The classification of the genus Colletotrichum is currently very unsatisfactory, and several species occur on the principal economic host (strawberry) which are regularly confused. As well as C. acutatum, these include the Glomerella cingulata anamorphs C. fragariae and C. gloeosporioides, all of which can be distinguished by isoenzyme analysis (Bonde et al., 1991). Studies are continuing. Colletotrichum xanthii appears to be an earlier name for C. acutatum, but more research is necessary before it is adopted in plant pathology circles.
Colonies in culture are usually white, pale grey or pale orange, sometimes producing strong pinkish-purple pigments. Conidiomata are usually poorly developed, with few or no setae, especially in culture. Conidiogenous cells are roughly cylindrical, sometimes borne in weak clusters, and produce conidia successively from single loci. Conidia are 8-16 x 2.5-4 µm in size, fusiform, thin-walled, aseptate and hyaline. Appressoria are few in number, 6.5-11 x 4.5-7.5 µm in size, clavate to circular and light to dark brown.
Some country records may refer instead to the Glomerella cingulata-Colletotrichum fragariae aggregate.
A record of C. acutatum in Chile (EPPO, 2009; CABI/EPPO, 2010) published in previous versions of the Compendium has been removed as the pathogen in the original source (Peredo et al., 1979) is now confirmed as a separate species, Colletotrichum pseudoacutatum (Damm et al., 2012). C. acutatum is a quarantine pest for Chile (Servicio Agrícola y Ganadero, 2013).
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
C. acutatum has not been considered to be a quarantine pest by EPPO or any other regional plant protection organization. A certain ambiguity remains on its geographical distribution and impact on the strawberry crop, due to confusion with other Colletotrichum spp. In several countries of mainland Europe, the names C. fragariae or C. gloeosporioides have been used for all fungi causing anthracnose on strawberry. C. acutatum was only described on strawberry in the 1960s (Simmonds, 1966) and it is not clear whether its subsequent appearance as a strawberry pathogen in the literature is due to geographical spread of a pathogen which previously had a restricted distribution, to the rise in importance of a pathogen which was previously insignificant, or simply to the clarification of a taxonomic situation which was previously confused. As C. acutatum attacks several other crops without being a serious cause of concern, and indeed many other plant species, it does not appear logical to attempt to control it by international phytosanitary measures. In addition, identification in imported consignments presents difficulties because of the confusion with related species. Pathogen-free certification of strawberry planting material seems the best approach.
Phytosanitary Measures
The inclusion of C. acutatum (and other Colletotrichum spp.) among the species covered by a strawberry certification scheme would ensure that healthy planting material is traded nationally and internationally. A suitable scheme has been recommended by EPPO (OEPP/EPPO, 1994).
The species has a very wide host range, but is economically most important on strawberries.
C. acutatum can apparently affect almost any flowering plant, especially in warm temperate or tropical regions, although its host range needs further clarification. It has rarely been noted on other than agricultural or forestry land.
The spread of the disease is often so rapid that by the time symptoms are noticed, the crop is in serious danger. For strawberry, fruit and occasionally petiole rots may be noticed, with sunken, water-soaked spots enlarging to cover the whole fruit within 2-3 days, with dark-brown fruit bodies producing pink spore masses. For other crops such as anemone and celery, crown rots and leaf curl may be the principal symptoms. In pine seedlings, the developing leaves around the apical bud are affected, with small, brown lesions appearing and rapidly extending. Severe stunting is eventually caused as the uninfected tissue beneath the apex continues to develop.
The conidia germinate to form appressoria on plant surfaces, from which penetration hyphae develop into plant cells. Infection may occur through almost any plant surface, but for the particularly susceptible herbaceous species such as strawberry and anemone, the crown with its relatively humid microclimate is often favoured. In suitable conditions, the fungus can grow rapidly inside the plant and cause severe symptoms very quickly, but in other circumstances the fungus may be quiescent inside host tissues for a period, in some cases only becoming apparent after harvest. Once the fungus has developed sufficiently inside the plant, dark fruit-bodies are produced, causing typical anthracnose symptoms. Conidia are formed liberally, and are normally dispersed by watersplash (Yang et al., 1992). They may lie dormant in the soil for some time, often overwintering in this fashion. Survival is longest under relatively cool, dry conditions (Eastburn and Gubler, 1992). The fungus can also remain dangerous for long periods in dead plant material on the surface or buried in the soil.
