Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Leotiomycetes
Subclass	Leotiomycetidae
Order	Helotiales
Family	Sclerotiniaceae
Genus	Monilinia

Scientific Name

Monilinia laxa

Scientific Name Synonyms

Monilia laxa

Sclerotinia cinerea

Sclerotinia laxa

Monilia cinerea

Common Name

brown rot blossom blight and spur infection

Author: Peter Abrahamian, University of Florida

Reviewed by: Jeffrey Rollins, University of Florida

Pathogen

Monilinia laxa is of economic importance because it is a major pathogen of stone fruits causing brown rot. It is of less significance on pome fruits (4). Monilinia laxa mainly infect stone fruits (Prunus spp.) including: apricots, sweet and sour cherries, nectarine, peach, plums, and almonds. Also, it can occur on apples (Malus x domestica), pears (Pyris communis), and quince (Cydonia oblonga) (5, 6). Apricot is the most susceptible stone fruit to blossom blight, whereas sweet cherries is most susceptible to fruit damage rather than blight (4).

Symptoms and Signs

Monilinia laxa causes disease on fruits, twigs, and blossoms. This pathogen does not cause significant fruit rotting as does the related species M. fructigena. However, it may still cause significant fruit rotting during post-harvest storage (5). The most significant damage and observable symptoms is blossom blight. All parts of the blossom (i.e., pistil, stamen, sepals) become necrotic (5, 6). Flowers either fall or remain attached to the twigs (4). Gum exudates are observed at the base of necrotic blossoms (6). Tissue surrounding blossoms become blighted, necrotic, and form cankers. Fungal signs include powdery sporulation (i.e., conidia) on the fruit and greyish mycelium on diseased twigs. The greyish powdery sporulation leads to fruit rotting and shriveling, until finally the fruit hardens and mummifies on the tree (5, 6).

Ecology and Spread

Monilinia laxa overwinters in different stages, either as: 1) mycelium in cankers, diseased twigs, and dried blossoms; or 2) pseudosclerotia in mummified fruits on the tree or orchard floor (6). Sources of inoculum are overwintered mycelium or conidia from the previous season on diseased tissue (5, 6). On the other hand, apothecia formation rarely or never occurs from mummified fruit on the orchard floor in contrast to other Monilinia spp. Apothecia produce asci with ascospores. Conidial infection of blossoms occurs by wind or rain splash and occasionally through insects (5, 6). Humidity, wetness duration, and temperature are important factors in disease severity and incidence (2, 5, 6). A longer wetness duration results in higher disease incidence. Monilinia laxa is active over a wide range of temperatures (4-30 °C). Usually, infection does not occur in dry weather (4). A high incidence (90%) of blossom blight can occur in sweet cherries at 15 °C with an eight hour wetness period (2).

Geographic Distribution

Monilinia laxa is a cosmopolitan disease. It occurs in almost all stone and pome fruit production areas (5, 6). The pathogen has not been found in the southeastern United States (6).

Management

Cultural practices are important to reduce fungal inoculum before infection and throughout the growing season. Twigs that are blighted and diseased should be pruned and burned. Also, mummy fruits on the tree and orchard floor should be collected. For larger orchards, deep tillage can be performed to bury the mummified fruits. Plant density should be reduced and excessive shoots regularly pruned so that trees are aerated. For small orchards, trees can be covered with polyethylene plastic sheets during bloom until harvest (6).

There are no resistant cultivars of stone fruits, however some cultivars are more susceptible than others (6).

Fungicides can be applied during different developmental stages such as, dormancy, bud-break, and before blossom. During the dormant stage, protective fungicides (e.g., copper, chlorothalonil, captan) provide adequate and almost complete control of M. laxa. Whereas curative fungicides, including demethylation inhibitors (e.g., tebuconazole, propiconazole, fenbuconazole), are commonly used to control sporulation during blooming. Some isolates of M. laxa have acquired resistance to some benzimadazoles fungicides (i.e., benomyl and thiophanate-methyl). Do not exceed more than 3-4 applications of curative fungicide (1). Consult your local extension specialist for legal and efficacious fungicide products available in your state. Remember, the label is the law and the product applicator is responsible for reading and following all chemical labeling.

Diagnostic Procedures

There are at least two other Monilinia spp. that can be confused for M. laxa due to similar morphology. Thus, reliance on microscopic identification most often leads to genus but not species identification. The fungus can be easily cultured on water agar and potato dextrose agar (PDA). PDA can be useful to differentiate M. laxa from other Monilinia spp. based on growth rate, colony margins, color, and conida characteristics (6). However, this is not foolproof, as M. laxa may often exhibit similar culture characteristics (5).

For fast, specific identification and diagnosis, molecular diagnostic methods such as PCR are available (3). The use of such tools requires expensive equipment and material.

Resources and References

1. Adaskaveg, J. E., Gubler, W. D., Duncan, R., Stapleton, J. J.,Holtz. B. A., Brown Rot Blossom Blight. 2012. UC ANR Publication 3431. http://www.ipm.ucdavis.edu/PMG/r3100111.html

2. Agrios, G.N. 2005. Plant Pathology. San Diego, CA: Elsevier.

3. Côté, M.J., Tardif, M.C. and Meldrum, A.J. 2004. Identification of Monilinia fructigena, M. fructicola, M. laxa, and Monilia polystroma on inoculated and naturally infected fruit using multiplex PCR. Plant Dis., 88: 1219-1225.

4. Holb, I. J. 2008. Brown rot blossom blight of pome and stone fruits: symptom, disease cycle, host resistance, and biological control. Int. J. Hort. Sci., 14: 15–21.

5. Hrustić, J., Mihajlović, M., Grahovac, M., Delibašić, G., Bulajić, A., Krstić, B., and Tanović B. 2012. Genus Monilinia on Pome and Stone Fruit Species. Pestic. Phytomed. (Belgrade), 27:283–297

6. Ritchie, D.F. 2000. Brown rot of stone fruits. The Plant Health Instructor. DOI: 10.1094/PHI-I-2000-1025-01. Updated 2005.

Acknowledgements

National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30708 as part of "Diagnostic Image Series Development for Supporting IPM in the Southern Region" (USDA-NIFA-RIPM-003351)