Asiatic brown fruit rot - Monilia polystroma
Monilia polystroma is the conidial form of an unknown apothecial ascomycete closely related to Monilinia fructigena, from which it has so far been distinguished by molecular means. Although M. fructigena and the other brown-rot species, M. fructicola and M. laxa, are known on various continents, Monilia polystroma was identified in Japan and initially known only in that country. A recent published report placed it in Hungary as well and there is unpublished data indicating that it occurs in China. This species may be widely distributed in Asia and perhaps Europe. In the absence of natural barriers, it may spread by means of airborne conidia. Long distance dispersal would most likely occur through infected planting stock or fruit. Monilia polystroma is a regulated pest for Canada while Monilinia fructigena is a regulated pest in the USA.
Monilia polystroma G.C.M. Leeuwen, Mycol. Pap. 106: 450. 2002.
Colonies on potato dextrose agar (PDA) growing to 50-60 mm diam after 6 days at 22°C under 12 h light/12 h dark cycle. Colony margin even, sporogenous tissue slightly elevated above the colony surface, 1-2 mm, buff/pale luteous. Stromatal initials forming 10-12 days after culture initiation; mature black stromatal plates at first discrete, later coalescing. Macroconidia globose, ovoid or limoniform, smooth, 12-21 × 8-12 µm, mean = 16.4 × 10.1 µm in distilled water when grown on cherry agar (CHA) at 22° under NUV; 11-20 × 8-11 µm, mean 14.9 × 9.1 µm, on pear fruit at 15°C. Thick hyphal layer of stroma on colonized fruit; conidial tufts buff to brownish-grey.
Additional details are found in van Leeuwen et al. (2002)
Distribution: Asia (China, Japan), Europe (Hungary).
Host: Causes as fruit rot on Cydonia, Malus, Prunus, Pyrus spp. (Rosaceae); survives on mummified fruit.
Notes: Descriptions of Monilinia fructigena, M. laxa, and M. fructicola should be compared in order to identify the most consistent morphological distinctions between their Monilia conidial forms and M. polystroma. An EPPO diagnostic protocol for M. fructicola (EPPO, 2003) includes a table of comparisons. The Japanese isolates identified as Monilia polystroma produced more stromata on cherry agar, had a significantly higher mean growth rate on PDA, and produced generally smaller conidia on both cherry agar and inoculated pear fruit than did isolates of M. fructigena. (Leeuwen et al., 2002)
The genus Monilia includes species that are the conidial anamorphs of Monilinia. Monilinia in the family Sclerotiniaceae (Helotiales, Ascomycota) is characterized by its conidial and stromatal anamorphs, apothecial ascomata, and ascospores (Byrde and Willets, 1977). Consequently, Monilia polystroma would be expected to have a Monilinia sexual state.
Three closely related fungi, Monilinia fructicola, M. fructigena and M. laxa, cause economically important diseases e.g., blossom and twig blights, brown fruit rot, of plants in fruit tree genera of the Rosaceae (e.g., Malus, Prunus, Pyrus). Some Monilinia species also attack ornamental flowering fruit trees.
Monilinia fructigena is primarily found in the Eastern Hemisphere, particularly in temperate Europe and Asia, and coexists in many areas with M. laxa. Monilinia fructicola and M. laxa, which produce similar disease symptoms and have common hosts, coexist in the Western Hemisphere, notably North America, and Australia. It is generally only in Central and Eastern Asia, where the host fruit trees originated, that all three species of Monilinia occur (Fulton et al., 1999).
Recent studies by Leeuwen et al. (2002) compared six isolates of M. fructigena collected in Japan on apple, Malus pumila, with the same number of isolates collected in Europe on Malus and Prunus. A general comparison of morphology revealed that there were significant differences between isolates from the two regions in colony characteristics, stroma formation, growth rate, and conidial dimensions. Differences between the two groups had previously been demonstrated using the ITS region of ribosomal DNA (Fulton et al., 1999). These studies suggested that the Japanese isolates were distinct enough from the European M. fructigena to be considered a separate species. Because no sexual form was observed, this species was named and described only in the asexual form as Monilia polystroma. It is likely that some Japanese specimens of the teleomorph, previously identified as M. fructigena, are the sexual form of the new species (Leeuwen et al., 2002) but currently none has been identified as such.
Monilina polystroma was first identified as a distinct species composed of Japanese isolates previously identified as Monilinia fructigena (Leeuwen et al., 2002). Petroczy and Palkovics (2009) have now reported it in Hungary. A DNA sequence from a Chinese isolate has been attributed to this species (NCBI, 2010). Isolates of Monilina fructigena from other areas of East Asia, including China, Korea and Russia, should be examined to determine whether some isolates belong to this newly described species (van Leeuwen et al., 2002).
RISK OF INTRODUCTION
The risk of introduction of this species is presumably similar to that of brown-rot species of Monilinia. Where these already occur, Monilia polystroma may be the equivalent of a new strain, which may have a differing host range or different levels of virulence on the same hosts. Where no brown rot pathogen is present in a new fruit-growing area, the introduction of any of the brown rot fungi is a significant threat to pome and stone fruit production. Where no natural barriers to tree-to-tree spread exist in Europe and Asia, the likelihood of introduction of Monilia polystroma depends on its yet undetermined current distribution. On other continents, the possibility depends largely on the quality of the regulatory barriers against importation of infected tree propagating material and fruit.
Monilia polystroma cannot be distinguished with certainty from the other brown-rot fungi except by laboratory examination.
