alternaria leaf blotch and fruit spot of apple in...

Alternaria leaf blotch and fruit spot of apple in Australia

Dalphy HarteveldPhD student

Tree Pathology Centre

Tree Pathology Centre (

Tree Pathology Centre ( A

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

Associate supervisor:Dr. Olufemi Akinsanmi (UQ)



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Alternaria leaf blotch symptoms



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Alternaria leaf blotch symptom: premature defoliation



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Alternaria fruit spot symptom

Alternaria leaf blotch and fruit spot distribution

Pathogen: Alternaria

First report leaf blotch Stanthorpe 1990’s

First report fruit spot Stanthorpe 2003



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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



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Improve our understanding of Alternaria leaf blotch and fruit spot of apples in Australia

1. Pathogen2. Disease cycle

This study will provide a better understanding of the diseaseswhich can serve as foundation for improved management options.

Research AimsTree Pathology Centre (


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1.The pathogen

1. What is the identity and 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?



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Identity and diversity of Alternaria speciesTree Pathology Centre (


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Experimental design

51 isolates obtained from leaf and fruit symptoms from different regions in six states of Australia

DNA sequencing 5 genes and morphological examination

Results

Three different Alternaria species involved:1. A. arborescens2. A. tenuissima3. A. alternata

None of the species was specific to leaf or fruit symptoms or region.

71% of isolates obtained from symptomatic fruit were identified as A. tenuissima and A. alternata from Queensland and New South Wales

70% of the isolates obtained from leaf symptoms were identified as A. arborescens, occurring in all states

Identity and diversity of Alternaria speciesTree Pathology Centre (


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2.Disease cycle

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

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

3. How do the diseases develop in the tree canopy?

4. What climatic conditions may influence disease expression in the field?



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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- now

Numbers of Alternaria spp conidia determined using a method from

Scherm et al. (2008)



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Source of inoculum

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



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Canopy leafTwigsBudsLeaf residueSeason

No leaves51633558Winter-’11

22379No buds959Autumn-’11

112161ResidueremovedSummer-’10/’11

25103No buds985Spring-’10

No leaves4106842Winter-’10

No buds

Disease incidence35.0

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

Alternaria leaf blotch disease incidence

A



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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

Disease development in the tree canopy

Royal Gala

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

Mea

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ount

of d

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aves

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Bottom

Middle

Top

FB22-47

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

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BottomMiddleTop

Alternaria leaf blotch disease mostly affecting leaves at the bottom level of the trees.

Disease initiates at all levels of tree canopy (indicates air dispersal of spores)



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Climate

Climate data obtained from Bureau of Meteorology (Applethorpe station)



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

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ture

(ºC

) /%

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Rain days

Mean temperature

Alternaria leaf blotch disease incidence



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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

Management suggestion so far

Reduction of infected apple leaf residue in the orchard by application of urea.

Orchard hygiene can reduce the amount of inoculum available to infect next season’s crop.



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AcknowledgementsTree Pathology Centre (


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alternaria leaf blotch and fruit spot of apple in...

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