Late Blight

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Late blight (LB) of potatoes and tomatoes, the disease that was responsible for the Euopean potato famine in 1840s, is caused by the fungus-like oomycete pathogen Phytophthora infestans.

It can infect and destroy the leaves, stems, fruits, and tubers of potato and tomato plants, and has been known to infect other plants of the Solanaceae family as well.

Late blight has been referred to as a ‘community disease’ due to its ability to spread rapidly from field to field under the right weather conditions. Asexual spores travel easily on the wind when the weather is cool and moist, and can rapidly infect neighboring fields. Phytophthora infestans can adapt very rapidly to selection pressures created by agrochemicals, which makes it a difficult pathogen to manage ( Rocha-castro et al 2014; Fry et al 2015).

Oospore of Phytophtora infestans
Late Blight on potato plant leaves
Infected leaves with Late Blight
Late Blight on potato plant leaves
Late Blight on stem of potato plant
Late Blight on potato plant
Late Blight on potato plant
Potato Late Blight infestation
Potato field infested by Late Blight
Potato infested by Late Blight
Irreglar reddish brown colored Late Bight lesions
Necrotic stratch marks from surface to the inner by Late Blight

Disease cycle of Phytophthora infestans the cause of potato late blight (Redrawn from Agrios by James Hutton Institute and reproduced by kind permission of Dr D.E.L. Cooke).”

Phytophthora infestans is an oomycete or water mold, a microorganism that causes the serious potato and to;ato disease known as late blight or potato blight. ( early blight is caused by Alternaria solani, is also often called “potato blight”.)

P. infestans is diploid, with about 11-13 chromosoms, and in 2009 scientists completed the sequencing of its genome. The genome was found to be considerably larger (240Mbp) than that of most other Phytophthora species whose genomes have been sequenced. This big genome code for around 18000 genes, 74% are repetative DNA.

It contains diverse variety of transponsons and gene family encoding for “effector proteins”. These “effectors” motif are involved in translocation of pathognen protein into host, and they are split in two groups, the one produce in the symplast (inside plant cells) and in the apoplast (between plant cells). These effector proteins produced in the symplast may contain a signal peptide (SP) followed by the canonical RXLR protein (Arginine X Leucine Arginine) domain. (Birch et al, 2006, Hein et al, 2009, Lamour et al 2012a).

Some RXLR are avirulence protein, meaning they can be recognized by the plant and lead to an hypersensitivity response which restricted the growth of the pathogen.

Most of resistant variety in potato are recognizing this kind of protein from the pathogen. The effector recognition inductible defense response is often by nucleotide biding, leucine-rich rpeat (NLR) disease resistance proteins, and the resulting incompatibility is known as effector triggered immunity (ETI) (Jones & Dangl, 2006; Dodds&Rathjen 2010, John et al 2016)

Effectors which are not recognized by the plant are describe as virulent.


Pictures from CIP collection, W. Perrez, C. Xiao, H. Li, X. Che, G. Mei.
Rocha-Castro et al, 2014 Molecular Plant-Microbe interactions 25: 910-919
Fry et al, 2015 Phytopathology 105: 966-981
Birch et al 2006, Food security 4: 477-508
Hein et al 2009, Molecular Plant Pathology 10: 547-562
Lamou et al 2012a, Molecular Plant Pathology 13: 329-337
Jones and Dangle 2006, Nature 444: 323-329
Dodds and Rathjen 2010, Nature reviews Genetics 11: 539-548
Jones et al 2016, Science 2: 354 (6316)



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