoliation in Lagerstroemia results from:

Cork cambium (phellogen) activity patterns
Differential growth of underlying tissues
Mechanical forces separating bark layers
Environmental factors (humidity, temperature)

Species Differences

Species	Exfoliation Quality
L. fauriei	Most pronounced, colorful
L. indica	Variable, often less dramatic
L. speciosa	Smooth, less exfoliating
Hybrids	Intermediate to fauriei-like

Environmental Factors

Factor	Effect
Age	Increases with maturity
Sun exposure	Enhances color intensity
Moisture	Wet conditions may reduce
Rubbing/cleaning	Can accelerate (controversial)

Crape Myrtle Bark Scale Biology

Pest Identification

Acanthococcus lagerstroemiae (formerly Eriococcus):

Characteristic	Details
Family	Eriococcidae
Origin	Asia (likely China)
First US detection	2004 (Texas)
Hosts	Primarily Lagerstroemia, some others

Life Cycle

Stage	Timing	Description
Egg	Spring	Under female covering
Crawler	Late spring-summer	Mobile dispersal stage
Nymph	Summer-fall	Settles, feeds, develops wax
Adult	Fall-spring	Produces eggs (parthenogenetic possible)

Generations: 2-3 per year depending on climate

Damage Mechanisms

Effect	Mechanism
Direct feeding	Phloem sap removal
Honeydew production	Substrate for sooty mold
Sooty mold	Reduces photosynthesis
Stress	Reduced vigor, flowering

Host Susceptibility

Research indicates variable susceptibility among cultivars:

Susceptibility	Examples
More susceptible	Some L. indica cultivars
Less susceptible	Some L. fauriei hybrids
Variable	Most cultivars

Resistance mechanisms not well characterized.

Biological Control

Predators identified:

Hyperaspis bigeminata (lady beetle)
Chilocorus cacti (twice-stabbed lady beetle)
Azya luteipes (lady beetle)
Various parasitoid wasps

Conservation biological control promising but not sufficient alone.

Research Frontiers

Genomic Resources Needed

Resource	Status	Priority
Reference genome	Not available	High
Transcriptomes	Limited	Moderate
Genetic maps	Sparse	Moderate
Marker-trait associations	Few	High

Key Research Questions

Molecular basis of disease resistance
CMBS resistance mechanisms
Flower color genetics
Cold hardiness determinants
Bark exfoliation control

Breeding Technology Opportunities

Approach	Feasibility	Status
Traditional hybridization	High	Ongoing
Marker-assisted selection	Moderate	Limited markers
Genomic selection	Future	Resources needed
Induced mutation	Possible	Historical use

Conservation Considerations

Wild Species

Species	Conservation Status
L. indica	Secure (wide distribution)
L. fauriei	Limited natural range
Other species	Variable, some threatened

Genetic Resource Preservation

Cultivar collections at arboreta
Living gene banks
Germplasm repositories
Documentation important

Conclusions

Crape myrtle improvement requires:

Enhanced genomic resources
Resistance screening for CMBS
Understanding of color genetics
Cold hardiness mechanisms
Integration of molecular and traditional breeding

The combination of ornamental value, adaptability, and emerging pest pressures makes crape myrtle an important subject for continued research investment.