The Peach Leaf Curl Disease (Taphrina deformans)

Leaf Distortions & Discolorations Caused by Peach Leaf Curl
Leaf Distortions & Discolorations Caused by Peach Leaf Curl

The Peach Leaf Curl caused by the ascomycete fungus Taphrina deformans. The disease is considered extremely serious as the pathogen causes significant damage to the tree and crop, including severe defoliation, a significant reduction in Peach production, and it might dry the tree completely.

In addition to Peach, T. deformans infects other Stone Fruits, as well as Almonds from Nuts.

The Peach Leaf Curl belongs to the genus Taphrina (syn. Exoascus), in which all the Exoascus species are classified. Of these, Taphrina wiesneri (syn. T. cerasi) infects the Cherry, T. pruni infects Damson Plum, and T. armeniacae infects the Apricot.

But even in this pathogens and diseases avalanche there are some good news: The good news is that both the Peach Leaf Curl and other Exoascus are treated extremely efficiently with timely interventions of various plant protection products.

Now whether and to what extent this event is comforting the professional growers of Peach as well as other fruit growers, the editorial team of ‘Kalliergeia‘ outspoken declares, its utter ignorance.

However, it is certain and most comforting the fact that there is a firm conviction in almost the entire scientific community, that the fungus was first arbitrarily introduced to European Peach growers in the distant 1841 coming directly from the native tree land, the (then) imperial China.

Sexual reproduction of Taphrina deformans occurs with ascospores.

Sectioned Leaf Shows Ascus With Ascospores of Taphrina deformans - © Bruce Watt, University of Maine, Bugwood.org
Sectioned Leaf Shows Ascus With Ascospores of Taphrina deformans - © Bruce Watt, University of Maine, Bugwood.org
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The Peach Leaf Curl Disease (Taphrina deformans) - Classification

Peach Leaf Curl is classified in the Kingdom of the Fungi and in the Subkingdom Dikarya. The complete taxon of the fungus is listed below.

Classification

Domain: Eukaryota  

Kingdom: Fungi

Subkingdom: Dikarya

Phylum: Ascomycota

 Subphylum: Taphrinomycotina

Class: Taphrinomycetes

Subclass: Taphrinomycetidae

Order: Taphrinales

Family: Taphrinaceae

Genus: Taphrina

Species: T. deformans 

Taphrina deformans (Berk.) Tul. (1866)

Teleomorph: Taphrina deformans (Berk.) Tul. (1866)

Anamorph: Lalaria deformans (Moore 1990)

Synonyms

  • Ascomyces deformans Berk. (1860)
  • Exoascus deformans (Berk.) Fuckel (1870)
  • Exoascus amygdali Jacz. (1926)
  • Taphrina amygdali (Jacz.) Mix (1936)

Common Names

  • Greek: Εξώασκος της Ροδακινιάς, Καρούλιασμα Φύλλου Ροδακινιάς
  • English: Peach Leaf Curl, Leaf Blister, Leaf Blister Of Peach, Leaf Curl Of Peach
  • Spanish: Abolladura Del Melocotonero, Arrufat (Melocotonero), Lepra Del Melocotonero, Verrucosis Del Durazno
  • French: Cloque De l’Amandier, Cloque Du Pecher
  • Germany: Kraeuselkrankheit, Pfirsich
  • Chinese: 畸形外囊菌
  • Arabic: الفطر المسبب

The Peach Leaf Curl Disease (Taphrina deformans)

The Peach Leaf Curl Disease (Taphrina deformans) - Biology & Ecology

The Taphrina deformans belongs to the phytopathogenic fungi, whose territory is planetary: it is sufficient to refer only to the extensive cultivation zone of Rodakinia, located between latitude 25 ° North and 45 ° South, to understand its range.

Its biological cycle is biphasic as it contains a parasitic and a saprophytic phase, reproduces both sexual with ascospores and asexual, with conidia (or blastospores), while the disease it causes is not polycyclic as it is rarely observed and secondary infections.

All of this, but also a little more, are discussed below. 

Biological Cycle

In early spring and with low temperatures and high relative humidity, the fungus mainly enters by its germinated bud-conidia in the host tissues.

There it settles in the intercellular spaces of the upper epidermis by developing a dense network of mycelial textures. With the appearance of the sexual reproductive organs, the asci, break through the cuticle and erupt the ascospores.

Ascospores by budding produce conidia, which are dispersed into new plant parts and leaves by drops of rain or irrigation water.

