Disease cycle of Alternaria in apple

Dalphy HarteveldPhD student (1st year)

Tree Pathology Centre

Tree Pathology Centre (A

gri-science QLD

& U

Q)

Principal supervisor:A/Prof. André Drenth (UQ&DEEDI)

Associate supervisor:Dr. Olufemi Akinsanmi (UQ)

Alternaria leaf blotch and fruit spot symptoms

Alternaria fruit spot symptoms

Premature defoliation in Royal Gala trees by Alternaria leaf blotch

Tree Pathology Centre (A

gri-science QLD

& U

Q)

Alternaria leaf blotch symptoms

Alternaria leaf blotch and fruit spot

Pathogen: Alternaria spp.

First report leaf blotch Stanthorpe 1990’s

Fruit losses (15–25 %) of high value apple varieties ‘Royal Gala’, Pink Lady™, ‘Fuji’ and ‘Red Delicious’.

Tree Pathology Centre (A

gri-science QLD

& U

Q)

Alternaria leaf blotch

Alternaria fruit spot

Problem

Erratic control of the diseases.

Identity of the Alternaria species involved is still uncertain.

No information on disease cycle.

Lack of understanding of the identity of the pathogen and its epidemiology in Australia hinders effective disease management

Tree Pathology Centre (A

gri-science QLD

& U

Q)

Elucidate the etiology and diversity of Alternaria leaf blotch and fruit spot of apples in Australia

Research Aims

Overwintering

Seasonal dynamics inoculum

2. Disease cycle

Sources of inoculum

1. Pathogen

Diversity

Distribution

Identity

3. Infection process

leaf

fruit

Tree Pathology Centre (A

gri-science QLD

& U

Q)

Climatic requirements

The pathogen

1. What is the identity/ diversity of the Alternaria species involved in causing the diseases?

2. What is the geographical distribution of the species?

3. Do the same species infect both leaf and fruit?

Tree Pathology Centre (A

gri-science QLD

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Q)

The pathogen

Most reported: Alternaria mali (Alternaria alternata f.sp. mali, Alternaria alternata apple pathotype)

In Australia anecdotal reports: Species not A. mali, but species of the A. alternata-complex.

Species within complex: A. alternata, A. infectoria, A. arborescens and A. tenuissima

Tools for identification: DNA Sequencing Morphology: species specific sporulation patterns

Tree Pathology Centre (A

gri-science QLD

& U

Q)

Identity and diversity of Alternaria species

Tree Pathology Centre (A

gri-science QLD

& U

Q)

DNA Sequencing genes:

- EndoPG (endopolygalacturonase)(Peever et al. (2004))

- Alt a1 (Hong et al. (2005))

Alternaria species could be differentiatedinto 2 groups

A. tenuissima/ A. alternata

A. arborescens

Disease cycle

1. What are the sources of inoculum in the orchard?

2.When during the season are symptoms expressed in the orchard?

3. What climatic conditions may influence inoculum production and infection?

Tree Pathology Centre (A

gri-science QLD

& U

Q)

Source of inoculum

Scherm H, Savelle AT, Boozer RT, Foshee WG (2008) Plant Disease 92(1), 47-50

Three orchards at Applethorpe, Queensland.

Monthly sample collection of 3 trees per orchard from July 2010- March 2011

Numbers of Alternaria spp conidia determined using a method from

Scherm et al. (2008)

Tree Pathology Centre (A

gri-science QLD

& U

Q)

Source of inoculum

Autumn

Summer

Spring

Winter

161

91

25

No leaves yet

Canopy leaf

102

161

103

41

Twigs

No buds

No buds

No buds

0

Buds

1053

Residueremoved

1969

6841

Leaf residueSeason

Sources of inoculum and average quantities of Alternaria spp. conidia per cm²

Tree Pathology Centre (A

gri-science QLD

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Disease incidence35.0

Alternaria fruit spot : end of January 2011- harvest February 2011

Alternaria leaf blotch disease incidence

A

Tree Pathology Centre (A

gri-science QLD

& U

Q) 0.0

5.0

10.0

15.0

20.0

25.0

30.0

Nov-10 Dec-10 Jan-11 Feb-11

% D

isea

se In

cide

nce

C

Fruit set Harvest

Climate

Climate data obtained from Bureau of Meteorology (Applethorpe station)

Tree Pathology Centre (A

gri-science QLD

& U

Q) 0

5

10

15

20

25

30

Jul-10 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11

Tem

pera

ture

(ºC

) /%

Dis

ease

inci

denc

e

0

5

10

15

20

25

30

35

40

45

50

Day

s

Rain days

Mean temperature

Alternaria leaf blotch disease incidence

Tree Pathology Centre (A

gri-science QLD

& U

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Fungus overwinters in leaf residue and twigs

Multiple Alternaria species involved

Symptom development

Leaf blotch: Nov–Feb

Fruit spot: end Jan-Feb

Temperature ± 20ºC + high rainfall

Disease cycle of

Alternaria in apple

Dispersal?

Infection?

AcknowledgementsTree Pathology Centre (A

gri-science QLD

& U

Q)