Variation in oat trichome

presence

Miller S., Hizbai B.T., Wight C.P.,

Gardner K.,Yan W., Tinker N.A

• Groat trichomes: hair like growths on the grain – Present a major health hazard to growers and

processors for harvesting, handling and processing of the grain.

– During threshing and handling, cause skin itching, respiratory congestion and eye irritation for operators.

– Lock the seeds together and cause bridging in seeders and stoppages in the moving of seed in conveyance equipment.

– Trichomes also attract and trap fungal spores and dust, which can lead to infection on the seed.

Trichomes are clearly a disadvantage and growers

and millers would like to have cultivars that lack them.

However, little is known about the genetic control of this trait.

• The only study to investigate genetics of groat trichomes in oat

– Burrows et al. 2001. Gene controlling reduced trichomes on oat

groats Canadian Journal of Plant Science, 81(3): 413-414,

10.4141/P00-183

• recessive gene Gt-1

• many genetic factors affect trichome expression

Efforts are underway to identify the genetic factors controlling

this trait.

• Objective

– To establish a numerical rating system for

groat trichome in oat varieties

– Evaluate hairiness of lines in the VAO 44 X

Leggett breeding population.

– Identify QTLs associated with groat trichome

in oat

Methods

• An F5:6 oat population consisting of 136 recombinant inbred lines

(RILs) developed from a cross between the cultivars ‘VAO-44’

(naked, bald) and ‘Leggett’ (covered, hairy) was used.

– 2 seeds/line/pot were planted in a greenhouse

– 1 panicle per plant (2 panicles/line) were harvested

– Panicles from the two plants representing a line were scored

separately as panicle A and Panicle B.

– 5 seeds from each panicle were analysed for hairiness

- groats were photographed using dissecting microscope at same

magnification

Quantity Length

0 = none very short = ½

½ = ± short = 1

1 = + long = 2

2 = ++

3 = +++

Initial attempt

- each kernel was rated for quantity (Q) and length (L) of trichomes

in 3 areas: brush, crease (ventral) and pericarp (dorsal)

- final score: INDEX = (Qb + Lb) + (Qv + Lv) + (Qd + Ld)

3

Hairiness index (Tricomidex) development

This became complicated and confusing

The initial approach was simplified

- 4 categories ranging from 1 (least hairy) to 4 (most hairy)

were established

- visual scoring

– 5 seeds from each panicle

– each seed was scored individually

– Mean of the five scores was used as the hairiness level of

the plant

Figure 1. Trichome Index developed from the VAO-44 X Leggett population

Results

A B Average

Min 1.20 1.40 1.53

Max 3.95 3.75 3.85

Mean 2.73 2.75 2.74

Table 1. Summary of hairiness level of the VAO-44 X Leggett population

• A summary of the hairiness levels for both plants are

presented in Table 1. The results for both panicles

were consistent as shown in the scatter plot in Fig 2.

Therefore an average of the two plants will be used as

a representative

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50

r = 0.77

• Results T

richom

e levels

of panic

le B

Trichome levels of panicle A

Figure 2. Scatterplots of the trichome index of plant A vs plant B

• The trichome index showed a normal distribution

with a progeny mean of 2.74 indicating that the

trait is controlled by many genetic factors. This is

consistent with Burrows et al (2001) findings.

• The frequency distribution (Fig. 3) shows there is

transgressive segregation of the trait in both

extremes indicating both parents carry alleles

that increase and decrease the trichome levels.

0

10

20

30

40

50

60

70

1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 3.75 4 More

Fre

quency

Hairiness level

Min 1.53

Max 3.85

Mean 2.74

VAO-44 Leggett

Fig 3. Frequency distribution for hairiness in 136 recombinant

inbred lines of the VAO-44 x Leggett population.

• Future work

– DNA for all the lines in the VAO-44 X Leggett

population has been sent for G by S scoring

– waiting for results!

• The genotypic data will be used to construct

a genetic map and for the identification of

qtls that explain variation in the trait. This is a

useful step in understanding the genetic

architecture of groat trichomes in oat.

• Stay tuned!

Thank You!