Both in the form of ascospores and conidia, Taphrina deformans will pass the summer on host tissues, where in autumn, again with low temperatures and high relative humidity, ascospores will produce new bud-conidia.

Gradually, as they become more numerous, the conidia will form a thin film on the host’s tissues, remaining there until spring.

Parasitic Phase

The parasitic phase of the Peach Leaf Curl starts by spores that produce a hypha which penetrates the cuticle and invades the plant tissues between the epidermal and the parenchyma cells and lasts until the dispersal of its native reproductive products, the ascospores, during late spring through early summer.

Saprophytic Phase

Saprophytic phase is manifested by the budding of ascospores and the formation of vegetative (asexual) products, the conidia (blastospores). With ascospores and blastospores, the fungus settles mainly on the bark of Peach tree in the summer, as well as other infested trees.

Sexual Reproduction

As the mycelium grows, ascogenic cells are formed. Ascogenic cells elongate perpendicular to the surface of the host, lifting the cuticle of leaves, while at the same time the individual nuclei of each cell unite to form a diploid (Zygote).

The diploid nucleus is divided by mitosis, and from the two resulting nuclei, one moves to the distal end of the elongated ascogenous cell while the other remains at the base. The cell is then divided by producing two unequal daughter cells.

The larger of these is the ascus mother cell, and the smaller, the stalk cell, connects the parent to the mycelial textures.

The forming asci growth upward, and rises the pierced or torn cuticle of the leaves and reveal on the surface appearing as a more or less continuous hymenium.

Within the asci, with successive nucleation, up to 8 haploid nuclei are formed, respectively formed up to 8 ascospores.

Eventually the ascosporia are dynamic expelled through an apical slit or rupture at the top of the asci which most often accumulate on the surface of the leaves, giving them the characteristic white or ash powdery condition.

Asexual Reproduction

Asexual reproduction of Taphrina deformans occurs with conidia (or blastospores). Conidia are produced by ascospores either by budding them into the asci, where they can form up to 16 to 18 conidia, or after the ascospores are released.

Conidia have the potential to produce mycelium or new conidia.

For the production of mycelium, during conidia budding their nucleus is divided. The resulting two nuclei move and divide at the same time, forming hyphae on the host whose cells are binuclear.

Overwintering

The Peach Leaf Curl overwintering with both conidia and ascospores – though with the latter less common. The conidia remain in the soil or are dispersed on the tree, in the folds of the bark, trunk and branches, as well as on the bud scales. Extremely resistant to adverse weather conditions, they can survive for more than two years.

Oversummering

The Peach Leaf Curl oversummering epiphytic or saprophytic, in high temperatures in summer, as ascospores and bud-conidia (blastospores), and in places on the tissues of the affected trees.

It mainly resides in the outer bark of Peach trees as part of the multitude of other non-harmful epiphytic fungal organisms and their colonies.

The Peach Leaf Curl Disease (Taphrina deformans)

Naked Asci of Taphrina deformans on Surface of Leaf - © Bruce Watt, University of Maine, Bugwood.org
Naked Asci of Taphrina deformans on Surface of Leaf - © Bruce Watt, University of Maine, Bugwood.org

The Peach Leaf Curl Disease (Taphrina deformans) - Morphology

Basic morphological elements of the Peach Leaf Curl are mycelium, asci, ascospores, and conidia.

Mycelium

The mycelium of Taphrina deformans is yellowish-cream to pinkish-cream, butyrous, and have a smooth and glossy surface. Its mycelial hyphae consist of cells whose shape is mainly oval to ellipsoid, 3.3 to 4.9 µm in diameter and 5.1 to 7.7 µm in length.

Aski

The aski are cylindrical-clavate shaped and rounded or truncate at the apex. Their length dimensions range between 17 and 56 µm, while the diameter is between 7 and 15 µm.

Ascospores

Within each ascus up to 8 ascospores are formed – sometimes only 2. They are unicellular, ovoid or ellipsoidal and vitreous, with length and diameter ranging from 3 to 7 µm.

Conidia

The conidia (blastospores) of the Peach Leaf Curl range in size from 2 to 6 µm in length and 4.5 µm in diameter.

The Peach Leaf Curl Disease (Taphrina deformans)

The Peach Leaf Curl Disease (Taphrina deformans) - Epidemiology

The Peach Leaf Curl occurs early in the spring. In the past, it was supposed that the trees were affected by mycelium which remained on the twigs until the following spring, and from there the inocula settled on the leaves at the opening of the buds of the tree.