Although the disease in strawberry crops tends to be more virulent in warm climates, where damage can be devastating, it frequently has its origins in cooler conditions where propagating material is grown (Opgenorth et al., 1989; Wilson et al., 1990; Sutton, 1992). The disease may possibly occur in all countries where strawberries are cultivated. However, it is reported to be absent from the premises of most major strawberry propagators in the UK, and it may be possible to exclude the fungus from these sites despite its presence elsewhere in the areas concerned. There is little information on the biology of C. acutatum other than for strawberry crops.
Most natural transmission is probably by conidia, although appressoria, hyphal fragments and appressorium-like thick-walled cells may also play a part (Nair et al., 1983). Local dispersal seems to be at least mostly by water-splash (Yang et al., 1990), with propagules sometimes overwintering in soil to affect strawberry crops planted in subsequent years (Eastburn and Gubler, 1990).
Long-distance transmission due to human influence is probably widespread, and has contributed to the rapid spread of the fungus in recent years. The disease is frequently intercepted on strawberry material imported into the UK.
The disease is significant worldwide on strawberry (on which it is considered the second most important pathogen after Botrytis cinerea), and also on a few other crops such as anemones. The disease on pine may not now be so severe as in recent years, judging from the decline in research papers. Little detailed information on economic losses is available. In France, the disease has caused up to 80% losses of unsprayed strawberry crops, especially of ever-bearing cultivars (Denoyes and Baudry, 1991). Crops sprayed for B. cinerea control have suffered much less. In the UK, where the disease is statutorily notifiable, presence forces the burning of crops and fumigation of the soil.
Recent studies in Australia showed that C. acutatum caused losses of 25-50% in celery crops in Queensland (Wright and Heaton, 1991).
Detection and Inspection
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No rapid methods exist, although early results from a detection system using monoclonal antibodies are promising. Current tests involve either inoculation of apples with strawberry petioles or paraquat treatment of petioles to stimulate sporulation of the pathogen (Cook, 1993). These tests are time-consuming and labour-intensive.
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
The only serious research on control has been in connection with strawberry crops. Some success was reported in New Zealand by spraying with dichlofluanid and a captan-benomyl mixture (Cheah and Soteros, 1984), with various chemicals in Australia (Washington et al., 1992), and in South Africa with captan (van Zyl, 1985). Recently in the USA, studies showed that no acceptable fungicide is effective (Milholland, 1989). Fungicide-resistant strains of related species have been reported in the USA and Japan (Chikuo and Kobayashi, 1991; McInnes et al., 1992). There have been considerable efforts in the USA to develop resistant strawberry cultivars, but limited success has been achieved due to the presence of varied races within the species (Delp and Milholland, 1981; Smith, 1985; Smith and Black, 1990; McInnes et al., 1992). Gupton and Smith (1991) have suggested some potentially useful directions for further research.
In the UK, the disease is rare owing to strict quarantine controls and a policy of destroying affected crops and fumigating soil. McInnes et al. (1992) found that nursery material derived from tissue culture which was free from the related species C. fragariae and planted in isolated fields remained healthy, suggesting that careful selection of disease-free stock and soil sterilization in affected beds might be at least as effective as attempting chemical control.
In celery crops, Wright and Heaton (1991) found both a variation in cultivar susceptibility and amenability to chemical control of the disease. For anemone, disease incidence decreased with storage of corms (Doornik and Booden, 1990), and treatment by soaking with hot water proved effective (Doornik, 1990). Yearsley et al. (1988) found that dipping of tamarillos in imazalil and prochloraz reduced the incidence of postharvest disease caused by C. acutatum. However, dipping strawberry plants in hot water or fungicides did not eliminate the disease.
For pine, regular applications of prochloraz have been found to be effective, as has dichlofluanid (Vanner, 1990).
Chikuo Y, Kobayashi N, 1991. [A study of strawberry anthracnose. Perfect state of the pathogen which originated from the northern area of Kyushu Island and its benomyl resistance]. Proceedings of the Association for Plant Protection of Kyushu, 37:23-26
Cook RTA, 1993. Strawberry black spot caused by Colletotrichum acutatum. In: Plant health and the European single market. BCPC Monograph, No. 54 [ed. by Ebbels, D.]. Farnham, UK: BCPC, 301-304
Denoyes B, Baudry A, 1991. Characterization of species of Colletotrichum isolated from strawberry in France, taxonomy and pathogenicity abstract. Strawberry Diseases and Breeding for Varietal Resistance International Workshop, Bordeaux 1991
Gupton CL, Smith BJ, 1991. Inheritance of resistance to Colletotrichum diseases in strawberry. Journal of the American Society for Horticultural Science, 116:724-727