In the past, identification of the three more widespread brown-rot species, Monilinia fructicola, M. fructigena and M. laxa, has primarily been based on morphological and cultural growth characteristics on artificial media (Byrde and Willets, 1977). More recently the species have also been differentiated based on sequence divergence within the internal transcribed spacer (ITS) region of the ribosomal DNA (rDNA). In this regard, comparisons of a large number of M. fructigena isolates in Europe and Japan demonstrated that isolates from Japan had four base substitutions in ITS 1 and one substitution in the ITS 2 region, when compared to the European isolates (Fulton et al., 1999).
Another study comparing the sequences of random amplified polymorphic DNA fragments from Monilinia fructigena and Monilia polystroma confirmed the close relationship between the two species. However, RAPD patterns were also sufficiently different to allow the two species to be distinguished using a multiplex PCR technique (Côté et al., 2004). This technique identified species in infected fruit as well as from pure culture.
NOTES ON CROPS/OTHER PLANTS AFFECTED
The type description by van Leeuwen et al. (2002) dealt only with isolates from apple (Malus pumila), and a recent discovery of the species in Hungary (Petroczy and Palkovics, 2009) also was on apple as the host. Detailed studies on the potential host range of this species have not yet been conducted. However, according to previous work carried out on Japanese isolates then identified as Monilinia fructigena (Harada, 1998), the fungus has a host range similar to M. fructigena in Europe, and is found on species of Cydonia, Malus, Prunus, and Pyrus.
Monilia polystroma causes the same or very similar symptoms to those reported for Monilinia fructigena and, therefore, is likely to be associated with blossom, twig and leaf blights, stem cankers and brown fruit rots (Byrde and Willets, 1977). For further information on symptoms, refer to the datasheet on M. fructigena.
BIOLOGY AND ECOLOGY
Life cycle: For background on the biology of a similar, more studied, species, refer to the datasheet on Monilinia fructigena. Monilia polystroma has so far only been observed as the conidium-producing anamorph. Like the Monilinia species that also have Monilia forms, it may persist over winter in mummified fruit and/or infected twigs and buds. Under favorable environmental conditions, the fungus will sporulate and conidia will be disseminated by wind to susceptible vegetative tissues and fruit. Secondary cycles of spread will occur as reported or other brown-rot pathogens.(Byrde and Willets, 1977).
Previous work indicated biological similarity between Japanese and European isolates of M. fructigena, so presumably this remains true for Monilia polystroma and M. fructigena. For example, the teleomorph of M. fructigena is rarely seen and therefore the teleomorph likely plays little or no role in the life-cycle of M. polystroma (van Leeuwen et al., 2002). It would presumably develop in spring from mummified fruit on or in the soil.
Limited studies made by van Leeuwen et al. (2002) indicate that Monilia polystroma appears to be almost identical to Monilinia fructigena. A comparison of lesion growth rate and sporulation on most of the inoculated pear and apple cultivars tested showed no significant differences between the two fungal species. However, some results indicate that M. polystroma may colonize fruits of some cultivars slightly faster than M. fructigena. In addition, the authors suggest that the abundant stromata formed by M. polystroma may enhance its survival by inhibiting decomposition of infected fruits, thus increasing the amount of primary inoculum produced in the next season over the level usually found with M. fructigena.
MOVEMENT AND DISPERSAL
Natural dispersal: Monilia conidia are primarily airborne, but may also be carried in rain splash.
Vector transmission: Insects or birds may carry the conidia nonspecifically on their bodies, but no observations of such transfer are published.
Accidental introduction: As with Monilinia species (Byrde and Willets, 1977), Monilia polystroma will presumably be spread by transport of infected nursery stock plants and infected fruits.
Plant parts liable to carry the pest in trade/transport:
- Fruits (inc. pods): Spores, hyphae; borne internally; borne externally; visible to naked eye.
- Flowers/Inflorescences/Cones/Calyx: Spores, hyphae; borne internally; borne externally; visible to naked eye.
- Leaves: Spores, hyphae; borne internally; visible to naked eye.
- Stems (above Ground)/Shoots/Trunks/Branches: Spores, hyphae; borne internally; borne externally; visible to naked eye.
Plant parts not known to carry the pest in trade/transport:
- Seedlings/Micropropagated Plants
- True Seeds (inc. grain)
SEEDBORNE ASPECTS OF DISEASE
Because fruit are not usually propagated from seed, the likelihood that infected fruit may contain infected or infested seed will seldom be of relevance to spread of the brown-rot fungi.
Impacts are presumed to be the same or very similar to those of Monilinia fructigena. See the datasheet on M. fructigena for details.
Regulations about importation of fruit tree propagating material, such as those of Canada (CFIA, 2006), should prevent introduction of the pathogen across natural barriers to spread. The brown-rot fungi are Regulated Pests for the USA as well (Cline and Farr, 2006).
Given the similarities to Monilinia fructigena, information on control of that pathogen is likely to apply to Monilia polystroma.
GAPS IN KNOWLEDGE/RESEARCH NEEDS:
The teleomorph for this species, whether it can be found fresh in nature or among Japanese specimens identified as M. fructigena, remains to be described.
The current distribution of Monilia polystroma, which is probably more widespread in Asia and has now been found in eastern Europe, is unknown. Likewise, the host range, though likely similar to that of the other brown-rot fungi, is undetermined. The virulence of M. polystroma on varieties grown in countries where it is present or those to which it is likely to spread due to the absence of natural barriers, is information important in establishing its possible impact and control.
Suggested citation: Chalkley, D. Systematic Mycology and Microbiology Laboratory, ARS, USDA. . Invasive Fungi. Asiatic brown fruit rot - Monilia polystroma . Retrieved July 31, 2014, from /sbmlweb/fungi/index.cfm .