It is now generally accepted that this is not the case. Infection occurs with the spores of the fungus, probably conidia, which have overwintered either in the bud scales or other plant tissues or even in the orchard soil.

Conditions for the Development of the Pathogen

In a laboratory environment, the optimum temperature for fungal growth is 20 °C (68 °F), while appropriate temperatures are those where the minimum is at 8.9 °C (48 °F), and the maximum ranges between 26 °C (79 °F) and 30.5 °C (87 °F).

For bud-conidia budding, high relative humidity of 95% or higher is required.

In the orchard, temperatures below 16 °C (61 °F) require at least 3 mm of rain and 12.5 hours for infection to occur, as long as the affected tissues remain wet.

If the tissues remain fully moistened for 2 or more days then the intensity of infestation is high.

If the temperature remains constant above 20.5 °C (69 °F) it is very likely that the symptoms of the infestation will not observed.

Also, when the minimum temperature is below 7.2 °C (45 °F), the maximum exceeds 30.5 °C (87 °F) and the humidity is low, then the intensity of the attack is reduced and /or the infection ceases.

Pathogen Growth

Infection occurs with the opening of the host’s buds, and before the differentiation of new vegetation tissues.

Ascospores and conidia of Taphrina deformans, by their germ tubes, pass through the leaves stomata or penetrate directly the cuticle and initially grow within the cuticular layer. From there they send the hypha to the intercellular spaces of the parenchyma and the epidermis cells, where they are finally established as mycelium.

With the development of its intercellular mycelium, the pathogen releases various substances, such as cytokines, auxins and enzymes, which cause changes in the size, shape and structure of the cells of the affected tissues.

It is typically reported that the release of cytokines results in an increased flow of nutrients to the affected tissue, which the fungus benefits from.

Eventually cellular dysfunction becomes clearly visible from the hyperplasia and enlargement of the host cells, which give the characteristic symptoms of the disease on the leaves and other susceptible plant tissues.

The Peach Leaf Curl Disease (Taphrina deformans)

The Peach Leaf Curl Disease (Taphrina deformans) - Symptoms

The Peach Leaf Curl infects many of the overground vegetation, but not to the same extent. Thus the disease occurs first on the leaves, and then on the fruits, on the twigs, and sometimes even on the flowers.

Leaves

Depending on the severity of the infection by Taphrina deformans, the disease is found either on a few leaves or on the whole foliage. Its typical manifestation is distortion.

The distortion of the leaves is due to the intense cellular hyperplasia, which is caused by abnormal function of the parenchymal tissues and is macroscopically manifested by local or total abnormal thickening of the lamina and their curling.

Moreover, the affected parts of the leaves become softer than the correspondingly intact.

The manifestation of the phenomenon also involves the discoloration of the leaf surface. The leaves first become chlorotic, then violet – red or purple, and then reddish yellow or yellow – ash.

During the reproduction period of the fungus, the ascospores of the pathogen appears in the swollen areas, giving the leaves powdery ash or velvety appearance.

At the final stage of infestation, the leaves become brown, gradually wither, dry, and then fall, in late spring with early summer.

In conditions of high disease severity extensive defoliation is observed, and the first spring vegetation wave can be completely destroyed. This is followed by the second vegetative wave, which strangely not affected by the fungus, but its growth greatly affects the tree. The consequence is the inevitably significantly reduced production.

Young Twigs

The Peach Leaf Curl infects the young twigs. In infected twigs, their color changes to light green or yellow, they become thicker, and observed growth retardation, distortion, and sometimes gum secretion is observed. Very often, as a result of the action of the pathogen, they are completely dried.

Fruits

Infected fruits show irregular and swollen colored areas on the surface.

These areas are usually wrinkled, without the usual health fuzz – when it comes to peach fruit – their color is yellowish-red, and look like they have been polished. Later, they acquire corky texture and tend to open.

Affected fruits rarely remain in the tree for long.

The Peach Leaf Curl Disease (Taphrina deformans)

The Peach Leaf Curl Disease (Taphrina deformans) - Control

Peach Leaf Curl can be treated in a variety of ways and means, both preventive and suppressive.

Preventive Treatment

Preventive treatment refers to the selection of those varieties of Peaches and Nectarines that show resistance or complete immunity to phytopathogenic fungus. Some of these are listed below.

