Fred Gmitter and Jude Grosser

Grapefruit Scion

Updates from

UF/IFAS

Florida Citrus Show - 2019

Four Progenitor Species

1. Pummelo (Citrus grandis L. Osbeck)

2. Mandarin (C. reticulata Blanco)

3. Citron (C. medica L.)

4. Papeda (C. micrantha Wester)

Grapefruit is a hybrid of Pummelo x Sweet orange:

Pummelo x (Pummelo + Mandarin)

First one

1700

Safety

Harbor,FL

1823

Grapefruit Origins

Walters

1887

Duncan

1840s

Marsh

1850?

1880?

Thompson

1913

Foster

1907

Flame

1987

Rio Red

1984

Ray Ruby

1977

Henderson

?

Star Ruby

1970

Fawcett

Red

1940

Ruby Red

1929

Hudson

1930

Radiation

What breeding options do we have?

• Mutation breeding

• Reconstructive breeding

• Genetic technologies

USDA-SCRI NIFA Project: Clemson, USDA, UF

New Red Grapefruit Somaclones – In DPI Parent Tree Program

- Clean budwood available for trial under MTA

1. Red Grapefruit N40-16-11-11; DPI-435-0003 bright red, high brix

2. Red Grapefruit N-11-17; DPI-435-0040 dark red, good blush

3. Red Grapefruit N11-29; DPI-435-0041 bright red, high yield

4. Red Grapefruit N40-11-7; DPI-435-0102 dark red, good blush, high brix

5. Red Grapefruit N40-16-11-15; DPI-435-N40-16-11-15 dark red, good blush

6. Red Grapefruit N40-16-11-3; DPI-N40-16-11-3 dark red, high brix

Table 1. Comparison between summer N2-28 ‘Summer

Gold Grapefruit’ and controls ‘Ruby Red’ and ‘Pink

Marsh” for the Brix, color and titrable acidity value

(average of 20 fruit per selection, test conducted July,

2013).

• Cybrid with ‘Dancy’ cytoplasm

• Sweeter than Ruby Grapefruit

• Harvest from December to August!

• No granulation or seed germination

N2-28 Summer Gold Grapefruit

Brix° Color Titrable

Acidity (ml)

Summer Gold

N2-28

11.6 34 0.98

‘Ruby Red’

grapefruit

9.4 34.5 0.85

‘Pink Marsh’

grapefruit

8.2 34.3 1.2

Cybrid Flame/Swingle tree showing good recovery from HLB when treated

with CRF + extra polycoated manganese sulfate. Fruit had 11-12 brix this year.

Dark Red Cybrid Flame (non-GMO) showing recovery from HLB!

INT

RO

DU

CT

ION

Highly Susceptible

Fresh fruit market

Highly Resistant

Grapefruit

Citrus paradisi

Kumquat

Fortunella crassifolia

CYBRIDIZATION PROCESS

• All genes are not housed in the nucleus. Both mitochondria and chloroplasts have

small genomes.

• Citrus cybridization often occurs in citrus somatic hybridization experiments (via

protoplast fusion).

• Citrus cybrids from embryogenic culture + leaf cell fusions always have the

mitochondrial genome from the culture cell parent, the chloroplast genome is

generally randomly inherited. Allows for study of nucleo-cytoplasmic interaction.

Ahmad Omar

Ahmad Omar

aro

ma

the

rap

ya

nd

mo

re.c

o.n

zw

ww

.myfo

od

bo

xe

s.c

om

2X[mt-B/cp-A] 2X[mt-B/cp-B]

Nucleus A

19 cybrids

mt-B

cp-A cp-B

123 cybrids

Grapefruit

Leaf-derived

protoplasts

Kumquat

Embryogenic callus

Example of grapefruit cybridization with kumquat cytoplasm

CITRUS CANKER RESISTANCE SCREENING

OB

JE

CT

IVE

2

Infiltration inoculation assay (attached leaf assay)

