Studies towards late blight control in potato

Abstract

Abstract

The oomycete Phytophthora infestans, which causes the devastating late blight disease of potato, is notorious for

developing resistance to conventional control strategies (fungicide application and resistance breeding by

introgression of R gene). To increase our tool box of disease management strategies available to combat P.

infestans, there is a need to explore several new approaches that can lead to more durable solutions to control late

blight disease. Using the potato-P. infestans pathosystem, different approaches were used in this thesis with an aim

to enhance potato defence and find new resistance sources to P. infestans. In the first approach, exogenous

application of a new natural agent, sugar beet extract (SBE), resulted in significant reduction of the size of the

infection lesions. The pattern was similar to that seen with application of a known defence-inducing compound, β-

aminobutyric acid (BABA). SBE triggered pathogenesis-related protein production with no toxic effect on pathogen

growth from SBE was noted, which suggests that the protection conferred by SBE is via induced resistance. BABA

is a non-protein amino acid that was shown to induce resistance in different plant species and against various

pathogens. However, its mechanism of induced resistance (IR) activation in potato to P.infestans is unclear. Thus, in

the second approach, a proteomic and transcriptomic study was conducted in an attempt to unravel the mechanism

of BABA-IR in potato. It became clear from our study that BABA results in direct activation of several hormonerelated

pathways and defence-related proteins. In the third approach, a constitutively activated defence was

discovered in one Phytophthora-resistant potato clone (out of two investigated), which could be an interesting

starting material in resistance breeding. In the fourth approach, engineering potato plants by in planta expression of

pathogen-associated molecular patterns (Pep13 and flg22) resulted in significant reduction of late blight severity,

which could be a suitable strategy to alleviate the severity of plant diseases. An integrated pest management

approach, including reduction of the use of the fungicides, is one of the recommendations of the recent EU directive.

Thus, it is anticipated that combining induced resistance principle and/or a properly designed transgenic approach

with conventional control strategies can reduce fungicide inputs and provide a more efficient and sustainable

solution for late blight problem.

Abstract (Swedish)

Popular Abstract in English

Plant diseases are directly associated with food security because they result in severe

reduction of plant yield and thus they add to the scarcity of foods in the world, which can

lead to negative repercussions on humankind. Late blight disease that severely hit Ireland in

1840s, which was caused by Phytophthora infestans and is mentioned in the historical

records as the Irish Famine, can be a testimony of the involvement of plant pathogens in

human tragedies and shaping the history of humankind. Through constant research and

discoveries, it became clear that control of plant diseases could be done by breeding resistant

varieties and by using agrochemicals, which led to enhanced plant protection and increased

yields. Plant pathogens became increasingly resistant to these conventional control strategies

due to their excessive and wide-spread use in different parts of the world. Taking P.infestans

as an example, recent research conducted in the areas of genome sequencing, pathogenicity,

and genetics revealed tactics used by this this devastating pathogen to defeat resistance

conferred by the resistant varieties and fungicides. It is now evident that this pathogen

contains several classes of transposons (jumping DNA elements) that can accelerate

pathogen evolution and also several types of pathogen proteins (named effectors) that affect

the host. Effectors can be viewed as a double-edged sword: they can either result in

resistance in plants that can have the required recognition system to recognize these

effectors so that the plants can be immunized against these pathogen isolates, or they can

result in disease initiation by suppression of the plant recognition system. Because of these

issues combined with the hazards that fungicides can have on health and environment, new

approaches to control plant diseases are now required. Plants are known to have their own

immune system and they induce various defence responses when they encounter different

stresses like pathogens. It was found, for example, that synthetic chemicals like analogues of

plant hormones or the non essential amino acid β-aminobutyric acid (BABA), when applied

to plants can result in enhanced resistance to pathogens because these chemicals, which are

called plant defence activators, activated plant defence responses and made the plant on the

alert against future plant infection in a more efficient way than the non-treated plants. This is

known as induced resistance and it is an interesting area of research with potential

application in modern agriculture. However, the prices of these chemicals can be prohibitive

for farmers. It stands to reason that natural and cheap agents that can have defence-inducing

ability can be an interesting alternative. I have found that sugar beet extract (SBE), extracted

through a simple extraction method from a large-scale plant waste product, could induce

defence in potato to P. infestans in a similar way in which the synthetic chemical BABA

does. The agent reduced the infection lesions on the plants and reduced the total number of

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infectious propagules (sporangia) in plants, which indicates a good potential for its possible

use in organic farming or in general plant disease control strategies. The need to understand

the mechanism of plant defence activators is important to study in order to effectively apply

these agents in large-scale application in agriculture. BABA is a well-known defence

inducing agent, thus its mechanism of induced resistance was studied in potato after BABA

treatment to understand why potato plants become more resistant to P. infestans. In order to

study the changes after BABA treatment, detailed proteomic and transcriptomic study was

conducted for this purpose, which found that direct activation of hormone-related pathways

and defence-related proteins was involved in the induced resistance. In another project, it

was found that a Phytophthora-resistant potato clone from potato breeding program

displayed constitutive activation of plant defences without any pathogen stress, which can be

a good basis for future breeding efforts. Resistance can be engineered by genetically

modifying plants. During plant-microbe interactions, some molecules are released from

pathogens, which are termed pathogen-associated molecular patterns (PAMPs) and which

are recognized by specific plant receptors to activate plant defences. I have found that by

expressing two PAMPs in potato plants, one from bacteria (flg22) and the other one from

Phytophthora spp. (pep13), significant reduction of late blight severity was achieved, which

can be an interesting strategy to control late blight disease. Moreover, it is possible to

combine the transgenic approach or the induced resistance breeding with the conventional

control strategies to provide a more efficient and durable solution for the late blight problem.

• author: Moushib, Laith
• supervisor: Erik Andreasson; Susanne Widell
• opponent: Jørgensen, Hans, University of Copenhagen, Molecular Plant Biology
• organization: Molecular Cell Biology; Department of Biology
• publishing date: 2013
• type: Thesis
• publication status: published
• subject: Biological Sciences
• keywords: Oomycetes, plant induced resistance, sustainable agriculture, plant defence activators, plant innate immunity, potato, late blight
• defense location: Crafoordsalen at Alnarp SLU
• defense date: 2013-03-27 09:12:00
• language: English
• LU publication?: yes
• additional info: The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Department of Cell and Organism Biology (Closed 2011.) (011002100), Molecular Cell Biology (432112241)
• id: 2c5190cc-36df-4dfa-9d28-9e70599dba49 (old id 3559283)
• date added to LUP: 2016-04-04 11:06:13
• date last changed: 2018-11-21 21:02:41