Resistance Cultivars of Peache

  • Frost
  • Indian Free
  • Muir
  • Q-1-8

Note: The Frost Peach variety needs preventive sprays the first 2 to 3 years after its establishment.

Resistance Cultivars of Nectarine

  • Kreibich

Cultural Practices

The cultural practices to assist in the management of the Peach Leaf Curl include:

  • Autumn pruning, to reduce the population of inoculumon trees (Spring pruning of the affected twwigs and branches is not effective)
  • Enhanced nitrogen fertilization of seriously affected trees
  • Increasing irrigation
  • The thinning of the fruits depending on the remain leaf surface of the trees

Biological Control

Preparations containing the bacterium Bacillus subtilis strain QST 713 are used for the biological control of the Peach Leaf Curl. Light infestations require an early spring application and two applications in case of severe attack.

Chemical Control

The Peach Leaf Curl is effectively treated with a timely, mainly preventive spray. The most favorable period for dealing with the pathogen is from late autumn, with 90% of the leaves falling, until the end of winter just before the buds swell.

However, therapeutic sprays can be applied in the spring, after the pathogen is installed.

The following are active substances that can be used to control Taphrina deformans.

Those active substances with the indication [E] are authorized for use in Greece (and most European Union countries) at the time of writing this article.

Active Substances

Conventional Farming
  • Bordeaux mixture [Ε]
  • Captan [Ε]
  • Dodine [Ε]
  • Chlorothalonil
  • Copper oxychloride [Ε]
  • Copper hydroxide [Ε]
  • Copper oxide [Ε]
  • Difenoconazole
  • Ferbam
  • Hexaconazole (Therapeutic, Spring, 3 applications / ten days)
  • Mancozeb [Ε]
  • Tebuconazole [Ε]
  • Thiram
  • Trifloxystrobin [Ε]
  • Ziram [Ε]
Organic Farming
  • Bordeaux mixture
  • Copper oxychloride
  • Copper hydroxide
  • Copper oxide

Absolutely Necessary Reminder

The reference to the active substances that can be used against Taphrina deformans is for purely informative reasons. Under no circumstances is their use implied or encouraged without the approval of the local agronomist.

The Peach Leaf Curl Disease (Taphrina deformans)

Symptoms of Peach Leaf Curl - © Lesley Ingram, Bugwood.org
Symptoms of Peach Leaf Curl - © Lesley Ingram, Bugwood.org

The Peach Leaf Curl Disease (Taphrina deformans) - Hosts

Peach Leaf Curl infects numerous plants, both fruitful and ornamental. The most important hosts of this phytopathogenic fungus are listed below.

Fruit Trees

  • Prunus persica (Peach)
  • Prunus persica var. nucipersica, syn. Prunus persica var. nectarina (Nectarine)
  • Prunus avium (Sweet Cherry)
  • Prunus domestica (Common Plum)
  • Prunus armeniaca (Armenian Plum)
  • Prunus dulcis (Almond)

Ornamental Plants

  • Prunus spp. – Ornamental varieties of Prunus

The Peach Leaf Curl Disease (Taphrina deformans)

The Peach Leaf Curl Disease (Taphrina deformans) - Geographical Distribution

What we stated ​in a previous article about the Apple Powdery Mildew is also true for the Peach Leaf Curl: its absence from the Poles is more than noticeable.

Section

The Peach Leaf Curl Disease (Taphrina deformans) - References

The References of this curly article of ‘Kalliergeia‘, such as that for Peach Leaf Curl disease, are presented by the excellent Daraa Tribes with their song titled Rohal.

  1. Agrios, G. N. (2005). Plant Pathology. Amsterdam, Netherlands: Elsevier.
  2. Khosla, K., & Bhardwaj, S. (2010). Control of Peach Leaf Curl by Pre-Bloom and Post Infection Applications of Fungicides. Plant Disease Research, (25), 66-68.
  3. Kurtzman, C., Fell, J., & Boekhout, T. (2011). The Yeasts: A Taxonomic Study. Amsterdam, Netherlands: Elsevier.
  4. Mason, P. G., & Gillespie, D. R. (2013). Biological Control Programmes in Canada 2001-2012. Wallingford, England: CABI.
  5. Ogawa, J. M., & English, H. (1991). Diseases of Temperate Zone Tree Fruit and Nut Crops. UCANR Publications.

 

With Pomp and Circumstance

Sounds of Daraa Tribes from the Daraa River Valley of southeast Morocco – via the Netherlands.

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