Genotype July 2015 September 2015

‘Marsh’ Grapefruit … 120.80 a

‘Flame’ Grapefruit 131.96 a 116.16 a

Cybrid M-81 … 96.52 b

Cybrid M-13 99.00 b 58.94 ef

Cybrid N-6 94.09 b 75.14 cd

Cybrid F-10 71.75 c 78.78 c

Cybrid F-13 … 70.56 cde

Cybrid M-10 64.00 c 61.13 ef

Cybrid M-9 58.37 c 68.94 cde

Cybrid M-11 … 68.38 cde

Cybrid F-3 … 66.36 de

Cybrid F-15 … 52.79 f

‘Meiwa’ Kumquat … 1.67 g

X Different letters within each assay

month indicate significant

differences (P<0.05) according to

Student-Newman-Keuls Test

Table 3. Mean of total number of lesions per leaf after infiltration inoculation

of Xanthomonas citri subsp. citri for regenerate cybrids and their progenitors

in two assaysx

Somatic cybrid plants of Grapefruit containing Mewia ‘Kumquat’ cytoplasm (mitochondrial genome).

Somatic cybrid plants of White Marsh, Flame and red somaclone N11-11 grapefruit containing Meiwa Kumquat cytoplasm (mitochondrial genome)

Reconstructive Breeding

• Can we recreate grapefruit?

• Parent selection

• Diploid or triploid?

• Is it truly grapefruit? No!

• Does this matter in the big picture?

Breeding for canker & HLB resistance: canker epidemic causing a

naturalscreen of CREC germplasm – leading to the identification of

superior canker &HLB tolerant diploid and tetraploid breeding parents

for use ininterploid crosses to generate seedless triploids – crosses

underway! Hundreds of triploids have been produced.

Red pummelo 8-1-99-5B Murcott+Chandler #81

somatic hybrid (4x)neighbor

X

Breeding Canker Tolerant Triploid Seedless Grapefruit-like Hybrids

Tetraploid Somatic Hybrid Canker Tolerant Pummelo

-Several good canker tolerant breeding parents now flowering

-Hundreds of triploid hybrids already produced

-Embryo rescue not required when tetraploid parent is used

as the female

Testing of Triploid Pummelo/Grapefruit Hybrids for Citrus Canker Resistance

Citrus leaves 4 weeks post inoculation with Xanthomonas citri var. citri, Meiwa kumquat on left

Wide Range of Response of Inoculations with Citrus Canker Among Offspring

Ave

rage

Nu

mb

er o

f Le

sio

ns

per

Ino

cula

tio

n S

ite

Pummelo/Grapefruit Triploid Offspring

Meiwa KumquatFlame and Ruby Red Grapefruit

Monster Pummelo

Love grapefruit but can’t

eat it because you’re taking

prescription drugs?

We may have the answer!!!

UF 914

• Red flesh color

• Attractive peel blush

• Grapefruit size (+)

• Grapefruit flavor and

aroma

• Tender and juicy flesh

• Very low in FC’s (GJE)

• Seedless

• Good brix, lower acid

• SWEETER!

What to think about UF 914?

• There is clearly a potential medical claim to make, to recapture the Senior Statin Market

• Focus group showed it is clearly distinguishable from grapefruit to ordinary consumers

• Is there a reason to market UF 914 other than the counter to the drug interaction?

• South Korea, what they buy, and how they use it• Red grapefruit, to mix with sugar and tea or “shojiu”• White fleshed “Sweeties” for fresh, but red is BETTER!

BUT THIS IS MUCH

MORE ABOUT HLB

THAN CANKER OR

FRUIT QUALITY!

GENETIC TECHNOLGIES

• Transgenics?

• Genome editing (i.e. CRISPR)?

• Several NIFA projects underway

• Grapefruit targeted in 3 different projects

• Gene target identification needed

• Successful editing and validation

• Only true grapefruit with HLB resistance

• Years away from now

• In the meantime?

THANK YOU!

NVDMCCRDF

The good grower-cooperators of Florida

USDA-NIFA